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  1. 1. Horticulture Post Harvest Technology Harvesting, Handling and Storage of Horticultural Crops A.S. Dhatt and B.V.C. Mahajan Punjab Horticultural Postharvest Technology Centre Punjab Agricultural University Campus, Ludhiana (16-07-2007) CONTENTS Introduction Harvesting Types of indices and their components Harvesting tools, containers and methods Handling Packing house operations Precooling of horticulture produce Packaging of horticulture produce Post harvest treatments Storage Controlled atmosphere storage Hypobaric storage or low-pressure system Ripening of fruits Keywords Harvesting, Handling, Storage, Horticultural crop 1
  2. 2. 1. Introduction The horticultural produce includes fruits, vegetables, flowers and other ornamental plants, plantation crops, aromatic and medicinal plants and spices. However, in this chapter, information on fruits and vegetables is only included. According to Oxford English Dictionary, fruit can be defined as ‘the edible product of a plant or tree, consisting of seed and its envelope, especially the latter when it is juicy or pulpy’. The consumer definition of fruit would be ‘plant products with aromatic flavours, which are either naturally sweet or normally sweetened before eating. The classification of fruits and vegetables is arbitrary and according to usage. Botanically many crops, defined as vegetables, are fruits (tomato, capcicum, melons etc.). Morphologically and physiologically the fruits and vegetables are highly variable, may come from a root, stem, leaf, immature or fully mature and ripe fruits. They have variable shelf life and require different suitable conditions during marketing. All fresh horticultural crops are high in water content and are subjected to desiccation (wilting, shriveling) and to mechanical injury. Various authorities have estimated that 20-30 percent of fresh horticultural produce is lost after harvest and these losses can assume considerable economic and social importance. That is why, these perishable commodities need very careful handling at every stage so that deterioration of produce is restricted as much as possible during the period between harvest and consumption. 2. Harvesting Fruits harvested too early may lack flavour and may not ripen properly, while produce harvested too late may be fibrous or have very limited market life. Similarly, vegetables are harvested over a wide range of physiological stages, depending upon which part of the plant is used as food. For example, small or immature vegetables possess better texture and quality than mature or over-mature vegetables. Therefore harvesting of fruits and vegetables at proper stage of maturity is of paramount importance for attaining desirable quality. The level of maturity actually helps in selection of storage methods, estimation of shelf life, selection of processing operations for value addition etc. The maturity has been divided into two categories i.e. physiological maturity and horticultural maturity. • Physiological maturity: It is the stage when a fruit is capable of further development or ripening when it is harvested i.e. ready for eating or processing. • Horticultural maturity: It refers to the stage of development when plant and plant part possesses the pre-requisites for use by consumers for a particular purpose i.e. ready for harvest. Importance of maturity indices: • Ensure sensory quality (flavour, colour, aroma, texture) and nutritional quality. • Ensure an adequate postharvest shelf life. • Facilitate scheduling of harvest and packing operations. • Facilitate marketing over the phone or through internet. Definitions related to maturity and ripening: i) Mature: It is derived from Latin word ‘Maturus’ which means ripen. It is that stage of fruit development, which ensures attainment of maximum edible quality at the completion of ripening process. 2
  3. 3. ii) Maturation: It is the developmental process by which the fruit attains maturity. It is the transient phase of development from near completion of physical growth to attainment of physiological maturity. There are different stages of maturation e.g. immature, mature, optimally mature, over mature. iii) Ripe: It is derived from Saxon word ‘Ripi’, which means gather or reap. This is the condition of maximum edible quality attained by the fruit following harvest. Only fruit which becomes mature before harvest can become ripe. iv) Ripening: Ripening involves a series of changes occurring during early stages of senescence of fruits in which structure and composition of unripe fruit is so altered that it becomes acceptable to eat. Ripening is a complex physiological process resulting in softening, colouring, sweetening and increase in aroma compounds so that ripening fruits are ready to eat or process. The associated physiological or biochemical changes are increased rate of respiration and ethylene production, loss of chlorophyll and continued expansion of cells and conversion of complex metabolities