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  • 1. Handbook of Fruits and Fruit Processing
  • 2. Handbook of Fruits and Fruit Processing Editor Y. H. Hui Associate Editors J´ zsef Barta, M. Pilar Cano, Todd W. Gusek, o Jiwan S. Sidhu, and Nirmal K. Sinha
  • 3. C 2006 Blackwell Publishing Danvers, MA 01923. For those organizations that haveAll rights reserved been granted a photocopy license by CCC, a sepa- rate system of payments has been arranged. The feeBlackwell Publishing Professional codes for users of the Transactional Reporting Service2121 State Avenue, Ames, Iowa 50014, USA are ISBN-13: 978-0-8138-1981-5; ISBN-10: 0-8138- 1981-4/2006 $.10.Orders: 1-800-862-6657Office: 1-515-292-0140 First edition, 2006Fax: 1-515-292-3348Web site: www.blackwellprofessional.com Library of Congress Cataloging-in-Publication DataBlackwell Publishing Ltd Handbook of fruits and fruit processing / editor, Y.H.9600 Garsington Road, Oxford OX4 2DQ, UK Hui; associate editors, J´ zsef Barta . . . oTel.: +44 (0)1865 776868 [et al.].— 1st ed. p. cm.Blackwell Publishing Asia Includes index.550 Swanston Street, Carlton, Victoria 3053, Australia ISBN-13: 978-0-8138-1981-5 (alk. paper)Tel.: +61 (0)3 8359 1011 ISBN-10: 0-8138-1981-4 (alk. paper) 1. Food industry and trade. 2. Fruit—Processing.Authorization to photocopy items for internal or per- I. Hui, Y. H. (Yiu H.) II. Barta, J´ zsef. osonal use, or the internal or personal use of specificclients, is granted by Blackwell Publishing, provided TP370.H264 2006that the base fee of $.10 per copy is paid directly to 664 .8—dc22the Copyright Clearance Center, 222 Rosewood Drive, 2005013055 The last digit is the print number: 9 8 7 6 5 4 3 2 1
  • 4. Contents Contributors, vii Preface, xiPart I Processing Technology 1. Fruit Microbiology, 3 A. Kalia and R. P. Gupta 2. Nutritional Values of Fruits, 29 C. S´ nchez-Moreno, S. De Pascual-Teresa, B. De Ancos, and M. P. Cano a 3. Fruit Processing: Principles of Heat Treatment, 45 I. K¨ rmendy o 4. Fruit Freezing Principles, 59 B. De Ancos, C. S´ nchez-Moreno, S. De Pascual-Teresa, and M. P. Cano a 5. Fruit Drying Principles, 81 J. Barta 6. Non-Thermal Pasteurization of Fruit Juice Using High Voltage Pulsed Electric Fields, 95 Zs. Cserhalmi 7. Minimally Processed Fruits and Fruit Products and Their Microbiological Safety, 115 Cs. Balla and J. Farkas 8. Fresh-Cut Fruits, 129 O. Mart´n-Belloso, R. Soliva-Fortuny, and G. Oms-Oliu ı 9. Food Additives in Fruit Processing, 145 P. S. Raju and A. S. Bawa10. Fruit Processing Waste Management, 171 J. Monspart-S´ nyi ePart II Products Manufacturing11. Manufacturing Jams and Jellies, 189 H. S. Vibhakara and A. S. Bawa12. Manufacturing Fruit Beverages, 205 E. Horv´ th-Kerkai a13. Fruit as an Ingredient in a Fruit Product, 217 Gy. P´ tkai a14. Fruit Processing Plant, 231 J. Barta15. Fruits: Sanitation and Safety, 245 S. Al-Zenki and H. Al-Omariah v
  • 5. vi ContentsPart III Commodity Processing16. Apples, 265 N. K. Sinha17. Apricots, 279 M. Siddiq18. Horticultural and Quality Aspects of Citrus Fruits, 293 M. J. Rodrigo and L. Zacar´as ı19. Oranges and Citrus Juices, 309 K. S. Sandhu and K. S. Minhas20. Sweet Cherries, 359 J. Alonso and R. Alique21. Cranberry, Blueberry, Currant, and Gooseberry, 369 K. K. Girard and N. K. Sinha22. Date Fruits Production and Processing, 391 J. S. Sidhu23. Grape Juice, 421 O. Mart´n-Belloso and A. R. Marsell´ s-Fontanet ı e24. Grapes and Raisins, 439 N. R. Bhat, B. B. Desai, and M. K. Suleiman25. Grape and Wine Biotechnology: Setting New Goals for the Design of Improved Grapevines, Wine Yeast, and Malolactic Bacteria, 453 I. S. Pretorius26. Olive Processing, 491 B. Gandul-Rojas and M. I. M´nguez-Mosquera ı27. Peach and Nectarine, 519 M. Siddiq28. Pear Drying, 533 R. de Pinho Ferreira Guin´ e29. Plums and Prunes, 553 M. Siddiq30. Processing of Red Pepper Fruits (Capsicum annuum L.) for Production of Paprika and Paprika Oleoresin, 565 A. P´ rez-G´ lvez, M. Jar´ n-Gal´ n, and M. I. M´nguez-Mosquera e a e a ı31. Strawberries and Raspberries, 581 N. K. Sinha32. Tropical Fruits: Guava, Lychee, Papaya, 597 J. S. Sidhu33. Banana, Mango, and Passion Fruit, 635 L. G. Occe˜ a-Po n34. Nutritional and Medicinal Uses of Prickly Pear Cladodes and Fruits: Processing Technology Experiences and Constraints, 651 M. Hamdi35. Speciality Fruits Unique to Hungary, 665 M. St´ ger-M´ t´ e ae Index, 679
  • 6. ContributorsRafael Alique (Chapter 20) Csaba Balla (Chapter 7)Instituto del Frío (CSIC) Corvinus University of Budapest, Faculty ofC/José Antonio Novais n◦ 10 Food Science, Department of Refrigeration28040 Madrid, Spain and Livestock Products TechnologyPhone: +34915492300 Hungary 1118, Budapest, Ménesi út 45 Phone: 36-1-482-6064Jesús Alonso (Chapter 20) Fax: 36-1-482-6321Instituto del Frío (CSIC) E-mail: csaba.balla@uni-corvinus.huC/José Antonio Novais n◦ 1028040 Madrid, Spain J´ zsef Barta, Ph.D. (Chapters 5, 14) oPhone: +34915492300 Head of the DepartmentE-mail: jalonso@if.csic.es Corvinus University of Budapest Faculty of Food ScienceHusam Al-Omariah (Chapter 15) Department of Food PreservationBiotechnology Department Budapest, Ménesi út 45Kuwait Institute for Scientific Research Hungary 1118P.O. Box 24885, 13109-Safat, Kuwait Phone: 36-1-482-6212 Fax: 36-1-482-6327Sameer Al-Zenki (Chapter 15) E-mail: jozsef.barta@uni-corvinus.huBiotechnology DepartmentKuwait Institute for Scientific Research A.S. Bawa (Chapters 9, 11)P.O. Box 24885, 13109-Safat, Kuwait Fruits and Vegetables TechnologyPhone: (965)-483-6100 Defence Food Research LaboratoryFax: (965)-483-4670 Siddarthanagar, Mysore-570 011, IndiaE-mail: szenki@kisr.edu.kw Phone: 0821-247-3783 Fax: 0821-247-3468Begoña De Ancos (Chapters 2, 4) E-mail: dfoodlab@sancharnet.inDepartment of Plant Foods Scienceand Technology, Instituto del Frío N. R. Bhat (Chapter 24)Consejo Superior de Investigaciones Arid Land Agriculture DepartmentCientíficas (CSIC) Ciudad Universitaria Kuwait Institute for Scientific ResearchE-28040 Madrid, Spain P.O. Box 24885, 13109-Safat, KuwaitE-mail: ancos@if.csic.es E-mail: nbhat@safat.kisr.edu.kw vii
  • 7. viii ContributorsM. Pilar Cano, Ph.D. (Chapters 2, 4) Beatriz Gandul-Rojas (Chapter 26)Director Group of Chemistry and BiochemistryInstituto del Frío-CSIC of Pigments. Food Biotechnology DepartmentC/Jose Antonio Novais, 10 Instituto de la Grasa (CSIC).Ciudad Universitaria Av. Padre García Tejero 4, 4101228040-Madrid, Spain Sevilla, SpainPhone: 34-91-5492300Fax: 34-91-5493627 Kristen K. Girard (Chapter 21)E-mail: pcano@if.csic.es Principal Scientist Ocean Spray Cranberries, Inc.Zsuzsanna Cserhalmi (Chapter 6) IngredientsCentral Food Research Institute 1 Ocean Spray Dr.Hungary 1022 Budapest, Hermann O. u. 15 Middleboro MA 02349, USAPhone: 36-1-214-1248 E-mail: kgirard@oceanspray.comFax: 36-1-355-8928E-mail: zs.cserhalmi@cfri.hu Rajinder P. Gupta (Chapter 1) Department of Microbiology,Sonia De Pascual-Teresa (Chapters 2, 4) College of Basic Sciences and HumanitiesDepartment of Plant Foods Science Punjab Agricultural Universityand Technology, Instituto del Frío Ludhiana-141004, IndiaConsejo Superior de Investigaciones rpguptag@rediffmail.comCientíficas (CSIC) Ciudad UniversitariaE-28040 Madrid, Spain Todd W. Gusek, Ph.D.E-mail: soniapt@if.csic.es Principal Scientist, Central Research Cargill, Inc.B. B. Desai (Chapter 24) PO Box 5699Arid Land Agriculture Department Minneapolis, MN 55440, USAKuwait Institute for Scientific Research Phone: (952)742-6523P.O. Box 24885, 13109-Safat, Kuwait Fax: (952)742-4925 E-mail: todd gusek@cargill.comJ´ zsef Farkas (Chapter 7) oCorvinus University of Budapest M. Hamdi (Chapter 34)Faculty of Food Science, Department Director, Department of Biochemical and Chemicalof Refrigeration and Livestock Products Engineering Microbial and Food ProcessesTechnology and Central Food Research Institute Higher School of Food IndustriesHungary 1118, Budapest, Ménesi út 45 National Institute of Applied Sciencesand, 1022, Budapest, Hermann O. u. 15 and Technology. BP: 676. 1080 TunisiaPhone: 36-1-482-6303 Phone: 216-98-326675Fax: 36-1-482-6321 Fax: 216-71-704-329E-mail: j.farkas@cfri.hu E-mail: moktar.hamdi@insat.rnu.tnRaquel de Pinho Ferreira Guin´ (Chapter 28) e Emoke Horváth-Kerkai (Chapter 12)Associate Professor Corvinus University of Budapest, FacultyDepartment of Food Engineering of Food Science, Department ofESAV, Polytechnic Institute of Viseu Food Preservation Hungary 1118Campus Politécnico, Repeses Budapest, Ménesi út 45.3504-510 Viseu, Portugal Phone: 36-1-482-6035E-mail: raquelguine@esav.ipv.pt Fax: 36-1-482-6327 E-mail: emoke.kerkai@uni-corvinus.hu
  • 8. Contributors ixY. H. Hui, Ph.D. Av. Padre García Tejero 4, 41012Senior Scientist Sevilla, SpainScience Technology System Phone: +34954691054P.O. Box 1374 Fax: +34954691262West Sacramento, CA 95691, USA E-mail: minguez@cica.es.Phone: 916-372-2655Fax: 916-372-2690 Kuldip Singh Minhas (Chapter 19)E-mail: yhhui@aol.com Professor Food Science and TechnologyManuel Jarén-Galán (Chapter 30) Punjab Agricultural UniversityGroup of Chemistry and Biochemistry Ludhiana, Punjab, Indiaof Pigments. Food Biotechnology Department Phone: 0161-2401960 Extn. 305Instituto de la Grasa (CSIC)Av. Padre García Tejero 4, 41012 Judit Monspart-Sényi (Chapter 10)Sevilla, Spain Corvinus University of Budapest, Faculty of Food Science, Department of Food PreservationAnu Kalia (Chapter 1) Hungary 1118, Budapest, Ménesi út 45Department of Microbiology, Phone: 36-1-482-6037College of Basic Sciences and Humanities Fax: 36-1-482-6327Punjab Agricultural University E-mail: judit.senyi@uni-corvinus.huLudhiana-141004, Indiakaliaanu@rediffmail.com Lillian G. Occeña-Po (Chapter 33) Department of Food Science and Human NutritionImre Körmendy (Chapter 3) Michigan State UniversityCorvinus University of Budapest, East Lansing, MI 48824, USAFaculty of Food Science, Department Phone: 517-432-7022of Food Preservation Hungary 1118 Fax: 517-353-8963Budapest, Ménesi út 45 E-mail: occena@msu.eduPhone: 36-1-482-6212Fax: 36-1-482-6327 Gemma Oms-Oliu (Chapter 8)E-mail: imre.kormendy@uni-corvinus.hu Department of Food Technology, University of Lleida Av. Alcalde Rovira Roure, 191. 25198Olga Martín-Belloso (Chapters 8, 23) Lleida, SpainDepartment of Food Technology, University Phone: +34-973-702-593of Lleida Av. Alcalde Rovira Roure, 191. 25198 Fax: +34-973-702-596Lleida, Spain E-mail: goms@tecal.udl.esPhone: +34-973-702-593Fax: +34-973-702-596 Györgyi Pátkai (Chapter 13)E-mail: omartin@tecal.udl.es Corvinus University of Budapest, Faculty of Food Science, Department of Food PreservationAngel Robert Marsellés-Fontanet (Chapter 23) Hungary 1118, Budapest, Ménesi út 45Department of Food Technology, University Phone: 36-1-482-6212of Lleida Av. Alcalde Rovira Roure, 191. 25198 Fax: 36-1-482-6327Lleida, Spain E-mail: gyorgyi.patkai@uni-corvinus.huPhone: +34 973 702 593Fax: +34 973 702 596 Antonio Pérez-Gálvez (Chapter 30)E-mail: rmarselles@tecal.udl.es Group of Chemistry and Biochemistry of Pigments, Food Biotechnology DepartmentM. Isabel Mínguez-Mosquera (Chapters 26, 30) Instituto de la Grasa (CSIC).Group of Chemistry and Biochemistry Av. Padre García Tejero 4, 41012,of Pigments. Food Biotechnology Department Sevilla, SpainInstituto de la Grasa (CSIC)
  • 9. x ContributorsIsak S. Pretorius (Chapter 25) East Lansing, MI 48824, USAThe Australian Wine Research Institute Phone: 517-355-8474PO Box 197, Glen Osmond Fax: 517-353-8963Adelaide, SA 5064 E-mail: siddiq@msu.eduAustraliaPhone: +61-8-83036835 Nirmal K. Sinha, Ph.D. (Chapters 16, 21, 31)Fax: +61-8-83036601 VP, Research and DevelopmentE-mail: Sakkie.Pretorius@awri.com.au Graceland Fruit, Inc. 1123 Main StreetP.S. Raju (Chapter 9) Frankfort, MI 49635, USAFruits and Vegetables Technology Phone: 231-352-7181Defence Food Research Laboratory Fax: 231-352-4711Siddarthanagar, Mysore-570 011, India E-mail: nsinha@gracelandfruit.comPhone: 0821-247-3783Fax: 0821-247-3468 Robert Soliva-Fortuny (Chapter 8)E-mail: dfoodlab@sancharnet.in Department of Food Technology, University of Lleida Av. Alcalde Rovira Roure, 191. 25198María Jesús Rodrigo (Chapter 18) Lleida, SpainInstituto de Agroquímica y Tecnología Phone: +34-973-702-593de Alimentos (CSIC). Apartado Postal 73 Fax: +34-973-702-59646100 Burjasot, Valencia, Spain E-mail: rsoliva@tecal.udl.esConcepción Sánchez-Moreno (Chapters 2, 4) Mónika Stéger-Máté (Chapter 35)Department of Plant Foods Science and Corvinus University of Budapest, FacultyTechnology, Instituto del Frío, Consejo Superior of Food Science, Department of Food Preservationde Investigaciones Científicas (CSIC) Hungary 1118, Budapest, Ménesi út 45Ciudad Universitaria, E-28040 Madrid, Spain Phone: 36-1-482-6034E-mail: csanchezm@if.csic.es Fax: 36-1-482-6327 E-mail: monika.stegernemate@uni-corvinus.huKulwant S. Sandhu (Chapter 19)Sr. Veg. Technologist (KSS) M. K. Suleiman (Chapter 24)Department of Food Science and Technology Arid Land Agriculture DepartmentPunjab Agricultural University Kuwait Institute for Scientific ResearchLudhiana - 141 004, Punjab, India P.O. Box 24885, 13109-Safat, KuwaitPhone: 0161-2405257, 2401960 extn. 8478(KSS) H.S. Vibhakara (Chapter 11)E-mail: ptc@satyam.net.in Fruits and Vegetables Technology Defence Food Research LaboratoryJiwan S. Sidhu, Ph.D. (Chapters 22, 32) Siddarthanagar, Mysore-570 011, IndiaProfessor, Department of Family Science Phone: 0821-247-3949College for Women, Kuwait University Fax: 0821-247-3468P.O. Box 5969, Safat-13060, KuwaitPhone: (965)-254-0100 extn. 3307 Lorenzo Zacarías (Chapter 18)Fax: (965)-251-3929 Instituto de Agroquímica y TecnologíaE-mails: jsidhu@cfw.kuniv.edu; de Alimentos (CSIC). Apartado Postal 73jiwansidhu2001@yahoo.com 46100 Burjasot, Valencia, Spain Phone: 34 963900022Muhammad Siddiq (Chapters 17, 27, 29) Fax: 34 963636301Food Processing Specialist E-mail: lzacarias@iata.csic.es orDepartment of Food Science & Human Nutrition cielor@iata.csic.esMichigan State University
  • 10. PrefaceIn the past 30 years, several professional reference Part III is from the commodity processing perspec-books on fruits and fruit processing have been pub- tive, covering important groups of fruits such as:lished. The senior editor of this volume was part of r Applesan editorial team that published a two-volume text on r Apricotsthe subject in the mid-nineties. r Citrus fruits and juices It may not be appropriate for us to state the ad- r Sweet cherriesvantages of our book over the others available in the r Cranberries, blueberries, currants, andmarket, especially in contents; however, each profes-sional reference treatise has its strengths. The deci- gooseberries r Date fruitssion is left to the readers to determine which title best r Grapes and raisins, including juices and winesuits their requirement. r Olives This book presents the processing of fruits from r Peaches and nectarinesfour perspectives: scientific basis; manufacturing and r Pearsengineering principles; production techniques; and r Plums and Prunesprocessing of individual fruits. r Red pepper fruits Part I presents up-to-date information on the funda- r Strawberries and raspberriesmental aspects and processing technology for fruits r Tropical fruits (guava, lychee, papaya, banana,and fruit products, covering: mango, and passion fruit)r Microbiologyr Nutrition Although many topical subjects are included in ourr Heat treatment text, we do not claim that the coverage is comprehen-r Freezing sive. This work is the result of the combined effortsr Drying of nearly fifty professionals from industry, govern-r New technology: pulsed electric fields ment, and academia. They represent eight countriesr Minimal processing with diverse expertise and backgrounds in the disci-r Fresh-cut fruits pline of fruit science and technology. An internationalr Additives editorial team of six members from four countriesr Waste management led these experts. Each contributor or editor was re- sponsible for researching and reviewing subjects ofPart II covers the manufacturing aspects of processed immense depth, breadth, and complexity. Care andfruit products: attention were paramount to ensure technical accu-r Jams and jellies racy for each topic. In sum, this volume is unique inr Fruit beverages many respects. It is our sincere hope and belief that itr Fruit as an ingredient will serve as an essential reference on fruits and fruitr A fruit processing plant processing for professionals in government, industry,r Sanitation and safety in a fruit processing plant and academia. xi
  • 11. xii Preface We wish to thank all the contributors for sharing TechBooks, Inc. for their time, effort, advice, andtheir expertise throughout our journey. We also thank expertise. You are the best judges of the quality ofthe reviewers for giving their valuable comments on this work.improving the contents of each chapter. All these pro-fessionals are the ones who made this book possible. Y. H. HuiWe trust that you will benefit from the fruits of their J. Bartalabor. M. P. Cano We know firsthand the challenges in developing T. W. Guseka book of this scope. What follows are the difficul- J. S. Sidhuties in producing the book. We thank the editorial N. Sinhaand production teams at Blackwell Publishing and
  • 12. Handbook of Fruits and Fruit Processing Edited by Y. H. Hui Copyright © 2006 by Blackwell Publishing Part IProcessing Technology
  • 13. Handbook of Fruits and Fruit Processing Edited by Y. H. Hui Copyright © 2006 by Blackwell Publishing 1 Fruit Microbiology Anu Kalia and Rajinder P. GuptaIntroduction feature of microbes advocates their unquestionableNormal Microflora of Fresh Fruits presence on external surface of plant and plant prod-Normal Microflora of Processed Fruit Products ucts, particularly skin of fruits and vegetables.Factors Affecting Microbial Growth Fruits and vegetables are vital to our health and Intrinsic Factors well being, as they are furnished with essential vi- Extrinsic Factor tamins, minerals, fiber, and other health-promoting Implicit FactorsFactors Affecting Microbial Quality and Fruit Spoilage phytochemicals. The present health-conscious gen- Preharvest Factors eration prefers a diet exhibiting low calories and Postharvest Handling and Processing low fat/sodium contents. A great importance of in-Fruit Spoilage take of fruits everyday has been found to half the True Pathogens risk of developing cancer and may also reduce the Opportunistic Pathogens risk of heart disease, diabetes, stroke, obesity, birthModes of Fruit Spoilage defects, cataract, osteoporosis, and many more toMethods to Evaluate Microbial Quality count. Over the past 20 years, the consumption of Conventional Techniques fresh fruits and vegetables in industrialized coun- New Methods for Rapid Analysis tries has increased. However, this has also hiked theMaintaining Microbial Quality of Fruits chances of outbreaks of food poisoning and food in- Postharvest and Storage ConsiderationsFruit Safety fections related to consumption of fresh fruits andAssociated Pathogens and Sources of Contamination uncooked vegetable salads. Many workers have de- Preharvest Sources of Contamination scribed the changes that may contribute to the in- Contamination During Postharvest Processing crease in diseases associated with the consumption ofSafety and Sanitation raw fruits and vegetables in industrialized countriesHealth Implications and foods in general (Hedberg et al., 1994; AltekruseFuture Perspectives and Swerdlow, 1996; Altekruse et al., 1997; PotterReferences et al., 1997; Bean et al., 1997). A healthy fruit sur- face harbors diverse range of microbes, which may be the normal microflora, or the microbes inoculatedINTRODUCTION during the processing of fresh produce (Hanklin andMicrobiology is the science that deals with the study Lacy, 1992; Nguyen and Carlin, 1994). However, theof microscopic critters inhabiting planet earth, and microflora could be plant pathogens, opportunisticof living organisms residing in earth. “Microbe” as a pathogens, or non-plant pathogenic species. Accord-general term features amalgam of a variety of diverse ing to Center for Disease Control and Preventionmicroorganisms with the range spanning from elec- (CDCP), among the number of documented out-tronmicroscopical cyrstallizable viruses, nucleoid– breaks of human infections associated with con-bearing unicellular prokaryotic bacteria to eukary- sumption of raw fruits, vegetables, and unpasteurizedotic multicellular fungi and protists. The omnipresent fruit juices, more than 50% of outbreaks occur with 3
  • 14. 4 Part I: Processing Technologyunidentified etiological agents. These new outbreaks NORMAL MICROFLORA OFof fresh-produce-related food poisoning include ma- PROCESSED FRUIT PRODUCTSjor outbreaks by tiny culprits as Escherichia coli0157:H7, Salmonella, Shigella, Cyclospora, Hepati- Postharvest processing methods include diversetis A virus, Norwalk disease virus, on a variety of range of physical and chemical treatments to enhancefruits as cantaloupes, apples, raspberries, and other the shelf life of fresh produce. The minimally pro-fruits. Erickson and Kornacki (2003) have even ad- cessed fresh-cut fruits remain in a raw fresh statevocated the appearance of Bacillus anthracis as a without freezing or thermal processing, or additionpotential food contaminant. Factors include global- of preservatives or food additives, and may be eatenization of the food supply, inadvertent introduction of raw or conveniently cooked and consumed. Thesepathogens into new geographical areas (Frost et al., minimally processed fruits are washed, diced, peeled,1995; Kapperud et al., 1995), the development of trimmed, and packed, which lead to the removal ofnew virulence factors by microorganisms, decreases fruit’s natural cuticle, letting easy access by outerin immunity among certain segments of the popula- true or opportunistic normal microflora to the internaltion, and changes in eating habits. disrupted tissues abrassed during processing. Gorny and Kader (1996) observed that pear slices cut with a freshly sharpened knife retained visual quality longer than the fruits cut with a dull hand-slicer.NORMAL MICROFLORA Rinsing of fresh produce with contaminated wa-OF FRESH FRUITS ter or reusing processed water adds E. coli 0157:H7,Fresh fruits have an external toughness, may be water Enterobacter, Shigella, Salmonella sp., Vibrio chlo-proof, wax-coated protective covering, or skin that reae, Cryptosporidium parvum, Giardia lamblia, Cy-functions as a barrier for entry of most plant clospora caytanensis, Toxiplasma gondii, and otherpathogenic microbes. The skin, however, harbors a causative agents of foodborne illnesses in humans,variety of microbes and so the normal microflora of thus increasing the microbial load of the fresh pro-fruits is varied and includes both bacteria and fungi duce that undergo further processing including addi-(Hanklin and Lacy, 1992). These microbes get tion of undesirable pathogens from the crop.associated with fruits, since a variety of sources such Fruits processed as fruit concentrates, jellies, jams,as the blowing air, composted soil, insects as preserves, and syrups have reduced water activ-Drosophila melanogaster or the fruit fly inoculate ity (aw ) achieved by sufficient sugar addition andthe skin/outer surface with a variety of Gram- heating at 60–82◦ C, that kills most of xerotolerantnegative bacteria (predominantly Pseudomonas, fungi as well as restrains the growth of bacteria.Erwinia, Lactobacillus). Likewise, hand-picking Thus, the normal microflora of such diligently pro-the fresh produce inoculates the fruit surfaces cessed fruit products may include highly osmophilicwith Staphylococcus. Contact with soil, especially yeasts and certain endospore-forming Clostridium,partially processed compost or manure, adds di- Bacillus sp. that withstand canning procedures. Sim-verse human pathogenic microbes generally of the ilar flora may appear for processed and pasteurizedfecal-oral type including the Enterobacter, Shigella, fruit juices and nectars that loose most vegetative bac-Salmonella, E. coli 0157:H7, Bacillus cereus, as teria, yeasts, and molds while retaining heat-resistantwell as certain viruses such as Hepatitis A Virus, ascospores or sclerotia producing Paecilomyces sp.,Rotavirus, and Norwalk disease viruses that are Aspergillus sp., and Penicillum sp. (Splittstoesser,transmitted by consumption of raw fruits. Normal 1991). Recently, Walls and Chuyate (2000) reportedfungal microflora of fruits includes molds such the occurrence of Alicyclobacillus acidoterrestris,as Rhizopus, Aspergillus, Penicillum, Eurotium, an endospore-forming bacteria in pasteurized orangeWallemia, while the yeasts such as Saccharomyces, and apple juices.Zygosaccharomyces, Hanseniaspora, Candida,Debaryomyces, and Pichia sp. are predominant.These microbes are restrained to remain outside on FACTORS AFFECTINGfruit surfaces as long as the skins are healthy and MICROBIAL GROWTHintact. Any cuts or bruises that appear during the Fruits are composed of polysaccharides, sugars, or-postharvest processing operations allow their entry ganic acids, vitamins, minerals which function as em-to the less protected internal soft tissue. inent food reservoirs or substrates dictating the kind
  • 15. 1 Fruit Microbiology 5of microorganisms that will flourish and perpetuate as ATP and DNA require neutrality (Brown, 1964).in the presence of specific microflora and specific The pH changes also affect the morphology of someenvironmental prevailing conditions. Hence, one can microbes as Penicillum chrysogenum that show de-predict the development of microflora on the basis creased length of hyphae at pH above 6.0. Corlettof substrate characteristics. Fresh fruits exhibit the and Brown (1980) observed varying ability of or-presence of mixed populations, and growth rate of ganic acids as microbial growth inhibitors in relationeach microbial type depends upon an array of factors to pH changes.that govern/influence the appearance of dominatingpopulation, which include the following. Water Activity (Moisture Requirement)Intrinsic Factors Water is a universal constituent required by all the liv- ing cells, and microbes are no exceptions but the exactThese imply the parameters that are an inherent part amount of water required for growth of microorgan-of the plant tissues (Mossel and Ingram, 1955) and isms varies. Hence, several preservation methods in-thus are characteristics of the growth substrates that volve drying or desiccation of the produce (Worboinclude the following. and Padilla-Zakour, 1999). The water requirement of microbes is defined as water activity (aw ) or ratio ofHydrogen Ion Concentration (pH) water vapor pressure of food substrate to that of vapor pressure of pure water at same temperatureMicrobial cells lack the ability to adjust their inter-nal pH, hence are affected by change in pH, so could p aw = ,grow best at pH values around neutral. Bacteria ex- pohibit a narrow pH range with pathogenic bacteria be- where p is the vapor pressure of the solution and poing the most fastidious; however, yeasts and molds is the vapor pressure of the solvent.are more acid-tolerant than bacteria. Fruits possess Christian (1963) related water activity to relativemore acidic pH (<4.4) favoring growth of yeasts and humidity as (Table 1.2)molds. Microbes, in general, experience increasedlag and generation times at either extremes of the RH = 100 × aw .optimum pH range, which is usually quite narrow.The small fluctuations in pH have elaborate impact Thus, the relative humidity of a food correspondingon microbial growth rates, and the pH changes be- to a lower aw tends to dry the surface and vice versa.come more profound if the substrate has low buffer- In general, most fresh produce has aw value aboveing capabilities leading to rapid changes in response 0.99 which is sufficient for the growth of both bacte-to metabolites produced by microorganisms during ria and molds; however, bacteria, particularly Gram-fermentation (Table 1.1). negative, are more stringent regarding aw changes, Adverse pH affects the functioning of respiring while molds could grow at aw as low as 0.80. Themicrobial enzymes and the transport of nutrients into lowest range of permeable aw values for halophilicthe cell. The intracellular pH of microbial cytoplasm bacteria, xerophilic fungi, and osmophilic yeasts isremains reasonably constant due to relative imper- 0.75–0.61. Morris (1962) elaborated the interactionmeability of cell membrane to hydrogen (H+ ) and of aw values with temperature and nutrition and ob-hydroxyl (OH− ) ions as key cellular compounds such served that at optimum temperature, range of aw val- ues remain wide, while lowering/narrowing aw values reduces growth and multiplication of microbes, andTable 1.1. Approximate pH Values of Some nutritive properties of substrate increase the range ofFresh Fruits aw over which microorganisms can survive (Fig. 1.1). Hence, each microbe has its own characteristic awFruits pH Values Fruits pH Values range and optimum for growth and multiplicationApples 2.9–3.3 Limes 1.8–2.0 which are affected by temperature, pH, oxygen avail-Bananas 4.5–4.7 Melons 6.3–6.7 ability, and nutritive properties of substrate as wellGrapefruit 3.4–4.5 Figs 4.6 as the presence of organic acids or other secondaryWatermelons 5.2–5.6 Plums 2.8–4.6 metabolites performing inhibitory action, thus nar-Oranges 3.6–4.3 rowing the aw range that culminates in decreasedSource: Adapted from Jay (1992). yield of cells and increased lag phase for growth,
  • 16. 6 Part I: Processing Technology Table 1.2. Lower Limit aw Values of Certain Microorganisms Bacteria Minimum aw Values Fungi Minimum aw Values Pseudomonas 0.97 Mucor 0.62 (0.94) E. coli 0.96 Rhizopus 0.62 Staphylococcus aureus 0.86 Botyritis 0.62 Bacillus subtilis 0.95 Aspergillus 0.85 Clostridium botulinum 0.93 Penicillum 0.95 Enterobacter aerogenes 0.94 Source: Adapted from Jay (1992). Pseudomonas 1 S.aureus 0.9 E.coli 0.8 B.subtilis 0.7 C.botulinum 0.6 0.5 E.aerogenes 0.4 Mucor 0.3 Rhizopus 0.2 Botyritis 0.1 Aspergillus 0 Penicillum Pseudomonas S.aureus E.coli B.subtilis Mucor C.botulinum E.aerogenes Rhizopus Botyritis Aspergillus PenicillumFigure 1.1. Graphical representation ofaW values of various microbes.and results in decreased growth rate and size of final accumulate polyhydric alcohols (Troller, 1986). Mi-population (Wodzinsky and Frazier, 1961). Lowering crobes thus attempt to compensate for increasedof water activity builds up stress and exerts adverse stress by accumulating compatible solutes.influence on all vital metabolic activities that requireaqueous environment. Charlang and Horowitz (1974) Redox Potential/Redox Poising Capacityobserved the appearance of non-lethal alterations incell membrane permeability of Neurospora crassa The type of microbial growth depends upon oxidationcells resulting in loss of various essential molecules, and reduction power of the substrate. The oxidation–as the dynamic cell membrane should remain in fluid reduction potential of a substrate may be defined asstate. the ease with which the substrate loses or gains elec- The exception to normal aw requirements are ba- trons and, in turn, gets oxidized or reduced, respec-sically the halophilic bacteria that grow under low tively. Aerobic microbes require oxidized (positiveaw values by accumulating potassium ions in the Eh values) substrates for growth and it is reverse forcell (Csonka, 1989), while osmophilic yeasts concen- the anaerobes (Walden and Hentges, 1975). The fruitstrate polyols as osmoregulators and enzyme protec- contain sugars and ascorbic acid for maintaining thetors (Sperber, 1983). Brown (1976) reported proline reduced conditions, though plant foods tend to haveaccumulation in response to low aw in halotolerant positive values (300–400 mV). Hence, aerobic bac-Staphylococcus aureus strains. Xerotolerant fungi teria and molds most commonly spoil fruits and fruit
