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Fresh Juice treated with PEF and Pascalisation (HPP)
 

Fresh Juice treated with PEF and Pascalisation (HPP)

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    Fresh Juice treated with PEF and Pascalisation (HPP) Fresh Juice treated with PEF and Pascalisation (HPP) Document Transcript

    • Innovative Food Science and Emerging Technologies 12 (2011) 235–243 Contents lists available at ScienceDirect Innovative Food Science and Emerging Technologies j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i f s e tComparing equivalent thermal, high pressure and pulsed electric field processes formild pasteurization of orange juice. Part I: Impact on overall quality attributesR.A.H. Timmermans a,⁎, H.C. Mastwijk a, J.J. Knol a, M.C.J. Quataert a, L. Vervoort b, I. Van der Plancken b,M.E. Hendrickx b, A.M. Matser aa Wageningen UR Food and Biobased Research, P.O. Box 17, 6700 AA Wageningen, The Netherlandsb Laboratory of Food Technology, Leuven Food Science and Nutrition Research Center, Department of Microbial and Molecular Systems, Katholieke Universiteit Leuven,Kasteelpark Arenberg 22 box 2457, 3001 Heverlee, Belgiuma r t i c l e i n f o a b s t r a c tArticle history: Mild heat pasteurization, high pressure processing (HP) and pulsed electric field (PEF) processing of freshlyReceived 3 March 2011 squeezed orange juice were comparatively evaluated examining their impact on microbial load and qualityAccepted 2 May 2011 parameters immediately after processing and during two months of storage. Microbial counts for treated juices were reduced beyond detectable levels immediately after processing and up to 2 months of refrigeratedKeywords: storage. Quality parameters such as pH, dry matter content and brix were not significantly different whenMild heat pasteurizationHigh pressure (HP) processing comparing juices immediately after treatment and were, for all treatments, constant during storage time.Pulsed Electric Field (PEF) processing Quality parameters related to pectinmethylesterase (PME) inactivation, like cloud stability and viscosity, wereQuality parameters dependent on the specific treatments that were applied. Mild heat pasteurization was found to result in theShelf life most stable orange juice. Results for HP are nearly comparable to PEF except on cloud degradation, where aOrange juice lower degradation rate was found for HP. For PEF, residual enzyme activity was clearly responsible for changes in viscosity and cloud stability during storage. Industrial relevance: Development of mild processing technologies with a minimal impact on fruit juice can be considered as a true alternative of fresh fruit. The present work presents a fair comparison of mild heat treated, high pressure (HP) and pulsed electric field (PEF) processed orange juice as an alternative for thermal pasteurization. Orange juices were monitored during two months of storage. © 2011 Elsevier Ltd. All rights reserved.1. Introduction Parish, 1993), and discoloration (Arreola et al., 1991; Li, Sawamura, & Kusunose, 1988; Tatum, Nagy, & Berry, 1975). To avoid quality Nowadays, consumers choose more and more for minimally degradation of orange juice by thermal processing, non-thermal pres-processed foods with characteristics closer to those of fresh foods ervation techniques such as high pressure and pulsed electric fields haveusing minimal processing or reducing chemical preservatives (Allenda, been studied during the last decade.Tomás-Barberán, & Gil, 2006; Oliveira & Oliveira, 1999). Juices are no High pressure processing (HP), when carried out around roomexception, and there is, therefore, a strong tendency towards consump- temperature, is one of the non-thermal processes, that inactivatestion of premium quality juices. These juices are directly obtained from bacterial cells, yeasts and molds without the use of heat, having afruits (not from concentrate), are distributed through the refrigerated minimal effect on the sensory qualities associated with ‘fresh-like’chain and have a relatively short shelf life (Esteve, Frígola, Rodrigo, attributes such as texture, color and flavor (Arroyo, Sanz, & Préstamo,& Rodrigo, 2005). Traditionally, thermal pasteurization is used to 1999; Bull et al., 2004; Hayashi, 1996). HP typically uses pressuresinactivate micro-organisms to prolong shelf life on the one hand, and to of 300–700 MPa for periods of 30 s up to a few minutes to destroyinactivate heat-stable pectinmethylesterase (PME) for preventing cloud pathogenic and spoilage bacteria. Bacterial spores may survive pres-loss on the other hand (Chen & Wu, 1998). Typically, for shelf stable sures above 1000 MPa at room temperature, but