into simple molecules. v) Senescence: Senescence can be defined as the final phase in the ontogeny of the plant organ during which a series of essentially irreversible events occur which ultimately leads to cellular breakdown and death. A. Types of indices and their components i) Visual a) Size and shape: Maturity of fruits can be assessed by their final shape and size at the time of harvest. Fruit shape may be used in some instances to decide maturity. For example, the fullness of cheeks adjacent to pedicel may be used as a guide to maturity of mango and some stone fruits (Figure 1). Immature Half mature Mature Fig 1 : Judging mango harvest maturity by shape of shoulder Immature Half mature Mature Fig 1 : Judging mango harvest maturity by shape of shoulder Immature Half Mature MatureImmature Half mature Mature Fig 1 : Judging mango harvest maturity by shape of shoulder Immature Half mature Mature Fig 1 : Judging mango harvest maturity by shape of shoulder Immature Half Mature Mature Figure 1. Judging mango harvest maturity by shape of shoulder (Source : Wardlaw and Leonard, 1936) Some cultivars of banana become less angular in cross section as development and maturation progress (Figure 2). Size is generally of limited value as a maturity index in fruit, though it is widely used for many vegetables, especially those marketed early in their development. With these produce, size is often specified as a quality standard, with large size generally indicating commercial over-maturity and under-sized produce indicating an immature state. The assumption, however, is not always a reliable guide for all-purpose. 3
  4. 4. Three-quarters Light full three -quarters Full three -quarters Full Three-quarters Light full three -quarters Full three -quarters Full Figure 2 : Cross section of the middle banana fingers showing the chanages in angularity as they mature on the plant (Source : Von Loesecke, 1949) The visual appearance of fruit and vegetable is the most important quality factor, which decides its price in the market. The consumer (wholesaler or retailer) observes the quality of fresh fruits and vegetables with their visual or external appearance. The produce should attain proper shape and size. Medium size produce is always preferred by the consumers, because they tend to view large fruits as more mature. The appearance of the product is the most critical factor in the initial purchase, while subsequent purchase may be more related to texture and flavour. Therefore, subjective evaluation of size and shape of the produce should be conducted to meet the desired quality characteristics. b) Colour: The loss of green colour of many fruits is a valuable guide to maturity as shown in Plate 1. There is initially a gradual loss in intensity of colour from deep green to lighter green and with many commodities, a complete loss of green colour with the development of yellow, red or purple pigments. Ground colour as measured by colour charts, is useful index of maturity for apple, pear and stone fruits, but is not entirely reliable as it is influenced by factors other than maturity. For some fruits, as they mature on the tree, development of blush colour, that is additional colour superimposed on the ground colour, can be a good indicator of maturity. Examples are red or red- streaked apple cultivars and red blush on some cultivars of peach. Objective measurement of colour is possible using a variety of reflectance or light transmitance spectrophotometer. Colour perception depends on the type and intensity of light, chemical and physical characteristics of the commodity, and person’s ability to characterize colour. Although human eye is used to evaluate colour but results can vary considerably due to human differences in colour perception. Therefore, an instrument (objective method) is used to provide a specific colour value based on the amount of light reflected off the commodity surface or light transmitted through the commodity. This instrument can measure small differences in colour accurately and can be automated in the packing line. This instrument is popularly known as Colour Difference Meter. This instrument use colorimetric method for colour measurement. 4
  5. 5. Plate 1: judging maturity of mango and tomato by colours ii) Physical indices a) Firmness: As fruit mature and ripen they soften by dissolution of the middle lamella of the cell walls. The degree of firmness can be estimated subjectively by finger or thumb pressure, but more precise objective measurement is possible with pressure tester or penetrometer (Plate 2). In many fruits such as apple, pear, peach, plum, guava, kinnow etc. firmness can be used to determine harvest maturity. Penetrometer measures the pressure necessary to force a plunger of specified size into the pulp of the fruit. Such pressure is measured in pounds and kilograms force. Plate 2 : PenetrometerPlate 2 : Penetrometer 5