  • 17. 1 Fruit Microbiology 7products. The O/R potential of food can be deter- be furnished by substrate since microorganisms aremined by unable to synthesize essential vitamins. In general,r Characteristic pH of food Gram-positive bacteria are least synthetic and requirer Poising capacity supply of certain vitamins before growth, whiler Oxygen tension of the atmosphere Gram-negative bacteria and molds are relatively in-r Atmospheric access of food dependent and could synthesize most of the vitamins. Thus, these two groups of microbes grow profusely Poising capacity could be defined as the extent to on foods relatively low in B-complex vitamins suchwhich a food resists externally effected changes in as fruits under the influence of usual low pH and pos-pH that depend on the concentration of oxidizing or itive Eh values.reducing compounds in the substrate. The capacity Each microbe has a definite range of food require-alters the ability of the living tissues to metabolize ments, with some species having wide range and abil-oxygen at specifically low Eh values that exist in ity to grow on a variety of substrates, while othersthe vacuum-packed foods. Aerobic microbes include having narrow range and fastidious requirement al-bacilli, micrococci, pseudomonas, and actinobacters, lowing growth on limited substrates.and require positive Eh values, while anaerobes suchas clostridia and bacteriodes require negative Eh val- Antimicrobial Factorsues. However, most yeast and molds are aerobic andfew tend to be facultative anaerobes. In the presence Certain naturally occurring substances in substrateof limited amounts of oxygen, aerobic or faculta- (food) work against the microbes, thus maintain-tive microbes may produce incompletely oxidized or- ing stability of food; however, these are directed to-ganic acids. Processing procedures such as heating or ward a specific group of microorganism and havepasteurization, particularly of fruit juices, make mi- weak activity. Song et al. (1996) reported that thecrobes devoid of reducing substances, but favorable presence of aroma precursor Hexal readily gets con-for the growth of yeasts. verted to aroma volatiles in vivo by fresh-cut apple slices. Hexal acts as antibrowning agent as well as inhibits growth of molds, yeasts, mesophilic and psy-Available Nutrients chrotropic bacteria (Lanciotti et al., 1999). HexanalFruits as substrate act as a reservoir of sugars (source and (E)-Hexenal in modified atmosphere packagingof energy), water, minerals, vitamins, and other (MAP) of sliced apples reduce spoilage microbe pop-growth-promoting factors, while the protein content ulations (Corbo et al., 2000).or nitrogen source appears to be little less in fruits. Spices contain essential oils such as eugenolCarbohydrates include sugars or other carbon sources (clove), allicin (garlic), cinnamic aldehyde andthat act as sources of energy because breakage of eugenol (cinnamon), allyl isothiocynate (mustard),bonds or oxidation of these compounds helps in the eugenol and thymol (sage), thymol and isothymolformation of energy currency of cell or ATP. (oregano) that have antimicrobial activity (Shelef, Microorganisms have varied nutrient require- 1983). Buta and Molin (1998) observed reductionments, which are influenced by other conditions such in mold growth on fresh-cut peppers by exogenousas temperature, pH and Eh values. The microbes be- application of methyl jasmonate.come more demanding at decreased temperatures, The antimicrobial compounds may originally bewhile under optimum temperature conditions, nutri- present in food, added purposely or developed byents control the microbial growth only when present associated microbial growth, or by processing meth-in limiting quantities. Thus, microorganisms that ods. Certain antifungal compounds applied to fruitsgrow on a product become the best-suited by ex- include benomyl, biphenyl, and other phenylic com-ploiting the product, as pectinolytic bacteria such as pounds that exist in small quantities as by-product ofErwinia cartovora, Pseudomonas sp., or pectinolytic phenol synthesis pathways. Beuchat (1976) observedmolds grow best on fruits and vegetables. that essential oils of oregano, thyme, and sassafras Nitrogen requirement is usually fulfilled by pro- have bacteriocidal activity, at 100 ppm, to V. para-teolysis of protein present in substrate and the use haemolyticus in broth, while cinnamon and clove oilsof amino acids, nucleotides, certain polysaccharides, at 200–300 ppm inhibit growth and aflatoxin pro-and fats under usual microbe-specific conditions. duction by Aspergillus parasiticus (Bullerman et al.,The accessory food substances or vitamins are to 1977). The hydroxy-cinnamic acid derivatives as
  • 18. 8 Part I: Processing Technologyp-coumaric, ferulic, caffeic, and chlorogenic acids Bacillus cereus, Staphylococcus aureus, andand benzoic acid in cranberries have antibacterial Clostridium perfringens. There exists a relationand antifungal activities and are present in most plant of temperature to growth rate of microorganismsproducts including fruits. between minimum and maximum temperature range by (Ratowsky et al., 1982) √Extrinsic Factor r = b(T − T0 ),Extrinsic factors include parameters imposed from where r is the growth rate, b is the slope of regres-the external environment encountered during storage sion line, and T0 is the conceptual temperature of nothat affect food, and the microbes that tend to develop metabolic significance.on it. These factors include the following. Relative Humidity of EnvironmentTemperature of Storage Success of a storage temperature depends on the rel-Microbes grow over a wide range of temperature, and ative humidity of the environment surrounding thechange in temperature at both extremes lengthens the food. Thus, relative humidity affects aw within a pro-generation time and lag periods. The range is quite cessed food and microbial growth at surfaces. A lowwide from −34◦ C to 90◦ C, and according to range aw food kept at high R.H. value tends to pick up mois-microbes could be grouped as follows. ture until the establishment of equilibrium, and foods with high aw lose moisture in a low-humidity envi-Psychrotrophs. These microorganisms grow well ronment. Fruits and vegetables undergo a variety ofat 7◦ C or below 7◦ C with the optima ranging surface growth by yeasts and molds as well as bac-from 20◦ C to 30◦ C. For example, Lactobacillus, teria, and thus are liable to spoilage during storageMicrococcus, Pseudomonas, Enterococcus, Psy- at low R.H. conditions. However, this practice maychrobacter, Rhodotorula, Candida and Saccha- cause certain undesirable attributes such as firmnessromyces (yeasts), Mucor, Penicillum, Rhizopus and texture loss of the climacteric (perishable) fruits(molds) and Clostridium botulinum, Listeria mono- calling for the need of altered gas compositions to re-cytogenes, Yersinia enterocolitica, Bacillus cereus tard surface spoilage without lowering R.H. values.(pathogenic psychrotrophs). The group of microbesthat grow from −10◦ C to 20◦ C with the optima of10–20◦ C are included as Psychrophiles and include Modified Atmosphere Storagecertain overlapping genera mentioned above. Altering the gaseous composition of the environ-Mesophiles. These include microbes growing best ment that retards the surface spoilage without re-between 20◦ C and 45◦ C with optimum range of ducing humidity includes the general practice of in-30–40◦ C. For example, Enterococcus faecalis, Strep- creasing CO2 (to 10%) and is referred as “controlledtococcus, Staphylococcus, and Leuconostoc. or modified atmosphere” (MA). MA retards senes- cence, lowers respiration rates, and slows the rate ofThermophiles. Microbes that grow well above tissue softening or texture loss (Rattanapanone and45◦ C with the optima ranging between 55◦ C and Watada, 2000; Wright and Kader 1997a; Qi et al.,65◦ C and with maximum of above 60–85◦ C are 1999). MA storage has been employed for fruitsknown as thermotolerant thermophiles. For exam- (apples and pears) with CO2 applied mechanicallyple, Thermus sp. (extreme thermophile), Bacillus or as dry ice, and this retards fungal rotting of fruitssternothermophilus, Bacillus coagulans, Clostrid- probably by acting as competitive inhibitor of ethy-ium thermosaccharolyticum are endospore-forming lene action (Gil et al., 1998; Wright and Kaderthermotolerants and grow between 40◦ C and 60◦ C 1997b).and create major problems in the canning industry. The inhibitory effect increases with decrease in temperature due to increase in solubility of CO2 atThermotrophs. This group includes microbes lower temperatures (Bett et al., 2001). Elevated CO2similar to mesophiles but grows at slightly higher levels are generally more microbiostatic than micro-temperature optima and includes pathogenic bac- biocidal probably due to the phenomena of catabo-teria in foods. For example, Salmonella, Shigella, lite repression. However, an alternative to CO2 ap-enterovirulent E. coli, Campylobacter, toxigenic plication includes the use of ozone gas at a few ppm
  • 19. 1 Fruit Microbiology 9concentration that acts as ethylene antagonist as well targeted toward inhibition of a narrow spectrumas a strong oxidizer that retards microbial growth. of microbes. Other bacteriocins produced by lac-Sarig et al. (1996) and Palou et al. (2002) reported tic acid bacteria include lactococcins, lacticins,control of postharvest decay of table grapes caused by lactacins, diplococcin, sakacins, acidophilocins, pe-Rhizopus stolonifera. A similar report on effect of diocins, and leuconosins. As an inhibitor of spore-ozone and storage temperature on postharvest dis- forming Clostridium spp., which cause cheese blow-eases of carrots was observed by Liew and Prange ing due to undesirable gas production, nisin was the(1994). In general, gaseous ozone introduction to first bacteriocin produced by lactic acid bacteria topostharvest storage facilities or refrigerated shipping be isolated and approved for use in cheese spreads.and temporary storage containers is reported to be op- Although mostly active against Gram-positive bacte-timal at cooler temperatures and high relative humid- ria, bacteriocins can be microbiocidal under certainity (85–95%) (Graham, 1997). The most reproducible conditions, even toward Gram-negative bacteria andbenefits of such storage are substantial reduction of yeasts, provided that their cell walls have been sen-spore production on the surface of infected produce sitized to their action. The antimicrobial action ofand the exclusion of secondary spread from infected nisin and of similar bacteriocins is believed to in-to adjacent produce (Kim et al., 1999; Khadre and volve cell membrane depolarization leading to leak-Yousef, 2001). age of cellular components and to loss of electrical Ozone treatment has been reported to induce pro- potential across the membrane. Propioniobacteriumduction of natural plant defense response compounds produces propionic acid that has inhibitory effectinvolved in postharvest decay resistance. Ozone de- on other bacteria. Certain microorganisms may pro-struction of ethylene in air filtration systems has been duce wide spectrum antimicrobial substances or sec-linked to extended storage life of diverse ethylene- ondary metabolites capable of killing or inhibitingsensitive commodities. wide range of microbes called “antibiotics.” How- ever, growth of one kind of microbe could lead to lowering of pH of substrate, making the environ-Implicit Factors ment unsuitable for other microbes to grow, whileImplicit factors include the parameters depending organic acid production or hydrogen peroxide for-on developing microflora. The microorganisms while mation could also interfere with the growth of back-growing in food may produce one or more inhibitory ground microbial population (Jay, 1992).substances such as acids, alcohols, peroxides, andantibiotics that check the growth of other microor- Biofilm Formationganisms. Most of the Gram-negative bacteria exhibit quorum sensing or the cell-to-cell communication phenom-General Interference ena that leads to the formation of a multicellularThis phenomena works when competition occurs be- structure in the life of a unicellular prokaryote thattween one population of microbes and another re- provides protection to bacterial species from the dele-garding the supply of the same nutrients. Normal terious environment by precipitation. Adoption ofmicroflora of fresh produce helps prevent the col- biofilm formation involves release of autoinducers,onization of pathogens and succeeds in overcoming particularly called the N-acyl homoserine lactonesthe contaminant number by overgrowth and efficient that either activate or repress the target genes in-utilization of available resources. volved in biofilm formation (Surette et al., 1999). Quorum sensing has a profound role in food safety in association with behavior of bacteria in food matrixProduction of Inhibitory Substances and regulates prime events such as spore germina-Some microbes can produce inhibitory substances tion, biofilm formation on surfaces (Frank, 2000b),and appear as better competitors for nutrient sup- and virulence factor production. Cells in biofilm areply. The inhibitory substances may include “bac- more resistant to heat, chemicals, and sanitizers dueteriocins,” the commonest being “nisin” produced to diffusional barrier created by biomatrix as well asby certain strains of Lactobacillus lactis, which is very slow growth rates of cells in biofilms (Costerton,heat stable, attached by digestive enzymes, labile 1995). Morris et al. (1997) have reported certainand non-toxic for human consumption, and is quite methods for observing microbial biofilms directly
  • 20. 10 Part I: Processing Technologyon leaf surfaces and also to recover the constituent the causative agent to other fruits. The postharvestmicrobes for isolation of cultivable microorganisms. rots are most prevalent in fruits, particularly the dam-Thus, biofilm formation has been emerging as a chal- aged or bruised ones (Sanderson and Spotts, 1995;lenge for the decontamination techniques routinely Bachmann and Earles, 2000). The processing meth-used in the food and beverage industries, and requires ods involve the use of temperature, moisture content,the advent of new revolutionary methods for decon- and ethylene control, thus include the extrinsic pa-tamination or the modification of the older techniques rameters discussed earlier.in vision of the current scenario (Frank, 2000a). FRUIT SPOILAGEFACTORS AFFECTING The fruit spoilage is manifested as any kind of phys-MICROBIAL QUALITY ical change in color or flavor/aroma of the productAND FRUIT SPOILAGE that is deteriorated by microflora that affects the cel-From quality standpoint, the fresh fruits and the pro- lulose or pectin content of cell walls which, in turn,cessed fruit products should possess certain charac- is the fundamental material to maintain the structuralteristics such as fresh-like appearance, taste, aroma, integrity of any horticultural product. Fresh fruitsand flavor that should be preserved during stor- possess more effective defense tactics including theage. Thus, if the primary quality attributes of pro- thicker epidermal tissue and relatively higher con-duce remain unoffended, the shelf-life characteristics centration of antimicrobial organic acids. The higherlengthen. As discussed before, fruits possess normal water activity, higher sugar content, and more acidicmicroflora as well as the microflora that is added dur- pH (<4.4) of fresh fruits favor the growth of xero-ing the handling and postharvest processing of fruits, tolerant fungi or osmophilic yeasts. Lamikarna et al.though harsh treatments during processing can kill or (2000) have reported bacterial spoilage in neutral pHinhibit certain or most of the microflora while letting fruits.specific types to become predominant and prevail in Normal microflora of fruits is diverse and includesthe finished product. A variety of factors that affect bacteria such as Pseudomonas, Erwinia, Enterobac-the microbial quality of fruits include the following. ter, and Lactobacillus sp. (Pao and Petracek, 1997), and a variety of yeasts and molds. These microbes remain adhered to outer skin of fruits and come fromPreharvest Factors several sources such as air, soil, compost, and insectThese factors basically involve production practices infestation. Brackett (1987) reported inoculation ofthat have tremendous explicit effect on the micro- Rhizopus sp. spores by egg laying in ruptured epi-bial quality of fruits. Management practices can af- dermal fissures of fruits by Drosophila melanogasterfect product quality since stressed produce or me- or the common fruit fly. The microbial load of thechanical injuries permit microbial contamination. fresh produce could be reduced by rinsing with waterMold growth and decay on winter squash caused by (Splittstoesser, 1987). However, the source and qual-Rhizoctoina result from fruits lying on the ground. ity of water dictate the potential for human pathogenFood safety begins in field as a number of food- contamination upon contact with the harvested pro-borne disease outbreaks have potential sources in duce.field that contaminate the fresh produce such as Lund and Snowdon (2000) reported certain com-the use of partially treated manure, irrigation with mon molds to be involved in fruit spoilage suchlivestock-used farm pond water, or storage near as Penicillum sp., Aspergillus sp., Eurotium sp.,roosting birds (Trevor, 1997). Wallace et al. (1997) Alternaria sp., Cladosporium sp., and Botrytisreported the presence of verocytotoxin producing cinerea of fresh and dried fruits (Fig. 1.2), whileE. coli O157:H7 from wild birds. certain molds producing heat-resistant ascospores or sclerotia such as Paecilomyces fulvus, P. niveus, Aspergillus fischeri, Penicillum vermiculatum, andPostharvest Handling P. dangeardii were observed to cause spoilage ofand Processing thermally processed fruits or the fruit productsImproper or harsh handling of produce causes skin exhibiting characteristic production of off-flavors,breaks, bruises, or lesions leading to increased visible mold growth, starch and pectin solubilization,chances of microbial damage. Handlers picking fresh and fruit texture breakdown (Beuchat and Pitt, 1992;produce with skin lesions could potentially transfer Splittstoesser, 1991).
  • 21. 1 Fruit Microbiology 11 tive external protective system, thus causing active invasion and active spoilage in fruits. The degrada- tive enzyme brigade includes the following. Pectinases These enzymes depolymerize the pectin, which is a polymer of ␣-1, 4-linked d-galactopyranosyluronic acid units interspersed with 1, 2-linked rhamnopy- ranose units. On the basis of site and type of reac- tion on the pectin polymer, pectinases are of three main types, i.e., pectin methyl esterases produced by Botrytis cinerea, Monilinia fructicola, Penicillum citrinum, and Erwinia cartovora (Cheeson, 1980), polygalacturonase, and pectin lyase.Figure 1.2. Degradation of fruit texture due to growthof cellulase/pectinase-producing bacteria followed byfungal growth. Cellulases Several types of cellulase enzymes attack the na- tive cellulose and cleave the cross-linkage between ␤-d-glucose into shorter chains. Cellulases con- Fruit safety risks could be increased by certain tribute toward tissue softening and maceration as wellspoilage types that create microenvironments suit- as yield glucose, making it available to opportunisticable for the growth of human pathogens as the pri- microflora.mary spoilage by one group of phytopathogens pro-duces substances required for nurturing growth and Proteasesdevelopment of human pathogens. Wade and Beuchat(2003) have well documented the crucial role of pro- These enzymes degrade the protein content of freshteolytic fungi and the associated implications on the produce giving simpler units of polypeptides, i.e.,changes in pH of the pericarp of the decayed and amino acids. The action of proteases is limiting indamaged raw fruits in survival and growth of various fruit spoilage as fruits are not rich in proteins.foodborne pathogens. Botrytis or Rhizopus spoilageof fruits could help create environment for the prolif- Phosphatidaseseration of Salmonella enterica serovar typhimurium These enzymes cleave the phosphorylated com-(Wells and Butterfield, 1997), while Dingman (2000) pounds present in cell cytoplasm and the energy re-observed the growth of E. coli 0157:H7 in bruised leased is utilized to cope with the increased respira-apple tissues. Similar reports of Riordan et al. (2000) tion rates.and Conway et al. (2000) depicted the impact of priormold contamination of wounded apples by Penicil-lum expansum and Glomerella cingulata on survival Dehydrogenasesof E. coli 0157:H7 and Listeria monocytogenes. These enzymes dehydrogenate the compounds, thus Technically, the fresh produce deteriorating mi- increasing the amount of reduced products that maycroflora is diverse and remains on surface skin of lead to increased fermentation reaction under mi-fruits, and the basis of invasion process could be of croaerobic/anaerobic conditions.two types. Opportunistic PathogensTrue Pathogens These microorganisms lack the degradative enzymeThese microbes possess ability to actively infect plant brigade and thus gain access only when the normaltissues as they produce one or several kinds of cellu- plant product defense system weakens, which is thelytic or pectinolytic and other degradative enzymes situation of mechanical injury or cuticular damageto overcome tough and impervious outer covering of caused by the insect infestation or by natural openingsfruits which acts as the first and the foremost effec- present on the surface of the fresh produce. Thus,
  • 22. 12 Part I: Processing Technology MODES OF FRUIT SPOILAGE Fruit spoilage occurs as a result of relatively strong interdependent abiotic and biotic stresses posed par- ticularly during the postharvest handling of produce (Fig. 1.5). Harvested fruits continue to respire by uti- lizing the stored available sugars and adjunct organic acids culminating to significant increase in stress- related/stress-induced carbon dioxide and ethylene production that leads to rapid senescence (Brecht, 1995). Moreover, postharvest processing that in- volves washing, rinsing, peeling, and other treat- ments result in major protective epidermal tissue damage and disruption which in turn leads to un-Figure 1.3. Growth of Aspergillus on surface of apple sheathing of the vacuole-sequestered enzymes andfruits visible due to formation of spores. related substrates and their amalgamation with the cy- toplasmic contents. Cutting/dicing increases the aw and surface area as well as stress-induced ethylenean opportunistic pathogen slips in through the dam- production which accelerates the water loss, while theage caused by biotic and abiotic stresses on the pro- sugar availability promptly invites enhanced micro-duce and generally involves movement via natural bial invasion and rapid growth (Wiley, 1994; Watadagateways as the lenticels, stomata, hydathodes, or and Qi, 1999). The physiological state of fruit alsothe other pores/lesions caused by insect infestation determines the pattern of spoilage to be followed asor invasion by true pathogens. Damage of the prod- with increase in age/maturity, the normal defenseuct during harvesting or by postharvest processing tactics of the plant produce deteriorates. Harvestedtechniques and equipments enables opportunistic mi- produce loses water by transpiration, thus gets de-croflora to invade the internal unarmed tissue and hydrated, followed by climacteric ripening, enzy-causes spoilage (Fig. 1.3). matic discoloration of cut surfaces to senescence, Hence, spoilage connotes any physical change in thus increasing possibilities of damage by microfloracolor, taste, flavor, texture, or aroma caused by micro- (Fig. 1.6). Harsh handling and ill-maintained equip-bial growth in fruit/fruit product, thereby resulting in ment during processing lead to increased damage orproduct that becomes unacceptable for human con-sumption (Fig. 1.4).Figure 1.4. Fungal hyphae and spores of Aspergillus Figure 1.5. White hyphal mass of Aspergillusniger on guava fruits. fumigatus on surface of orange fruit.
  • 23. 1 Fruit Microbiology 13 Abiotic forces Biotic forces Damage by Damage by external Preharvest Postharvest State of sources insect damage by produce infestation microbes damage pH wind blown sand lesions invasion water activity rubbing egg-laying fermentation transpiration harvesting degradative ethylene processing enzymes production procedures damage of and outer senescence equipments layer INTERNAL TISSUE INVASION PHYSICAL CHANGES IN PRODUCE RAPID SOFTENING OF PRODUCE SHRINKAGE OF PRODUCE DECAY DECREASED SHELF LIFE OF PRODUCEFigure 1.6. Modes of fruit spoilage and factors responsible for spoilage.removal of the outer cuticle leading to tissue disrup- grow faster than the molds and this usually includestion that provokes stress-induced increased respira- the genera such as Cryptococcus, Rhodotorula, andtion and microbial decay (Gorny and Kader, 1996). Saccharomyces sp. in fresh fruits, and Zygosaccha-Spanier et al. (1998) reported the development of romyces rouxii, Hanseniaspora, Candida, Debary-off-flavors in fresh-cut pineapple that appeared un- omyces, and Pichia sp. in dried fruits.damaged physically, in lower portion of container Thus, senescence and spoilage depend on prod-kept at 4◦ C for 7–10 days. Walls and Chuyate (2000) uct type, abiotic factors, and microbes involved inreported survival of acid- and heat-tolerant Alicy- deterioration process, and it is convenient to de-clobacillus acidoterrestris that produces 2-methoxy scribe spoilage on the basis of visible symptoms.phenol or guaiacol imparting phenolic off-flavor in Thus, a customary approach is to name the spoilagepasteurized orange and apple juices. Jay (1992) re- type by symptomatological appearance such as softported osmophilic yeasts to be associated primarily rot or black rot. However, this definitely results inwith the spoilage of cut fruits due to their ability to discrepancy in ascertaining the causal pathogen of
  • 24. 14 Part I: Processing Technologyspoilage and this ambiguity could be overruled by present in a given sample. This method ushers littleclassifying on the basis of causal microbe such as value for the determination of microbiological statusRhizopus rot, Cladosporium rot, etc. of a food sample as usually total cell counts exceed 105 cfu per g or ml of the sample. New variationsMETHODS TO EVALUATE of microscopes render researchers the capability toMICROBIAL QUALITY predict the presence of pathogens on the surfaces of fruits clinging or attached to internal surfaces. Con-Food quality and safety are ensured by analysis of focal scanning laser microscopy has been reported tofood for the presence of microbes, and such mi- show the presence of E. coli 0157:H7 on surfacescrobial analyses are routinely performed as quaran- and internal structures of apple (Burnett et al.,tine/regulatory procedures. The methods employed 2000).for adjudging the quality of food include an array of Drawbacks: This technique suffers from a ma-microbiological to biochemical assays to ascertain jor drawback of not providing the types of bacteriathe acceptability or unacceptability of a food prod- present in the sample as well as it does not differenti-uct for human consumption or a processing/handling ate between the normal microflora and the pathogen-practice that needs to be followed. Thus, enumerating causing spoilage.the microbial load of the produce could help in de-termining the quality as well as the related safety as-pects of product and effectiveness of the processingtechnique employed to kill spoilage microbes. Aerobic Plate Counts (APC) or Total Plate Microbiological methods for pathogen identifica- Counts (TPC)tion primarily involve conventional cultural tech- It is the most practical approach to determine theniques of growing microbes on culture media and ob- presence of cultivatable microbes in a sampled foodserving the ability to form viable countable colonies product having ability to spoil food. This technique,showing characteristic growth on such media as well thus, reveals the total number of microbes in a foodas the direct microscopic methods for various groups product under a particular set of incubation temper-of microbes. ature, time, or culture media and can be used to pref- Hence, microbiological criteria are specifically erentially screen out a specific group of microbes,employed to assess: thereby, helping in determining the utility of foodr Safety of food or food ingredient added for specific purpose. How-r Shelf life of perishable products ever, the APC of the refrigerated fruits/fruit productsr Suitability of food or ingredient for specific indicate utensil or equipment conditions prevailing purpose during storage and distribution of the product.r Adherence to general manufacturing practices Drawbacks: Though APC bacterial count is the most practical and easy technique, it suffers from The routine culturing techniques require longer certain inherent drawbacks as listed below:time to obtain results. To overcome this hurdle, r It provides the viable cell count that does notnowadays, use of indicator organisms that providerapid, simple, and reliable information without the reflect the quality of raw material used forrequirement of isolation and identification of specific processing. r It is unable to record the extent of quality loss atpathogens is performed. However, such tests could beused as the presumptive ones with the confirmation low count levels. r It provides negligible information regardingprovided by a battery of biochemical tests, and mayinclude specialized serological typing also (Swami- organoleptic quality that is degraded at lownathan and Feng, 1994). The microbiological tech- counts. r It requires scrupulous researcher to interpret APCniques could be summarized as follows. results.Conventional Techniques Certain variations to APC method are now available to classify according to the types of microbes asDirect Microscopic Count molds, yeasts, or thermophilic spore counts. TheseThis method involves the microscopic examination counts are basically used for microbiological analy-for evaluating the viable or non-viable microbes sis of the canned fruits/fruit products.