outgrowth can bejuices, processing times for thermal pasteurization are equivalent to prevented by temperature control (refrigerated storage) and low90 °C for 1 min (Eagerman & Rouse, 1976). Thermal processing has a pH conditions (e.g. acid products or acidification). In contrast to heatnegative impact on the quality of orange juice such as loss of fresh pasteurization, HP at room temperature showed no complete in-flavor (Braddock, 1999), degradation of ascorbic acid (Chen, Shaw, & activation of pectinmethylesterase (PME) after pressure treatments (Basak & Ramaswamy, 1996; Goodner, Braddock, & Parish, 1998; Van den Broeck, Ludikhuyze, Van Loey, & Hendrickx, 2000; Van den ⁎ Corresponding author. Tel.: + 31 317 481305; fax: + 31 317 48 3011. Broeck, Ludikhuyze, Van Loey, Weemaes, & Hendrickx, 1999). It has E-mail address: rian.timmermans@wur.nl (R.A.H. Timmermans). been suggested that residual PME activity following high pressure1466-8564/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.doi:10.1016/j.ifset.2011.05.001
    • 236 R.A.H. Timmermans et al. / Innovative Food Science and Emerging Technologies 12 (2011) 235–243treatment is due to the persistence of a HP resistant PME fraction 2.2. Selection of process conditionsthat corresponds with the heat-stable PME fraction (Duvetter et al.,2009; Goodner et al., 1998; Van den Broeck et al., 2000). Although Process conditions were selected to result in an equivalentthere is some residual PME activity, the cloud of orange juice was processing impact, with respect to microbial safety and spoilagestable for more than 50 and 60 days at 4 °C, using conditions of 1 min micro-organisms (Matser, Mastwijk, Bánáti, Vervoort, & Hendrickx,at 700 MPa and 800 MPa respectively (Goodner et al., 1998; Nienaber 2010). The Food and Drug Administration recommends a 5-log& Shellhammer, 2001). reduction of the “pertinent micro-organism”, which is the most resistant Pulsed electric field (PEF) processing, when carried out with micro-organism, in orange juice E. coli O157:H7 (FDA, 2004).limited energy input, is another non-thermal preservation process. As a guideline FDA recommends a minimum temperature–timeIn a PEF process, food is treated in a chamber with two electrodes equivalent for juice of 71.1 °C for 3 s for products with a pH in thegiving short electric pulses to inactivate micro-organisms, in order to range of 3.6–4.0. However, this specific temperature–time is insuffi-increase the shelf life of treated food products with a minimal effect cient to inactivate spoilage organisms.on product quality. Effects on enzyme inactivation largely depend Furthermore, these minimum conditions have to be translated inon the thermal history of the sample during the PEF treatment. process conditions for large-scale heat exchangers as used in this study,Application of short pulses of high electric fields with a duration of concerning limitations in heat penetration in large scale systems. Formicroseconds and intensities in the order of 20–80 kV/cm minimize particulate and more viscous products both the average temperaturethe heating of food (Altunakar, Gurram, & Barbosa-Cánovas, 2007; and processing time must be increased to guarantee that a minimumZhang, Qin, Barbosa-Cánovas, & Swanson, 1995), although the applied sufficient degree of processing has occurred. The industrial conditionspulse causes irreversible loss of the cell membrane functionality, for heat pasteurization of premium juices are equivalent to 90 °C forleading to inactivation of microbial cells. Effectiveness of microbial 2 s or 84 °C for 20 s (Mazzotta, 2001). However, these processinginactivation by PEF depends on process parameters including electric conditions by far exceed the criterion for microbial inactivation andfield strength, total treatment time, pulse width and pulse waveform, at these temperatures the quality of treated orange juice is far tooand on medium related parameters such as conductivity, composition, much compromised for the scope of this comparative study. In thistemperature and microbial parameters (Aronsson & Rönner, 2001; study, 72 °C for 20 s was used as a reference treatment for mild heatBarsotti & Cheftel, 1999; Vega-Mercado et al., 1997; Wouters & pasteurization of orange juice.Smelt, 1997). Concerning the inactivation of PME, it is suggested that For high pressure treatment, literature reports 1–5 min at 350–a higher electric field strength and longer treatment time are more 500 MPa to inactivate E. coli in orange juice (Damar, Bozoglu, Hizal,effective (Yeom, Streaker, Zhang, & Min, 2000a,b). Yeom, Zhang, and & Bayindirh, 2002; Erkmen & Dogan, 2004; Linton, McClements,Chism (2002) reported a 90% reduction in PME activity from orange & Patterson, 1999). Industrial conditions used are 1–2 min at 500–juice by applying 25 kV/cm for 250 μs. However, at these conditions 600 MPa to show optimal safety and quality. For this study thereforethe thermal load to the product is equivalent to 149 °C. Van Loey, 1 min at 600 MPa was used at an industrial HP production line.Verachtert, and Hendrickx (2002) reported an inactivation of less For pulsed electric field processing, conditions recommended tothan 10% at 35 kV/cm for 1000 pulses of 1 μs at temperatures where inactivate E. coli and other pathogens are 25–35 kV/cm during 20–inactivation of enzymes due to heat could be excluded. 