  6. 6. b) Specific gravity: As fruit mature, their specific gravity increases. This parameter is rarely used in practice to determine when to harvest a crop but it could be where it is possible to develop a suitable sampling technique. It is used, however, to grade crops into different maturities. To do this the fruit or vegetable is placed in a tank of water; those that float will be less mature that those that sink. To give greater flexibility to the test and make it more precise, a salt or sugar solution can be used in place of water. This changes the density of the liquid, resulting in fruits or vegetables that would have sunk in water floating in the salt or sugar solution. iii) Chemical Measurement Measurement of chemical characteristics of produce is an obvious approach to the problem of maturity determination. The conversion of starch to sugars during maturation is a simple test for the maturity of some apple cultivars. It is based on the reaction between starch and iodine to produce a blue or purple colour. The intensity of the colour indicates the amount of starch remaining in the fruit. The total soluble solids of the fruit can be measured with refractometer, which indicate the harvest maturity of fruits. Acidity is readily determined on a sample of extracted juice by titration with 0.1 N NaOH. The sugar acid or TSS acid ratio is often better related to palatability of fruit than either sugar or acid level alone. a) Soluble Solids Content (SSC): Soluble solid content (SSC) also called total soluble solids (TSS), can be determined in a small sample of fruit juice using hand refractometer (Plate 3). The spectrometer measures the refractive index, which indicates how much a light beam will be slowed down when it passes through the fruit juice. The refractometer has different scales (0-32O B), (28- 62O B) and (56-92O B) which can be read directly. For large size fruits, these should be cut from stem to blossom end and to the centre of the fruit to account for variability in SSC from top to bottom and inside to outside of the fruit. The fruit tissues should be mescerated thoroughly in pastle motor and then from the mescerated pulp the juice is extracted by passing through muslin cloth. A drop of juice is then put on the prism of the refractometer and TSS content can be read directly on the scale. However, in case of small fruits like grapes, the juice content can be extracted by simply pressing the whole fruit. Plate 3 : RefractrometerPlate 3 : Refractrometer 6
  7. 7. The temperature of the juice is a critical factor for accuracy, because all materials expand when heated and becomes less dense. Good quality refractometers have a inbuilt temperature compensation capability. Always clean the refractometer before each reading and to standardize it with distilled water. b) Titratable acidity: Titratable acidity (TA) can be determined by titrating a know volume of juice with 0.1N NaOH to end point of pink colour as indicated by phenolphethalin indicator. The milliliters of NaOH needed are used to calculate the TA. The TA expressed as per cent malic, citric or tartaric acid can be calculated as follows: TA = ml NaOH x N (NaOH) x acid meq. Factor* x 100 Juice titrated * the following acid meq. factor may be used for different fruits Acid Acid meq. factor Commodities Citric 0.0064 Berries, citrus fruits, pineapple Malic 0.0067 Apple, pear, peach, tomato Tartaric 0.0075 Grape iv) Calculated indices: a) Calendar Date : For perennial fruit crops grown in seasonal climate which are more or less uniform from year to year, calendar date for harvest is a reliable guide to commercial maturity. Time of flowering is largely dependent as temperature and the variation in number of days from flowering to harvest can be calculated for some commodities by use of degree-day concept. Such harvesting criteria can be developed by the growers based on their experiences. b) Heat Units An objective measure of the time required for the development of the fruit to maturity after flowering can be made by measuring the degree days or heat units in a particular environment. It has been found that a characteristics number of heat unit or degree-days is required to mature a crop under usually warm conditions, maturity will be advanced and under cooler conditions, maturity is delayed. The number of degree days to maturity is determined over a period of several years by obtaining the algebraic sum from the differences, plus or minus, between the daily mean temperatures and a fixed base temperature (commonly the minimum temperature at which growth occurs). The average or characteristic number of degree-days is then used to forecast the probable date of maturity for the current year and as maturity approaches, it can be checked by other means. Maturity Indices for selected fruits and vegetables Fruits/ Vegetables Maturity indices or characteristics Almonds splitting of hull, separation of hull from shell, development of abscission zone Apple ‘Golden Delicious’ 12% SSC, 18 lb firmness ‘Red Delicious’ 11% SSC, 18 lb firmness Asian Pears Pathar Nakh Baggugosha skin colour change from green to yellowish green 145 days after fruit set 135 days after fruit set 7