  • 25. 1 Fruit Microbiology 151. Howard Mold Count. This technique involves the formats and diverse technologies that are quite spe- enumeration of molds in products such as the cific and more sensitive (Mermelstein et al., 2002). canned fruits and provides the inclusion of the Some of the assays involved in the rapid enumeration moldy material. of pathogens in food samples are as follows.2. Yeasts and Mold Counts. The high sugar prod- ucts such as fruit drinks or fruit beverages are Modification of Conventional Techniques prone to contamination and overgrowth by yeasts and molds more than the bacterial counterparts r Miniaturized Biochemical Assays: The use of and thus enumeration of these microbes gives the certain biochemical test kits for identification of presumptive glimpse of the microbiological status pure cultures of bacterial isolates delivers results of the product. A similar kind of count involves in less than 1 day with high accuracy of 90–99% the heat-resistant mold count providing the pres- comparable to conventional techniques making ence of molds such as Aspergillus fischeri and the procedure simpler, cost- and Byssochlamys fulva in heat-processed fruit prod- performance-effective (Hartman et al., 1992). ucts such as the fruit concentrates. r Modified Process/Specialized Media: Use of3. Thermophilic Spore Count. The technique again petrifilms (Curiale et al., 1991) and hydrophobic advocates the presence of spore-forming bacteria grid membrane filters eliminates the need for as the major contaminants of canned fruits, fruit media preparation, thus economizes storage and beverages, and fruit juices that are being thermally incubation space as well as simplifies disposal processed by pasteurization and thus specifically after analysis while the use of chromogenic enriches the spore-forming genera. (ONPG/X-gal) or fluorogenic (MUG/GUD) substances provides quick measure of specific enzyme activities to quickly ascertain theNew Methods for Rapid Analysis presence of a specific microbe, and theThe physical characteristics of food result in non- bioluminescence assays provide quick assessmentuniform distribution of microbes and thus such a non- of direct live cell counts with sensitivity to provideuniform homogenate results in inconsistent presence results with low counts within few minutes.of specific pathogen providing non-reproducible re-sults following the analysis of the same sample. Thus, DNA-Based Assaysthe drawbacks of the conventional microbiologicalanalysis criteria are: Use of DNA probes technically fishes out the tar-r Requirement of the selective or enrichment media get gene sequence specific to a particular pathogenic microbe in the concoction of sample DNA obtained for isolation of foodborne pathogen suffers from from the food sample with unique sensitivity and involvement of several days to provide results.r Normal microflora interferes with the isolation reproducibility, and has been developed for detec- tion of most of the foodborne pathogens (Guo et al., and identification protocols of low infectious dose 2000; Feng et al., 1996; Lampel et al., 1992; Saiki and low number pathogens that may be et al., 1988; Schaad et al., 1995). However, if the sub-lethally injured during the accomplishment of target DNA contains several targets, then PCR as- a variety of processing procedures employed. says can be used in a multiplex format that ensures These microorganisms that exist in state of shock the elimination of culturing steps prior to produc- after vigorous heat/chemical/radiation treatments ing the results (Chen and Griffith, 2000; Hill, 1996; need specific enriched culture media to overcome Jones and Bej, 1994). PCR protocols can detect very the shock (Jiang and Doyle, 2003). Thus, unless small number/few cells of particular pathogens and the injured cells could resuscitate, they could be have been successfully developed for various fas- easily outgrown by other bacteria in the sample. tidious/uncultivatable pathogens (Guo et al., 2000, Zhao and Doyle (2001) have reported the use of a 2002). DNA fingerprinting methods are the most re- universal pre-enrichment broth for growth of cent ones for the detection of pathogens in fresh pro- heat-injured pathogens in food. duce and a semi-automated fluorescent AFLP tech-Hence, these rapid methods shorten the assay time nique for genomic typing of E. coli 0157:H7 hasby a simple modification of conventional methods been developed (Zhao et al., 2000). Another report ofor may also involve an array of molecular assay occurrence of Acidovorax avenae subsp. citrulli in
  • 26. 16 Part I: Processing Technologywatermelon seeds has been provided by Walcott and Rhizoctonia, results from the fruits lying on theGitaitis (2000). ground, which can be alleviated by using mulch. Evi- dently, food safety also begins in the field, and should be of special concern, since a number of outbreaks ofAntibody-Based Assays foodborne illnesses have been traced to the contami-These include the classical agglutination assays as nation of produce in the field. Management practiceswell as the immunodiffusion techniques that are such as unscrupulous picking and harsh handlingrather simple, quick, and useful methods for con- of the fresh produce markedly affect the quality offirmation of microbial isolates from food sample but fruits (Beaulieu et al., 1999). Crops destined for stor-possess low sensitivity. Hence, the new immunolog- age should be as free as possible from skin breaks,ical protocols hail the use of ELISA (basic sandwich bruises, spots, rots, decay, and other deterioration.ELISA method) scoring high sensitivity (Candish, Bruises and other mechanical damage not only affect1991) and immunoprecipitation techniques that pro- appearance, but also provide entrance to the decay or-vide the results within few minutes as these are auto- ganisms as well. Postharvest rots are more prevalentmated requiring less manual expertise. in fruits that are bruised or otherwise damaged. More- over, mechanical injury also increases moisture loss that may hike up to 400% in a single badly bruisedOther Techniques apple.These rather unconventional methods involve the useof immunomagnetic separations, chromatographic Postharvest and Storagedetection of certain organic acids produced by the Considerationspathogen during growth and recent techniques as The fresh produce once harvested has to be storedthe flow cytometery for deciphering the survival and for shipment and this is the critical period that ex-growth of human fecal-oral pathogens in raw pro- hibits most of the loss regarding microbial decay andduce. Orr et al. (2000) have detected the presence spoilage of produce. The extrinsic factors governingof Alicyclobacillus acidoterrestris in apple juice by microbial growth play an important role during thissensory and chromatographic analysis of compounds critical period and involve temperature and water ac-produced by bacteria. The magnetic separation tech- tivity.nique is now being employed in both clinical andfood microbiology (Olsvik et al., 1994; Safarik andSafarikova, 1999; Bennett et al., 1996). Jung et al. Temperature(2003) have used immunomagnetic separation tech- Temperature is the single most important factor innique in conjunction with flow cytometery to detect maintaining fruit quality after harvest. Refrigeratedthe presence of Listeria monocytogenes in food. storage retards the following elements of deteriora- tion in perishable crops:MAINTAINING MICROBIAL r Aging due to ripening, softening, andQUALITY OF FRUITS textural/color changes r Undesirable metabolic changes and respiratoryThe microbial quality of fruits or fruit products needs heat productionto be maintained at various levels of processing and r Moisture loss/wiltingpackaging. Production practices have a tremendous r Spoilage due to invasion by bacteria/fungi/yeastseffect on the quality of fruits at harvest, on postharvestquality, and on shelf life. Cultivar or fruit variety, abi- Refrigeration controls the respiration rate of crop,otic or environmental factors such as soil type, tem- which is evil enough as this generates heat due toperature, frost, and rainy weather at harvest may ad- oxidation of sugars, fats, and proteins in the cells re-versely affect the storage life and quality of produce. sulting in loss of these stored food reserves leading toFresh produce that has been stressed by too much or decreased food value, loss of flavor, loss of saleabletoo little water, high rates of nitrogen application, weight, and more rapid deterioration. Recent work ofor mechanical injury (scrapes, bruises, abrasions) Sharma et al. (2001) has provided the insight aboutis particularly susceptible to postharvest diseases. the fate of Salmonellae in calcium-supplemented or-Mold decay on winter squash, caused by the fungus ange juice at refrigeration temperature. Since the
  • 27. 1 Fruit Microbiology 17respiration rate of fruits strongly determines their and stimulate the other apples to ripen too quickly,transit and postharvest life, a constant cold temper- making them more susceptible to diseases. Ethyleneature maintained over a span of storage period de- “producers” such as apple, apricot, avocado, ripeningcreases the deterioration; however, the produce has to banana, cantaloupe, honeydew melon, ripe kiwifruit,be precooled to relieve the field heat (heat held from nectarine, papaya, passionfruit, peach, pear, persim-sun and ambient temperature) by an array of meth- mon, plantain, plum, prune, quince, and tomato showods such as room cooling, forced air cooling, vacuum decreased quality, and reduced shelf life with appear-cooling, hydrocooling, and top or ice cooling. ance of specific symptoms of injury (Gorny et al., However, during refrigeration certain fruits having 2000, 2002). Respiration-induced ethylene produc-higher water content get injured over a time period tion causes:(chilling injury) but store best at 45–55◦ F. The ef- r Softening and development of off-flavor infect of chilling injury may be cumulative in some watermelonscrops with the appearance of chilling symptoms be- r Increased ripening and softening of mature greencoming evident as pitting or other skin blemishes, tomatoesinternal discoloration, or failure to ripen. Fruits such r Shattering of raspberries and blackberries.as muskmelons, peppers, winter squash, tomatoes,and watermelons are moderately sensitive to chill-ing injury, but if tomatoes, squash, and peppers are Packagingover-chilled, then they may particularly become moresusceptible to decay by fungal genera such as by This process is crucial in preventing contaminationAlternaria. by microbes as it avoids inward movement of light and air, thus keeping produce dry/moist and this pre- vents any changes in the textural integrity of produceRegulation of Water Activity along with convenient division of the produce in suit-Transpiration rates are determined by the moisture able portions needed for transportation, handling, andcontent of the air, which is usually expressed as rel- sale.ative humidity. Water loss at low R.H. values canseverely degrade quality since sugar-rich perishable Vacuum Packaging. Elimination of air from a gas-fruits such as grapes may shatter loose from clusters impermeable bag in which food product has beendue to drying out of their stems and this would de- placed and sealed reduces the pressure inside thecrease the aesthetic value of the product as well as bag, thus creating vacuum. While continuous respi-saleable weight loss culminating in reduced profits. ration of the microbes present in/on the food productThus, the relative humidity of the storage unit directly leads to exhaustion of available oxygen with a respec-influences water loss in fresh produce. Most fruit and tive increase in carbon dioxide level that troubles thevegetable crops retain better quality at higher relative execution of biochemical processes and related mi-humidity (80–95%) maintaining saleable weight, ap- crobial enzymes, the cells fail to survive the hikedpearance, nutritional quality and flavor, and reduction gaseous changes.in wilting, softening, and juiciness but it encouragesdisease growth. This situation could be overruled by Hyperbaric Packaging. High pressure processingstorage at cool temperatures but stringent sanitary (HPP) or high hydrostatic pressure (HHP) or ultrapreventative protocols have to be enforced. Unfortu- high pressure (UHP) processing subjects liquid andnately, refrigeration inevitably extracts moisture from solid foods, with or without packaging, to pressuresfruit surfaces, thus necessitating the use of proper between 100 and 800 MPa at higher temperaturespackaging. that relatively increases microbial inactivation. Wa- ter activity and pH are among the critical process factors in the inactivation of microbes by HPP. Tem-Control of Respiration and peratures ranging from 194◦ F to 230◦ F (90–110◦ C)Ethylene Production in conjunction with pressures of 500–700 MPa haveEthylene, a natural phytohormone, produced by some been used to inactivate spore-forming bacteria suchfruits upon ripening promotes additional ripening of as Clostridium botulinum (Patterson et al., 1995).produce exposed to it (Gorny et al., 1999). Damaged Storage of fruit product under low pressure andor diseased apples produce high levels of ethylene temperature conditions at high relative humidity
  • 28. 18 Part I: Processing Technologyreduces the oxygen availability. Thus, during the stor- other halogenated compounds, particularly chlo-age and transportation of various commodities, their rine.compatibility regarding temperature, relative humid- 3. Iodine. Aqueous iodine solutions and iodophorsity, atmosphere (oxygen and carbon dioxide), pro- could be used to sanitize the processing equip-tection from odors, and protection from ethylene re- ments and surfaces and possess greater antimi-quirements must be considered. crobial action range affecting yeasts and molds, reducing vegetative bacterial cells at very low con-Edible Film Packaging. This is rather a new pack- centrations and lower exposure times (Odlaug,aging advancement regarding fresh or minimally pro- 1981). Moreover, readily water-soluble iodophorscessed fruits as these edible coatings and films extend have little corrosive action and are not skin irri-the shelf life by creating a modified atmosphere and tants.preventing water loss (Ahvenainen, 1996; Baldwinet al., 1995a, b; Nisperos and Baldwin, 1996). Cereal Ozonation. Ozone is a powerful disinfectant andbiopolymers such as proteins and polysaccharides are has long been used to sanitize drinking water, swim-attractive raw materials for use as materials in pack- ming pools, and industrial wastewater. The dumpaging applications as these are inexpensive, easily tanks used for fruit precooling could be sanitizedprocessable, thermoplastically originating from re- by using ozone treatment, as it is an efficient nat-newable resources, edible, and biodegradable, and ural species to destroy foodborne pathogens as wellpossess good mechanical properties, thus function- as spoilage-causing microbes (Kim et al., 1999), buting as excellent gas and grease barriers (Stading et for certain fresh products as blackberries, ozonational., 2001; Baldwin et al., 1996; Arvanitoyannis and treatment may lead to development of or increase inBlanshard, 1994). Ghaouth et al. (1991) reported ef- amount of anthocyanin pigment content (Barth et al.,fects of chitosan coatings on storability and quality 1995). Kim et al. (2000) have reported the impact ofof fresh strawberries. use of electrolyzed oxidizing and chemically modi- fied water on various types of foodborne pathogens.Sanitizing Agents Hydrogen Peroxide. Hydrogen peroxide could also be used as a disinfectant. Concentrations of 0.5%Halogenated Sanitizers or less are effective for inhibiting development of1. Chlorine. Chlorine has been used to treat drink- postharvest decay caused by a number of fungi. Hy- ing water, wastewater, as well as to sanitize food drogen peroxide has a low toxicity rating and is gener- processing equipments and surfaces in processing ally recognized as having little potential for environ- environments (Botzenhart et al., 1993). Sodium mental damage (Sapers and Simmons, 1998). The use hypochlorite solution CloroxTM or dry, powdered of lactic acid dippings along with the treatment by hy- calcium hypochlorite at 50–200 ppm concentra- drogen peroxide could lead to inactivation of E. coli tion and an exposure time of 1–2 min can be used O157:H7, S. enteridtis, and Listeria monocytogenes in hydrocooling or wash water as a disinfectant on apples, oranges, and tomatoes (Venkitanarayanan as it forms hypochlorous acid which is the ac- et al., 2002). tive species required to perform the microbicidal Use of certain antibacterial solutions could also action (Hendrix, 1991). Norwood and Gilmour help in decreasing the bacterial load. McWatters et al. (2000) have reported the growth and resistance (2002) reported the consumer acceptance of raw ap- of Listeria monocytogenes to sodium hypochlo- ples treated with antibacterial solution used routinely rite in steady-state multispecies biofilm. However, in household. this antimicrobial action is reduced by a variety of abiotic factors such as temperature, light, and Irradiation. Non-ionizing ultraviolet radiations presence of soil and organic debris (Combrink and could be used for surface sterilization of food- Grobbelaar, 1984; Folsom and Frank, 2000). A handling utensils, as these rays do not penetrate foods careful inspection and monitoring of wash water (Worobo, 2000), while ionizing gamma radiations should be performed periodically with a monitor- (Chervin and Boisseau, 1994) that penetrate well, ing kit. oxidize sensitive cellular constituents (radapperti-2. Bromine. Bromine alone is not as effective as zation), and thus require moistening of produce to chlorine but shows an additive or synergistic produce peroxides. Gamma irradiation has been used increase in antimicrobial action upon use with for the decontamination of a range of products such
  • 29. 1 Fruit Microbiology 19as fresh produce including fruits and vegetables as survival of human pathogens in raw fruits and veg-well as certain other spoilage labile fresh products etables (Table 1.3).such as seafoods and meat (Gunes et al., 2000). Arecent report has provided the information regardingmarketing of irradiated strawberries for consumption Preharvest Sourcesin the United States (Marcotte, 1992). of Contamination Environmental contamination: Human pathogensFRUIT SAFETY may enter produce through various pathways or natu- ral structures such as stem, stem scars, or calyx of cer-Fruit safety is related to an amalgam of unprece- tain produce (Zhuang et al., 1995), or through dam-dented agronomical procedures that while accom- aged surface parts such as wounds, cuts, splits, andplishment culminate toward elimination of vari- punctures caused during maturation by insect infes-ous human pathogenic species present on the fruits tation (Michailides and Spotts, 1990; Beuchat, 1996;(Meng and Doyle, 2002). Several incidences of trans- Olsen, 1998; Janisiewicz et al., 1999; Iwasa et al.,mission of infection by consumption of raw fruits and 1999; Shere et al., 1998; Wallace et al., 1997), dam-vegetables have been documented such as Salmonella age caused by sand storms and hail/frost (Hill andtyphi infection by consuming a variety of fresh prod- Faville, 1951; Hill and Wenzel, 1963), damage oc-ucts (Sanchez et al., 2002; Pixley, 1913), Salmonella curred during the harvesting of fruits (Carballo et al.,and E. coli in fruit juices as well as certain parasitic 1994; Sugar and Spotts, 1993; Wells and Butterfield,helminths primarily Fasciola hepatica, Fasciolopsis 1997), and damage occurred during processing pro-buski have been observed to encyst on plants and cedures or equipments utilized.cause human illnesses. Recently, viruses followingthe fecal-oral route as Hepatitis A virus and Norwalkdisease virus have been observed to be associated Contamination Duringwith consumption of raw fruits such as raspberries, Postharvest Processingstrawberries, and melons. Waterborne Contamination Processing procedures such as rinsing and wash-ASSOCIATED PATHOGENS AND ing with contaminated water may contribute towardSOURCES OF CONTAMINATION the microbial contamination of fruits and vegetablesA healthy fruit surface may get contaminated during (Petracek et al., 1998; Buchanan et al ., 1999). Thus,the long route of processing and storage dramatically water if not potable could act as source of an ar-including diverse external sources such as environ- ray of human pathogenic microbes such as E. colimental factors, water used, processing equipments, 0157:H7, Salmonella sp., Vibrio chloerae, Shigellaor procedures performed. Bacteria such as Clostrid- sp., Cryptosporidium parvum, Giardia lamblia, Cy-ium botulinum, Bacillus cereus, and Listeria mono- clospora cayetanensis, Norwalk disease virus, andcytogenes are normal inhabitants of soil, whereas Hepatitis A virus.Salmonella, Shigella, E. coli, and Campylobacter areresident microflora of the rumen of ruminant animals Cross Contaminationand stomachs of human beings that could potentiallycontaminate raw fruits and vegetables through con- Cross contamination of products can occur from pro-tact with feces, sewage, untreated irrigation water, or cessing equipment and the environment. Eisenbergsurface water, while viruses of the fecal-oral route and Cichowicz (1977) noted that tomato and pineap-and parasites in form of cysts of liver flukes, tape- ple products can become contaminated with the moldworms, and Giaradia lamblia contaminate produce Geotrichum candidum, while the same organism wasby contact with sewage, feces, and irrigation water observed to contaminate orange and grapefruit juices,(Mead et al., 1999; King et al., 2000; Buck et al., apples, and ciders (Senkel et al., 1999) indicating a2003). Food pathogens such as Clostridium, Yersinia, kind of cross contamination during processing oper-and Listeria can potentially develop on minimally ations. Any pathogen internalized in the fruit mustprocessed fruits and vegetables under refrigerated or survive there to cause illness afterwards but the veryhigh-moisture conditions (Doyle, 2000a, b, c; Meng survival depends on the physical and chemical at-and Doyle, 2002). Beuchat (2002) has reviewed sev- tributes of fruit, postharvest processes, and consumereral ecological factors that influence the growth and use (Burnett and Beuchat, 2000; 2001). Salmonella
  • 30. 20 Part I: Processing TechnologyTable 1.3. Types of Fungal Spoilage of FruitsProduct Type of Spoilage Mold InvolvedCitrus fruitsOranges Blue rot Penicillum italicumTomatoes, citrus fruits Sour rot Geotrichum candidumCitrus fruits Green mold rot Penicillum digitatumCitrus fruits Alternaria rot Alternaria sp.Citrus fruits Stem end rot Phomopsis citri, Diplodia natalensis, Alternaria citriPeaches/apricotsPeaches Brown rot Monilinia fructicolaPeaches Pink rot Trichothecium sp.Peaches, apricots Black mold rot Aspergillus nigerPeaches, cherries Cladosporium rot Cladosporium herbarumApples/pearsApples Soft rot Penicillum expansumApples, pears Lenticel rot Cryptosporidium malicorticus, Phylctanea vagabunaApples, pears Black spot/scab Venturia inaequalisApples, pears Brown rot Monilinia fructigenaPears Erwinia rot Erwinia cartovoraBananasBananas Bitter rot (Anthracnose) Colletotrichum musaeBananas Finger rot Pestalozzia, Fusarium, Gleosporium sp.Bananas Crown rot Ceratocystis paradoxa, Fusarium roseum, Colletotrichum musae, Verticillium theobromaeOther fruitsPineapples Pineapple black rot Ceratocystis paradoxaWater melons Anthracnose C. lagenariumStrawberries Grey mold rot Botrytis cinereaGrapes Grey mold rot Botrytis cinereaSource: Adapted from Jay (1992).can grow rapidly on cut surfaces of cantaloupe, wa- hygiene practices during storage and processing oftermelon, and honeydew melon held at room temper- produce as well as the regulation of stringent quaran-ature (Golden et al., 1993), while E. coli 0157:H7 tine measures for rapid detection and identificationcan grow in ground apples stored at various temper- of these microbes in processed products.atures (Fisher and Golden, 1998) and in apple juiceat 4◦ C (Miller and Kaspar, 1994; Fratamico et al.,1997; Splittstoesser et al., 1996), in orange juice at4◦ C (Fratamico et al., 1997), on surface of citrus fruits SAFETY AND SANITATION(Pao and Brown, 1998). Aerobacter, Xanthomonas, Sanitation is of great concern as it protects produceand Achromobacter can grow inside the citrus fruits against postharvest diseases as well as protects con-(Hill and Faville, 1951), while Leuconostoc and Lac- sumers from foodborne illnesses caused by an ar-tobacillus in orange juice and Listeria in orange juice ray of human pathogens residing in the intestinesat 4◦ C (Parish and Higgins, 1989). Sometimes these of ruminants and humans that can get transmittedhuman pathogens could be traced to contamination. via the fecal-oral route such as E. coli 0157:H7,These findings indicate the accomplishment of fa- Salmonella, Cryptosporidium, Hepatitis A virus, andvorable environment for the survival and growth of Cyclospora by contamination of fruits and vegeta-human pathogenic microbes in/on the fresh produce, bles. Disinfection of produce by chlorination (Zhaothus alerting the empowerment of strict safety and et al., 2001), use of hydrogen peroxide, ozonation,
  • 31. 1 Fruit Microbiology 21use of quaternary ammonium salts in wash water can of foodborne human pathogens. The development ofhelp to prevent both postharvest and foodborne dis- new techniques of film coatings for fresh produceeases. Effectiveness of disinfectant depends on the involving the use of yeasts and lysozyme combina-nature of the cells as well as the characteristics of tions to fight against rot-causing microbes keeps thefruit tissues and juices. Han et al. (2002) reported the fruits fresh for longer periods or the advent of trans-inactivation of E. coli 0157:H7 on green peppers by genic fruits which act as vehicles for various dis-ozone gas treatment. Earlier a similar report on the ef- eases such as cancer, Hepatitis, etc. have revolution-fect of ozone and storage temperature on postharvest ized the very idea of consuming fruits. Consumptiondiseases of carrots was provided by Liew and Prange of cranberry juice was observed to prevent recur-(1994). Castro et al. (1993) have reported the use of rent urinary-tract infections in women (Stapleton,rather unusual technique of pulsed electric fields for 1999; Henig and Leahy 2000; Howell, 2002). Bacte-inactivation of microbes in foods. riocins have been long noticed as potential inhibitors or cidal agents against sensitive microorganisms un- der certain conditions, but these in foods may causeHEALTH IMPLICATIONS moderate antimicrobial activity followed by micro-Human pathogens such as enteric bacteria and bial growth, which may indicate development ofviruses cause illnesses exhibiting initial symptoms resistance, application of inadequate quantities ofsuch as diarrhea, nausea, vomiting, altered peri- bacteriocin, or its inability to find all cell microen-staltic movement of the intestine, fever that may vironments to inactivate the target microorganism.debilitate patient’s health and could aggravate to- The potential for commercial use of bacteriocinsward certain advanced complications or group of ail- may be enhanced when they are used in multihurdlements/syndrome sometimes resulting in death of vul- preservation systems. The use of robots for faster in-nerable age/immunocompromised patients. spection and screening of produce during processing E. coli: E. coli O157:H7 causes abdominal cramps enlarges the horizons for instant food inspection,and watery diarrhea/bloody diarrhea (hemorrhagic while with the use of DNA-based techniques, thecolitis) along with fever and vomiting and the in- whole scenario of conventional isolation and cumber-cidence recovery within 10 days. However, infection some identification protocols has speeded up to rapidof E. coli 0157:H7 in young children and elderly enumeration of very low infective dose pathogens,patients results in life-threatening complications as with even the detection of presence of several uncul-hemolytic uremic syndrome (HUS), which is char- tivatable microbes. The future techniques presentlyacterized by acute renal failure, hemolytic anemia, available as research trials would not only detect theand thrombocytopenia. microbes but also eradicate them or the toxic chemi- Salmonella enteritidis/S. typhimurium: The symp- cals produced by using tiny molecule/protein-coatedtoms share the similarity to E. coli infection along computer chips. Thus, future scenario holds the pos-with abdominal pain and cholera-like disease and sibilities of better product shelf life and little risksubsides within 2–4 days or may result in prolonged regarding the consumption of fresh fruits or their pro-enteritis with passage of mucus and pus in feces and cessed products.typhoidal speticaemic fever. Shigella sp.: This bacterium causes shigellosis/bacillary dysentery upon ingestion at very less in- REFERENCESfective dose by forming shiga toxin and produces Ahvenainen, R. 1996. New approaches in improvinginflammation of intestine, capillary thrombosis lead- the shelf life of minimally processed fruits anding to transverse ulceration or bacteremia manifested vegetables. Trends in Food Science and Technologyas bloody, mucoid scanty feces with tenesmus, fever, 7:179–186.and vomiting. HUS may also appear as a rare com- Altekruse, S.F., Cohen, M.L. and Swerdlow, D.L.plication in certain cases. 1997. Emerging foodborne diseases. Emerging Infectious Diseases 3:285–293.FUTURE PERSPECTIVES Altekruse, S.F. and Swerdlow, D.L. 1996. The changing epidemiology of foodborne diseases.The future era in fruit microbiology connotes the ad- American Journal of Medical Science 311:23–29.vent of fully automatized packaging, detection, and Arvanitoyannis, M. and Blanshard, J.M. 1994. Studystatus analyzers that would ensure stringent regula- of diffusion and permeation of gases in undrawn andtions to minimize losses by spoilage and transmission unaxially drawn films made from potato and rice
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  • 38. 28 Part I: Processing Technology Aerobacter aerogenes. Journal of Bacteriology Zhao, S.H., Mitchell, S.E., Meng, J.H., Kresovich, S., 81:353–358. Doyle, M.P., Dean, R.E., Casa, A.M. and Weller,Worbo, R. and Padilla-Zakour, O. 1999. Food safety J.W. 2000. Genomic typing of Escherichia coli and you. Venture Winter 99 1(4):1–4. O157:H7 by semi-automated fluorescent AFLPWorobo, R.W. 2000. Efficacy of the CiderSure 3500 analysis. Microbes Infection 2:107–113. Ultraviolet Light Unit in Apple Cider. Cornell Zhao, T. and Doyle, M.P. 2001. Evaluation of universal University, Department of Food Science and pre-enrichment broth for growth of heat-injured Technology, Ithaca, NY, p.1–6. pathogens. Journal of Food ProtectionWright, K.P. and Kader, A.E. 1997a. Effect of slicing 64:1751–1755. and controlled atmosphere storage on the ascorbate Zhao, T., Doyle, M.P., Zhao, P., Blake, P. and Wu, F.M. content and quality of strawberries and 2001. Chlorine inactivation of Escherichia coli persimmons. Postharvest Biology and Technology O157:H7 in water. Journal of Food Protection 10:39–48. 64:1607–1609.Wright, K.P. and Kader, A.E. 1997b. Effect of Zhuang, R.Y., Beuchat, L.R. and Angulo, F.J. 1995. controlled atmosphere storage on the quality and Fate of Salmonella montevideo on and in raw carotenoid content of sliced persimmons and tomatoes as affected by temperature and treatment peaches. Postharvest Biology and Technology with chlorine. Applied Environment Microbiology 10:89–97. 61(6):2127–2131.
  • 39. Handbook of Fruits and Fruit Processing Edited by Y. H. Hui Copyright © 2006 by Blackwell Publishing 2 Nutritional Values of Fruits Concepci´ n S´ nchez-Moreno, Sonia De Pascual-Teresa, o a Bego˜ a De Ancos, and M. Pilar Cano nIntroduction ing responsible in part for the antioxidant propertiesMacronutrients of fruits and foods of fruit origin. Water Manufacturing processes are changing the nutri- Carbohydrates tional properties of some foods. For instance, partial Fiber hydrogenation of vegetable oil results in the forma- Fats tion of trans-fatty acids, and heat treatment of pro- ProteinsMicronutrients tein solutions in an alkali environment results in the Vitamins formation of lysinoalanine. Both of these have been Minerals shown to have detrimental health effects. On the otherBioactive Compounds hand, some nutrients and bioactive compounds that Carotenoids are naturally present in fruits may undergo transfor- Flavonoids mations during food processing that neither decrease Phytosterols their nutritional value nor bioactive value but may in-References crease it by favoring their absorption and metabolism in the human body. In general, vitamins, minerals, water, and fibers are considered to be the main nutrients contributedINTRODUCTION by fruits to a balanced diet, and thus special atten-Nutrient is defined as a substance obtained from food tion should be addressed to this group of nutrientsand used in the body to promote growth, mainte- (Villarino-Rodr´guez et al., 2003). ınance, and repair of body tissues, or simply as a sub- In this chapter, we will present what we considerstance that provides nourishment. to be the contribution of fruits to human nutrition Broadly speaking, nutrients are classified into two in order to understand how the different processinggroups, namely macronutrients (also called energy- methods used in the food industry may modify theirproducing nutrients or energy-yielding nutrients) and contents, structure, and biological activity in humans.micronutrients (which are characterized by their es-sentiality for human health and the low quantities inwhich they need to be ingested). Energy-producing MACRONUTRIENTSnutrients include carbohydrates, fats, and proteins. WaterMicronutrients often refer to vitamins and minerals. Phytochemicals, also called bioactive compounds, Water plays two fundamental roles as a nutrient: (1)are substances present in foods in low levels that may protective and regulatory, by being a substrate of bio-have a role in health maintenance in humans. logical reactions or acting as the matrix or vehicle in Fruits have proved to be essential for a balanced which those reactions take place, and (2) an essentialdiet. This is believed to be mainly due to their content role as the temperature and pH regulator in the humanof vitamins, fibers, and phytochemicals, the latter be- body. Water also has a plastic function through the 29
  • 40. 30 Part I: Processing Technologymaintenance of the cell and tissue integrity. Around from 70% to 95% of the eatable part of the fruit (seetwo-thirds of the human body is composed of water, Table 2.1). For this reason, they are, together withand in general, the higher the metabolic activity of a vegetables, a very good source of water in the dietgiven tissue, the higher its percentage of water. within the solid foods. The content of water in a fruit Most of the body water is found within three may be greatly affected by the processing technology,body compartments: (1) intracellular fluid, which and in fact, some technologies used to increase thecontains approximately 70% water, (2) extracellu- shelf life of fruits do so through the reduction of theirlar fluid, which is the interstitial fluid, and (3) blood water content. It is important to bear in mind that theplasma. These two compartments contain ∼27% wa- water content of a fruit also changes during matura-ter. The body controls the amount of water in each tion, therefore the optimum degree of maturation ofcompartment by controlling the ion concentrations a fruit for a given processing technology may be dif-in those compartments. Therefore, gains or losses of ferent than for another processing technology. Thiselectrolytes are usually followed by shifts of fluid to will also affect the water content in the final product.restore osmotic equilibrium. Although a low intake of water has been associated Carbohydrateswith some chronic diseases, this evidence is insuffi-cient to establish water intake recommendations. In- Energy is required for all body processes, growth, andstead, an adequate intake of water has been set by the physical activity. Carbohydrates are the main sourceFood and Nutrition Board of the Institute of Medicine of energy in the human diet. The energy producedin the United States, to prevent deleterious effects of from carbohydrate metabolism may be used directlydehydration. This adequate intake of total water is to cover the immediate energy needs or be trans-3.7 l for men and 2.7 l for women. Fluids should rep- formed into an energy deposit in the body in the formresent 81% of the total intake, and water contained of fat. Carbohydrates also have a regulatory func-in foods represent the other 19% (IM, 2004). tion, for instance, by selecting the microflora present The body has three sources of water: (1) ingested in the intestines. Fructose has been known to in-water and beverages, including fruit juices, (2) the crease plasma urate levels due to rapid fructokinase-water content of solid foods, and (3) metabolic wa- mediated metabolism to fructose 1-phosphate. Thister. Fruits have a high percentage of water that ranges increase in plasma urate levels seems to cause an Table 2.1. Fruit Composition (Grams per 100 g of Edible Portion) Fruit Water Carbohydrates Protein Fat Fiber Apple 86 12.0 0.3 Tr 2.0 Apricot 88 9.5 0.8 Tr 2.1 Avocado 79 5.9 1.5 12 1.8 Banana 75 20.0 1.2 0.3 3.4 Cherry 80 17.0 1.3 0.3 1.2 Grape 82 16.1 0.6 Tr 0.9 Guava 82 15.7 1.1 0.4 5.3 Kiwi fruit 84 9.1 1.0 0.4 2.1 Mango 84 15.0 0.6 0.2 1.0 Melon 92 6.0 0.1 Tr 1.0 Orange 87 10.6 1.0 Tr 1.8 Papaya 89 9.8 0.6 0.1 1.8 Peach 89 9.0 0.6 Tr 1.4 Pear 86 11.5 0.3 Tr 2.1 Pineapple 84 12.0 1.2 Tr 1.2 Plum 84 9.6 0.8 Tr 2.2 Raspberry 86 11.9 1.2 0.6 6.5 Strawberry 91 5.1 0.7 0.3 2.2 Watermelon 93 8.0 1.0 Tr 0.6 Source: Moreiras et al. (2001).