300 μs (Alvarez & Heinz, 2007; Wouters, Dutreux, Smelt, & Lelieveld, There are many studies on the effect of mild preservation tech- 1999). However, for this technology, actual design of the equipment,niques on micro-organisms, quality and shelf life of food products. especially the treatment chamber, strongly influences the effective-Variance in initial quality of the food, caused by use of different ness of the treatment and the temperature reached during the PEFspecies, maturity and storage conditions, and the use of different treatment itself (Mastwijk et al., 2007). PEF conditions were usedprocess conditions make it difficult to compare the results obtained. that were in line with the literature data and that shown in previousThe objective of this work was to compare the impact of mild heat studies to result in safe and stable orange juices (Matser, Schuten,pasteurization, high pressure processing and pulsed electric field Mastwijk, & Lommen, 2007).processing of freshly squeezed orange juice on nutritional, qualityand sensorial parameters and consumer preference during 2 months 2.3. Preparation and processingof storage. Processing conditions were defined in such a way thatimmediately after processing equivalent products in terms of Juice from 1300 kg of oranges was extracted in a single batchmicrobial inactivation were obtained. In this research three parties using an automatic juice extractor (Master Zumoval, Valencia, Spain)were involved, Katholieke Universiteit Leuven (Leuven, Belgium), to obtain 650 L of orange juice with pulp. After pressing, the juiceCentral Food Research Institute (Budapest, Hungary) and Wagenin- was sieved (mesh 3.5 mm) and transported via a cooling vessel to agen UR Food & Biobased Research (Wageningen, The Netherlands). storage tank (4–6 °C), and stirred until filling. The juice was sub-This paper reflects part I of the work (Fig. 1). The impact on specific jected to different treatments: fresh/untreated, mild heat treatment,chemical and biochemical quality parameters is described in part II by high pressure processing (HP) and pulsed electric field (PEF), seeVervoort et al. (under review) and the sensorial aspects, part III, are Fig. 1. Orange juice was bottled under hygienic conditions in 250 mLdescribed by Magyar-Horváth et al. (under review). The consumer PET bottles and sealed with PE caps. The bottles and caps werestudy will be published in a separate publication. pre-sterilized by gamma irradiation at 15 kGy (Isotron, Ede, The Netherlands).2. Material and methods 2.3.1. Mild heat pasteurization2.1. Product Heating was performed using a pilot-scale, continuous flow tubular heat exchanger (inner diameter 10 mm). Orange juice was sieved for Orange juice was derived from a mixture of three varieties of a second time prior to pasteurization because of technical parametersoranges Valencia, Pera and Baladi, supplied by a commercial fresh of the tubular heat exchanger. The juice was preheated to 45 °C, thenjuice producer located in The Netherlands. The oranges, present in heated to 72 °C and subsequently held at this temperature for 20 s.equal proportions, were brushed, washed, hand sorted and washed Directly after the holding tube, the juice was cooled down to 2 °C andagain one day before the trial by the supplier at 7 °C, and were stored manually filled under hygienic conditions in a laminar flow cabinetin a clean plastic box at 4–6 °C. into the PET bottles.