  8. 8. Banana Ber disappearance of angularity in a cross section of the finger colour break stage (when light yellow colour appear) Cherry TSS = 14-15%, light red colour Grapes (table) minimum SSC % of 14 to 17.5, depending on cultivars, SSC/TA of 20 or higher. Guava colour break stage ( when skin colour changes from dark green to light green) Lemon 30% or more juice by volume Lychee/litchi TSS: total acid ratio of 30-40, bright red in colour Kinnow TSS/acid ratio 12:1 to 14:1 Kiwi fruit TSS – 6.5%, Firmness = 14 lbs Mango changes in shape (increase fullness of cheeks or bulge of shoulder), flesh colour yellow to yellowish-orange Papaya skin shows yellowing Peaches ground colour change from green to yellow (varied for different cultivars) Plums skin colour changes Pomegranate minimum 1.85% TA and red juice colour Strawberries 2/3 of berry surface showing pink or red colour Beans Pods are filled, seeds immature. Brinjal Immature, glossy skin, 40days from flowering. Broccoli Adequate diameter, compact, all florets should be closed. Cabbage Firm head Cantaloup ¾ to full slip under slight pressure, abscission from vine. Carrot Immature, roots reached adequate size. Cauliflower Mature and atleast 6” in diameter, compact Cucumber Immature and glossy skin Garlic Well filled bulbs, tops dry down Ginger 8-9 months after planting Melon Ground colour change to white with greenish tint, slightly waxy peel. Mushroom Caps well rounded, partial veil completely intact. Okra Pod 2-4” long, not fibrous, tips of pods pliable. Onion (dry bulbs) When 10-20% of tops fall over Peas Pods well filled but not faded in colour. Pepper Fruit size and colour (depends on colour and intended market) Potatoes Harvest before vines die completely, cure to heal surface wounds. Radish (spring) 20 to 30 days after planting. Radish (winter) 45 to 70 days after planting. Tomatoes Seeds fully developed, gel formation advanced in atleast one locule. Watermelon Flesh colour 75% red, TSS = 10% Source : Lisa Kitinoja and James Gorny, 1998 B. Harvesting tools, Containers and Methods Majority of fruits and vegetables are harvested by hands using scateurs, clippers or diggers (Figure 3). Mechanical harvest in currently used for fresh market crops that are roots, tubers, rhizomes and nut crops. A number of commodities destined for processing such as wine grapes, prunes, peaches etc. are harvested with machines because harvest damage does not significantly affect the quality of processed product as the commodities are processed quickly. Harvesting practices should cause as 8
  9. 9. little mechanical damage to produce as possible. The following points should be kept in mind while harvesting the crop.: 1. Gentle picking and harvesting will help reduce crop losses. 2. Wearing cotton gloves, trimming finger nails, and removing jewellary such as rings and bracelets can help reduce mechanical damage during harvest. 3. Produce should be harvested during coolest part of the day not wet from dew or rain. 4. Empty picking containers with care. 5. Keep produce cool after harvest (provide shade). Fig 3 : Different tools used during harvesting (Source : Lisa Kitinoja and James Gorny, 1998) 9
  10. 10. Clean harvesting tools and containers should be used to protect the produce quality. Disinfect tools with one part chlorine bleach: one part clean water solution before use. The use of containers that can be easily filled and carried by workers minimizes damage to produce. The containers that are smooth on the inside, or provide clean, disposable liners made from paper or cardboard should be used. i) Picking bag: Cloth bag with openings on both ends can be easily worn over the shoulders with an adjustable harnesses (Figure 4). In case metallic buckets are to be used for harvesting, fitting cloth over the opened bottom can reduce damage to crop. Fitting canvas bags with adjustable harnesses, or by simply adding some carrying straps to baskets also helps to reduce handling losses. Fig.4: Picking Bags (Source : Friend manufacturing Co. , 1993) ii) Picking poles and catching sacks: These tools can be easily made by hand. A long pole attached to a collection bag, allow the harvester to cut catch produce growing on a tree without climbing on tree. The collection bags can be hand woven from strong cord or sewn from canvas. The hoop used as the collection bag rim and sharp cutting edges can be made from sheet metal, steel tubing or recycled scrap metal. iii) Clippers and Knives: Some fruits such as citrus, grapes and mangoes, need to be clipped or cut from the plant (Figure 3). Clippers or knives should be kept well sharpened and clean. Peduncles, woody stems or spurs should be trimmed as close as possible to prevent fruit from damaging neighboring fruits during transport. Care should be taken to harvest pears so that the spurs are not damaged. Pruning shears can be used for harvesting fruits and some vegetables. iv) Tripod ladders: A ladder with three legs is very convenient and more stable than a common ladder (Figure 3). A ladder help harvesting crops such as mango, kinnow, pears, peaches, plums without damaging tree branches. 10