  • 41. 2 Nutritional Values of Fruits 31increase in plasma antioxidant capacity in humans acts as a laxative because of osmotic transfer of water(Lotito and Frei, 2004). into the bowel. In general, the carbohydrates are classified into Sucrose is the most abundant oligosaccharide inthree groups: monosaccharides, oligosaccharides, fruits; however, there are others such as maltose,and polysaccharides. Monosaccharides include pen- melibiose, raffinose, or stachyose that have beentoses (arabinose, xylose, and ribose) and hexoses described in grapes, and 1-kestose in bananas. Other(glucose, fructose, and galactose). Oligosaccha- oligosaccharides are rare in fruits. Starch is presentrides are sucrose, maltose, lactose, raffinose, and in very low amounts in fruits, since its concentrationstachyose. Polysaccharides include starch (com- decreases during maturation. The only exception isposed of amylose and amylopectine, both polymers banana that may have concentrations of starch higherof glucose), glycogen, and other polysaccharides, than 3% (Belitz and Grosch, 1997).which form part of fiber which we will review in During food processing, carbohydrates are mainlythe following section. involved in two kinds of reactions: on heating they The recommended dietary allowance (RDA) for darken in color or caramelize, and some of them com-carbohydrates is 130 g/day, except in the cases bine with proteins to give dark colors known as theof pregnancy (when it is 175 g/day) and lacta- browning reaction.tion (210 g/day). With respect to the total energyconsumed per day, carbohydrates should represent Fiber45–65% (IM, 2002). After water, carbohydrates are the main compo- Fiber is often referred to as unavailable carbohy-nent of fruits and vegetables and represent more than drate. This definition has been a controversy for90% of their dry matter. The main monosaccharides years. Fiber is a generic term that includes those plantare glucose and fructose. Their concentration may constituents that are resistant to digestion by secre-change depending on the degree of maturation of the tions of the human gastrointestinal tract. Therefore,fruit. The relative abundance of glucose and fructose dietary fiber does not have a defined composition, butalso changes from one fruit to another (Table 2.2). varies with the type of foodstuff. Perhaps we can sayFor instance, in peaches, plums, and apricots, there that fiber may not be a carbohydrate and it may beis more glucose than fructose and the opposite occurs available.in the case of apples or pears. Other monosaccharides, Fiber has mainly a regulatory function in the hu-such as galactose, arabinose, and xylose, are present man body. The role of fiber in human health has beenin minimal amounts in some fruits, especially orange, the subject of many studies in the last 30 years. Inlemon, or grapefruit. Fruits such as plums, pears, and most of these studies, the results have suggested im-cherries also contain the sugar alcohol sorbitol, which portant roles of fiber in maintaining human health. Table 2.2. Sugar Contents of Fruits (Grams per 100 g of Edible Portion) Fruit Fructose Glucose Sucrose Maltose Total Sugar Apple 5.6 1.8 2.6 – 10.0 Apricot 0.4 1.9 4.4 – 6.7 Avocado 0.1 0.1 – – 0.2 Banana 2.9 2.4 5.9 – 11.3 Cherry 6.1 5.5 – – 11.6 Grapefruit 1.6 1.5 2.3 0.1 5.7 Grape 6.7 6.0 0.0 0.0 12.9 Mango 3.8 0.6 8.2 – 12.7 Orange 2.0 1.8 4.4 – 8.3 Peach 4.0 4.5 0.2 – 8.7 Pear 5.3 4.2 1.2 – 10.7 Plum 3.2 5.1 0.1 0.1 8.6 Strawberry 2.3 2.6 1.3 – 6.2 Watermelon 2.7 0.6 2.8 – 6.2 Source: Belitz and Grosch (1997) and Li et al. (2002).
  • 42. 32 Part I: Processing TechnologyThe role of fiber in human health is mainly protective Fatty acids are also needed to form cell struc-against disease, e.g., diseases of the gastrointestinal tures and to act as precursors of prostaglandins. Fattytract, circulation related diseases and metabolic acids are part of triglycerides, which are the princi-diseases (Saura-Calixto, 1987). ple form in which fat occurs. Fatty acids may oc- The major components of dietary fiber are the cur naturally with various chain lengths and differentpolysaccharides celluloses, hemicelluloses, pectins, numbers of double bonds. They may be saturatedgums, and mucilages. Lignin is the other component (butyric, caproic, caprylic, capric, lauric, palmitic,that is included in most definitions of fiber but it is stearic, and myristic acids), monounsaturated (oleicnot a carbohydrate. and palmitoleic acid), and polyunsaturated (linoleic, Fiber may be classified as water soluble and in- linolenic, and arachidonic acids) also known assoluble. Gums, mucilages, some hemicelluloses, and PUFAs. Linoleic and linolenic acids cannot be syn-pectins are part of the soluble fiber. Celluloses, hemi- thesized in the body and are known as essential fattycelluloses, and lignins are insoluble fibers. Fruits are acids. They are needed to build and repair cell struc-good sources of both classes of fibers, especially tures, such as the cell wall and, notably, tissues in thesoluble fiber. Fiber, together with vitamins, is the central nervous system, and to form the raw materialmain nutritional reason for using fruits for a balanced for prostaglandin production. Inflammatory and otherdiet. chronic diseases are noted for exhibiting a deficiency There are several fiber-associated substances that of polyunsaturated fatty acids in the bloodstream.are found in fruit fiber, which may have some nutri- Fatty acids that contain double carbon bonds can existtional interest. Among them are phytates, saponins, in either of two geometrically isomeric forms: cis andtannins, lectins, and enzyme inhibitors. Saponins, trans. Trans-fatty acids are produced in the hydro-which are mainly present in some tropical fruits, genation process in the food industry and may playmay enhance the binding of bile acids to fiber and a role in atherosclerotic vascular disease (Sardesai,reduce cholesterol absorption. Tannins are polyphe- 1998).nolic compounds widely distributed in fruits, which In general, fat should represent between 20% andcan bind proteins and metals and reduce their ab- 35% of the total energy consumed per day in ordersorption. Lectins, which are present in bananas and to reduce risk of chronic disease while providing in-some berries, are glycoproteins that can bind specific takes of essential nutrients. This fat should includesugars and affect the absorption of other nutrients. 10–14 g/day of linoleic acid and 1.2–1.6 g/day of The RDA for fiber is 25–30 g/day, depending on linolenic acid.age and sex, except in the case of children from 1 to Fat content in fruits is in general very low (see3 years, in which case it is 19 g/day. Table 2.1). However, in cherimoya (1%) and avocado Dietary fiber is present in fruits in amounts that (12–16%), the lipid levels are higher. In avocado, themay be as high as 7% of the eatable part of the fruit most abundant fatty acids are palmitic, palmitoleic,(see Table 2.1). Within fiber, the most common com- stearic, oleic, linoleic, and linolenic acids, but theponents in fruits are celluloses, hemicelluloses, and amounts may change a lot with the variety, matu-pectins. Pectins are important in the technological rity, processing, and storage conditions (Ansorena-process, since they may be deeply modified and this Artieda, 2000).modification not only has an influence on the nutri-tional value of the final food, but also has an impacton the texture and palatability of the product. Proteins The importance of protein in the diet is primarily to act as a source of amino acids, some of which areFats essential because the human body cannot synthesizeFat has three important roles as a nutrient: it is a them. From the 20 amino acids that are part of thehighly concentrated source of energy, it serves as a structure of proteins, almost half of them are con-carrier for fat-soluble vitamins and there are some sidered to be essential, including isoleucine, leucine,fatty acids that are essential nutrients that can only be lysine, methionine, phenylalanine, threonine, tryp-ingested with fat. Fat also serves as a carrier for some tophan, and valine. The RDA for proteins is 34–of the bioactive compounds present in fruits such as 56 g/day, depending on age and sex, and in the case ofphytoestrogens and carotenoids that are lypophylic. pregnancy and lactation, it is 71 g/day. With respect
  • 43. 2 Nutritional Values of Fruits 33to the total energy consumed per day, carbohydrates the optimal levels of intake for these micronutrients(proteins) should represent 10–35%. in order to achieve maximum health benefit and the Proteins are essential structural components of all best physical and mental performance.cells and are needed by the human body to buildand repair tissues, for the synthesis of enzymes, hor- Vitamin Cmones, and others. They are also involved in the im-mune system, coagulation, etc. Therefore, proteins Antioxidants have important roles in cell function andplay both regulatory and plastic roles in the human have been implicated in processes that have their ori-body. gins in oxidative stress, including vascular processes, Proteins are made up of a long chain of amino inflammatory damage, and cancer. L-Ascorbic acidacids, sometimes modified by the addition of (L-AA, vitamin C, ascorbate) is the most effectiveheme, sugars, or phosphates. Proteins have primary, and least toxic antioxidant. Vitamin C may also con-secondary, tertiary, and quaternary structures, all of tribute to the maintenance of a healthy vasculaturewhich may be essential for the protein to be active. and to a reduction in atherogenesis through the regu-The primary structure of a protein is its amino acid lation of collagen synthesis, prostacyclin production,sequence and the disulphide bridges, i.e., all covalent and nitric oxide (Davey et al., 2000; S´ nchez-Moreno aconnections in a protein. The secondary structure is et al., 2003a, b). The second US National Health andthe way a small part, spatially near in the linear se- Nutrition Examination Survey reported that a low in-quence of a protein, folds up into ␣-helix or ␤-pleated take of vitamin C is associated with blood concen-sheets. The tertiary structure is the way the secondary trations of vitamin C = 0.3 mg/dl, whereas bloodstructures fold onto themselves to form a protein or concentrations in well-nourished persons fluctuatea subunit of a more complex protein. The quaternary between 0.8 and 1.3 mg/dl. An increase in intakestructure is the arrangement of polypeptide subunits of vitamin C is associated with health status (Simonwithin complex proteins made up of two or more sub- et al., 2001).units, sometimes associated with non-proteic groups. Vitamin C is an essential nutrient for humans; un-Food processing may affect these four structures in like most mammals, we cannot synthesize vitaminmany ways, thus modifying the activity of the protein C, and therefore must acquire it from the diet. Forand also its nutritional value. Amino acids and pro- adults, dietary needs are met by a minimum intaketeins containing lysine or arginine as their terminal of 60 mg/day. However, the preventative functionsamino acids are also involved in the Maillard reac- of vitamin C in aging related diseases provide com-tions that have a nutritional and sensory impact on pelling arguments for an increase in dietary intakesprocessed foods. and RDAs. Men and women who consumed four Nitrogenated compounds are present in fruits in daily vegetable and fruit servings had mean vitaminlow percentages (0.1–1.5%). From a quantitative C intakes of 75 and 77 mg, respectively. Men andpoint of view, fruits are not a good source of pro- women who consumed five daily vegetable and fruitteins, however, in general berries are a better source servings averaged 87 and 90 mg vitamin C, respec-than the rest of the fruits. Cherimoya and avocado tively (Taylor et al., 2000).also present higher levels of proteins than other fruits The primary contributors to daily vitamin intake(Torija-Isasa and C´ mara-Hurtado, 1999). a are fruit juices (21% of total), whereas all fruits to- There are some free amino acids that may be char- gether contributed nearly 45% of total vitamin C in-acteristic of a certain fruit. This is the case of proline take. Relatively high amounts of vitamin C are foundwhich is characteristic of oranges but cannot be found in strawberries and citrus fruits, although the avail-in strawberries or bananas. ability of vitamin C within these food sources will be influenced by numerous factors. Virtually all of the vitamin C in Western diets is derived from fruits andMICRONUTRIENTS vegetables. In general, fruits tend to be the best food sources of the vitamin. Especially rich sources of vi-Vitamins tamin C are blackcurrant (200 mg/100 g), strawberryThirteen vitamins have been discovered to date, and (60 mg/100 g), and the citrus fruits (30–50 mg/100 g).each has a specific function. Vitamins must be sup- Not all fruits contain such levels, and apples, pears,plied in adequate amounts via the diet in order to meet and plums represent only a very modest source ofrequirements. Scientists are interested in determining vitamin C (3–5 mg/100 g). However, much fruit is
  • 44. 34 Part I: Processing TechnologyTable 2.3. Vitamin Content of Fruits (Value per 100 g of Edible Portion) Vitamin Vitamin E (mg) Vitamin A Thiamin Riboflavin Niacin Pyridoxine FolateFruit C (mg) (␣-tocopherol) (␮g RAE) (mg) (mg) (mg) (mg) (␮g)Apple 4.6 0.18 3 0.017 0.026 0.091 0.041 3Apricot 10.0 0.89 96 0.030 0.040 0.600 0.054 9Avocado 10.0 2.07 7 0.067 0.130 1.738 0.257 58Banana 8.7 0.10 3 0.031 0.073 0.665 0.367 20Cherry 7.0 0.07 3 0.027 0.033 0.154 0.049 4Grape 10.8 0.19 3 0.069 0.070 0.188 0.086 2Guava 183.5 0.73 31 0.050 0.050 1.200 0.143 14Kiwi fruit 75.0 – 9 0.020 0.050 0.500 – –Orange 53.2 0.18 11 0.087 0.040 0.282 0.060 30Papaya 61.8 0.73 55 0.027 0.032 0.338 0.019 38Passion fruit 30.0 0.02 64 0.000 0.130 1.500 0.100 14Peach 6.6 0.73 16 0.024 0.031 0.806 0.025 4Pear 4.2 0.12 1 0.012 0.025 0.157 0.028 7Pineapple 36.2 0.02 3 0.079 0.031 0.489 0.110 15Plum 9.5 0.26 17 0.028 0.026 0.417 0.029 5Raspberry 26.2 0.87 2 0.032 0.038 0.598 0.055 21Strawberry 58.8 0.29 1 0.024 0.022 0.386 0.047 24Source: USDA (2004).Note: RAE—retinol activity equivalents.eaten raw and the low pH of fruits stabilizes the equivalents (␣-TE). One ␣-TE is defined as the bi-vitamin during storage (Davey et al., 2000). ological activity of 1 mg RRR-␣-tocopherol. One A summary of the average vitamin C content of IU is equal to 0.67 ␣-TE (Brigelius-Floh´ et al., ecertain fruits (mg per 100 g of edible portion) is given 2002).in Table 2.3. Recent research evidences the role of vitamin E in reducing the risk of developing degenerative disease. This role is suggested on the hypothesis that pre-Vitamin E venting free radical-mediated tissue damage (e.g., toVitamin E is the generic term for a family of related cellular lipids, proteins, or DNA) may play a key rolecompounds known as tocopherols and tocotrienols. in delaying the pathogenesis of a variety of degenera-Naturally occurring structures include four toco- tive diseases (Bramley et al., 2000; S´ nchez-Moreno apherols (␣-, ␤-, ␥ -, and ␦-) and four tocotrienols et al., 2003b).(␣-, ␤-, ␥ -, and ␦-). Of the eight naturally occur- There is some controversy about the optimumring forms of ␣-tocopherol (RRR-, RSR-, RRS-, RSS-, range of vitamin E intake for associated healthSRR-, SSR-, SRS-, and SSS-), only one form, RRR- benefits. Some authors recommend intakes of 130–␣-tocopherol, is maintained in human plasma and 150 IU/day or about 10 times the US Food and Nutri-therefore is the active form of vitamin E (Trumbo tional Board (15 mg/day) on the basis of the protec-et al., 2003). tion in relation to cardiovascular disease. Other au- ␣-Tocopherol is the predominant tocopherol form thors indicate that the optimal plasma ␣-tocopherolfound naturally in foods, except in vegetable oils concentration for protection against cardiovascularand nuts, which may contain high proportions of disease and cancer is >30 mmol/l at common plasma␥ -tocopherol (Bramley et al., 2000). lipid concentrations. A daily dietary intake of only The vitamin E activity of tocopherols is fre- about 15–30 mg ␣-tocopherol would be sufficient toquently calculated in international units (IU), with maintain this plasma level, an amount that could be1 IU defined as the biological activity of 1 mg all- obtained from the diet (Bramley et al., 2000).rac-␣-tocopheryl acetate. Recently, the US National The richest sources of vitamin E are vegetable oilsResearch Council has suggested that vitamin E and the products made from them, followed by breadactivity could be expressed as RRR-␣-tocopherol and bakery products and nuts. Vegetables and fruits
  • 45. 2 Nutritional Values of Fruits 35contain little amount of vitamin E (Bramley et al., and nucleotide metabolism. The RDA for folate is2000). 400 ␮g/day. Excellent food sources of folate from Table 2.3 shows the range of concentrations fruits (>55 ␮g/day) include citrus fruits and juices.(mg per 100 g of edible portion) of vitamin E Table 2.3 shows the range of concentrations(␣-tocopherol) from certain fruits. (amount per 100 g of edible portion) of thiamin, ri- boflavin, niacin, pyridoxine, and folate from selected fruits.Vitamin B-1, B-2, B-3, B-6, FolateThiamin (vitamin B-1), riboflavin (vitamin B-2),niacin (vitamin B-3), and pyridoxine (vitamin B-6), Mineralsare used as coenzymes in all parts of the body. They An adequate intake of minerals is essential for a highparticipate in the metabolism of fats, carbohydrates, nutritional quality of the diet, and it also contributesand proteins. They are important for the structure and to the prevention of chronic nutrition related dis-function of the nervous system (IM, 1998; ASNS, eases. However, even in Western societies, intake of2004; Lukaski, 2004). some minerals such as calcium, iron, and zinc is often Thiamin diphosphate is the active form of thiamin. marginal in particular population groups e.g., smallIt serves as a cofactor for several enzymes involved children or female adolescents, while the intake ofin carbohydrate catabolism. The suggested intake for sodium or magnesium, reach or exceed the recom-thiamin is 1.15 g/day. Thiamin requirement depends mendations.on energy intake, thus the suggested RDA is 0.5 Table 2.4 shows the mineral content (amount permg/1000 kcal. 100 g of edible portion) from certain fruits. Riboflavin is required for oxidative energy produc-tion. Because riboflavin is found in a variety of foods,either from animal or vegetable origin, riboflavin de- Ironficiency is uncommon in Western countries. Recom-mendations for riboflavin intake are based on energy Iron (Fe) is an essential nutrient that carries oxy-intake. It is suggested that an intake of 0.6 mg/1000 gen and forms part of the oxygen-carrying proteins,kcal will meet the needs of most healthy adults. The hemoglobin in red blood cells and myoglobin incurrent RDA is 1.2 g/day. muscle. It is also a necessary component of various Niacin (nicotinic acid and nicotinamide). Nicoti- enzymes. Body iron is concentrated in the storagenamide is a precursor of nicotinamide adenine forms, ferritin and hemosiderin, in bone marrow,(NAD), nucleotide, and nicotinamide adenine din- liver, and spleen. Body iron stores can usually beucleotide phosphate (NADP), in which the nicoti- estimated from the amount of ferritin protein innamide moiety acts as electron acceptor or hydrogen serum. Transferrin protein in the blood transports anddonor, respectively, in many biological redox reac- delivers iron to cells (Lukaski, 2004).tions. The RDA is expressed in milligram niacin The body normally regulates iron absorption inequivalents (NE) in which 1 mg NE = 1 mg niacin or order to replace the obligatory iron losses of about60 mg tryptophan. For individuals above 13 years of 1–1.5 mg/day. The RDAs for iron are 10 mg for menage, the RDA is 16 mg NE/day for males and 14 mg over 10 years and for women over 50 years, and 15 mgNE/day for females. for 11- 50-year-old females (ASNS, 2004). The chemical name of vitamin B-6 is pyridoxine Non-heme iron is the source of iron in the diethydrochloride. Other forms of vitamin B-6 include from plant foods. The absorption of non-heme ironpyridoxal, and pyridoxamine. Vitamin B-6 is one of is strongly influenced by dietary components, whichthe most versatile enzyme cofactors. Vitamin B-6 in bind iron in the intestinal lumen. Non-heme ironthe form of pyridoxal phosphate acts as a cofactor absorption is usually from 1% to 20%. The mainfor transferases, transaminases, and decarboxylases, inhibitory substances are phytic acid from cerealused in transformations of amino acids. The RDA for grains and legumes such as soy, and polyphenol com-vitamin B-6 is 1.6 mg/day. pounds from beverages such as tea and coffee. The Folate is an essential vitamin that is also known main enhancers of iron absorption are ascorbic acidas folic acid and folacin. The metabolic role of from fruits and vegetables, and the partially digestedfolate is as an acceptor and donor of one-carbon peptides from muscle tissues (Frossard et al., 2000;units in a variety of reactions involved in amino acid Lukaski, 2004).
  • 46. 36 Part I: Processing TechnologyTable 2.4. Mineral Content of Fruits (Value per 100 g of Edible Portion)Fruit Fe (mg) Ca (mg) P (mg) Mg (mg) K (mg) Na (mg) Zn (mg) Cu (mg) Se (␮g)Apple 0.12 6 11 5 107 1 0.04 0.027 0.0Apricot 0.39 13 23 10 259 1 0.20 0.078 0.1Avocado 0.55 12 52 29 485 7 0.64 0.190 0.4Banana 0.26 5 22 27 358 1 0.15 0.078 1.0Cherry 0.36 13 21 11 222 0 0.07 0.060 0.0Grape 0.36 10 20 7 191 2 0.07 0.127 0.1Guava 0.31 20 25 10 284 3 0.23 0.103 0.6Kiwi fruit 0.41 26 40 30 332 5 – – –Orange 0.10 40 14 10 181 0 0.07 0.045 0.5Papaya 0.10 24 5 10 257 3 0.07 0.016 0.6Passion fruit 1.60 12 68 29 348 28 0.10 0.086 0.6Peach 0.25 6 20 9 190 0 0.17 0.068 0.11Pear 0.17 9 11 7 119 1 0.10 0.082 0.1Pineapple 0.28 13 8 12 115 1 0.10 0.099 0.1Plum 0.17 6 16 7 157 0 0.10 0.057 0.0Raspberry 0.69 25 29 22 151 1 0.42 0.090 0.2Strawberry 0.42 16 24 13 153 1 0.14 0.048 0.4Source: USDA (2004).Calcium adult contains about 400–500 g. The greatest amount of body phosphorus can be found primarily in boneCalcium (Ca) is the most common mineral in the hu- (85%) and muscle (14%). Phosphorus is primarilyman body. Calcium is a nutrient in the news because found as phosphate (PO4 2− ). The nucleic acids—adequate intakes are an important determinant of deoxyribonucleic acid (DNA) and ribonucleic acidbone health and reduced risk of fracture or osteo- (RNA)—are polymers based on phosphate esterporosis (Frossard et al., 2000). monomers. The high-energy phosphate bond of ATP Approximately 99% of total body calcium is in the is the major energy currency of living organisms. Cellskeleton and teeth, and 1% is in the blood and soft membranes are composed largely of phospholipids.tissues. Calcium has the following major biological The inorganic constituents of bone are primarily afunctions: (a) structural as stores in the skeleton, calcium phosphate salt. The metabolism of all ma-(b) electrophysiological—carries a charge during an jor metabolic substrates depends on the functioningaction potential across membranes, (c) intracellular of phosphorus as a cofactor in a variety of enzymesregulator, and (d) as a cofactor for extracellular en- and as the principal reservoir for metabolic energyzymes and regulatory proteins (Frossard et al., 2000; (ASNS, 2004).ASNS, 2004). The RDAs for phosphorus (mg/day) are based The dietary recommendations vary with age. on life stage groups. Among others, for youthAn amount of 1300 mg/day for individuals aged 9–18 years, the RDA is 1250 mg, which indicates9–18 years, 1000 mg/day for individuals aged 19– the higher need for phosphorus during the adoles-50 years, and 1200 mg/day for individuals over the cent growth. Adults 19 years and older have a RDAage of 51 years. The recommended upper level of of 700 mg (IM, 1997; ASNS, 2004).calcium is 2500 mg/day (IM, 1997; ASNS, 2004). Calcium is present in variable amounts in all thefoods and water we consume, although vegetables are Magnesiumone of the main sources. Of course, dairy products are Magnesium (Mg) is the fourth most abundant cationexcellent sources of calcium. in the body, with 60% in the bone and 40% dis- tributed equally between muscle and non-muscular soft tissue. Only 1% of magnesium is extracellular.Phosphorus Magnesium has an important role in at least 300 fun-Phosphorus (P) is an essential mineral that is found damental enzymatic reactions, including the transferin all cells within the body. The body of the human of phosphate groups, the acylation of coenzyme A in
  • 47. 2 Nutritional Values of Fruits 37the initiation of fatty acid oxidation, and the hydrol- proteins, and nucleic acids. Zinc also plays a ma-ysis of phosphate and pyrophosphate. In addition, jor role in gene expression (Frossard et al., 2000;it has a key role in neurotransmission and immune Lukaski, 2004).function. Magnesium acts as a calcium antagonist The RDAs for zinc are 8 and 11 mg/day for womenand interacts with nutrients, such as potassium, vita- and men, respectively (ASNS, 2004).min B-6, and boron (Lukaski, 2004; ASNS, 2004). The RDA, from the US Food and Nutrition Board,vary according to age and sex. The RDAs for mag- Coppernesium are 320 and 420 mg/day for women and men Copper (Cu) is utilized by most cells as a component(adults over 30 years), respectively (IM, 1997; ASNS, of enzymes that are involved in energy production2004). (cytochrome oxidase), and in the protection of cells from free radical damage (superoxide dismutase).Potassium Copper is also involved with an enzyme that strength- ens connective tissue (lysyl oxidase) and in brainPotassium (K) in the form of K+ is the most essen- neurotransmitters (dopamine hydroxylase) (ASNS,tial cation of the cells. Its high intracellular concen- 2004).tration is regulated by the cell membrane through The estimated safe and adequate intake for copperthe sodium–potassium pump. Most of the total body is 1.5–3.0 mg/day (ASNS, 2004).potassium is found in muscle tissue (ASNS, 2004). The estimated minimum requirement for potas-sium for adolescents and adults is 2000 mg or Selenium50 mEq/day. The usual dietary intake for adults isabout 100 mEq/day. Most foods contain potassium. Selenium (Se) is an essential trace element thatThe best food sources are fruits, vegetables, and functions as a component of enzymes involvedjuices (IM, 2004; ASNS, 2004). in antioxidant protection and thyroid hormone metabolism (ASNS, 2004). The RDAs are 70 ␮g/day for adult males, andSodium 55 ␮g/day for adult females. Foods of low proteinSodium (Na) is the predominant cation in extracel- content, including most fruits and vegetables, pro-lular fluid and its concentration is under tight home- vide little selenium. Food selenium is absorbed withostatic control. Excess dietary sodium is excreted in efficiencies of 60–80% (ASNS, 2004).the urine. Sodium acts in consort with potassium tomaintain proper body water distribution and bloodpressure. Sodium is also important in maintaining BIOACTIVE COMPOUNDSthe proper acid–base balance and in the transmission Carotenoidsof nerve impulses (ASNS, 2004). The RDAs for sodium ranges from 120 mg/day Carotenoids are lipid-soluble plant pigments com-for infants to 500 mg/day for adults and children mon in photosynthetic plants. The term carotenoidabove 10 years. Recommendations for the maxi- summarizes a class of structurally related pigments,mum amount of sodium that can be incorporated mainly found in plants. At present, more than 600into a healthy diet range from 2400 to 3000 mg/day. different carotenoids have been identified, althoughThe current recommendation for the general healthy only about two dozens are regularly consumed bypopulation to reduce sodium intake has been a mat- humans. The most prominent member of this groupter of debate in the scientific community (Kumanyika is ␤-carotene. Most carotenoids are structurally ar-and Cutler, 1997; IM, 2004; ASNS, 2004). ranged as two substituted or unsubstituted ionone rings separated by four isoprene units containing nine conjugated double bonds, such as ␣- and ␤-carotene,Zinc lutein, and zeaxanthin, and ␣- and ␤-cryptoxanthinZinc (Zn) acts as a stabilizer of the structures of (Goodwin and Merce, 1983; Van den Berg et al.,membranes and cellular components. Its biochemical 2000). These carotenoids, along with lycopene, anfunction is as an essential component of a large num- acylic biosynthetic precursor of ␤-carotene, are mostber of zinc-dependent enzymes, particularly in the commonly consumed and are most prevalent in hu-synthesis and degradation of carbohydrates, lipids, man plasma (Castenmiller and West, 1998).