    • R.A.H. Timmermans et al. / Innovative Food Science and Emerging Technologies 12 (2011) 235–243 237 Valencia Pera Baladi oranges oranges oranges Brushing & washing Handsorting Washing Extraction Juice Bottling Heat pasteurization PEF treatment HP Bottling Bottling Untreated HP treated Heat treated PEF treated orange juice orange juice orange juice orange juice Distribution Microbiology Quality aspects Nutritional Sensorial Consumer aspects aspects study Food & Food & Katholieke Katholieke Central Food Food & Biobased Biobased Universiteit Universiteit Research Biobased Research Research Leuven Leuven Institute Research (Wageningen) (Wageningen) (Leuven) (Leuven) (Budapest) (Wageningen) Separate Part I Part II Part III publication Fig. 1. Overview of the production, handling and analysis of orange juice samples and dissemination of publications.2.3.2. High Pressure Processing (HP) 2.3.3. Pulsed Electric Field (PEF) Untreated juice packed in PET bottles with PE caps was subjected For PEF processing a continuous flow pilot plant described in moreto HP treatment. detail by Mastwijk (2006) and Lelieveld, Notermans, and De Haan An industrial unit, WAVE 6000/55 high pressure unit (NC Hyper- (2007) was used. Prior to processing, the entire pilot plant systembaric, Burgos, Spain) was used to treat the orange juice at 600 MPa for was cleaned (CIP) and pre-sterilized (SIP 120 °C for 20 min). The1 min. Water of 17 °C was used as pressure fluid, where it took 3 min temperature of the juice in the storage tank was 11 ± 2 °C. First, theto come up to the desired pressure, and less than 5 s to depressurize. juice was heated to 38 °C in a preheating section. Then PEF treat-The temperature rise during compression was 3 °C/100 MPa. ment was applied using monopolar pulses of 2 μs duration at nominal
    • 238 R.A.H. Timmermans et al. / Innovative Food Science and Emerging Technologies 12 (2011) 235–243electric field strength of 23 kV/cm. The treatment device was a content was determined gravimetrically as residue remaining aftercolinear chamber with a 20 mm gap. The outlet temperature was drying. Samples were cooled in a desiccator prior to weighing.58 °C at a repetition rate of 90 Hz and a flow rate of 130 L/h. Pulseenergy yields 31 ± 3 J per pulse, specific energy input was 76 ± 4 J/mL 2.10. Cloud stabilityand number of pulses was 18 ± 2. Directly after PEF treatment thejuice was cooled back to 14 °C and samples were manually bottled in Cloud stability was investigated by measurements of sedimenta-250 mL PET bottles under hygienic conditions in a laminar air flow tion rate and scoring the opacity of the cloud. The sedimentation ratecabinet. was characterized by recordings of the height of the interface of the sediment and cloud in bottles that were left undisturbed during2.4. Storage and sampling refrigerated storage time. In addition, the opacity of the cloud in the bottles was scored on a 1–5 scale (1 transparent to 5 opaque) by visual Immediately after filling bottles were stored at 4 °C, with tem- appearance to have an indication on the rate of changes from opaqueperature measurements taken at 30 min intervals using calibrated tem- to transparent.perature data loggers (I-button DS1921G, Maxim Direct, Dallas, U.S.A.).Fresh/untreated samples were also stored frozen below −40 °C as a 2.11. Viscosityreference sample for sensorial analysis. The samples were analyzed intriplicate for microbiological, chemical and physical properties after 1, 2, The apparent viscosity of the juices was measured after centrifu-9, 20, 28 and 58 days of storage. gation (10 min at 360 xg) using a Brookfield viscometer (model LV DV-E, Brookfield Engineering Laboratories, Stoughton, USA). A2.5. Microbial analysis volume of 16 mL of the juice was placed in the UL-adapter, with corresponding spindle. Viscosity was determined at temperatures Samples were taken before and after filling, from the raw and in the range of 21.5–22.5 °C. Measurements were performed indifferent types of treated orange juice. These samples were analyzed triplicate.in triplicate on total plate count, Enterobacteriaceae, E. coli, Lactic acidbacteria, yeast and molds following methods ISO 4833, ISO 21528–2, 2.12. Statistical analysisISO 16649–2, ISO 15214, and ISO 7954 respectively. During storage ofthe orange juice at 4 °C, samples were taken at indicated times and Changes in the quality parameters (color, brix, pH, dry matter,analyzed in triplicate. viscosity, cloud stability) for the different treatments (untreated, heat, HP, PEF) were quantified. Initial changes that were observed directly after processing were determined together with small changes that2.6. Color were observed during storage by linear regression. A single sided t-test was used to quantify the differences between the various treat- Color measurements were executed at 22 ± 1 °C, using a Hunterlab ments. Differences in the initial level and during storage were con-ColorFlex (Hunterlab, Reston, Virgina, U.S.A.). This spectrophotometer sidered significant when the confidence level (CL) was larger thanuses an illuminant of D65 and a 10° angle observer as reference. The 95% (P b 0.05).instrument was standardized each time with a black and whiteceramic plate. Samples were filled in glass cuvets, and Hunter values 3. Results and