  11. 11. v) Harvesting containers: Plastic crates are relatively expensive to purchase, but are reusable and easy to clean. These have required features like stacking strength, ventilation holes and long life. These can be used for harvest, storage, cooling, transport and even for display in retail markets. Various brands and styles are manufactured, but all can be stacked securely if they are not over- filled. Picking baskets, bags and buckets can easily be carried and filled by workers. Harvesting containers can be made by fitting fabric over opened bottom of ready-made baskets, fitting ready made canvas bags. All of these will reduce mechanical damage to produce. Harvesting: Once the quality crop is produced, it should be harvested with great care for marketing as shown in Plate 4. The goals of harvesting systems are: a) To gather the commodity from the field at proper stage of maturity. b) With a minimum amount of damage and losses. c) In a cost effective way. Method of Harvesting: Harvesting of crops can be done manually or mechanically. i) Hand Harvesting: Usually done for fruits destined for fresh markets. Primary Advantages • Harvesting of fruit or vegetable can be done at appropriate maturity. • The produce will suffer minimum damage. Disadvantages • It is a time consuming process. • More labour is required during harvesting season. 11 Plate 4 : Harvesting Techniques
  12. 12. ii) Mechanical Harvesting Primary Advantages • The produce can be harvested at a faster rate. • Less manpower is required as compared to hand harvesting . Disadvantages • Damage can occur to crops. • Not suitable for marketing of fresh commodities. The fruits required for processing may be harvested mechanically, but it is important to process them soon, otherwise deterioration can take place. Field packing: Selection, sorting, trimming and picking the produce in the field at the time of harvest is refered to as field packing and has great potential to reduce mechanical damage by reducing the number of handling steps between field and consumer. 3. Handling A) Packing house operations: The packing house operations include the following steps:- - Dumping / collection - Pre-sorting - Washing / Cleaning - Sizing / Grading - Bunching / Wrapping - Postharvest Treatments - Packing - Cooling It is important to minimize mechanical damage by avoiding drops, rough handling and bruising during the different steps of pack house operations. Secondly the pack house operations should be carried out in shaded area. Shade can be created using locally available materials like, shade cloth, woven mats, plastic tarps or a canvas sheet hung from temporary poles. Shade alone can reduce air temperatures surrounding the produce by 8-17°C. i) Dumping: The first step of handling is known as dumping. It should be done gently either using water or dry dumping. Wet dumping can be done by immersing the produce in water. It reduces mechanical injury, bruising, abrasions on the fruits, since water is more gentle on produce. The dry dumping is done by soft brushes fitted on the sloped ramp or moving conveyor belts. It will help in removing dust and dirt on the fruits. ii) Pre-sorting: It is done to remove injured, decayed, mis-shapen fruits. It will save energy and money because culls will not be handled, cooled, packed or transported. Removing decaying fruits are especially important, because these will limit the spread of infection to other healthy fruits during handling. iii) Washing and Cleaning: Washing with chlorine solution (100-150 ppm) can also be used to control innoculum build up during pack house operations. For best results, the pH of wash solution should be between 6.5-7.5 12
  13. 13. - Mangoes, bananas should be washed to remove latex. - Kiwifruit should be dry cleaned or brushed after curing or storage. iv) Sizing / Grading: Grading can be done manually or by automatic grading lines. Size grading can be done subjectively (visually) with the use of standard size gauges. Round produce units can be easily graded by using sizing rings. 80 mm 75 mm 70 mm Several types of mechanical sizes are available for small scale operations. One type is composed of a long slanted tray with a series of opening which coverage (largest at the top, smallest at the bottom). This type of sizes works best with round commodities. The grading of fruits plays an important role in domestic and export marketing of fruits. Different fruits have different grades on the basis of their size and weight. Grade designation and quality of fruits: Minimum requirements are : Fruits should be a) clean, round, free from any visible foreign matter b) fresh in appearance, free of pests c) free from damage caused by pests or diseases d) free of any foreign smell and/or taste The grades of different fruits and vegetables suggested by Directorate of Marketing and Inspection (DMI) are as under: Kinnow Size code Fruit Size (diameter) mm No. of fruits in 10 kg pack A 60-64 84 B 65-69 72 C 70-72 60 D 72-74 54 E 75-79 51 F 80-85 45 13