  • 48. 38 Part I: Processing Technology I 4 16 17 19 20 18 5 3 7 9 11 13 15 14 12 10 8 6 1 2 2 6 1 8 10 12 14 15 13 11 9 7 3 16 17 5 18 20 19 4 IIFigure 2.1. Structure and numbering of the carotenoid carbon skeleton. (Source: Shahidi et al., 1998.) All carotenoids can be derived from an acyclic radical cation (Canfield et al., 1992; Sies and Krinsky,C40H56 unit by hydrogenation, dehydrogenation, 1995; Van den Berg et al., 2000; S´ nchez-Moreno et acyclization and/or oxidation reactions (Fig. 2.1). All al., 2003c).specific names are based on the stem name carotene, Carotenoid intake assessment has been shown towhich corresponds to the structure and numbering in be complicated mainly because of the inconsisten-Figure 2.1 (Shahidi et al., 1998). cies in food composition tables and databases. Thus, The system of conjugated double bonds influences there is a need for more information about indi-their physical, biochemical, and chemical properties. vidual carotenoids. The estimated dietary intake ofBased on their composition, carotenoids are subdi- carotenoids in Western countries is in the range ofvided into two groups. Those contain only carbon 9.5–16.1 mg/day. To ensure the intake of a sufficientand hydrogen atoms, which are collectively assigned quantity of antioxidants, the human diet, which real-as carotenes, e.g., ␤-carotene, ␣-carotene, and ly- istically contains 100–500 g/day of fruit and vegeta-copene. The majority of natural carotenoids contain bles, should contain a high proportion of carotenoid-at least one oxygen function, such as keto, hydroxy, or rich products. No formal diet recommendation forepoxy groups, and are referred to as xanthophylls or carotenoids has yet been established, but some ex-oxocarotenoids. In their natural sources, carotenoids perts suggest intake of 5–6 mg/day, which is aboutmainly occur in the all-trans configuration (Goodwin twice the average daily U.S. intake. In the case of vi-and Merce, 1983; Van den Berg et al., 2000). tamin A, for adult human males, the RDA is 1000 ␮g Carotenoid pigments are of physiological interest retinyl Eq/day, and for adult females, 800 ␮g retinylin human nutrition, since some of them are vita- Eq/day (O’Neill et al., 2001; Trumbo et al., 2003).min A precursors, especially ␤-carotene. ␣-Carotene, Citrus fruits are the major source of ␤-and ␣- and ␤-cryptoxanthin possess provitamin A cryptoxanthin in the Western diet. The major fruitactivity, but to a lesser extent than ␤-carotene. On contributors to the carotenoid intake in Western dietsthe basis of epidemiological studies, diet rich in fruits are orange (␤-cryptoxanthin and zeaxanthin), tanger-and vegetables containing carotenoids is suggested to ine (␤-cryptoxanthin), peach (␤-cryptoxanthin andprotect against degenerative diseases such as cancer, zeaxanthin), watermelon (lycopene), and banana (␣-cardiovascular diseases, and macular degeneration. carotene). Other relatively minor contributors areRecent clinical trials on supplemental ␤-carotene kiwi fruit, lemon, apple, pear, apricot, cherry, melon,have reported a lack of protection against degener- strawberry, and grape (Granado et al., 1996; O’Neillative diseases. Much of the evidence has supported et al., 2001).the hypothesis that lipid oxidation or oxidative stressis the underlying mechanism in such diseases. To Flavonoidsdate carotenoids are known to act as antioxidantsin vitro. In addition to quenching of singlet oxygen, Flavonoids are the most common and widely dis-carotenoids may react with radical species either by tributed group of plant phenolics. Over 5000 differentaddition reactions or through electron transfer reac- flavonoids have been described to date and they aretions, which results in the formation of the carotenoid classified into at least 10 chemical groups. Among
  • 49. 2 Nutritional Values of Fruits 39Flavones R1 OH B HO O R1 A C Apigenin H Luteolin OH OH OFlavonols R1 OH HO O R1 R2 R2 Kaempferol H H OH Quercetin OH H Myricetin OH OH OH OFlavanols OH OH HO O R1 R2 Catechin H OH R1 Epicatechin OH H R2 OHFlavanones R1 R2 R1 R2 HO O Naringenin H OH Hesperetin OH OCH3 OH OAnthocyanidins R1 OH R1 R2 Cyanidin OH H HO O Pelargonidin H H R2 Malvidin OCH3 OCH3 OH OHIsoflavones R1 HO O Daidzein H Genistein OH Figure 2.2. Structures of the main flavonoids in fruits. (Source: R1 O OH Harborne, 1993.)them, flavones, flavonols, flavanols, flavanones, an- Numerous epidemiological studies support thethocyanins, and isoflavones are particularly common concept that regular consumption of foods and bever-in fruits (Fig. 2.2). The most-studied members of ages rich in antioxidant flavonoids is associated withthese groups are included in Table 2.5, along with a decreased risk of cardiovascular disease mortality.some of their fruit sources (Bravo, 1998). There is also scientific evidence that flavonoids may
  • 50. 40 Part I: Processing Technology Table 2.5. Classification of Flavonoids and Their Presence in Fruits Subclasses Flavonoids Fruits Flavones Apigenin, luteolin Apples, blueberries, grapefruit, grapes, oranges Flavonols Quercetin, kaempferol, myricetin Apples, berries, plums Flavanols Catechin, epicatechin, Apples, berries, grapes, plums epigallocatechin gallate Flavanones Hesperetin, naringenin Citrus fruits Anthocyanins Cyanidin, pelargonidin, malvidin Berries, grapes Isoflavones Genistein, daidzein Currants, passion fruit Source: De Pascual-Teresa et al. (2000) and Franke et al. (2004).protect against some cancers. It has been shown in the Factors like modification on the flavonoid struc-past that flavonoid content and structure may change ture or substitution by different sugars or acids maywith technological processes increasing or decreas- deeply affect the biological activity of flavonoids anding their contents and biological activity (Garc´a- ı in this sense different processing of the fruits may alsoAlonso et al., 2004). influence their beneficial properties for human health. Most of the existing flavonoids in fruits have shownantioxidant activity in in vitro studies, and almost allthe fruits that have been screened for their antioxidant Phytosterolsactivity have shown to a lower or higher extent some Plant-based foods contain a large number of plantantioxidant and radical scavenger activity. sterols, also called phytosterols, as minor lipid com- Other biological activities of flavonoids seem to ponents. Plant sterols have been reported to includebe independent of their antioxidant activity. This is over 250 different sterols and related compounds. Thethe case of the oestrogen-like activity showed by most common sterols in fruits are ␤-sitosterol, and itsisoflavones. Isoflavones have also shown an effect 22-dehydro analogue stigmasterol, campesterol andon total and HDL cholesterol levels in blood. avenasterol (4-desmethylsterols). Chemical struc- Anthocyanins have shown to be effective in de- tures of these sterols are similar to cholesterol dif-creasing capillary permeability and fragility and also fering in the side chain (Fig. 2.3). ␤-Sitosterol andhave anti-inflammatory and anti-oedema activities. stigmasterol have ethyl groups at C-24, and campes- Flavonols inhibit COX-2 activity and thus may terol has a methyl group at the same position. Plantplay a role in the prevention of inflammatory diseases sterols can exist as free plant sterols, and as boundand cancer (De Pascual-Teresa et al., 2004). conjugates: esterified plant sterols (C-16 and C-18 21 22 24 26 24 24 18 20 23 25 12 R R 11 16 27 sitosterol campesterol 19 D 1 C 2 15 A B 22 7 24 HO 4 6 R R 5α-cholestan-3β-οl stigmasterol Δ5-avenasterolFigure 2.3. Structures of cholesterol (5␣-cholestan-3␤-ol), sitosterol, campesterol, stigmasterol, and 5 -avenasterol. (Source: Piironen et al., 2003.)
  • 51. 2 Nutritional Values of Fruits 41fatty acid esters, and phenolic esters), plant steryl stanols, sitostanol, and campestanol, were found inglycosides (␤-D-glucose), and acylated plant steryl specific fruits such as pineapple.glycosides (esterified at the 6-hydroxy group of thesugar moiety). All of these forms are integrated intoplant cell membranes (Piironen et al., 2000, 2003). REFERENCES Plant sterols are not endogenously synthesized in Ansorena-Artieda D. 2000. Frutas y Frutos Secos. In:humans, therefore, are derived from the diet entering Astiasar´ n I, Martinez A (Eds), Alimentos, athe body only via intestinal absorption. Since plant Composici´ n y Propiedades. 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  • 53. 2 Nutritional Values of Fruits 43Sies H, Krinsky NI. 1995. Antioxidant vitamins and Trumbo PR, Yates AA, Schlicker-Renfro S, Suitor C. ␤-carotene in disease prevention. The American 2003. Dietary reference intakes: revised nutritional Journal of Clinical Nutrition 62S:1299S–1540S. equivalents for folate, vitamin E and provitamin ASimon JA, Hudes ES, Tice JA. 2001. Relation of carotenoids. Journal of Food Composition and serum ascorbic acid to mortality among US adults. Analysis 16:379–382. Journal of the American College of Nutrition USDA. 2004. National Nutrient Database for Standard 20:255–263. Reference, Release 16-1.Taylor JS, Hamp JS, Johnston CS. 2000. Low intakes Van den Berg H, Faulks R, Granado F, Hirschberg J, of vegetables and fruits, especially citrus fruits, lead Olmedilla B, Sandmann G, Southon S, Stahl W. to inadequate vitamin C intakes among adults. 2000. The potential for the improvement of European Journal of Clinical Nutrition 54:573– carotenoid levels in foods and the likely systemic 578. effects. Journal of the Science of Food andTorija-Isasa ME, C´ mara-Hurtado MM. 1999. a Agriculture 80:880–912. Hortalizas, verduras y frutas. In: Villarino-Rodr´guez A, Garc´a-Fern´ ndez MC, ı ı a Hern´ ndez-Rodriguez M, Sastre-Gallego A (Eds), a Garcia-Arias MT. 2003. In: Garc´a-Arias MT, ı Tratado de Nutrici´ n. D´az de Santos, Madrid, o ı Garc´a-Fern´ ndez MC (Eds), Frutas y Hortalizas en ı a pp. 413–423. Nutrici´ n y Diet´ tica. Universidad de Le´ n. o e oTrautwein EA, Guus SM, Duchateau JE, Lin Y, Secretariado de publicaciones y medios Melnikov SM, Molhuizen HOF, Ntanios FY. 2003. audiovisuales, Le´ n, pp. 353–366. o Proposed mechanisms of cholesterol-lowering Wiehrauch JL, Gardner JM. 1978. Sterols content of action of plant sterols. European Journal of Lipid food of plant origin. Journal of the American Science and Technology 105:171–185. Dietetic Association 73:39–47.
  • 54. Handbook of Fruits and Fruit Processing Edited by Y. H. Hui Copyright © 2006 by Blackwell Publishing 3 Fruit Processing: Principles of Heat Treatment Imre K¨ rmendy oReview of Heat Treatment Processes and Basic Ideas of Safety theoretical knowledge is needed for an industrial Survey of Industrial Processes process, as Figure 3.1 illustrates. Food processing Background of Microbial Safety involves the fields of microbiology, plant biology,Heat Treatment Equipment thermophysics, food rheology and chemistry, pack- Classification aging technique, unit operations, reactor techniques, Batch-Type Pasteurizers and Sterilizers for “Food in construction and materials science, machinery, and Container” Treatment Continuous Pasteurizers and Sterilizers for “Food in electrophysics. Container” Treatment The most important factors (besides the nature of Statements for Both Batch-Type and Continuous the raw material and type of product) for constructing Apparatus a plant are as follows: Flow-Through Type Pasteurizers and Sterilizers r type and size of the container (e.g., from smallHeat Propagation Under Heat Treatment Conditions Heat Conduction in Food Holding Containers cans up to large tanks), and r mode of heat treatment (e.g., batch or continuous Natural and Forced Convection Heating of Food Holding Containers pasteurization of closed containers; full aseptic Heat Transfer in Flow-Through Type Heat Treatment process or some combination; temperature Units and pressure above or below 100◦ C and absoluteLoad and Deformation of Containers Under Heat Treatment pressure of 100 kPa). Conditions Containers and Their Characteristic Damages Deformation Versus Load Calculations Background of Microbial SafetyQuality Attribute Changes Attribute Kinetics Early perceptions (Ball and Olson, 1957) initiated Attribute Intensity Versus Time-dependent Temperature the use of first-order (exponential) inactivation ki- in Food Holding Containers netics for microbes, including constants as D, Dr , Calculation Methods for Flow-Through Type Apparatus Tr , z and calculation of the heat treatment equiv-List of symbols alent (F-value). These early ideas continue to beReferences followed. Meanwhile, concepts have been refined with the availability of computer programs designed to calculate “risk analysis” for food safety in indus-REVIEW OF HEAT TREATMENT trial food processing.PROCESSES AND BASIC IDEAS The two safety aspects are health protection andOF SAFETY control of spoilage. The critical (cold) point or zone is the location in the food, where the maximum concen-Survey of Industrial Processes tration of surviving microorganisms is expected. Cal-The greatest quantity of processed fruit is preserved culating and measuring the concentration of surviv-by heat treatment. A wide range of practical and ing microorganisms in the cold zone is an important 45
  • 55. 46 Part I: Processing Technology Transport processes Quality attribute Receptacle Apparatus ←→ ←→ in food materials ←→ changes Containers Heat treatment of filled Heat conduction Inactivation and Cans and closed containers multiplication of Glass jars microbes Pouches Batch process Natural convection Boxes Changes of chem. Continuous process Forced convection concentrations and Tanks enzyme activities Fluid mechanics Portable Flow-through type (Newtonian and Sensory and physical Fixed (aseptic and non-Newtonian) attributes quasi-aseptic processes) Kinetics theory Reactor technics Load and deformation Design of Ohmic and dielectric of receptacles heat exchangers heating Extreme values and averages. H. treatment equivalentsFigure 3.1. Co-operation between science and technology for achievements in heat treatment processes.part of health protection and food safety. Table 3.1 The cold zone is (in most cases) near the center ofsummarizes the cold zones in the food processing a can, but it can shift toward the surface when fillingindustry. Only surviving pathogens are involved in and closing of hot food, because the surface zonethe “cold point” calculations. cools down first. Control of spoilage means that the number of non- Liquid food leaving a flow-through type sterilizerpathogenic survivors which can multiply in the steril- is a mixture of elements (including microbes) havingized food is limited by the process parameters, so that different residence time periods. No distinction canthe ratio of spoiled cans (s) is very low. For example, be made between maximum and average concentra-if one in 10,000 cans (s = 10−4 ) is spoiled, and one tions of surviving pathogens in this case. However,can initially contains N0 V = 103 harmful microbes when food pieces are dispersed in a liquid, the max-(V is the can volume, N0 is the initial concentration imum survivor concentration will be expected in theof microbes), then a pasteurization process is needed center of the greatest piece with the shortest residencewhich reduces 103 /10−4 = 107 microbes to one sur- time.vivor. Assuming first-order kinetics [see Eq. 3.5] and Most fruit products belong to the groups ofdecimal reduction time D = 0.7 min at 70◦ C reference medium- and high-acid foods (pH < 4). Typicaltemperature, the necessary pasteurization equivalent pathogenic bacteria are the Salmonella and Staphy-(see later) is lococcus species, while lactic acid producing bacte- ria (Lactobacillus, Leuconostoc), though inhibitingP = (log 107 ) × 0.7 = 7 × 0.7 = 4.9 min. growth of pathogens, can cause spoilage. Yeasts and
  • 56. 3 Fruit Processing 47Table 3.1. Location of the Critical Zone or Critical Sample When Inactivating MicrobesProcess Characteristics Location of the Critical Zone or SampleFood in container: Central zone in the container Heat conduction Natural convection Forced convectionNatural or forced convection + food pieces Central zone in the container + the core of food pieceFlow-through type, full aseptic: Calculation of the average of survivors’ concentration Liquid food or puree at the exitLiquid food or puree + food pieces Calculation of survivors’ concentration in the core of the largest piece with shortest residence timeFlow-through type heating + hot filled Surface zone in the container (after cooling) containers (quasi-aseptic): Liquid food or pureeLiquid food or puree + food pieces Surface zone of liquid food or in the largest piece with shortest residence time at the container wallmolds can also be harmful. The heat-resistant mold injection and infusion into viscous purees andByssochlamys fulva cannot be destroyed by tempera- evaporation cooling have also been adopted (astures under 100◦ C (Stumbo, 1973; Ramaswamy and well as microwave applications).Abbatemarco, 1996). Contrary to sterilization (pH > 4.5, T > 100◦ C),no generally accepted reference temperature ex- Batch-Type Pasteurizers andists for pasteurization, nor agreement on which or- Sterilizers for ‘‘Food in Container”ganisms are dangerous. Even the criteria for safe Treatmentshelf-life (time, temperature, etc.) may be uncertain. Open pasteurization tanks, filled with water, areHowever, pathogenic species must not survive and heated by steam injection and cooled by cold wa-N /N0 = 10−8 reduction of either pathogenic or other ter. Racks holding containers are lifted in and outspecies causing spoilage would do. from above by a traveling overhead crane. Heating and cooling in the same tank in one cycle is un- economical. However, steam and water consumptionHEAT TREATMENT EQUIPMENT can be decreased by modifications (e.g., hot waterClassification reservoirs). Horizontal retorts are favored by plants where dif-The major factors to consider are: ferent products are processed in small or medium1. Whether the food is pasteurized after filling volumes. A wide variety of construction is available, individual containers or in bulk before filling (full usually with the following features (see Fig. 3.2). aseptic and quasi-aseptic processes). Container holding racks are carried into the re-2. Type, size, and material of the container or tank. tort and fixed to a metal frame, which can be ro-3. Highest retort temperature under or above 100◦ C tated at variable speed to increase heat transfer. The and pressure equal to or above atmospheric retort door with bayonet-lock cannot be opened un- pressure. der inside overpressure. An insulated upper reservoir4. Operational character, batch or continuous serves as storage for hot water at the end of the heating operation. period. Automatic control provides for uniform rep-5. Physical background of heating and cooling, etition of sterilization cycles. Temperatures and heat considering both the equipment and food material. treatment equivalent are registered. Heating is pro- A great variety of applications can be found. Be- vided by steam (injection or heat exchanger), cooling sides steam, hot-, and cold-water applications, by water. new methods include combustion heating of cans Vertical retorts had been used up to the second half or ohmic heating in aseptic processes. Steam of the last century.
  • 57. 48 Part I: Processing TechnologyFigure 3.2. A horizontal retort with hot water reservoir and mechanism for the rotation of containers.Continuous Pasteurizers and In tunnel pasteurizers horizontal conveyors carrySterilizers for ‘‘Food in Container” containers through insulated heating and cooling sec-Treatment tions. Hot- and cold-water spray, sometimes com- bined with water baths, would be applied in counter-Continuous operation is advantageous in those plants current flow to container travel. Atmospheric steamwhere large volumes are processed for a long period. is also used (see Fig. 3.3).The specific energy and water consumption of a con- In combustion heated pasteurizers, cylindricaltinuous apparatus would be less than in its batch-type cans are rolled above gas-burners along guide-pathsequivalent. (Rao and Anantheswaran, 1988). 3 4 1 2 8 7 6 5 9 40−50 °C 80−95 °C 11 10 50−60 °C 40−50 °C ∼20 °C 30−40 °CFigure 3.3. Tunnel pasteurizer with hot- and cold-water spray: (1) container feed, (2) section for preheating,(3) maximum temperature zone, (4) zone of counter-current cooling, (5) container discharge, (6) cold-water section,(7) tepid water section, (8) medium hot water cooling section, (9) spray-nozzles, (10) water pump, and (11) filter tothe pump (altogether six units).
  • 58. 3 Fruit Processing 49 sterilizers protrude from the plant building as a (in- sulated) tower. It is possible to reduce the height of the sterilizer by applying serially connected lower columns on both the inlet and outlet sides. Such construction needs special control systems on both sides. Hungarian construction with the commercial name “Hunister” works with six 4 m high columns (equivalent to a 24 m high unit) and can be placed into a processing 3 hall of about 8 m inner height (Schmied et al., 1968; P´ tkai et al., 1990). a 4 Pasteurizers and sterilizers with a helical path 5 and can-moving reel (commercial name: “Steril- H matic”) are popular in the United States. Heating 6 and cooling units are serially connected in the nec- essary number. Cans rotate or glide along the heli- cal path. Cylindrical units are equipped with feeding and discharge devices, and special rotating valves 7 serve for units under inside overpressure. The hor- 8 izontal arrangement is favorable. The long produc- tion and maintenance praxis of machinery coun- 2 terbalance the drawbacks of somewhat complicated mechanisms. 9 Statements for Both Batch-Type 1 and Continuous Apparatus The output of an apparatus, i.e., the number of con- tainers pasteurized in unit time (Q) can be calculated by the formula:Figure 3.4. Hydrostatic sterilizer: (1) container feed,(2) container holding shell, (3) conveyor, (4) water Wcolumn for heating, (5) room under steam Q= , (3.2)overpressure, (6) water column for cooling at V tmdecreasing pressure, (7) U-shaped cooling bath, and(8) discharge section of the conveyor. W is the inside volume filled with containers, heat transfer mediums, and the transport mechanism. The symbol tm denotes the total treatment time, i.e., cy- cle period for batch type and total residence time for continuous operation. V is the volume of a single con- Hydrostatic sterilizers are the best energy and wa- tainer. is the compactness ratio, i.e., the volume ofter saving devices with safe operational characteris- all containers per inside volume. Greater and shorttics. Containers enter and leave the heating chamber tm are advantageous and mean better compactnessthrough hydrostatic columns (see Fig. 3.4). and heat transfer intensity (including the use of ele- The hydrostatic pressure at the bottom level of a vated temperatures).column balances the chamber’s overpressure: The process diagram (see Fig. 3.5) presents ambi- p = H␳g. (3.1) ent and container temperatures and pressures depend- ing on treatment time (0 ≤ t ≤ tm ) for a sterilizer. For example, if column height (H = 24 m) bal- Treatment time is the time needed for the progress ofances a chamber pressure ( p = 230 kPa), then the container in a continuous unit. Instrumentationthe saturated steam temperature is T = 125◦ C. Such enables quick creation of such diagrams.
  • 59. 50 Part I: Processing Technology Table 3.2 presents specific energy and water re-T T PP quirements of a heat treatment apparatus, as theseKC K make a considerable contribution to the total con- °C bar sumption of a plant. Reduction can be achieved by 1 heat recuperation and water reuse (filtration, disin- fection, etc.). 2100 Flow-Through Type Pasteurizers and Sterilizers 3 Typical flow-through type equipment consists of a 3 pump which propels liquid food through heating, 4 constant high temperature, and cooling units for (aseptic) filling and sealing (see Fig. 3.6). 50 2 Low viscosity liquids are apt to be moved through tubular or plate heat exchangers. Fruit pulps, purees, and other comminuted fruits (containing occasion- ally dispersed particles) would be processed in units 1 provided with mixers and forwarding devices like scraped surface heat exchangers. A B C D Well-designed equipment consumes energy and water with the same low specific values as hydrostatic 0 10 20 30 40 t, min sterilizers (see Table 3.2). Pulpy, fibrous juices and concentrates belong to the pseudoplastic or plasticFigure 3.5. Process diagram of a hydrostatic category of non-Newtonian fluids. In addition to flowsterilizer: (1) ambient temperature (TK ), (2) centraltemperature in the food (TC ), (3) ambient resistance and heat transfer calculations, the resultspressure (pK ), and (4) pressure in the container (p). of (chemical) reactor techniques should be adopted(A–D) Heating (rising temperature), constant for quality attribute change calculations, includingtemperature, first cooling section, and second cooling the inactivation of enzymes and microbes. Such con-section, respectively. cepts as residence time distribution of food elements, macro- and micro-mixing, etc., are involved here. Special problems arise from undesirable deposits and burning on the food side of heat transmission walls.Table 3.2. Specific Consumption of Steam (400 kPa, Saturated) and Water (About 20◦ C) of HeatTreatment ProcessesPasteurization or Specific Consumption (kg/kg)SterilizationProcess (Notes) Equipment (Notes) Steam Water“Food in container” treatment Tank pasteurizer 0.40–0.55 4–8 (values are related to the Vertical retort (without heat 0.20–0.36 2–4 mass of food + container) recuperation); horizontal retort (with heat recuperation) Tunnel pasteurizer 0.15–0.20 1.5–2 Hydrostatic sterilizer 0.08–0.12 1.2–2Flow-through type treatment Tubular and plate apparatus (without 0.12–0.18 – (values are related to the heat recuperation) mass of food) Tubular and plate apparatus (with heat 0.06–0.12 – recuperation)
  • 60. 3 Fruit Processing 51 4 3 1 5 2 6Figure 3.6. Flow-through type pasteurization: (1) feed tank, (2) pump, (3) scarped surface heat exchangers,(4) isolated tube for keeping the food at constant temperature, (5) scarped surface cooling units, and (6) aseptictank for pasteurized food.HEAT PROPAGATION UNDER tion of time-dependent temperatures in food is basedHEAT TREATMENT CONDITIONS on the differential equations of unsteady-state heat conduction with initial and boundary conditions. TheHeat Conduction in Food Holding application of the Duhamel theory is also needed inContainers case of time-dependent variation of the retort temper-Experience has shown that heat propagation in many ature (Geankoplis, 1978; Carslaw and Jaeger, 1980).food materials under the circumstance of pasteuriza- While analytical solutions are limited to a few sim-tion can be calculated using the principles of conduc- plified tasks, a wide range of industrial problems cantion. All food products might be treated as conduc- be solved using methods of finite differences and fi-tive, in which no major convective currents develop nite elements. Figure 3.7 illustrates the elementaryduring heat treatment. Small local movements from annuli (and cylinders) of a cylindrical can. Figure 3.8density differences or induced vibrations increase the illustrates a time-dependent change in ambient tem-apparent thermal diffusivity. As a consequence, the perature and the approximation using step-wise vari-best way to measure thermophysical constants is by ation. Both figures explain a finite difference method,the “in plant” method. Results of “in plant” measure- where differential quotients have been substituted byments are often 10–20% higher than respective data quotients of suitably small differences (K¨ rmendy, ofrom the literature (P´ tkai et al., 1990). The calcula- a 1987).
  • 61. 52 Part I: Processing TechnologyFigure 3.7. Geometry belonging to afinite difference method. (A–I)Elementary annuli and cylinders. Bia ,Bib , Bi p : Biot numbers (bottom, cover,and jacket, respectively). TR °C TR, j+1 TR,jFigure 3.8. Retort temperature (TR )and its step-wise approximation in a TR,1 Δtjfinite difference calculating system.Hollow circles illustrate input data(temperature vs time). Time intervals( t j ) are divided into sufficiently small t1 tj tj+1 t, min Δtjequal time steps ( t j ).
  • 62. 3 Fruit Processing 53Natural and Forced Convection consideration the relationship between dimension-Heating of Food Holding Containers less terms (Bi, Gr, Nu, Pr, Re, St, We), geometri- cal proportions, and temperature and viscosity ratiosNatural convection heat transfer inside containers is (Rao and Anantheswaran, 1988; Rao et al., 1985;based on fluid circulation induced by temperature Sablani and Ramaswamy, 1995; Akterian, 1995).and density differences. The phenomenon is typi- The usual methods based on the determinationcal for low viscosity liquids. Temperature differences of the values: f h , jh , f c , jc (Ramaswamy andare the greatest at the container wall, while the cen- Abbatemarco, 1996) are adequate for convective heattral bulk is of near uniform temperature. Practical transfer calculations (if proper simulation has beencalculations are based on a heat balance including used in case of forced convection). For conductivethe mean temperature of food and ambient temper- heating, however, it seems advisable to use the pre-ature. The relation Nu = C (Gr × Pr)m between di- vious values for the evaluation of the relevant ther-mensionless terms (groups) can be applied for the mophysical constants and enter the latter values into“from wall to food” heat transfer. Treatment time is a computer program that calculates with the help ofdivided into consecutive intervals to enable the use of finite differences.temperature-dependent physical constants for com-puter analysis. The result is the time-dependent aver-age temperature in the container (K¨ rmendy, 1987). o Heat Transfer in Flow-Through Type The expression of forced convection would be ap- Heat Treatment Unitsplied to all those achievements, where the effect ofmixing is gained by mechanical energy input into a When liquid food (including non-Newtonian slurriesfluid, slurry, or paste. The rate of heat flow may be and purees) is pumped through channels (tubular, an-increased considerably by mixing the food in a con- nular, and plate-type heat exchangers), three majortainer. Actual accomplishment of mixing is done by flow types would form: sliding (peristaltic), laminar,rotating or tilting the containers. Machines often ro- or turbulent. Heat transfer calculations are availabletate the containers as a consequence of conveyance. for all three types of publications from the unit oper-Some hydrostatic sterilizers incorporate periodic tilt- ations field (Geankoplis, 1978; Gr¨ ber et al., 1963). oing. The rotational speed or tilting rhythm depends Relationships between dimensionless terms are ap-on the conveyance speed in this equipment. plied as previously described. A number of rotational speeds are available in hor- A number of publications are available on scrapedizontal retorts. Frictional, gravitational, and inertial surface heat exchangers, including heat transfer char-forces and their (periodic) variation acting on ro- acteristics (Geankoplis, 1978).tating food elements jointly influence mixing. Thevolume of the headspace also influences the mixingeffect (K¨ rmendy, 1991). An optimum speed exists, o LOAD AND DEFORMATION OFbecause at high rotational speed the mixing effect de- CONTAINERS UNDER HEATcreases as the food reaches a new equilibrium state TREATMENT CONDITIONSunder the overwhelming centrifugal (inertial) force Containers and Their(Eisner, 1970). Characteristic Damages Many products contain fruit pieces in a syrup orjuice. Heat is transferred from the container wall into The main load on containers under heat treatmentthe fluid constituent by convection, while the fruit conditions originate from the difference in ambientpieces are heated by conduction. Time-dependent and inside pressure. The deformation or damage thattemperatures are obtained by using equations for con- occurs from this load depends on the geometry andvection and conduction, including initial and bound- material of the container, the design of closure, andary conditions (Bimbenet and Duquenoy, 1974). the headspace volume. Heat transfer coefficients have been developed Metallic containers display reversible deforma-through extensive research. Results are heat trans- tion at small loads and permanent deformations atfer coefficients from container wall to liquid food higher loads (see Fig. 3.9). Excess inside overpres-and from liquid food to pieces of food, depending on sure causes permanent bulging at the end plates ofcontainer geometry, rotational speed, product, and a cylindrical can, while outside overpressure mightheating and cooling programs. Coefficients take into indent the jacket.