discussiona* (redness), b* (yellowness), and L* (lightness) were measured intriplicate. Color difference, ΔE, was calculated from L*, a*, and b* 3.1. Microbiological analysisparameters, using Hunter-Scotfields equation ΔE = (Δa 2 + Δb 2 +ΔL 2) 1/2 where a = a–a0, b = b–b0 and L = L–L0. The subscript ‘0’ The batch of samples that was produced (n = 12) was evaluatedindicates initial color, and the y-intercept of linear regression models within 24 h after processing. All samples in the batch complied withwas taken for this number. ΔE was calculated for each treatment and EC regulation 2073/2005, which describes microbial criteria forzero-values for each treatment were used as comparison. Depending foodstuffs. Microbial assessment during storage aimed to characterizeon the value of ΔE the development in color difference during storage the effects of processing, hygiene and spoilage (Table 1). Duringtime could be estimated as not noticeable (0–0.5), slightly noticeable storage at 4 °C microbial counts were analyzed on the days specified.(0.5–1.5), noticeable (1.5–3.0), well visible (3.0–6.0) and great (6.0– For each day of sampling, three PET bottles were randomly chosen12.0) (Cserhalmi, Sass-Kiss, Tóth-Markus, & Lechner, 2006). and analyzed. Untreated orange juice showed to have low microbial counts until t = 9 days, where at t = 20 days growth was observed.2.7. Brix High quality oranges were used in this study, since one normally could expect initial populations of viable aerobic bacteria in raw juice The °brix of centrifuged samples of orange juice (10 min at 360 xg) between 10 3 and 10 5 cfu/mL even up to 10 8. For yeast and molds,was measured by a digital hand-held refractometer at 22 °C ± 1 °C counts of 10 3 cfu/mL up to 10 5 cfu/mL could be found, depending(PR-1, Atago, Japan). on species, maturity and storage conditions (Bull et al., 2004; Elez- Martínez, Soliva-Fortuny, & Martín-Belloso, 2006). All samples treated2.8. pH by mild heat, HP and PEF showed to be under detection limit after 2 months of storage at 4 °C. The latter corresponds to the expecta- The pH measurements of orange juice (22° ± 1 °C) were per- tions, since all process conditions were selected on equivalentformed with a pH meter (Metrohm, 826 pH mobile) with a glass- processing, with respect to microbial food safety and spoilage.electrode (Metrohm) and calibrated before every measurement at pH4 and 7. 3.2. Color2.9. Dry matter content Color differences between untreated and the different types of treated orange juice were determined at different time-intervals Moisture in 10 g orange juice was evaporated from the sample by during storage. Hunter L*, a* and b* values were measured, and resultsoven drying, 4 h at 70 °C followed by 20 h at 105 °C. Total dry matter of regression kinetics and t-test are shown in Tables 2 and 3.
    • R.A.H. Timmermans et al. / Innovative Food Science and Emerging Technologies 12 (2011) 235–243 239Table 1 The overall trend for the color of orange juices during storageMicrobial counts evaluated at different times during storage of untreated, mild heat time showed that lightness (L* value) decreased, redness (a* value)treated, high pressure processed (HP) and pulsed-electric field (PEF) treated orangejuice. increased, and yellowness (b* value) decreased, which is consistent with research of Nienaber and Shellhammer (2001) (data not shown). 0 days 1 days 2 days 9 days 20 days 28 days 58 days There are no significant differences in color parameters between HP E.Coli (ISO 16649-2) cfu/g treated and untreated orange juice, where mild heat pasteurized and Untreated PEF treated orange juice showed differences for all L*, a* and b* values directly after production. Heat pasteurized <10 n.d. Mild heat pasteurized orange juice was significantly lighter than HP HP and untreated orange juice, having less red color and more yellow- PEF ness. PEF treated samples showed the opposite: significantly darker in Enterobacteriaceae (ISO 21528-2) cfu/g color than untreated, HP and heat, with significantly more red and less yellow tints. Untreated Yeom et al. (2000a) and Min, Jin, Min, Yeom, and Zhang (2003) Heat pasteurized <10 reported a significant lighter appearance of PEF treated juice over heat HP treatment. PEF Despite the significant differences in L* a* b* color attributes of samples, it is more valuable from a practical point of view to compare the Total aerobic plate count (ISO 4833) cfu/g DE values of orange juice. DE values, indicated in Fig. 2, are the sum of L* Untreated 1.4*105 1.4*105 n.d. a* and b* values, which is more associated to consumer perception than Heat pasteurized singular L* a* or b* values, since consumers do not judge each particular <1000 attribute, but the combination of them (Cserhalmi et al., 2006). HP <1000 Based on the observed DE values, it was found that all types of PEF orange juice showed a noticeable (DE 0.5–1.5) difference in color Yeast (ISO 7954) cfu/g compared to its color on day 1. There were no noticeable color Untreated 910 990 420 420 6.2*104 1.1*105 n.d. differences between the different treatments. Heat pasteurized <10 3.3. Brix HP PEF In citrus juices, °brix is used to indicate the percentage of soluble Mould (ISO 7954) cfu/g sugars and is one of the most important factors for grading the quality Untreated 17 12 11 19 320 4700 n.d. of a citrus juice (McAllister, 1980). °Brix varies for juices obtained from different species of oranges and during seasons, and it is there- Heat pasteurized fore not easy to compare °brix values with other studies. PEF treated HP <10 orange juice gave a slightly lower °brix after processing (Fig. 3). PEF However, during storage no significant changes were observed in the Lactic acid bacteria (ISO 15214) cfu/g samples (for none of the processing methods). Untreated 1000 810 640 530 4.7*104 1.2*105 n.d. 3.4. pH Heat pasteurized HP <100 The effect of mild heat treatments on pH of orange juice is shown PEF in Fig. 4. No significant differences between untreated and differentn.d. = not determined. types of treated juice were found. There was no variation duringTable 2Regression of kinetic parameters for frozen untreated, untreated, mild heat treated, high pressure processed (HP) and pulsed-electric field (PEF) treated orange juice. Untreated frozen Untreated Pasteurized HP PEF Color L Slope − 0.04 ± 0.01 − 8.68E-03 ± 1.47E-03 − 1.02E-02 ± 1.23E-03 − 1.94E-02 ± 8.54E-04 t=0 57.00 ± 0.04 57.22 ± 0.08 57.60 ± 0.04 57.10 ± 0.03 56.31 ± 0.02 Color a Slope − 4.53 E-03 ± 4.21E-03 3.02E-03 ± 6.22E-04 3.30E-03 ± 4.61E-04 3.19E-03 ± 3.70E-04 t=0 1.94 ± 0.02 1.95 ± 0.02 1.83 ± 0.02 1.98 ± 0.01 2.07 ± 0.01 Color b Slope − 0.05 ± 0.02 − 0.05 ± 0.00 − 0.04 ± 0.00 − 0.05 ± 0.00 t=0 63.51 ± 0.09 61.84 ± 0.11 62.51 ± 0.07 61.93 ± 0.05 61.61 ± 0.05 Brix Slope 1.32E-03 ± 6.27E-03 1.07E-03 ± 7.86E-04 6.70E-04 ± 8.17E-04 2.22E-03 ± 7.06E-04 t=0 11.73 ± 0.06 11.59 ± 0.03 11.54 ± 0.02 11.59 ± 0.02 11.39 ± 0.02 pH Slope − 8.60E-03 ± 1.80E-03 − 2.96E-04 ± 4.25E-04 − 3.94E-04 ± 3.70E-04 − 9.32E-05 ± 3.95E-04 t=0 3.34 ± 0.01 3.37 ± 0.01 3.35 ± 0.01 3.35 ± 0.01 3.35 ± 0.01 Dry matter content Slope − 0.03 ± 0.01 3.34E-03 ± 1.35E-03 3.52E-03 ± 1.70E-03 2.42E-03 ± 1.57E-03 t=0 9.48 ± 0.01 10.09 ± 0.05 9.96 ± 0.04 9.92 ± 0.05 9.83 ± 0.04 Viscosity Slope − 2.67E-03 ± 2.46E-03 3.11E-04 ± 2.91E-04 1.24E-03 ± 5.52E-04 2.73E-03 ± 2.95E-04 t=0 1.56 ± 0.02 1.57 ± 0.01 1.53 ± 0.01 1.60 ± 0.02 1.46 ± 0.01
    • 240 R.A.H. Timmermans et al. / Innovative Food Science and Emerging Technologies 12 (2011) 235–243Table 3Differences in quality parameters between various groups given by the confidence level after a one-sided t-test. Statistically significant differences with CL N 95% are indicated in bold. untr.—past.⁎ untr.—HP⁎ untr.—PEF⁎ past.—HP⁎⁎ past.—PEF⁎⁎ HP—PEF⁎⁎ Color L Slope 99.2% 98.9% 94.5% 78.8% 99.9% 99.9% y-intercept 99.9% 91.9% 99.9% 99.9% 99.9% 99.9% Color a Slope 96.4% 97.1% 96.4% 65.5% 57.9% 57.9% y-intercept 99.9% 88.5% 99.9% 99.9% 99.9% 99.9% Color b Slope 53.9% 65.5% 53.9% 97.7% 53.9% 99.4% y-intercept 99.9% 75.8% 97.1% 99.9% 99.9% 99.9% Brix Slope 50.0% 53.9% 55.7% 52.3% 86.3% 91.8% y-intercept 90.3% 57.9% 99.9% 91.9% 99.9% 99.9% pH Slope 99.9% 99.9% 99.9% 57.9% 65.5% 72.6% y-intercept 91.9% 86.4% 91.9% 61.8% 53.9% 61.8% Dry matter Slope 99.9% 99.9% 99.9% 53.9% 65.5% 69.1% y-intercept 97.7% 99.4% 99.9% 75.7% 98.6% 90.3% Viscosity Slope 88.5% 94.3% 98.6% 93.2% 99.9% 99.1% y-intercept 99.7% 90.2% 99.9% 99.9% 99.9% 99.9% Cloud sedimentation Slope 86.7% 91.0% 99.7% 93.9% 99.0% 99.8% y-intercept 83.5% 68.4% 86.3% 93.5% 93.9% 92.9% ⁎ Evaluated for the first 9 days.⁎⁎ Evaluated over the entire period of 58 days.storage time, except for the untreated orange juice, in which pH showed a slight decrease in the first 9 days, but this decrease is onlydecreases significantly over the first 9 days. This is mainly caused by noticed because a small number of data points during storage werethe limited number of measurements during storage included in data used for regression. Similar dry matter values were found at t = 1, 2analysis for the untreated samples (spoiled after day 9) compared to and 9 days for the treated juices, however the treated juices werethe treated samples (data available until day 58). analyzed for a longer storage time, and therefore the small decrease during the first days of storage did not contribute to the overall trend in their