  14. 14. Mangoes Grade Fruit weight (g) Max. permissible difference between fruits within packages (gm) A 100-200 50 B 201-350 75 C 351-550 100 D 551-800 125 Grapes Grade Large berries bunch weight (g) Small berries bunch weight (g) Extra class 200 150 Class I 150 100 Class II 100 75 Guava Size code Weight (gm) Diameter (mm) A >350 >95 B 251-350 86-95 C 201-250 76-85 D 151-200 66-75 E 101-150 54-65 F 61-100 43-53 Litchi Grade Fruit Diameter (mm) Extra class 33 Class I 28 Class II 23 Pomegranate Grade Fruit weight (g) Diameter (mm) A 400 90 B 350 80 C 300 70 D 250 60 E 200 50 14
  15. 15. Cabbage Size Code Weight in gms. A 201-600 B 601-1200 C 1201 and above Tomato Diameter (in mm.)Size Code Minimum Maxiumum 1 From 30 to 34 2 From 35 to 39 3 From 40 to 46 4 From 47 to 56 5 From 57 to 66 6 From 67 to 81 7 From 82 to 101 8 From 102 and above Onion Size code Diameter (in mm.) Difference between the diameter of the smallest and largest onion in the same package (in mm.) A 10-20 5 B 21-40 15 C 41-70 20 D 71 and above 30 B) Precooling of Horticulture Produce Pre-cooling of the produce soon after their harvest is one of the important components of the cool chain, which ultimately affect the shelf life of the produce. The main purpose of precooling is to immediately remove the field heat from the produce. Method of pre-cooling : - Room cooling - Forced air cooling - Hydrocooling - Vacuum cooling - Package icing 15
  16. 16. i) Room cooling : It is low cost and slow method of cooling. In this method, produce is simply loaded into a cool room and cool air is allowed to circulate among the cartons, sacks, bins or bulk load. Advantages: - Produce can be cooled and stored at the same room thus saves on handling costs. - No extra cost for pre-cooling equipment. - Suits for crops, which are marketed soon after harvest. Disadvantages: - It is too slow method of cooling - Space requirements for room cooling are more as compared to storage, thus loss of storage capacity. - Unsuitable for packed produce. - Excessive water is lost from the produce due to slow cooling. Horticulture crops suitable for rooms cooling are: Potato, onion, apple and citrus ii) Forced-air cooling: Forced air-cooling is mostly used for wide range of horticultural produce. This is the fastest method of pre-cooling. Forced air-cooling pulls or pushes air through the vents/holes in storage containers. In this method uniform cooling of the produce can be achieved if the stacks of pallet bins are properly aligned. Cooling time depends on (i) the airflow, (ii) the temperature difference between the produce and the cold air and (iii) produce diameter. Advantages: • Fast method of pre cooling • Suitable for wide range of highly perishable commodities. • Uniform cooling, if palletized containers or bins are properly aligned. • Cooling times can be controlled for different types of produce by controlling the air flow rate. Horticultural produce suitable for forced air cooling are: Grapes, Berries, Pears, Peach, Oranges, Strawberries tomato, and other tropical and subtropical fruits. iii) Hydrocooling : The use of cold water is an old and effective cooling method used for quickly cooling a wide range of fruits and vegetables before packaging. For the packed commodities it is less used because of difficulty in the movement of water through the containers and because of high cost involved in water tolerant containers. This method of cooling not only avoids water loss but may even add water to the commodity. The hydrocooler normally used are of two types : a) Shower type : In this type of hydrocooler, cold water is pumped to an overhead perfortated pan which produces a shower over the produce which may be in bins or boxes or loose on a conveyer belt passing beneath. The water leaving the produce may be filtered to remove debris, then passed over refrigeration coil where it is recooled. b) Immersion type: In this type of hydrocooler, the produce is brought in contact with cold water by using a conveyor (flume type) or by lowering bins / boxes in tank of water which is continuously cooled by mechanical refrigeration system. Poor cooling would result if the product simple moved with the water. Flume hydrocoolers convey the product either against (counter flow) or across (cross flow) the flow. Efficient cooling depends upon adequate water flow over the product surface. Immersion type hydrocoolers usually take longer time to cool produce than shower type cooler. Generally the small quantity chlorine or other chemicals are added in the water to sanitize it. 16