  • 63. 54 Part I: Processing Technology ΔV(cm3) 60 55 50 45 40 35 30 25 20 15 5 −0.4 −0.3 −0.1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 −5 Δp(bar) −10Figure 3.9. Volume change ( V ) −15versus pressure difference ( p) relationof a tinplate can. −20 Rigid containers like glass jars and bottles undergo andvery small (and resilient) deformation. Excess insideoverpressure can open or cast down the cover. The VG = VC0 [1 + ␣VC (TC − TC0 )] + V − Vf0temporary opening of the cover effects air exhaust × [1 + ␣Vf (Tf − Tf0 )] . (3.4)or food loss, depending on the position (vertical orhorizontal) of the jar. Additional relationships and data are needed as Plastic bags are susceptible to large deforma- time-dependent variations of ambient pressure andtions, while inside overpressure easily rips the bags. temperature, temperatures of the container wall,Table 3.3 includes critical loads for some types of headspace, and food (average). Initial values (at thecontainers. moment of closing) include volumes, pressures, and temperatures. According to Equation 3.3, the inside pressure of the container is the sum of the vaporDeformation Versus Load pressure of food and of the partial pressure of gasCalculations components. According to Equation 3.4, the actualTwo basic equations are used to calculate the inside headspace volume (VG ) can be calculated by addingpressure of a container, the respective pressure dif- the container volume (increased exclusively by heatference, and container volume: expansion) to the pressure difference induced volu- metric container deformation ( V ), and subtracting n RTG m Gi the volume of food expanded by heat. The measuredp = pf + = pf VG Mi relationship between V and the pressure difference i=1 ( p, e.g., see Fig. 3.9) is also required for the formula TG + ( p0 − pf0 ) , (3.3) (K¨ rmendy and Ferenczy, 1989; K¨ rmendy et al., o o VG TG0 1994, 1995).
  • 64. 3 Fruit Processing 55Table 3.3. Critical Loads of Tinplate Cans and Glass Jars Container Critical load (kPa)Material V0 d j ep p1 p2 NotesTinplate can 860 99 0.18 0.18 103 −52 p1: bulging 0.22 0.22 138 −60 of end plates 0.24 0.24 159 −67 3200– 153 0.28– 0.3– 75– −43 p2 : 4760 0.30 0.32 95 −53 indentation at the jacket 6830 160 0.28 0.3 78 −51Glass jar + – 79 – 0.24 107 – p1 : opening twist-off lid of the lid of tinplateNote: V0 —volume (cm3 ); j—jacket thickness (mm); d—can diameter or lid diameter for jars (mm); ep–end plate thickness orlid plate thickness (mm).QUALITY ATTRIBUTE CHANGES andAttribute Kinetics D = Dr × 10(T −Tr )/z . (3.6)Besides the concentration of favorable and unfavor- The first equation is valid for constant temperature,able constituents, enzyme activity, sensory attributes, the second one describes the variation of the deci-related physical properties, etc., the concentration of mal reduction time (D) versus temperature (T). Dr ,surviving microbes can also be regarded as a quality Tr are arbitrary (though expedient) reference values.attribute. Namely, similar descriptive kinetic meth- Time-dependent variation of the logarithm of the con-ods, concepts of extreme values and averages are used centration of surviving microbes is linear. The valuefor changes in microbial concentration. of z is the temperature increment effecting the deci- The typical method to measure variations of time- mal reduction of D. Naturally, D is not the decimaldependent attributes in food is by laboratory testing at reduction time in non-exponential relationships.a number of different constant temperatures, provid- Reaction theory principles should be used to deter-ing for all major conditions of (industrial) heat treat- mine changes in time-dependent chemical concen-ment. The next step is the fitting of expertly chosen trations (Levenspiel, 1972; Froment and Bischoff,relationships to data, and the simultaneous evaluation 1990). However, mostly fitted relationships are usedof kinetic constants. instead of more exact calculations. Kinetic constants Heat inactivation of microbes belongs to the popu- are: rate constant (k, or rate constants), energy of acti-lation change dynamics field. Since early years (about vation (Ea ), reference temperature (Tr ), and reference1920), first-order equations had been used, mean- rate constant (kr ). The rate constant is independentwhile, a number of other equations were also fitted to of the initial concentration if the kinetic equation isexperimental results (Casolari, 1988; K¨ rmendy and o based on a sound chemical background, otherwise aK¨ rmendy, 1997). The method that shows promise o fitted rate constant might only be valid for a fixed ini-is based on the distribution of lethal time of the in- tial concentration (see more details in the publicationdividual microbes combined with the two paramet- of K¨ rmendy and M´ sz´ ros, 1998). o e aric Weibull distribution (Peleg and Penchina, 2000; Empirical (i.e., fitted) equations describe the time-K¨ rmendy and M´ sz´ ros, 1998). The Weibull distri- o e a dependent variation of sensory attributes and of re-bution is useful for fitting to diverse types of time- lated physical properties (color, consistency, etc.).dependent inactivation courses by selecting appro- Concentration based attributes follow a linear mix-priate constants. ing law, i.e., the attribute intensity of a mixture of dif- The generally used first-order (exponential) ferent volumes and intensities is the weighted meanequations are of component intensities. This evident rule is not valid for sensory attributes (see K¨ rmendy, 1994; for oN = N0 × 10−t/D , (3.5) food color measurements).
  • 65. 56 Part I: Processing TechnologyAttribute Intensity Versus Equation 3.7 is applicable in all those cases, where at-Time-dependent Temperature tribute intensity at constant temperature depends onlyin Food Holding Containers on t/D or kt. There are methods for other variable tem- perature changes (K¨ rmendy and K¨ rmendy, 1997; o oTemperature always varies during a heat treatment Peleg and Penchina, 2000). Equations 3.6 and 3.7process (see Fig. 3.5). No general procedure exists undergo modifications, when the z-value is replacedfor calculating time-dependent attribute intensity at by the energy of activation (Hendrickx et al., 1995).variable temperature from constant temperature ex- The attribute intensity at the end of a process is eas-periments. Notwithstanding, a few useful methods ily available by substituting Tr , Dr (or kr ) and thehave been developed since about 1920 and more are equivalent time (F, P, E, C) into the constant temper-expected in the future. ature intensity versus time relation [e.g., into Eq. 3.5]. The equivalent sterilization time (F) at constant Computerized calculation should provide three inten-reference temperature (Tr ) induces the same lethal sities in a container: the maximum, the minimum, andeffect as the actual time-dependent temperature the average (see “Background of Microbial Safety”variation: and Table 3.1). The “cold point” of a vertically posi- tm tioned container is near the bottom, at a distance less T (t)−TrF= 10 z dt. (3.7) than 25% of the container height, in case of natural 0 convection. The previous integral was used later for pasteuriza-tion (P), enzyme inactivation (E), chemical and sen- Calculation Methods forsory attribute variation (C), replacing the symbol F Flow-Through Type Apparatusby P, E, C (cooking value), respectively. Equation 3.7had been derived originally for first-order (i.e., ex- The residence time is uniform for all food elementsponential) destruction. It could be proved later that in case of in-container pasteurization. As a contrast, E (t) exp (−kt) . E (t) min−1 4.10−2 exp (−kt) . E (t) 0.3 3.10−2 ∞Figure 3.10. Average attribute ∫ exp (−kt) . E (t) dtintensity at the discharge valve of a 0.2 2.10−2 0flow-through type unit. E(t ) =time-dependent density (frequency)function of the residence timedistribution, k = first-order rate 0.1 1.10−2constant, exp(−kt) = time-dependent E (t)intensity variation per initial intensity.The definite integral gives the averagedischarge intensity per initial intensity,illustrated by the hatched area. t p , ␶ : 0 5 10 t, mindead time and expectation value ofE(t), respectively. tp τ
  • 66. 3 Fruit Processing 57food elements reside for different time intervals in a fc , fh cooling and heating rate indexes: timeunit of a flow-through type apparatus, and a distribu- needed for the decimal reduction of thetion function characterizes residence time. A sample difference between outside and insideat the discharge port of a unit is a mixture of food temperatures (min)elements of different residence time intervals. It has F sterilization or lethality value (equivalent,been proved for liquid food that the average of the min)concentration of surviving microbes at the exit can F average of Fbe calculated according to the equation: g gravitational constant (m/s2 ) Gr Grashof number ∞ H water column height (m)N=N E(t) × 10−t/D dt, (3.8) jc , jh cooling rate and heating rate lag factors 0 k rate constant (for first-order kinetics, min−1 )if food temperature is constant (suspended parti- m dimensionless exponentcles are small enough too) and exponential inac- mG mass of a gas component (kg)tivation law exists [see Eq. 3.5]. Equation 3.8 is M molar weight of a gas componentbased on macromixing principles (Levenspiel, 1972) (kg/kmol)and can be easily converted for other inactiva- n number of gas componentstion kinetics. Figure 3.10 demonstrates the essence N concentration of living or survivingof calculation useful for a constant temperature microbes (cm−3 )unit. N average of N (cm−3 ) No definite solution exists for a variable tempera- Nu Nusselt numberture unit, presumably the approximation of Bateson p absolute pressure in a container (kPa)(1971) will be useful in the future. As a consequence P pasteurization value (equivalent, min)of his idea, an average temperature (T ) can be as- Pr Prandtl numbersessed for a variable temperature unit and the per- Q number of containers pasteurized in unittaining value: D substituted into Equation 3.8. The time (min−1 )heat treatment equivalent for average attribute inten- R universal gas constant [kJ/(kmol K)]sity (F) is now: Re Reynolds number s spoilage ratio N St Stanton numberF = − log . (3.9) N0 t time (min) tm total treatment time (min) The overall equivalent of an apparatus with serially T temperature (K, ◦ C)connected units (e.g., heating, constant temperature, V volume in connection with aand cooling) is the sum of the individual units equiv- container (m3 )alents (K¨ rmendy, 1994, 1996). o W inside volume of an apparatus (m3 ) We Weber number z temperature increment for the decimalLIST OF SYMBOLS reduction of D (K, ◦ C)Bi Biot number ␣v volumetric heat expansion coefficientC dimensionless constant (K−1 , ◦ C−1 )C cooking value (min) p pressure difference, inside minus outsideD decimal reduction time or time constant pressure (Pa, kPa) (min) V volume change of a container due toD average of D (min) mechanical load (m3 )E enzyme inactivation value (min) ␳ density of water (kg/m3 )Ea energy of activation (kJ/kmol) compactness ratioE(t) density function of the residence time Indexes: C = container, f = food, G = distribution (earlier: frequency headspace, i = serial number of gas components, distribution, min−1 ) 0 = initial value, r = reference value.
  • 67. 58 Part I: Processing TechnologyREFERENCES K¨ rmendy, I., Koncz, L. and S´ rk¨ zi, I. 1994. o a o Deformation versus load relations of tinplate cans.Akterian, S. G. 1995. Numerical simulation of Interpolation between extreme loading cycles. Acta unsteady heat transfer in canned mushrooms in Aliment. 23:267. brine during sterilization. J. Food Eng. 25:45. K¨ rmendy, I., Koncz, L. and S´ rk¨ zi, I. 1995. o a oBall, C. O. and Olson, F. C. W. 1957. Sterilization in Measured and calculated pressures and pressure Food Technology. McGraw-Hill, New York. differences of tinplate cans under sterilizationBateson, R. N. 1971. The effect of age distribution on conditions. Acta Aliment. 24:3. aseptic processing. Chem. Eng. Prog. Syst. Ser. 108 K¨ rmendy, I. and K¨ rmendy, L. 1997. Considerations o o 67:44. for calculating heat inactivation processes whenBimbenet, J. J. and Duquenoy, A. 1974. Simulation semilogarithmic thermal inactivation models are non mathematique de phenomenes interessant les linear. J. Food Sci. 34:33. industries alimentaires. I. Transfer de chaleur au K¨ rmendy, I. and M´ sz´ ros, L. 1998. Modelling o e a cours de la sterilisation. Ind. Aliment. et Agricoles of quality attribute variations in food under 91:359. heat treatment conditions. Important aspects.Carslaw, H. S. and Jaeger, J. C. 1980. Conduction of In: Proceedings of the Third Karlsruhe Heat in Solids. Oxford University Press, UK. Nutrition Symposium, Part 2. Karlsruhe,Casolari, A. 1988. Microbial death. In: Bazin, M. J. Germany:312. and Prosser, J. I. (Eds), Physiological Models in Levenspiel, O. 1972. Chemical Reaction Engineering. Microbiology, vol. II. CRC Press, Boca Raton, Wiley and Sons, New York. FL:1–44. P´ tkai, G., K¨ rmendy, I. and Erd´ lyi, M. 1990. a o eEisner, M. 1970. Einf¨ hrung in die Technik und u Outline of a system for the selection of the Technologie der Rotations Sterilisation. G¨ nter u optimum sterilization process for canned foods. Hempel, Braunschweig, Germany. Part II. The determination of heat transferFroment, G. F. and Bischoff, K. B. 1990. Chemical coefficients and heat conductivities in some Reactor Analysis and Design. Wiley and Sons, industrial equipments for canned products. Acta New York. Aliment. 19:305.Geankoplis, C. J. 1978. Transport Processes and Unit Peleg, M. and Penchina, C.M. 2000. Modelling Operations. Allyn and Bacon, Boston, MA. microbial survival during exposure to a lethal agentGr¨ ber, H., Erk, S. and Grigull, U. 1963. Die o with varying intensity. Crit. Rev. Food Sci. Nutr. Grundgesetze der W¨ rme¨ bertragung. Springer, a u 40:159. G¨ ttingen, Germany. o Ramaswamy, H. S. and Abbatemarco, C. 1996.Hendrickx, M., Maesmans, G., De Cordt, S., Noroha, J. Thermal processing of fruits. In: Somogyi, L. P., and Van Loey, A. 1995. Evaluation of the integrated Ramaswamy, H. S. and Hui, Y. H. (Eds), Processing time–temperature effect in thermal processing of Fruits: Science and Technology, vol. 1. Technomic, foods. Crit. Rev. Food Sci. Nutr. 35:231. Lancaster, CA:25–66.K¨ rmendy, I. 1987. Outline of a system for the o Rao, M. A. and Anantheswaran, R. C. 1988. selection of the optimum sterilization process for Convective heat transfer to fluid foods in cans. Adv. canned foods. I. Calculation methods. Acta Aliment. Food Res. 32:39. 16:3. Rao, M. A., Cooley, H. J., Anantheswaran, R. C. andK¨ rmendy, I. 1991. Thermal processes, para 5.1.1. to o Ennis, R. W. 1985. Convective heat transfer to 5.1.4. In: Szenes, E. and Ol´ h, M. (Eds), a canned liquid foods in a Steritort. J. Food Sci. Konzervipari K´ zik¨ nyv (Handbook of Canning). e o 50:150. Integra-Projekt Kft., Budapest, Hungary:163–188 Sablani, S. S. and Ramaswamy, H. S. 1995. Fluid to (in Hungarian). particle heat transfer coefficients in cans duringK¨ rmendy, I. 1994. Variation of quality attributes in o end-over-end processing. Lebensm.-Wiss. serially connected independent food reactor units. u.-Technol. 28:56. Part 1. Chem. Eng. Proc. 33:61. Schmied, J., Ott, J. and K¨ rmendy, I. 1968. oK¨ rmendy, I. 1996. Variation of quality attributes in o Hydrostatic sterilizer with automatic temperature serially connected independent food reactor units. control. Hungarian Licence No.: KO-2206, Part 2. Chem. Eng. Proc. 35:265. No. of Registration: 158292. Budapest,K¨ rmendy, I. and Ferenczy, I. 1989. Results of o Hungary. measurements of deformation versus load relations Stumbo, C. R. 1973. Thermobacteriology in Food in tin cans. Acta Aliment. 18:333. Processing. Academic Press, New York.
  • 68. Handbook of Fruits and Fruit Processing Edited by Y. H. Hui Copyright © 2006 by Blackwell Publishing 4 Fruit Freezing Principles Beg´ na De Ancos, Concepci´ n S´ nchez-Moreno, o o a Sonia De Pascual-Teresa, and M. P. CanoIntroduction points (HACCP) principles as those used in freshFreezing Principles products. The quality of the frozen fruits is very Freezing Rate dependent on other factors such as the type of fruit,Factors Affecting Frozen Fruit Quality varietal characteristics, stage of maturity, pretreat- Preparing, Pretreatments, and Packaging ments, type of pack, and the rate of freezing. The Effect of Freezing, Frozen Storage, and Thawing on freezing process reduces the fruit temperature to a Fruit Tissues: Physical, Chemical, and Biochemical Changes storage level (−18◦ C) and maintaining this temper- Stability of Frozen Fruit ature allows the preservation of the frozen product Thawing for 1 year or more. Fruits are frozen in different Microbiological Quality and Safety of Frozen Fruits shapes and styles: whole, halves, slices, cubes, inFreezing Methods sugar syrup, with dry sugar, with no sugar added, orFuture Perspectives as juices, purees, or concentrates, depending on theAcknowledgments industrial end-use. The influence of freezing, frozenReferences storage, and thawing on fruit quality has been exten- sively reviewed (Skrede, 1996; Reid, 1996; Hui et al., 2004). The objective of this chapter is to describeINTRODUCTION the main principles of manufacturing and processingFreezing is one of the best methods for long-term stor- of frozen fruits (selection of raw material, pretreat-age of fruits. Freezing preserves the original color, ments, packaging, freezing process, and frozen stor-flavor, and nutritive value of most fruits. Fresh fruits, age) and review the current topics on the sensorialwhen harvested, continue to undergo chemical, bio- and nutritional quality and safety of frozen fruits.chemical, and physical changes, which can cause de-terioration reactions such as senescence, enzymaticdecay, chemical decay, and microbial growth. The FREEZING PRINCIPLESfreezing process reduces the rate of these degrada- The freezing process reduces food temperature un-tion reactions and inhibits the microbiological activ- til its thermal center (food location with the highestity. However, it should be recognized that a number temperature at the end of freezing) reaches −18◦ C,of physical, chemical, and biochemical reactions can with the consequent crystallization of water, the mainstill occur and many will be accentuated when rec- component of plant tissues. Water in fruit and fruitommended conditions of handling, production, and products constitute 85–90% of their total composi-storage are not maintained. Although few microor- tion. From a physical point of view, vegetable and an-ganisms grow below −10◦ C, it should be recognized imal tissues can be considered as a dilute aqueous so-that freezing and frozen storage is not a reliable bio- lution, which is the natural medium where chemicalcide. The production of safe frozen fruits requires and biochemical cellular reactions take place and mi-the same maximum attention to good manufacturing croorganisms grow. Crystallization of water duringpractices (GMP) and hazard analysis critical control freezing reduces water activity (aw ) in these tissues 59
  • 69. 60 Part I: Processing Technology the risk of enzymatic and chemical reactions, e.g., enzymatic browning or oxidation–reduction, with ad- A 20 verse effects on frozen fruit quality. A short B–C sec- tion increases the quality of frozen fruit. This means TEMPERATURE (°C) 10 that a fast rate freezing produces a better quality frozen fruit (see curves b and c of Fig. 4.1). Sec- B tion C–D corresponds with the cooling of the prod- 0 S C uct until the storage temperature, with an important S increase of solute concentration in the unfrozen por- −10 tion. Below −40◦ C, new ice formed is undetected. Up to 10% of the water can be unfrozen, mainly −20 c b a joined to protein or polysaccharide macromolecular D structures that take part in the physical and biochem- −30 ical reactions. In frozen foods the relationship be- 0 1 2 tween the frozen water and the residual solution is TIME (HOURS) dependent on the temperature and the initial soluteFigure 4.1. Typical freezing curves of foods at different concentration. The presence of ice, and an increaserates: (a) very slow; (b) fast; and (c) very fast in solute concentration, has a significant effect on the(Fennema, 1976). reactions and state of the fruit matrix. The concen- tration of the solute increases as freezing progresses; and thus, solute concentration of the unfrozen matrixand consequently produces a decline in chemical and can leach out of the cellular structures causing lossbiochemical reactions and microbial growth. Freez- of turgor and internal damage. Solute-induced dam-ing also involves the use of low temperatures and age can occur whether freezing is fast or slow, andreactions take place at slower rates as temperature cryoprotectants, such as sugars, are usually added tois reduced. The study of temperature changes during aqueous solution to reduce the cell damage. (Reid,freezing is basic to an understanding of how prod- 1996; Rahman, 1999).ucts are processed. Figure 4.1 shows typical freezingcurves at different freezing rates. When the product Freezing Rateis cooling down to 0◦ C, ice begins to develop (seesection A–S, Fig. 4.1). The exact temperature for Controlling the freezing rate is an important aspect ofthe formation of first ice crystal depends on the type reducing cell damage, which causes important qual-of product and is a consequence of the constituents ity losses in frozen fruits. Three types of cell damageconcentration independent of water content; for ex- due to freezing have been reviewed:ample, fruits with high water content (≈90%) have r solute-induced damagea freezing point below −2◦ C or −3◦ C, while meat r osmotic damagewith less water content (≈70%) has a freezing point r structural damage.of −1◦ C; the main difference being the high sugarand organic acid concentration in fruits. Ice forma- Although solute-induced damage is present in fasttion takes place after the product reaches a temper- and slow freezing processes, it can be minimized byature below its freezing point (−5◦ C to −9◦ C) for slow speed. Osmotic and structural damages are de-only a few seconds. This process is known as super- pendent on the rate of freezing.cooling (position S in Fig. 4.1). After that, due to heat Freezing rate is the speed at which the freezingrelease during the first ice formation, the temperature front goes from the outside to the inside of the prod-increases until the freezing point is reached (position uct, and depends on the freezing system used (me-B in Fig. 4.1). Section B–C in Fig. 4.1 corresponds to chanical or cryogenic), the initial temperature of thethe freezing of most of the tissue water at a tempera- product, the size and form of the package, and theture that is practically constant, with a negative slope type of product. The freezing process (as a functionfrom a decline of the freezing point due to solute of the rate) can be defined as follows (IIR, 1986):concentration. The increase of solute concentration r Slow, 1 cm/has freezing progresses causes the unfrozen portion to r Semiquick, 1–5 cm/hundergo marked changes in such physical properties r Quick, 5–10 cm/has ionic strength, pH, and viscosity. This increases r Very quick, 10 cm/h.
  • 70. 4 Fruit Freezing Principles 61 1 2 Cytoplasma Solute concentration 3 4 Cell wall Water losses due to osmotic pressure Ice crystal formation: slow speed Cytoplasma and solution intercrystals Cell wall Ice crystal formation: fast speedFigure 4.2. Ice crystal formation in plant tissues at slow speed (Fig. 4.2, up) and at fast speed (Fig. 4.2, down).Generally, quick freezing produces better quality be released, leading to different effects such as off-frozen fruits. Rates between 5 and 10 cm/h for “in- flavors and color and textural changes, etc. These ef-dividual quick freezing” is an efficient way to obtain fects can be prevented by applying prefreezing treat-individual frozen fruits with high quality. The rate of ments like the addition of chemicals or by blanching,freezing is very important in plant tissues because it a heat treatment that denatures the enzymes. In a rapiddetermines the size, form, and status of the ice crys- rate freezing process, small size and round ice crys-tals, factors that affect cell wall integrity. If the rate tals increase at the same time, both inside and outsideof freezing is very slow, large ice crystals are formed of the cell, and structural and osmotic damages areslowly in the outer of cells and water from the cells minimal (Fig. 4.2, down). Although fast freezing ismigrate out by osmotic pressure (Fig. 4.2, up). Then, better than slow freezing in fruit and vegetable prod-the cellular membranes are damaged during thawing, ucts, the importance of freezing speed is sometimesand the consequence of migration is an important drip misleading. The initial advantage obtained by fastloss. freezing can be lost during storage due to recrystal- Also, in slow cooling, large sharp ice crystals are lization as a consequence of temperature fluctuations.formed and may cause damage to delicate organelle Also, some products, such as whole fruits, will crackand membrane structure of the cell. As a conse- if they are exposed to extremely low temperature.quence enzymatic systems and their substrates may This is due to volume expansion, internal stress, and
  • 71. 62 Part I: Processing Technologythe contraction and expansion phenomenon (Reid, r stability of frozen fruits (TTT factors)1996; Rahman, 1999). r thawing r microbiological quality and safety of frozen fruits.FACTORS AFFECTING FROZEN Selection of Suitable Product forFRUIT QUALITY FreezingThe freezing of fruits slows down, but does not stop, High-quality frozen fruit requires high-quality rawthe physical, chemical, and biochemical reactions material. Generally, quality cannot be gained fromthat produce their deterioration. There is a slow pro- processing, but it certainly can be lost. Fruits aregressive change in sensorial and nutritional quality best when frozen fully ripe but still firm and at theduring frozen storage that becomes noticeable af- peak of quality, with a pleasing color, texture, flavor,ter a period of time. Safe, high-quality frozen fruits and maximum nutritional value. Great differences ofwith maximum nutritional values can be produced if frozen fruit quality exist between fruit varieties anddiligent controls are maintained at all times. These cultivars based on chemical, biochemical, and phys-include temperature control, extended quality shelf ical characteristics that determine the sensorial andlife, microbiological safety, and the retention of nu- nutritional quality. Differences in cell wall structure,trients. enzyme activity, amounts of pigments, sugars, or- Two principles dominate the control of quality ganic acids, volatile compounds, vitamins C, A, andand safety in frozen foods: product-process-package E, and other components are factors that affect thefactors (PPP) and time-temperature-tolerance factors differences in sensorial and nutritional quality of raw(TTT). PPP factors need to be considered at an early fruits. Freezing potential of fruit varieties or culti-stage in the production of frozen fruits and they are vars are evaluated with practical trials after freezing,the bases of commercial success of the product. The frozen storage, and thawing of the fruit products.PPP factors are as follows: The suitability of varieties or cultivars for freezingr Product: High-quality frozen food requires can be studied on the basis of physical (texture and high-quality raw materials and ingredients. color), physical–chemical (pH, acidity, and solubler Process: The speed and effectiveness of the solids), chemical (volatile, pigments, and polyphe- freezing operations and the use of additional nol compounds), nutritional (vitamins and dietary processes (blanching, etc.). fiber content), and sensorial aspects (firmness, color,r Package: Packaging offering physical and and taste). These kinds of studies have been done chemical barriers. with different fruits such as kiwi (Cano and Mar´n, ı 1992; Cano et al., 1993a), mango (Mar´n et al., 1992; ı TTT factors maintain the quality and safety during Cano and Mar´n, 1995), pineapple (Bartolom´ et al., ı estorage. TTT concepts refer to the relationship be- 1996a, b, c), papaya (Cano et al., 1996a; Lobo andtween storage temperature and storage life. For dif- Cano, 1998), raspberry (De Ancos et al., 1999, 2000a,ferent foods, different mechanisms govern the rate b; Gonz´ lez et al., 2002), strawberry (Castro et al., aof quality degradation and the most successful way 2002), and other fruits. Another criterion for selec-of determining practical storage life is to subject the tion of suitable variety or cultivar can be the enzy-food to long-term storage at different temperatures. matic systems activity (polyphenoloxidase, perox-TTT relationships predict the effects of changing or idase, lipoxygenase, etc.), in raw fruit and duringfluctuating temperatures on quality shelf life (IIR, freezing and frozen storage. Employing varieties with1986). low enzymatic activities could reduce the develop- Safe, high-quality frozen fruits with maximum nu- ment of browning, off-flavors and off-odors, andtritional values can be produced if the directions given color and textural changes (Cano et al., 1990b, 1996b,below are followed: 1998; Gonz´ lez et al., 2000). ar selection of suitable product for freezing Harvesting fruits at optimum level for freezing pur-r PPP factors poses is difficult. The need for efficient productionr knowledge of the effect of freezing, frozen often implies the use of mechanical harvesting at a storage, and thawing on the fruit tissues that time when the fruit has reached an acceptable matu- causes physical, chemical, and biochemical rity level to avoid mechanical damage. Postharvest changes techniques allow the storage of unripe climateric
  • 72. 4 Fruit Freezing Principles 63fruits at specific atmosphere, temperature, and hu- Pretreatmentsmidity conditions until they reach proper maturity The importance of enzyme content to fruit qual-levels to be frozen (Cano et al., 1990a, b; Mar´n et al., ı ity has been extensively reviewed (Philippon and1992). Nonclimateric fruits (strawberries, raspber- Rouet-Mayer, 1984; Browleader et al., 1999;ries, etc.) are harvested, preferably when fully ripe Robinson and Eskin, 1991; Friedman, 1996). En-but still firm, cooled immediately after picking, and zymes, namely polyphenoloxidase (PPO), peroxi-frozen as soon as possible (G´ nzalez et al., 2002). o dase (POD), lipoxygenase (LOX), catalase (CAT),However, the quality advantages of immediate freez- and pectinmethylesterase (PME) are involved in theing could not be detected after a long frozen storage fast deterioration of fruit during postharvest hand-period (6–12 months) (Plocharski, 1989). ling and processing. Enzymes not inactivated be- fore freezing can produce off-flavors, off-odors, colorPreparing, Pretreatments, and changes, development of brown color, and loss of vi-Packaging tamin C and softness during frozen storage and thaw- ing. Water blanching is the most common methodSuccessful freezing should retain the initial quality for inactivating vegetable enzymes (Fellows, 2000).present in the raw fruit selected for freeze processing It causes denaturation and therefore, inactivation ofaccording to freshness, suitability varietal for freez- the enzymes that also causes destruction of thermo-ing, and sensorial and nutritional characteristics. Re- sensitive nutrients and losses of water-soluble com-taining this quality level prior to freezing is a factor of pounds such as sugar, minerals, and water-solublemajor importance to obtain high-quality frozen fruits. vitamins. Blanching is rarely used for fruits be- cause they are usually consumed raw and heat treat-Preparing ment causes important textural changes. An alter- native to blanching fruit is to use ingredients andFruits must be prepared before freezing according chemical compounds that have the same effect asto the frozen fruit end-use. Washing, rinsing, sorting, blanching.peeling, and cutting the fruits are not specific steps forfrozen fruits; these are preparatory operations similar Blanching. Heat treatment to inactivate vegetableto other types of processing but must be carried out enzymes can be applied by immersion in hot wa-quickly and with great care to avoid damaging the ter, by steam blanching or by microwave blanching.fragile fruit tissue. Peeling, stone removal, and cut- Hot water blanching is usually done between 75◦ Cting in cubes, slices, or halves are usually mechanical and 95◦ C for 1–10 min, depending on the size of theoperations. Decreasing the size of the product before vegetable pieces. Hot water blanching also removesfreezing results in a faster freezing and consequently tissue air and reduces the occurrence of undesirablea better frozen fruit quality. For economical factors, oxidation reactions during freezing and frozen stor-certain fruits like peaches, apricots, and plums are age. Steam blanching reduces the water-soluble com-frozen whole immediately after harvesting and peel- pounds losses and is more energy efficient than watering; stone removal and cutting is done after a partial blanching. Of all the enzymes involved in vegetablethawing. quality losses during processing, POD and CAT seem Consumption of fruit juices and nectars has in- to be the more heat stable, and thus could be used ascreased in the world due to recommendations for bet- an index of adequate blanching. Generally, a qual-ter nutrition and healthier diets. Fruits and fruit juices ity blanched vegetable product permits some PODmeet these recommendations. Nectars and fruit juices and CAT activity. Complete POD inactivation in-can be manufactured with fresh fruit but with frozen dicates overblanching. Blanching also helps to de-fruit higher yields are obtained. stroy microorganisms on the surface of the vegetable. At present, frozen juices represent an important Blanching destroys semipermeability of cell mem-segment of the international drink industry. Preparing branes and removes cell turgor. Reduced turgor isfruit for frozen juice requires different steps: press- perceived as softness and lack of crispness and juici-ing, clarification, heat treatment, and concentration. ness. These are some of the most important sensorialAlso purees and pulps represent an important in- characteristics of eating fruit. Although loss of tissuegredient for the manufacturing industries for dairy firmness in blanched frozen fruits after thawing indi-products, cakes, ice-creams, jellies, and jams (Chen, cates that blanching is not a good pretreatment for the1993).