regression lines.3.5. Dry matter content 3.6. Cloud stability There is no change in dry matter content during storage for anytreatment (Fig. 5). The dry matter content of untreated orange juices Cloud loss is considered as a quality defect in shelf stable citrus juices derived from concentrate and it is one of the main reasons for 5 3.5 4 well visible DE value 3 3.4 noticeable pH 2 3.3 1 slightly noticeable 0 not noticeable 0 10 20 30 40 50 60 3.2 Time (days) 0 10 20 30 40 50 60 Time (days)Fig. 2. Total color difference (DE-value) for untreated ( ), mild heat pasteurized ( ),high pressure processed (HP) (●) and pulsed electric field (PEF) ( ) processed orange Fig. 4. pH for untreated ( ), mild heat pasteurized ( ), high pressure processed (HP)juice. (●) and pulsed electric field (PEF) ( ) processed orange juice during storage at 4 °C. 10.6 12.0 10.4 11.8 Dry matter (%) 10.2 Brix (°) 11.6 10.0 11.4 9.8 11.2 9.6 11.0 9.4 0 10 20 30 40 50 60 0 10 20 30 40 50 60 Time (days) Time (days)Fig. 3. °Brix of serum of centrifuged orange juice (10 min 360 xg) for untreated ( ), Fig. 5. Dry matter content for untreated ( ), mild heat pasteurized ( ), high pressuremild heat pasteurized ( ), high pressure processed (HP) (●) and pulsed electric field processed (HP) (●) and pulsed electric field (PEF) ( ) processed orange juice during(PEF) ( ) processed orange juice during storage at 4 °C. storage at 4 °C.
    • R.A.H. Timmermans et al. / Innovative Food Science and Emerging Technologies 12 (2011) 235–243 241Fig. 6. Observed sedimentation and cloud loss of untreated, mild heat pasteurized, high pressure pasteurized (HPP) and pulsed electric field (PEF) processed orange juice bottlesduring the first 115 days of storage at 4 °C.the level of heating in heat pasteurization, where 90–100% of PME is regression could be applied to the data of the differences (Squires,inactivated (Goodner et al., 1998, 1999; Goodner, Braddock, Parish, & 1988). After a storage time of 2 months, all treatments showed toSims, 1999; Irwe & Olsson, 1994). However, it is doubtful to consider reach an equilibrium, having the same level of sedimentation.cloud loss as a quality defect in fresh juice, since consumers accept Therefore, it is more interesting to evaluate the rate of sedimentation.the degradation (Parish, 1998). Moreover, modern transparent Samples with a high degree of sedimentation during the first days ofpackaging actively shows the extent of cloud degradation, referring storage were considered to have a high sedimentation rate, having ato the natural degradation process in fresh squeezed orange juice. low cloud stability. PEF treated orange juice had the highest degree ofNevertheless, it is an interesting parameter to evaluate and compare sedimentation (P ≤ 0.05), followed by HP, mild heat pasteurizationthe different preservation techniques. and untreated orange juice, respectively (Fig. 7). Cloud stability was measured evaluating the degree and rate of The opacity of the cloud was scored by visual observation to obtainsedimentation, by recording the height of the interface of the sedi- an indication which mild treatment gives the fastest transition ofment and cloud from bottles shown in Fig. 6. Degree of sedimentation opaque to transparent (scores from 5 to 1). This is a qualitativewas calculated as percentage, where the height of the sediment was measure of the cloud loss, caused by activity of the endogenous PME.expressed as a function of the total height. Sedimentation of 0% Results shown in Fig. 8, showed that untreated orange juice is thecorresponds to a completely stable orange juice, having no cloud loss. fastest in getting transparent, which suggests that it has the highestDuring storage time, the orange juices are sedimented according to enzyme activity, followed by PEF, HP and heat pasteurization.a non-linear response (Fig. 7). To compare the cloud stability ofdifferent treatments, a direct evaluation of the observed differencesbetween different treatments during storage was conducted. Sincethe point-wise differences in height are sufficiently small, linear 5 Judgement by vision 4 Sedimentation of cloud (%) 100 3 80 60 2 40 1 20 0 0 1 2 9 20 28 58 85 115 0 20 40 60 80 100 120 Time (days) Time (days) Fig. 8. Judgement of color of cloud serum of untreated ( ), mild heat pasteurized ( ),Fig. 7. Sedimentation of cloud observed from untreated ( ), mild heat pasteurized ( ), high pressure processed (HP) ( ) and pulsed electric field (PEF) ( ) processed orangehigh pressure processed (HP) (●) and pulsed electric field (PEF) ( ) processed orange juice during storage at 4 °C from 1 (transparent) to 5 (opaque) to have an indication forjuice stored at 4 °C. cloud stability.