  • 73. 64 Part I: Processing Technologymajority of the fruits, some results have been interest- hydrochloric acid solution (1%) could be a com-ing (Reid, 1996). Hot water blanching peeled bananas mercial pretreatment for browning control and qual-prior to slicing, freezing, and frozen storage produced ity maintenance of frozen litchi fruit (Yueming-complete PPO and POD inactivation and a product Jiang et al., 2004). Although all the fruits containwith acceptable sensorial quality (Cano et al., 1990a). polyphenolic compounds, some fruits as peaches,Microwave blanching has not been an effective pre- apricots, plums, prunes, cherries, bananas, apples,treatment for banana slices (Cano et al., 1990b) but and pears show a greater tendency to develop brown-interesting results have been obtained with frozen ba- ing very quickly during processing. Research effortsnana purees (Cano et al., 1997) have been done to develop new natural antibrowning agents in order to replace sulfites, the most powerfulAddition of Chemical Compounds. Substitutes and cheapest product until now, but they cause ad-for thermal blanching have been tested with differ- verse health effects in some asthmatics. In this frame-ent enzymatic inhibitors. They are mainly antibrown- work, maillard reaction products have been recog-ing additives such as sulfiting agents (sulfur dioxide nized as a strong apple PPO inhibitor (Billaud et al.,or inorganic sulfites salts) and ascorbic acid, which 2004). Also, some frozen fruits like apples and che-are applied by dipping or soaking the fruit in dif- rimoya are pretreated by dipping its slices in sodiumferent solutions before freezing (Skrede, 1996). En- chloride solutions (0.1–0.5%) in combination withzymatic browning involving the enzyme PPO is the ascorbic or citric acid, in order to remove intracel-principal cause of fruit quality losses during posthar- lular air and reduce oxidative reactions (Reid, 1996;vest and processing. PPO catalyzes the oxidation of Mastrocola et al., 1998).mono- and orthodiphenols to quinones, which can Fruit texture is greatly changed by freezing, frozencyclize, undergo further oxidation, and polymerize storage, and thawing. Fruits have thin-walled cellsto form brown pigments or react with amino acids rich in pectin substances, in particular in the middleand proteins that enhance the brown color produced lamella between cells, and with a large proportion of(Fig. 4.3). intracellular water, which can freeze resulting in cell The proposed mechanisms of antibrowning addi- damage. Freezing–thawing also accelerates the re-tives that inhibit enzymatic browning are (1) direct lease of pectin, producing de-esterification of pectinsinhibition of the enzyme; (2) interaction with inter- and softens the fruit tissue. Optimum freezing rate re-mediates in the browning process to prevent the re- duces tissue softening and drip loss, and the additionaction leading to the formation of brown pigments; of calcium ions prior to freezing increases the firm-or (3) to act as reducing agents promoting the re- ness of fruit after thawing. These ions fortify the fruitverse reaction of the quinone back to the original phe- by changing the pectin structure. Calcium maintainsnols (Fig. 4.3). (Friedman, 1996; Ashie et al., 1996). the cell wall structure in fruits by interacting with theOther acid treatments such as dipping in citric acid or pectic acid in the cell walls to form calcium pectate. OH R PPO + O2 OH O PPO + O2 Complex Brown R OH R O PolymersFigure 4.3. Enzyme-catalyzedinitiation of browning by PPO Amino Acidsshowing the point of attack by Proteinsreducing agents. Reducing Agent
  • 74. 4 Fruit Freezing Principles 65Dipping in calcium chloride solution (0.18% Ca) or types of berries treated with a 20% or 40% syruppectin solution (0.3%) improves the quality of frozen concentration before freezing and long-term frozenand thawed strawberries (Suutarinen et al., 2000). storage between 6 months and 3 years (Skrede, 1996). The effects of dehydrofreezing process on the qual-Osmotic Dehydration: Addition of Sugars and ity of kiwi, strawberry, melon, and apples have beenSyrups. Dipping fruits in dry sugar or syrups is reported (Garrote and Bertone, 1989; Tregunno anda traditional pretreatment to preserve color, flavor, Goff, 1996; Spiazzi et al., 1998; Talens et al., 2002,texture, and vitamin C content and to prevent the 2003). The quality and texture of dehydrofrozen andbrowning of freezing–thawing fruits. Sugar or syrups thawed fruit has been improved by using osmoticare used as cryoprotectants by taking out the fruit solutions in combination with ascorbic acid solu-cell water by osmosis and excluding oxygen from tion (antibrowning treatment) and/or calcium chlo-the tissues. Partial removal of water before freezing ride or pectin solutions (Skrede, 1996; Suutarinenmight reduce the freezable water content and de- et al., 2000; Talens et al., 2002, 2003; Zhao and Xie,crease ice crystal damage, making the frozen fruit 2004). Another important factor contributing to fruitstable. Therefore, minor damage to cellular mem- quality improvement is vacuum impregnation, whichbranes occurs and oxidative reactions and enzymatic is useful in introducing functional ingredients into thedegradation reactions are minimized. The process fruit tissue structure, conveniently modifying theirof dehydration before freezing is known as dehy- original composition for development of new frozendrofreezing (Fito and Chiralt, 1995; Robbers et al., products enriched with minerals, vitamins, or other1997; Bing and Da-Wen, 2002). During osmotic de- physiologically active nutritional components (Zhaohydration, the water flows from the fruit to the os- and Xie, 2004).motic solution, while osmotic solute is transferredfrom the solution into the product, providing an im- Packagingportant tool to impregnate the fruit with protectivesolutes or functional additives. Syrup is considered Packaging of frozen fruits plays a key role in protect-a better protecting agent than dry sugar. Dry sugars ing the product from air and oxygen that produce ox-are recommended for fruits, such as sliced peaches, idative degradation, from contamination by externalstrawberries, figs, grapes, cherries, etc., that produce sources, and from damage during passage from theenough fruit juice to dissolve the sugar. Dipping fruit, food producer to the consumer. Package barrier prop-whole or cut, in syrup allows a better protection than erties protect the frozen fruit from ingress of oxygen,dry sugar because the sugar solution is introduced in- light, and water vapour, each of which can result inside the fruit. Syrup concentrations between 20% and deterioration of colors, oxidation of lipids and unsat-65% are generally employed, although 40% syrup is urated fats, denaturation of proteins, degradation ofenough for the majority of the fruits. Sucrose is the ascorbic acid, and a general loss of characteristic sen-osmotic agent most suitable for fruits although other sory and nutritional qualities. Similarly, barrier prop-substances, including sucrose, glucose, fructose, lac- erties protect against the loss of moisture from thetose, L-lysine, glycerol, polyols, maltodextrin, starch frozen food to the external environment to avoid ex-syrup, or combinations of these solutes can be used ternal dehydration or “freezer burn” and weight loss.(Bing and Da-Wen, 2002; Zhao and Xie, 2004). The primary function of food packaging is to protectOsmotic dehydration is carried out at atmospheric the food from external hazards. In addition, packag-pressure or under vacuum. Among developments in ing materials should have a high heat transfer rate toosmotic treatments, vacuum impregnation may be the facilitate rapid freezing. Also, the package materialnewest. The exchange of partial freezable water for should not affect the food in any way, as indicated byan external solution is promoted by pressure, pro- European Directives on food contact materials, in-ducing different structural changes and lower treat- cluding migration limits (EC Directives 1990, 1997)ment time than osmotic dehydration at atmospheric and the Code of Federal Regulations in the Unitedpressure. Successful applications of dehydrofreez- States regarding food contact substances (CFR 2004).ing and vacuum impregnation on fruits have been A wide range of materials has been used for packag-recently reviewed (Zhao and Xie, 2004). Great color, ing of frozen fruits, including plastic, metals, and pa-flavor, and vitamin C retention have been achieved in per/cardboard, or polyethylene bags. Laminates canfrozen–thawed strawberries, raspberries, and other provide a combination of “ideal” package properties.
  • 75. 66 Part I: Processing TechnologyTable 4.1. Relative Oxygen and Water Vapour Permeabilities of Some Food Packaging Materials(References Values Measured at 23◦ C and 85% RH) Relative PermeabilityPackage Material Oxygen (ml m−2 day−1 atm−1 ) Water Vapour (g m−2 day−1 )Aluminum <50 (Very high barrier) <10 (very high barrier)Ethylene vinyl acetate (EVOH) <50 (Very high barrier) variablePolyester (PET) 50–200 (High barrier) 10–30 (high barrier)Polycarbonate (PC) 200–5000 (Low barrier) 100–200 (medium barrier)Polyethylene (PE)High density (HDPE) 200–5000 (Low barrier) <10 (very high barrier)Low density (LDPE) 5000–10,000 (Very low barrier) 10–30 (high barrier)Polypropylene (PP) 200–5000 (Low barrier) 10–30 (high barrier)Source: Atmosphere Controle 2000 (http://atmosphere-controle.fr/permeability.html).Board and paper packages are often laminated withsynthetic plastics to improve the barrier properties. VacuoleTable 4.1 shows some comparisons of barrier prop- Cytoplasm Mitochondrionerties for a range of common package materials. Fruitproducts can be packaged before freezing (fruits with Nucleoussugar or syrup, purees and juices concentrated or not)or after freezing (whole or cut fruits). The impor-tance of packaging material to the stability of frozen Cell Wallfruits has been reviewed (Skrede, 1996). In general,quality differences (pigment content, ascorbic acidretention, color, and consistency) between frozen Cell Membraneproducts packaged in different types of packages aremainly detected after a long period of frozen storage Chloroplast(>3 months) and at temperatures over −18◦ C. Endoplasmic Reticulum Figure 4.4. Cross-section of a plant cell.Effect of Freezing, Frozen Storage,and Thawing on Fruit Tissues:Physical, Chemical, and BiochemicalChanges the plastids (chloroplasts, leucoplasts, amyloplasts, or chromoplasts) (Fig. 4.4).Plant Cell Structure An important property of the plant cell is its ex-Understanding the effect of freezing on fruit requires tensive vacuole. It is located in the center of the cella short review of plant cell structure. A relationship and makes up the largest part of the cells volumebetween cell structure properties and freezing cell and is responsible for the turgor. It helps to main-damage has been extensively reviewed (Reid, 1996; tain the high osmotic pressure of the cell and theSkrede, 1996). Plant cells are surrounded by a mem- content of different compounds in the cell, amongbrane and interspersed with extensive membrane sys- which are inorganic ions, organic acids, sugars,tems that structure the interior of the cell into nu- amino acids, lipids, oligosaccharides, tannins, an-merous compartments. The plasmalemma or plasma thocyanins, flavonoids, and more. Vacuoles are sur-membrane encloses the plasma of the cell and is the rounded by a special type of membrane, the tonoplast.interface between the cell and the extracellular sur- The cell wall of plants consists of several stacked cel-roundings. Contrary to animal cells, plant cells are lulose microfibrils embedded in a polysaccharide ma-almost always surrounded by a cell wall and many trix able to store water thereby increasing the cell vol-of them contain a special group of organelles inside: ume (hydration and absorbtion). According to their
  • 76. 4 Fruit Freezing Principles 67capacity to bind or store water, the polysaccharides Chemical and Biochemical Changesinvolved in the matrix can be classified as follows: and Qualitypectin>hemicellulose>cellulose>lignin. The chemical and biochemical reactions related to Pectins are mainly polygalacturonic acids with sensorial and nutritional quality changes of fruits arediffering degrees of G-galactosyl, L-arabinosyl or delayed but not completely stopped at subzero tem-L-rhanmosyl residue and are predominant in the perature. Quality changes, such as loss of the originalmiddle lamella, the layer between cells. The de- fruit color or browning, developing off-odour and off-esterification process of pectin is related to the soft- taste, texture changes, and oxidation of ascorbic acid,ness of fruit tissues during ripening and processing. are the main changes caused by chemical and bio- chemical mechanisms that affect fruit quality. Also,Physical Changes and Quality pH changes in fruit tissues detected during freezing and frozen storage can be a consequence of theseVolume Expansion. The first factor that produces degradation reactions.mechanical damage to the cell is the volume expan-sion due to the formation of ice that affects the in-tegrity of cell membrane. Color Changes. Color is the most important qual- ity characteristic of fruits because it is the first at-Recrystallization. Ice crystals can change the tribute perceived by the consumers and is the basisquality of frozen fruits in different ways. First, the for judging the product acceptability. The most im-speed of freezing affects frozen–thawing fruit qual- portant color changes in fruits are related to chemi-ity. Slow speed freezing produces large and sharp ice cal, biochemical, and physicochemical mechanisms:crystals that can produce mechanical damage to the (a) breakdown of cellular chloroplasts and chromo-fragile plants cell membranes, causing the cell or- plasts, (b) changes in natural pigments (chlorophylls,ganelles to collapse and lose their contents (sugars, carotenoids, and anthocyanins), and (c) developmentvitamins, pigments, volatile compounds, phenol, en- of enzymatic browning.zymes, etc.) and a breakdown of the pectin fraction in Mechanical damage (ice crystals and volume ex-the cell wall which affects fruit tissue texture. During pansion) caused by the freezing process can disinte-frozen storage, retail-display, or the carry-home pe- grate the fragile membrane of chloroplasts and chro-riod, fluctuations in product temperature produces ice moplasts, releasing chlorophylls and carotenoids,recrystallization that affects the number, size, form, and facilitating their oxidative or enzymatic degra-and position of the ice crystal formed during freezing. dation. Also, volume expansion increases the loss ofFrequent large fluctuation produces partial fusion of anthocyanins by lixiviation due to disruption of cellice and the reforming of large and irregular ice crys- vacuoles.tals that can damage cellular membranes and produce (i) Chlorophylls. Chlorophylls are the green pig-a freeze-dried product, allowing sublimed or evapo- ment of vegetables and fruits, and their structuresrated water to escape. are composed of tetrapyrroles with a magnesium ion at their center. Freezing and frozen storage of greenSublimation: Freezer Burn. The sublimation of vegetables and fruits cause a green color loss due tothe ice may occur during frozen storage if the pack- degradation of chlorophylls (a and b) and transfor-aging product is unsuitable. Moisture loss by evapo- mation in pheophytins, which transfers a brownishration from the surface of the product leads to “freezer color to the plant product (Cano, 1996). One exam-burn,” which is recognized as a light-colored zone on ple is kiwi-fruit slices that show a decrease in chloro-the surface of the product. Dehydration of the prod- phyll concentration between 40% and 60%, depend-uct can be avoided by improving the type of package, ing on cultivar, after freezing and frozen storage atincreasing humidity, and decreasing the storage tem- −20◦ C for 300 days (Cano et al., 1993a). Differ-perature. ent mechanisms can cause chlorophyll degradation; The recrystallization and freezer burn dehydration loss of Mg due to heat and/or acid, which transformsincrease with temperature fluctuations, but the harm- chlorophylls into pheophytins; or loss of the phytolful effect of these two processes on frozen fruit qual- group through the action of the enzyme chlorophyl-ity can be decreased by lowering the storage temper- lase (EC 3.1.1.14), which transforms chlorophyll intoature below −18◦ C (IIR, 1996) pheophorbide. Loss of the carbomethoxy group may
  • 77. 68 Part I: Processing Technology Uncolored CHLOROPHYLL a, b forms (Blue-green/Yellow-green) Mg2+ phytol chlorophyllase H+ PHEOPHYTIN a, b CHLOROPHYLLIDE (Brown/Greyish) (Blue-green/Yellow-green) H+ − CH3CO2 heat H+ Mg2+ PYROPHEOPHYTIN a, b phytol PHEOPHORBIDE a, b (Brown/Greyish) (Brown/Greyish) H+ heat − phytol CH3CO2Figure 4.5. Pathways of chlorophyll PYROPHEOPHORBIDE a, bdegradation. (Brown/Greyish)also occur and pyropheophytin and pyropheophor- fruits. Important sources of these pigments are asbide can be formed (Fig. 4.5.) (Heaton et al., follows (Figure 4.6):1996). r ␤-cryptoxanthin: oranges Acids, temperature, light, oxygen, and enzymes r lycopene: tomatoes, watermelon, papaya andeasily destroy the chlorophylls. Thus, blanching persimmon(temperature/time), storage (temperature/time), and r ␣-carotene: banana and avocadoacidity are the important factors to be controlled r zeaxanthin: orange and peachduring processing in order to preserve chlorophylls.Other chlorophyll degradation mechanism can cause Carotenoids are affected by pH, enzymatic activ-degradation by the action of peroxides, formed in the ity, light, and oxidation associated with the conju-fruit tissue due to the oxidation reaction of polyunsat- gated double bond system. The chemical changesurated fatty acids catalyzed by the enzyme LOX. An occurring in carotenoids during processing haveimportant quality parameter employed to determine been reviewed by several authors (Simpson, 1986;the shelf life of frozen green fruits is the formation of Rodriguez-Amaya, 1997). The main degradation re-pheophytins from chlorophylls. As different types of action that damages carotenoid compounds is isomer-enzymes can be involved in chlorophyll degradation ization. Most plants appear to produce mainly trans(LOX, POD, and chlorophyllase), blanching and ad- forms of carotenoids but with increased temperature,dition of inorganic salts such as sodium or potassium the presence of light, and catalysts such as acids, iso-chloride and sodium or potassium sulphate are effi- merization to the cis forms increases, and the biolog-cient treatments to preserve green color (IIR, 1986; ical activity is dramatically reduced. However, heatCano and Mar´n, 1992; Cano et al., 1993a, b). ı treatments of products rich in carotenoids reduce the (ii) Carotenoids. Carotenoids are among the most degradation of carotenoids because of the inactiva-abundant pigment in plant products and are respon- tion of enzymes LOX and POD. Blanching fruits be-sible for the yellow, orange, and red color of most of fore freezing could be efficient in the preservationthe fruits. All of them are tetraterpenes and contain 40 of carotenoids due to enzyme inactivation. Al-carbon atoms in eight isoprenes residues. ␤-carotene though most carotenoids are heat resistant, someand lutein are the carotenoids present in most of the carotenoids, such as epoxycarotenoids, could be
  • 78. 4 Fruit Freezing Principles 69 Lycopene β-Carotene α-CaroteneHO β-Cryptoxanthin OHHO Zeaxanthin OH Figure 4.6. Structure of more frequentHO Lutein carotenoids present in fruits.affected. Carotenoids are fat-soluble pigments and var (pH, fats, antioxidants, etc.) and the processingbreakdown of chromoplasts, by heat treatment or conditions (temperature, time, light, oxygen, etc.)mechanical damage, improves their extraction with (Simpson, 1986; Rodriguez-Amaya, 1997).organic solvents and bioavailability but not their (iii) Anthocyanins. Anthocyanins are one classloss by lixiviation (Hof et al., 2000). Freezing with- of flavonoid compounds, which are widely dis-out protector pretreatment slightly decreases total tributed plant polyphenols, and are responsible forcarotenoid concentration (20%) of some fruits rich the pink, red, purple, or blue hue of a great num-in carotenoids, such as mango and papaya. But after ber of fruits (grape, plum, strawberry, raspberry,12 months of frozen storage at −18◦ C, an important blackberry, cherry, and other types of berries).decrease of total carotenoid concentration (between They are water-soluble flavonoid derivatives, which40% and 65%) occurred, although the carotenoid pro- can be glycosylated and acylated. The effect offile was unchanged (Cano and De Ancos, 1994; Cano freezing, frozen storage, and thawing in differentet al., 1996b). Similar results have been found with fruits rich in anthocyanins pigments have been re-frozen tomato cubes. A pronounced stability of total viewed by Skrede (1996). Anthocyanins in cherrycarotenoids, ␤-carotene, and lycopene was recorded fruit underwent pronounced degradation during stor-up to the 3rd month of storage. But after 12 months of age at −23◦ C (87% after 6 months), but they arestorage at −20◦ C, the losses of carotenoids reached relatively stable at −70◦ C storage (Chaovanalikt and36%, of ␤-carotene 51%, and of lycopene 48% Wrolstad, 2004). But in raspberry fruit, the stabil-(Lisiewska and Kmiecik, 2000). Freezing and frozen ity of anthocyanins to freezing and frozen storagestorage could affect the carotenoid structure and con- depends on the seasonal period of harvest. Springcentration depending on the type of fruit and culti- cultivars were practically unaffected by freezing and
  • 79. 70 Part I: Processing Technologyfrozen storage for 1 year at −20◦ C, but autumn different products present in the fruit matrix: ascor-cultivars showed a decreasing trend in total bic acid, acetaldehyde, proteins, leucoanthocyanins,anthocyanin content (4–17%)(De Ancos et al., phenols, quinones, metals (Fe3+ and Al3+ ), hydrogen2000b). In general, the freezing process does not af- peroxide, etc. (Escribano-Bailon et al., 1996).fect the level of anthocyanins in raspberry fruit (De (iv) Enzymatic Browning. Browning usually oc-Ancos, 2000; Mullen et al., 2002). Authors explain curs in certain fruits during handling, processing, anddegradation of anthocyanins during frozen storage by storage. Browning in fruit is caused by enzymatic oxi-different chemical or biochemical mechanisms. An- dation of phenolic compounds by PPO(EC 1.10. 3.1)thocyanins are water-soluble pigments located in the (Mart´nez-Whitaker, 1995). PPO catalyzes either one ıvacuoles of cell and are easily lost by lixiviation when or two reactions involving molecular oxygen. Thethe cell membranes break down. Also oxidation can first type of reaction is hydroxylation of monophe-play an important role in anthocyanin degradation nols, leading to formation of o-hydroxy compounds.catalyzed by light. PPO and POD enzymatic activ- The second type of reaction is oxidation of o-hydroxyities have been related to anthocyanin degradation. compounds to quinones that are transformed intoThus, frozen–thawed cherry discoloration disap- polymeric brown pigment (Fig. 4.3). Freezing, frozenpeared when the fruits were blanched before freezing. storage, and thawing of fruits, like mangoes, peaches,The changes in pH during processing can affect an- bananas, apples, apricots, etc., quickly develop colorthocyanin stability. Maintenance of red fruit requires changes that result in nonreversible browning oran acid medium (pH < 3.5). The flavylium cation darkening of the tissues. Freezing does not inactivatestructure of anthocyanins transfers a red color to the enzymes; however, some enzyme activity is slowedfruit. But an increase in pH value produces a change during frozen storage (Cano et al., 1998). Browningfrom red to blue until the product is colorless, a conse- by PPO can be prevented by the addition of sulfites,quence of transforming flavylium cation into a neutral ascorbic acid, citric acid, cysteine, and others. The ad-structure (Fig. 4.7). dition of antibrowning agents has been discussed in The loss of characteristic red color can also be pro- the pretreatments section. Selection of varieties withduced by formation of the anthocyanin complex with low PPO activity could help to control browning in Malvidin 3-Glucoside (25°C; 0.2 M ionic strength) R R OH OH + O O +H+ HO O R R OGI OGI OH OH A: Quinoidal base (blue) AH+: Flavylium cation (red ) +H2O −H+ R R OH OH OH O O OH R HO R HO OGI OGIFigure 4.7. Effect of pH on OH OHanthocyanins. C: Chalcone (colorless) D: Carbinol pseudo-base (colorless)
  • 80. 4 Fruit Freezing Principles 71frozen–thawed fruits (Cano et al., 1996b; Cano et al., 1996; Reid, 1996). Ice recrystallization also leads to1998). greater damage during frozen storage (Reid, 1996). Pectin is an important component of fruit cell wall.Flavor and Aroma Changes. Volatile compounds In fact, a decrease of the pectin fraction duringforming the fruit flavor (alcohols, esters, aldehydes, freezing and frozen storage has been related to aketones, acids, furans, terpenes, etc.) are produced reduction of firmness in different fruits (Lisiewskathrough metabolic pathways during harvest, posthar- and Kmiecik, 2000).vest, and storage and depend on many factors re-lated to species, variety, and type of processing. Al- Nutritional and Antioxidant Status Changes.though freezing is the best way to preserve fruit aroma Consumption of fruits is related to a good nutritional(Skrede, 1996), frozen storage and thawing can mod- status and contributes to the prevention of degenera-ify the natural fresh aroma of some fruits such as tive processes, particularly the lowering of the inci-strawberries (Larsen and Poll, 1995), but other fruits dence and mortality rate of cancer and cardiovascu-like kiwi (Talens et al., 2003) or raspberry fruits (De lar disease (Steinmetz and Potter, 1996; Tibble et al.,Ancos, 2000) do not significantly modify the aroma 1998; Willcox et al., 2003). Nutritional compoundsprofile. Freezing, frozen storage, and thawing affect found in fruits are vitamins, sugars, minerals, pro-fruits volatile profile in different ways depending on teins, and fats. Fruits are the main dietary source ofthe type of fruit and variety. vitamins C, A, and E, which are indispensable for Instead of being destroyed during freezing, some human life. The protective effect of a rich fruit dietenzymes are released. This can cause cell disruption has been attributed to certain bioactive compoundsand is one factor in the development of off-flavors with antioxidant and antimutagenic properties. Vita-and off-odors in plant products during frozen storage. mins A, and C, carotenoids, and phenolics are theBlanching is the main tool used to inactivate enzymes main bioactive compounds that contribute to the an-before freezing, but most fruits suffer important tex- tioxidant characteristics of fruits (Rice-Evans et al.,tural changes when blanched. POD enzyme activity 1996; Miller and Rice-Evans 1997; Boileau et al.,has been related to the presence of different volatile 1999; Gardner et al., 2000). Retention of the nutri-compounds such as hexanal, which is produced dur- tional and antioxidant value of fruit is the main goal ofing lipid oxidation and confers an unpleasant odor to all the processing methods, and freezing and frozenthe frozen–thawed product. Cell structure disruption storage can be one of the less destructive methods induring freezing and frozen storage favors an increase terms of long-storage periods.in or preserved important enzymatic POD activity (i) Vitamin C. Freezing processes have only a slightlevels in different thawed fruits [mango (Mar´n et al., ı effect on the initial vitamin C content of fruit (Cano1992) and papaya (Cano et al., 1998)]. It is impor- and Mar´n, 1992; Mar´n et al., 1992; De Ancos, ı ıtant to select the suitable fruit varieties for freezing, 2000). The destruction of vitamin C (ascorbic acid)based on high volatile compounds concentration and occurs during freezing and frozen storage, and thislow enzymatic activity, to obtain high-quality frozen parameter has been employed to limit the frozen stor-fruit. age period of frozen fruit. The main cause of loss of vitamin C is the action of the enzyme ascorbate ox-Textural Changes. Texture of frozen fruits is de- idase. If pretreatments or freezing processes do notpendent on chemical and biochemical modifications destroy this enzyme, it is continuously active duringof the cell wall and middle lamella components the frozen storage. Vitamin C degradation depends(pectins, hemicelluloses, and celluloses). Freezing on different factors, such as time–temperature con-causes severe texture loss due to the cryoconcen- ditions, type of fruit, variety, pretreatments, type oftration phenomena, which can induce cell wall package, freezing process, etc. (Skrede, 1996). Thusdegradation and a decrease in liquid retention. The as the frozen storage temperature decreases, highersize and location of ice crystals cause cell membrane vitamin C retention is achieved for different fruits likerupture that promotes enzyme and/or chemical berries, citrus, tomato, etc. (Skrede, 1996; Lisiewskaactivity and contributes to mechanical damage in and Kmiecik, 2000). Also, significantly different vi-cell wall material. The influence of freezing rate tamin C retention values have been achieved betweenon tissue integrity, texture, and drip loss has been varieties of fruits such as raspberry (De Ancos, 2000),reviewed by different authors (Skrede, 1996; Cano, mango (Mar´n et al., 1992), and kiwi (Cano and ı
  • 81. 72 Part I: Processing TechnologyMar´n, 1992), which were frozen and stored under ı slight decrease in ellagic acid content because of PPOthe same conditions. Vitamin C stability in freez- enzyme activity, frozen storage is a good methodol-ing and frozen storage of strawberries seems to be ogy to preserve phenolic compounds during long-more dependent on storage temperature than on the term periods (De Ancos, 2000).type of freezing process. Nonstatistical differences (iv) Antioxidant Capacity. Radical scavenging ca-were observed between strawberries processed by pacity, a measure of the antioxidant capacity of fruitfast rate freezing (at −20◦ C) and quick rate freez- extracts, was not affected by freezing and long-terming (at −50◦ C to –100◦ C), but great loss was shown frozen storage (De Ancos, 2000).between strawberries stored at −18◦ C and −24◦ C (v) Dietary Fiber. Comparative studies on dietary(Sahari et al., 2004). fiber content between fresh fruit pulp and the corre- (ii) Provitamin A and Antioxidant Carotenoids. sponding frozen fruit pulp have shown that frozenSome carotenoids, like ␤-carotene, ␣-carotene, and fruit pulp has lower fiber content than fresh fruit␤-cryptoxanthin, are recognized as precursors of vi- pulp. Freezing and frozen storage induced significanttamin A. These provitamin A carotenoids, in addition dietary fiber losses ranging from 18% for mango toto lycopene and lutein, constitute the group of an- 50% for other fruits like guava (Salgado et al., 1999).tioxidant carotenoids. The prevailing opinion is thatfreezing and frozen storage do not prevent degra- Stability of Frozen Fruitdation of carotenoids. The content of ␤-carotene,and consequently the provitamin A value, was de- Physical, physicochemical, chemical, and biochemi-creased during frozen storage of mango (Mar´n et al., ı cal changes that occur in frozen fruit during the stor-1992), kiwi (Cano and Mar´n, 1992), papaya (Cano, ı age period lead to a gradual, cumulative and irre-1996), and tomato (Lisiewska and Kmiecik, 2000). versible loss of quality that limits the storage lifeThe losses were mainly due to the activity of en- of frozen fruit. Temperature and length of storagezymes (POD, LOX, and CAT), particularly during time are the principal factors that limit the frozenfrozen storage in an oxygen environment. Lycopene, storage period of fruit and are known as TTT fac-a characteristic carotenoid in tomato fruit, has been tors. In general, lower storage temperatures lead torecognized as a powerful antioxidant (Rao and Agar- longer storage life. TTT data for each fruit was de-wal, 1999; Lavelli et al., 2000). After 3 months of termined by different quality analysis of samples offrozen storage (−20◦ C and −30◦ C), great stability of the same product, identically processed, and storedlycopene was recorded. After this period, slow losses at different temperatures in the range of −10◦ C tooccurred, the rate being faster at the higher storage −40◦ C. At certain intervals of frozen storage, sampletemperature. After 12 months at −20◦ C and −30◦ C, quality was analyzed. Sensorial analysis, loss of vi-the lycopene content was 48% and 26%, respectively, tamin C, and changes of chlorophylls to pheophytin,lower than that in the raw material (Lisiewska and or other types of pigment degradation, are the qual-Kmiecik, 2000). Other authors have reported an in- ity analyses used to determine the storage life of thecrease in the extraction of lycopene after 1 month of frozen fruit. On the basis of TTT data, different termsfrozen storage, although after 3 and 6 months the loss have been established to determine the suitable frozenof lycopene concentration was significantly higher storage life. “High-Quality Life” has been defined asthan 40% (Urbanyi and Horti, 1989). Papaya fruit the storage period quality of a frozen product com-could be an important source of lycopene, but freez- pared to a similar quality of a product just frozen.ing and frozen storage at −20◦ C during 12 months After this time, frozen fruits are still suitable forproduced a significant loss of lycopene concentration consumption, and a second term has been defined(34%) in frozen papaya slices (Cano, 1996). as “Practical Storage Life” or the storage time pe- Further discussion on the effect of freezing, frozen riod that provides frozen foods suitable for humanstorage, and thawing on carotenoid stability are in- consumption. Table 4.2 shows the “Practical Stor-cluded in the section of color changes. age Life” for different frozen fruits stored at −12◦ C, (iii) Phenolic Compounds. The freezing process −18◦ C, and −24◦ C. Fruit frozen with sugar or syrupdoes not modify either total phenolic content or el- added is more sensitive to an increase in frozen stor-lagic acid concentration in raspberry fruit. There is an age temperature because they freeze at lower tem-increasing interest in ellagic acid, a dimeric deriva- perature than fruit frozen without sugar. Thus, straw-tive of gallic acid, due to its anticarcinogenic and an- berries without sugar stored at −12◦ C have longertioxidant effects. Although frozen storage produces a “Practical Storage Life” (5 months) than fruit with
  • 82. 4 Fruit Freezing Principles 73Table 4.2. “Practical Storage Life” at Different Frozen Storage Temperatures (In Months)Fruit −12◦ C −18◦ C −24◦ CStrawberry/raspberry/peach 5 24 >24(Strawberry/raspberry/peach) + sugar 3 24 >24Apricot/cherry 4 18 >24(Apricot/cherry) + sugar 3 18 >24Fruit juice (concentrated) – 24 >24Source: Institute of International Refrigeration (IIR, 1986).sugar (3 months). These times for suitable storage bution, and food preparation (Beuchat, 2002). Freez-were obtained on the basis of high-quality raw prod- ing halts the activities of spoilage microorganisms inucts, processing in suitable conditions, and without foods but can also preserve some microorganisms fortemperature fluctuations during frozen storage. In- long periods of time. During the freezing process, mi-creasing and fluctuating temperature may occur dur- crobial growth can occur when freezing does not takeing transport and retail display. Temperature fluctua- place rapidly due to increasing temperature or fluc-tions shorten the storage life of frozen foods because tuations during frozen storage, transport or retail dis-of accelerated degradation reactions and increased play (greater than −18◦ C), and during slow thawing.quality loss (IIR, 1986; Cano, 1996). Frozen foods have an excellent overall safety record. However, the few outbreaks of food-borne illness as- sociated with frozen foods indicate that some, but notThawing all, human pathogenic microorganisms are killed byThe quality of the original fruit, preserved by freez- freezing processes. Outbreaks associated with frozening, is retained by quick thawing at low temperature foods have been reviewed by Lund (2000). Freezingin controlled conditions. During incorrect thawing, does not destroy Clostridium botulinum, the spoilagechemical and physical damage and microorganism organism that causes the greatest problems in plantcontamination can also occur. Fruit products exhibit food processing. However, C. botulinum will notlarge losses of ascorbic acid (up to 40%) and color grow and produce botulin toxin (a poison) at frozenchanges when thawed for an unusually long period, storage temperature below −18◦ C or low pH of fruit.e.g., 24 h at room temperature. Good results in terms Acid media of fruit is a protective factor againstof vitamin C and anthocyanins retention (90%) were microorganism growth. The effect of freezing andachieved by thawing small frozen fruits such as bil- frozen storage on the microbiology of some frozenberry, raspberry, black currant, red currant, and straw- fruit products has been reviewed (Skrede, 1996). Al-berry at room temperature (18–20◦ C/6–7 h), in a though spoilage microorganisms are not a great prob-refrigerator (2–4◦ C/18 h), or in a microwave oven. lem in frozen fruit and fruit juices, some outbreaksColor and ascorbic acid retention of fruit was equally and illnesses associated with frozen food consump-affected by thawing temperature and time. Thorough tion have been due to fruit products. Cases of hep-thawing must be determined by taking into account atitis A that were produced by frozen raspberriesthe size of the fruit and/or the type of packaging in the United Kingdom (Reid and Robinson, 1987)(Kmiecik et al., 1995). and frozen strawberries in the United States (DHHS, 1997) have been referenced. When thawing frozen food, it is important to remember that if the raw prod-Microbiological Quality and Safety uct is contaminated and freezing does not totally de-of Frozen Fruits stroy spoilage and pathogenic microorganisms, as theFruit microflora are dominated by spoilage yeast, temperature of food rises, there may be microorgan-moulds, and bacteria, but occasionally the presence ism growths, mainly on the surface of the product. Toof pathogenic bacteria, parasites, and viruses ca- preserve safety in frozen fruits, recommended tem-pable of causing human infections has also been perature requirements exist for each stage of the colddocumented. Fruits can become contaminated with chain. It is recommended that frozen fruits be main-pathogenic microorganisms while growing in fields, tained at −18◦ C or colder, although exceptions areorchards, vineyards, or greenhouses, or during allowed during brief periods as during transportationharvesting, postharvest handling, processing, distri- or local distribution (−15◦ C). Retail display cabinets
  • 83. 74 Part I: Processing Technologyshould be at −18◦ C and never warmer than −12◦ C regulatory control over the safety of the nation’s food(IIR, 1986). supply and are ruled by GMP (FDA, 2004). HACCP Freezing effects on different types of microor- and Application Guidelines were first adopted byganisms have been recently studied (Archer, 2004). The National Advisory Committee on Microbiolog-Yeast, moulds, viruses, bacteria, and protozoa are ical Criteria For Foods (NACMCF) for astronautsaffected in different ways by freezing, frozen stor- (1970), seafood (1995), low-acid canned food andage, and thawing cycles. Although Gram-negative juice industry (2002–2004). Other food companies,bacteria (Salmonella spp. Escherichia coli, etc.) are including frozen foods, already use the HACCP sys-more susceptible to freezing than Gram-positive ones tem in their manufacturing processes (NACMCF,(Listeria monocytogenes, Staphylococcus aureus, 1997). The Codex Alimentarius also recommendedetc.), the nature of the food can change the survival of a HACCP-based approach to enhance food safetysome former organisms. Freezing kills microorgan- (Codex Alimentarius, 1999).isms by physical and chemical mechanisms, and fac- The central goal of The European Commission ontors related to freezing parameters (ice formation, rate food safety policy is to ensure a high level of protec-of cooling, temperature/time of storage, etc.), or food tion for human health and consumer interests in re-matrix composition and nutritional status, or phase of lation to food. The Commission’s guiding principle,growth determine the survival of the microorganism primarily set out in its White Paper on Food Safety,(Lund, 2000). Several mechanisms have been pro- is to apply an integrated approach from farm to tableposed to explain the damage caused to microorgan- covering all sectors of the food chain, feed produc-isms by freezing. Cellular damage caused by internal tion, primary production, food processing, storage,or external large ice crystals and increase of external transport, and retail sale. The establishment of theor internal solute concentration are some of the mech- European Food Safety Authority (EFSA) was oneanisms proposed. Better understanding of the interac- of the key measures contained in the Commission’stions between physical and chemical changes in the White Paper on Food Safety. EFSA is the keystone ofmicroorganism cell and food matrix during freezing, European Communities (EC, 2002) risk assessmentfrozen storage, and thawing processes could lead to regarding food.the designing of safe freezing processes where themicroorganisms, if they are present, would not sur-vive. For spoilage and pathogenic microorganisms,the freezing process becomes an important hurdle to FREEZING METHODSovercome (Archer, 2004). The rate of freezing and the formation of small ice crystals in freezing are critical to reduce tissue dam-Legislation age and drip loss in fruit thawing. Different types of freezing systems are designed for foods. The se-Special rules for frozen food safety regulations lection of suitable freezing systems is dependent onhave not been adopted by either the United States the type of product, the quality of frozen product,or the “European Communities (EC)” authorities. desire, and economical reasons. Freezing systemsFrozen food is regulated by the general rules are divided according to the material of the heat-for food processing safety. Codex Alimentarius transmission medium (Rahman, 1999):Commission adopted special rules for frozen foods–Recommended International Code of Practice for 1. Freezing by contact with cooled solid or plateProcessing and Handling of Quick Frozen Food. The freezing: The product is placed between metalCommission recognized not only temperature as the plates and then adjusted by pressure. This methodmain consideration to maintain frozen food qual- is used for block or regular form products.ity (Codex Alimentarius, 1976) but also other fac- 2. Freezing by contact with cooled liquid or immer-tors. The production of safe frozen food requires sion freezing: The fluids usually used are sodiummaximum attention to GMP and HACCP princi- chloride solutions, glycol and glycerol solutions,ples in all the production chain, from raw material and alcohol solutions.(farm) to consumer freezer (table), and to all the 3. Freezing with a cooled gas in cabinet or air-blaststeps in between. In the United States, the minimum freezing: Air-blast freezing allows quick freez-sanitary and processing requirements for producing ing by flowing cold air (−40◦ C) at relatively highsafe and wholesome food are an important part of speed between 2.5 and 5 m/s.
  • 84. 4 Fruit Freezing Principles 754. Cryogenic freezing: Food is frozen by direct con- tested with different fruit tissues. Fruit tissues were tact with liquefied gases, nitrogen and carbon frozen under pressure. Peach and mango were also dioxide. Nitrogen boils at −195.8◦ C and the sur- cooled under pressure (200 MPa) to −20◦ C without rounding food temperature reaches temperatures ice formation, and then the pressure was released to below −60◦ C. This is a very fast method of 0.1 MPa. By scanning electron microscope , it was freezing and the rapid formation of ice crystals observed that the cells of fruits frozen under pres- reduces the damage caused by cell rupture, pre- sure were less damaged compared to those frozen us- serving sensorial and nutritional characteristics. ing traditional freezing process, including cryogenic Cryogenic freezing is recommended for cubes, freezing (Otero et al., 2000). slices, medium or small whole fruits but is not ap- propriate for whole medium and large fruits such High-Pressure Thawing. Thawing occurs more as prunes, peaches, etc., due to the risk of crushing. slowly than freezing. During thawing, chemical and physical damage can occur, as well as microorgan- ism contamination that can reduce the quality of theFUTURE PERSPECTIVES frozen/thawed product. From a textural point of view,Irradiation. Ionizing radiation has been used as an incorrect thawing can produce an excessive soft-a safe and effective method for eliminating bacte- ening of the plant tissue. A quick thawing at low tem-rial pathogens from different foods and disinfecting perature to avoid rising temperature could help in as-fruit, vegetables, and juices. The application of low- suring the food quality. High-pressure thawing woulddose (<3 kGy) irradiation to a variety of frozen plant be a new application of high-pressure freezing. Re-foods to eliminate human pathogens has been stud- cent studies showed that high-pressure thawing canied. The amount of ionizing radiation necessary to re- preserve food quality and reduce the necessary thaw-duce the bacterial population increases with decreas- ing time. High-pressure thawing was more effectiveing temperature. Significant softening was achieved in texture improvement than was atmospheric pres-at −20◦ C, but textural changes were not shown when sure thawing (Bing and Da-Wen, 2002).lower ionization doses were employed at higher tem-peratures (−5◦ C) (Sommers et al., 2004). ACKNOWLEDGMENTSHigh Pressure. The quality of frozen/thawed prod- This work was financed by the Spanish nationaluct is closely related to freezing and thawing pro- research projects, AGL-2002-04059-C02-02 andcesses (Cano, 1996). The rate of freezing and the AGL-2003-09138-C04-01, from Ministry of Sci-formation of small ice crystals in freezing are critical ence and Technology and the Spanish projectto minimize tissue damage and drip loss in thawing. 07G/0053/2003 from Consejer´a de Educaci´ n, Co- ı oSeveral reports have studied the use of high pres- munidad Aut´ noma de Madrid. osure at subzero temperature (Bing and Da-Wen, 2002;LeBail et al., 2002). The physical state of food canbe changed by the external manipulation of pres- REFERENCESsure and temperature according to the water phasediagram. The main advantage of high-pressure freez- Archer, L.D. 2004. Freezing: an underutilized food safety technology? International Journal of Fooding is that when pressure is released, a high supercool- Microbiology 90:127–138.ing can be obtained, and as a result the ice-nucleation Ashie, I.N.A., Simpson, B.K., Smith, J.P. 1996.rate is greatly increased and the initial formation of Mechanisms for controlling enzymatic reactions inice is instantaneous and homogeneous throughout foods. Critical Reviews in Food Science andthe whole volume. The use of high pressure facili- Nutrition 36(1):1–30.tates supercooling, promotes uniform and rapid ice Bartolom´ , A.P., Ruperez, P., F´ ster, C. 1996a. e unucleation and growth, and produces small size crys- Freezing rate and frozen storage effects on color andtals, resulting in a significant improvement of product sensory characteristics of pineapple fruit slices.quality (LeBail et al., 2002; Bing and Da-Wen, 2002). Journal of Food Science 61:154. From a structural point of view, damage to cells Bartolom´ , A.P., Ruperez, P., F´ ster, C. 1996b. e uduring processing is diminished due to the small size Changes in soluble sugars of two pineapple fruitof ice crystals, resulting in a significant improve- cultivars during frozen storage. Food Chemistryment of product quality. These advantages have been 56:163.
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  • 88. 4 Fruit Freezing Principles 79 During Processing, edited by Finley, J.W., pp. Talens, P., Escriche, I., Mart´nez-Navarret, N., Chiralt, ı 409–441. Westport, CT: AVI. A. 2003. Influence of osmotic dehydration andSkrede, G. 1996. “Fruits”. In Freezing Effects on Food freezing on the volatile profile of kiwi fruit. Food Quality, edited by Lester, E.J., pp. 183–245. Research International 36:635–642. New York: Marcel Dekker Inc. Tibble, D.L., Benson, J., Curtin, K., Ma, K.-N.,Sommers, C., Fan, X., Niemira, B., Rajkowski, K. Schaeffer, D., Potter, J.D. 1998. Further evidence of 2004. Irradiation of ready-to-eat foods at USDA’S the cardiovascular benefits of diets enriched in Easter regional research center-2003 update. carotenoids. American Journal of Clinical Nutrition Radiation Physics and Chemistry 71:509–512. 68:521–522.Spiazzi, E.A., Raggio, Z.I., Bignono, K.A., Tregunno, N.B., Goff, H.D. 1996. Mascheroni, R.H. 1998. Experiments on Osmodehydrofreezing of apples: structural and dehydrofreezing of fruits and vegetables mass textural effects. Food Research International. transfer and quality factors. Advances in the 29:471–479. Refrigeration Systems, Food Technologies and Cold Urbanyi, G., Horti, K. 1989. Color and carotenoid Chain, IIF/IIR 6:401–408. content of quick-frozen tomato cubes during frozenSteinmetz, K.A., Potter, J.D. 1996. Vegetables, fruit storage. Acta Alimentaria 18:247–267. and cancer prevention: a review. Journal American Willcox, J.K., Catignani, G.L., Lazarus, S. 2003. Diet Association 53:536–543. Tomatoes and caridovascular health. CriticalSuutarinen, J., Heiska, K., Moss. P., Autio, K. 2000. Reviews in Food Science and Technology 43: The effects of calcium chloride and sucrose 1–18. pre-freezing treatments on the structure of Yueming-Jiang, Yuebiao-Li, Jianrong-Li. 2004. strawberry tissues. Lensmittel Wissensachaft und Browning control, shelf live extension and Technologie 33:89–102. quality maintenance of frozen litchi fruit byTalens, P., Escriche, I., Mart´nez-Navarret, N., Chiralt, ı hydrochloric acid. Journal of Food Engineering A. 2002. Study of the influence of osmotic 63(2):147–151. dehydration and freezing on the volatile profile of Zhao, Y., Xie, J. 2004. Practical applications of vacuum strawberries. Journal of Food Science impregnation in fruit and vegetable processing. 67(5):1648–1653. Food Science and Technology 15:434–451.
  • 89. Handbook of Fruits and Fruit Processing Edited by Y. H. Hui Copyright © 2006 by Blackwell Publishing 5 Fruit Drying Principles J´ zsef Barta oFruit Drying remains soft. In the United States, blackberries, cow-State of Water in Fruits berries (ligonberries), and grapes are dried, while in Equilibrium States Spain, red grapes are dried.Principles of Water Removal Apricots, dates, plums, and tropical fruits are dried Moisture Transport in Solid Material in the sun in several countries, while apples, pears, Drying Procedure prunes, and peaches are dried by artificial means. Effect of the Drying Air Characteristics on the Drying Process Dryers with natural air ventilation were used in thePrinciples of the Technological Calculations 19th century in California for apple drying or to finishDryers products that have previously been dried by the sun.Drying Technology of Fruits Fruits dried in the sun or in dryers with natural air Preparative Procedures ventilation are referred to as “evaporated fruit,” while Drying Procedure fruits dried in dryers with artificial ventilation are Secondary Procedures described as “dehydrated fruits.”Specific References Fruits can be dried whole, in halves, or as slices,General References or alternatively can be chopped after drying. The residual moisture content varies from small (3–8%) to large (16–18%) amounts, according to the typeFRUIT DRYING of fruit. Significant amounts are packaged in smallFruit drying has a long tradition. Inhabitants living portions (200–1000 g) in manufacturing plants. Of-close to the Mediterranean Sea and in the Near East ten, countries importing dried fruit repackage it totraded fruits that had been dried in the open sun. Dried meet the needs of consumers and large kitchens. Fruitfruit is a delicacy, because of the nutritive value (66– mixtures are widely consumed both in the United90% carbohydrate) and shelf life. For example, in- States and Europe. Fruit is packed as a mixture orhabitants of hillside villages isolated from the outside each component is packed separately in a transparent,world by snow ate diets consisting primarily of seeds appealing packaging. Well-known components areand dried fruits. round slices of apples, apricots and peaches, pear Today, the production of dried fruits is widespread. halves, prunes, sour cherries, and dates. Often, wal-Nearly half of the dried fruits in the international nuts and almonds are also added to the mixture.market are raisins, followed by dates, prunes, figs, Dried fruit is widely used by the confectionery,apricots, peaches, apples, pears, and other fruits. Sig- baking, and sweets industries. Soup manufacturingnificant amounts of sour cherries, cherries, pineap- plants use dried fruits in the various sauces, garnish-ples, and bananas are also dried. The selection of ments, puddings, and ice powders, and food for in-fruit for drying depends on local circumstances and fants and children. Dried fruits are used in variouscustoms. For example, in the Middle East, lemons teas, e.g., rose hips, and by the distilling industrywith thin peel are dried whole. The taste and aroma (dried prunes, apricots). Applications include fruitare preserved in the brownish inner fleshy part, which powders processed from juices or pulps that dissolve 81
  • 90. 82 Part I: Processing Technologyquickly. The development of the fruit powders The moisture content characterizes the state of thewas possible through processing, which preserves material, i.e., its water content expressed in kg relatedcolor and flavor (vacuum drying, lyophilization, and to 1 kg of dried material. The equilibrium betweenswelling). Artificial drying made it economically the atmosphere and the wet material is highly af-possible to use raw materials at competitive prices fected by temperature. Knowledge of the correlationand of high quality; examples are apples, prunes, and between the various factors influencing equilibriumrose hips. Various milling procedures make it pos- has primary importance for drying technology, sincesible to dry highly valuable berries with soft flesh the air moistening state determines the final mois-(strawberries, raspberries) and mature stone-fruits ture content being reached at the drying temperature.(apricots, peaches) (Burits and Berki, 1974). The relationship among the three features of the state makes it possible to have three types of planar repre-STATE OF WATER IN FRUITS sentations.Fruit drying involves removing water in different r The sorption isotherm represents the function offorms (both free and bound) and different amounts. the moisture content of the material with theThe amount and manner of water removal change water activity at constant temperature.the structure of fruit depending on the type of bond- r The sorption isobar is the function of theing, and also determine the character of the recon- temperature and the moisture content of thestituted dried material. Among the various bonding material at the equilibrium relative humidityforms of water, the strongest is the chemical, physico- (ERH).chemical bonding, followed by adsorption, osmotic, r The sorption isostheta represents the watermicro- and macro-capillary, and, finally, rehydration activity as a function of the temperature at(Imre, 1974). During drying, the weakest bound wa- constant moisture content of the material.ter is removed first; removing moisture by breakingstronger bonds requires energy. Removal of free wa- Drying technology uses the sorption isothermster does not change the character of the material in most frequently. Determination of the sorptioneither the dried or rehydrated states. Significantly isotherms is done by actual or theoretical mea-higher energy and special procedures are required surements. For representation of isotherms, severalto remove bound water, i.e., to decompose the higher empirical correlations were proposed (e.g., Halsey,bonding energies (Ginzburg, 1968, 1976). 1948; Henderson, 1952; Chung and Pfost, 1967). Several authors dealt with correlations of sorp-Equilibrium States tion data for fruits. Requirements necessary for aBy putting wet material into a closed space, water good correlation can be found in numerous reportsmolecules change to the gaseous state forming a mix- (Ratti et al., 1989; Crapiste and Rotstein, 1986;ture of air and water vapor. At the same time, the Guggenheim, 1966; Iglesias and Chirife, 1976; Pfostmolecules of the water vapor adsorb on the surface et al., 1976; Thompson, 1972). Several methods existof the material by moistening it. After a given time, for determination of the sorption isotherms of fruitsthe number of molecules adsorbed on the surface of by measurements. One method consists of the mea-the material and the number of molecules that change surement of the relative moisture content and tem-to the gaseous state becomes equal. At this time, there perature at equilibrium by placing the material withis a state of equilibrium between the gaseous atmo- a known moisture content into a closed air space.sphere in the space and the solid material. The state The measured relative moisture content is equal toof the gaseous atmosphere can be characterized by its the equilibrium relative vapor content. Air moisturewater activity, which is the ratio of the partial pres- values measured at the same temperature but differ-sure of water vapor to the saturated partial pressure. ent levels of moisture gives sorption isotherms for aThe equilibrium relative humidity of the material can specific fruit. Other methods of measuring sorptionbe determined from the water activity: isotherms make use of air space with a constant rel- ative vapor content established either by cooling and p1aw = , (5.1) heating of the saturated air or by salt crystal solutions p2 in a desiccator. The moisture content of the materialwhere aw is the water activity, p1 is the partial pres- put into the air space becomes constant, reaching asure of water in the food, and p2 is the saturated vapor state of equilibrium. The relative vapor content andpressure of water at the same temperature. the moisture content of the material measured at the
  • 91. 5 Fruit Drying Principles 83 70 Water content, % 60 50 40 apple 30 apricot prune 20 10 0 0 10 20 30 40 50 60 70 80 90 Relative moisture content, %Figure 5.1. Sorption isotherms of some fruits.temperature of the air space will be one point on PRINCIPLES OF WATERthe sorption isotherm (Jowitt et al., 1983; Mazza, REMOVAL1984; Wolf and Jung, 1985). Figure 5.1 shows sorp-tion isotherms of some fruit. Drying a moist material and decreasing the water Knowledge of the sorption isotherms of a material activity mean evaporation of bound water from in-is of primary importance from a practical point of side the solid material into the atmosphere. Breakingview (Wolf et al., 1985). To ensure a product with water bonds, releasing, and transferring heat con-the required moisture content, sorption isotherms are nected to phase change require energy. Drying canused to determine the state of the air (temperature, be done with different types of drying energy: con-relative vapor content) (Shatadal and Jayas, 1992). vective (warm air), contact (cooled surface), radiativeThe temperature and relative vapor content predict (infrared rays), and excitation (microwave) energies.the remoistening and deterioration of a dried product With convective drying, the heated air low in mois-with a given moisture content during storage. Further, ture content meets the wet material and as a result,it has great importance in selecting the drying proce- the moisture moves onto the surface of the mate-dure and predicting dryability, the binding strength of rial and then into the drying air. Tasks of the warmthe moisture, and the shelf life of the fruit (Maroulis air are to transfer heat to the material being dried toet al., 1988). If on the sorption isotherm, low mois- establish the drying potential and to transfer moistureture content relates to high aw value, the material into the air. For contact drying, the heat expanded byis highly hygroscopic, and drying can be done only conduction from the cooled surface of the materialwith care in a climate-controlled space or in vacuum. evaporates the moisture. With infrared drying, theDrying procedures with dry air can also be used for heat spreads from a radiating body—which can befruit having higher moisture content, e.g., fruit at a a spot lamp, a piece of heated metal, or ceramic—low aw value. The design of any process in which directly to the material being dried. This methodthe transfer of heat is involved requires knowledge can be well-applied using vacuum drying for veryof density as well as thermal properties of fruits be- small or chopped material (Szab´ , 1987). For heat ex- oing processed. Properties of fruits are discussed by change by excitation, materials consisting of highlyLewis (1987), Lozano et al. (1979), and Constenla polarized molecules absorb the energy of excitation,et al. (1989). Empirical equations are proposed for resulting in heat necessary for drying the material.modeling using density and thermal properties of Using this method, liquids, pastes, and highly milledthe fruits being processed (Heldman, 1975; Choi and materials can be handled quickly and without a deteri-Okos, 1986; Singh and Mannapperuma, 1990; Singh, oration of the product. Vacuum drying can be used for1992). heat-sensitive materials with low moisture content. In
  • 92. 84 Part I: Processing Technologya vacuum with no transferring medium, convective form of energy mentioned above occurs together withheat exchange cannot be applied. diffusion and moisture transport that is a function of the type of material and circumstances. For industrialMoisture Transport in calculations, the various forms of water transport canSolid Material be handled together by means of an effective apparent diffusion parameter. Using the average apparent dif-The phenomenon of drying is similar regardless of fusion parameter (De , m2 /s) the mass flow (qm , kg/s)the drying method. This section deals with convec- of the moisture is in a stationary state:tive drying, the most widely used method in the fruitprocessing industry. The wet material (fruit) is placed dX q m = cs D e A, (5.2)in an air space with relative moisture content lower dzthan the ERH of the material; moisture is transferred where A is the surface area perpendicular to the direc-from the solid material (fruit) into the drying medium tion of the moisture transport (m2 ), cs is the concen-(air space). tration of the solid material (kg/m3 ), z is the length in Mass flow of the moisture (qm in kg/s) is qm = direction of the moisture transport (m), and X is the␤y (Ys − Yg ) A, where ␤y is the material exchange moisture content of the material, i.e., the amount offactor at the gaseous side (kg/m2 s), Ys , Yg are the water related to 1 kg dry material.absolute vapor content of the air at the surface of The relationship above can be derived from Fick’sthe material and in the air, respectively, (kg/kg), A is law. In a non-stationary state, the material equationthe surface area (m2 ). written for water results in a second order, non- Simultaneously, the moisture content of the ma- linear, parabolic differential equation, which can beterial is decreased. The water moves from the solid given together with the initial and boundary condi-(fruit) and changes to vapor either inside or on the tions (e.g., material exchange on the surface). Thesurface of the solid material. This vapor moves to the moisture distribution along the length can be de-surface and goes into the air. In certain materials, such termined at an arbitrary drying period (Gion, 1986,as gels, moisture transport is caused by diffusion flow 1988; K¨ rmendy, 1985; Mohr, 1984). oof the water in the given material. This diffusion flowis initiated by the moisture difference of the material Drying Procedure(Barta et al., 1990). Most foods are capillary-colloidalporous materials in which simultaneous liquid–vapor At steady-state conditions (constant temperature, airtransport can occur. The character and direction of flow rate, and air moisture content), the experimen-this transport depend on the texture, shape, and re- tal results of drying are plotted by time. Generally,lationship of capillaries and pores. The vapor pro- the moisture content (X ) related to dry material isduced by water evaporation in the capillary-porous shown as a function of time (t). This is presented instructure flows by diffusion to the surface. The so- Figure 5.2.called Knudsen flow in the micro-capillaries can be This plot shows a typical case where the mois-several orders of magnitude larger than Poiseuille ture from the solid material evaporates first fromflow in macro-capillaries. In foods, the conduction the moisture layer on the surface and decreases 9 8 7 6 x (kg/kg) 5 4 3 2 1 0Figure 5.2. Drying curve of a wet 0 10 20 30 40 50 60 70material. t (min)
  • 93. 5 Fruit Drying Principles 85 7 6 (dx/dt) × 103 5 4 3 2 1 0 0 10 20 30 40 50 60 70 Figure 5.3. Drying rate curve as a t (min) function of time. 7 6 (dx/dt) × 103 5 4 3 2 1 0 0 1 2 3 4 5 6 7 8 Figure 5.4. Drying rate curve as a x (kg/kg) function of the moisture content.continuously until water evaporates from the inside moisture content related to the relative vapor contentof the solid material. It can be seen in the figure that of the air. Figure 5.5 shows a curve for the averagevariations in the drying rate depend on time and mois- temperature of the material.ture content of the fruit product. This change can be At the initial period of drying, the temperatureseen better if the drying curve is differentiated and of the material reaches the temperature of a weta drying flow rate curve is derived. Drying rate can thermometer. The temperature does not change inbe presented as a function either of the drying period the constant rate period until reaching the criti-(Fig. 5.3), or the moisture content of the material cal moisture content. The temperature of the ma-(Fig. 5.4). terial increases in the falling rate period and be- Curves for the drying rate and drying flow rate can comes equal to the temperature of the drying airbe divided into several parts. These parts are the re- when drying stops. Dimensions of the material beingsult of the inner mechanism of drying and of changes dried are of primary importance in drying technologyoccurring during drying. In the first step of drying, (Figure 5.6).temperature equalization and moisture transport oc- Linear variation of the size of the material changescur. In the next step, which is the constant rate period, the drying period to the second power. Increasing thethere is a constant moisture flow to the surface, there- drying temperature, and therefore the drying rate,fore, the surface is always wet. The average moisture the drying period is shortened and the capacity ofmeasured at drying of the surface is the so-called the equipment is raised. This method is useful onlycritical moisture content. The drying rate decreases in the constant rate period because the higher tem-after reaching the critical moisture content. Drying perature of drying air does not result in significantstops and the drying rate becomes equal to zero when increases in the temperature of the material. The in-the average moisture content reaches the equilibrium crease in the drying rate is hindered by some stresses
  • 94. 86 Part I: Processing TechnologyFigure 5.5. Average temperature ofd