    • 242 R.A.H. Timmermans et al. / Innovative Food Science and Emerging Technologies 12 (2011) 235–243 2.0 With this study it was shown that HP and PEF are good novel preservation techniques to increase microbial shelf life of orange juice 1.8 from 9 to 20 days up to two months when stored at 4 °C, maintaining Viscosity (cP) the fresh character. As equivalent processing was chosen with respect 1.6 to food safety, it seems that mild heat pasteurization is a good alternative as well, since it resulted in a comparable quality. However, it can be expected, that when more realistic industrial processing 1.4 conditions are chosen, the quality of heat pasteurized orange juice will be lower. HP and PEF conditions used in this research are also used in 1.2 the limited applications of these technologies on industrial scale, and 0 10 20 30 40 50 60 therefore HP and PEF are considered to be the best options to enlarge Time (days) shelf life based on results of quality parameters. As shown in Fig. 1, other parameters are described in part II (Vervoort et al., underFig. 9. Viscosity of serum of centrifuged (10 min at 360 xg) untreated ( ), mild heatpasteurized ( ), high pressure processed (HP) (●) and pulsed electric field (PEF) ( ) review) and part III (Magyar-Horváth et al., under review).processed orange juice during storage at 4 °C. Acknowledgements In part II of this study (Vervoort et al., under review), PMEinactivation levels of 85, 92 and 34% were measured at day 1 for heat, This study has been carried out with financial support from theHP and PEF pasteurization respectively. This high enzyme activity of Commission of the European Communities, Framework 6, Priority 5PEF treated orange juice corresponds to the results shown in Figs. 7 “Food Quality and Safety”, Integrated Project Novel Q FP6-CT-2006-and 8, where the PEF treated juice showed to have to least stable 015710.cloud of treated products. Although the PME activity of the HP treatedjuice was slightly more reduced than heat pasteurized juice (Vervoortet al., under review), more cloud was retained for heat pasteurized Referencesjuice than HP treated orange juice. This disagreement is difficult to Allenda, A., Tomás-Barberán, F. A., & Gil, M. I. (2006). Minimal processing for healthyinterpret. Possibly it may be related to the existence of a heat-labile traditional foods. Trends in Food Science and Technology, 17(9), 513–519.and heat-stable fraction of PME. In addition, it should be mentioned Altunakar, B., Gurram, S. R., & Barbosa-Cánovas, G. V. (2007). Applications of pulsed electric fields for food preservation. In H. L. M. Lelieveld, S. Notermans, & S. W. H. dethat the juice for heat pasteurization contained pulp particles of Haan (Eds.), Food preservation by pulsed electric fields: From research to application.similar size compared to the juice for HP pasteurization because of Abington, UK: Woodhead Publishing.sieving. Alvarez, I., & Heinz, V. (2007). Hurdle technology and the preservation of food by pulsed electric fields. In H. L. M. Lelieveld, S. Notermans, & S. W. H. de Haan (Eds.), Food preservation by pulsed electric fields. From research to application. Cambridge UK:3.7. Viscosity Woodhead Publishing. Aronsson, K., & Rönner, U. (2001). Influence of pH, water activity and temperature on Viscosity of the serum of centrifuged orange juice was measured the inactivation of E. Coli and S. cerevisiae by pulsed electric fields. Innovative Food Science and Emerging Technologies, 2(2), 105–112.during storage time. The observed changes in viscosity were small Arreola, A. G., Balaban, M. O., Marshall, M. R., Peplow, A. J., Wei, C. I., & Cornell, J. A.(Fig. 9, Table 2). Just after processing, the viscosity was significantly (1991). Supercritical carbon dioxide effects on some quality attributes of singledifferent for mild heat pasteurized and PEF treated orange juice. strength orange juice. Journal of Food Science, 56(4), 1030–1033. Arroyo, G., Sanz, P. D., & Préstamo, G. (1999). Response to high-pressure, low-During storage, viscosity of mild heat pasteurized juice remained temperature treatment in vegetables: Determination of survival rates of microbialstable, whereas the viscosity of HP and PEF treated juice increased. populations using flow cytometry and detection of peroxidase activity usingThis effect was observed by Cserhalmi et al. (2006) and Polydera, confocal microscopy. Journal of Applied Microbiology, 86(3), 544–556. Barsotti, L., & Cheftel, J. C. (1999). Food processing by pulsed electric fields: II. BiologicalStoforos and Taoukis (2005) as well, but considered to be more aspects. 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