  17. 17. Advantages : • Less energy is used as compared to forced air cooling. • Hydrocooler can be easily integrated into an packing operations and become a step within a simple packing line. • Moisture loss does not take place. Disadvantages : • Most of the packages don’t tolerate wetting. • Wax layer of some fruits like pear, plum, apple are removed by using spray type of hydrocooler : Horticultural produce suitable for hydrocooling are: Mango, peach, cherry, sparagus etc. iv) Vacuum cooling:Vacuum cooling take place by water evaporation from the product at very low air pressure. In this method, air is pumped out from a larger steel chamber in which the produce is loaded for pre-cooling. Removal of air results in the reduction of pressure of the atmosphere around the produce, which further lowers, the boiling temperature of its water. As the pressure falls, the water boils quickly removing the heat from the produce. Vacuum cooling cause about 1 per cent produce weight loss (mostly water) for each 6 0 C of cooling. Advantages : • Packed produce can be cooled if the pack allows moisture transfer. • Fast and uniform cooling takes place. • Most energy efficient method. Disadvantages : • High capital cost • Produce losses more moisture To overcome the more loss of water from the produce, another method of water spray vacuum is used, (modification of vacuum cooling), called hydro-vac cooling. v) Package-icing :In some commodities, crushed or flaked ice is packed along with produce for fast cooling. However, as the ice comes in contact with the produce, it melts, and the cooling rate slows considerably. The ice keeps a high relative humidity around the product. Package ice may be finely crushed ice, flake ice or slurry of ice. Liquid icing distributes the ice throughout the container, achieving better contact with the product. Packaged icing can be used only with water tolerant, non- chilling sensitive products and with water tolerant packages (waxed fiberboard, plastic or wood). C. Packaging of Horticulture Produce What is Packing? According to UK institute of packaging A coordinated system of preparing goods for transport, distribution, storage, retailing and end use. A means of ensuring safe delivery to the ultimate consumer in sound conditions at minimum cost. Objective of Packaging: 1. It helps in safe transportation, storages, marketing and distribution of produce. 2. It protects the produce from pilferage, microorganisms and adverse weather condition. 17
  18. 18. 3. It is also used to advertise the product. Requirements of a Good Package: Should be environment friendly. Should have sufficient strength in compression and against impact and vibrations Should be stable during the entire distribution chain. Should be compatible with the automatic packing/filling, handling machines (mechanical filling systems) Should facilitate special treatments like pre-cooling. Should have consumer appeal. Should be easily printable. Should be cost effective. Materials for Packaging: Wood – boxes, bins, trays, barrels, pallets Jute/canvas – sacks Paper and card board – liners, boxes, trays Plastic – Rigid - crates, pallets, trays Flexible – films (single & multi layered) Polystyrene boxes / trays Combined materials – CFB and plastic CFB has almost replaced wood and jute and is considered as most important package material to be used in combination with other materials. Some materials used for fresh horticultural produce include: Wooden box having CFB liners. CFB box with plastic film wraps CFB trays with wooden corner supports CFB laminated or waxed containers. CFB box with plastic retailer packs (strawberry boxes) CFB or polystyrene trays/boxes with plastic film wraps. Packaging Type: There are many types of packing containers available for horticultural produce, and they come in a huge range of sizes. i) Bags and Sacks: Paper, polyethylene film, woven polypropylene. These give little protection to the crop from handling and transport damage, potato, onion, canots etc. ii) Woven Baskets: These are traditional containers in which crops are placed after harvest. The produce is damaged in these baskets when they are stacked one above the other during transport and distribution. iii) Wooden field box: These are made from thin pieces of wood, widely spread so they are light in weight and cheep to make. These can be used for all types of fruits and vegetables. iv) Plastic field boxes: They are strong and durable. They are made from moulded polyvinyl chloride, poly propylene or polyethylene. They have smooth surface, which does not damage the produce. Initially, they are expensive to buy, but can be used repeatedly. v) Pallet boxes: They are most commonly base on the standard size for a European pallet of 1 x 1.2 m and about 0.5 m high. These have capacity of about 500 kg. They are usually made from wood but plastic ones are also available. They are used for whole range of crops, which are commonly loaded into them in the field and transported directly to the store. 18
  19. 19. vi) Fiberboard boxes: They are made from either laminated or more commonly corrugated fiberboard. They may be used for directly field packing of produce and transported to pack house or destination market. vii) Polystyrene boxes : Popularly called thermocol boxes, provides enough protection to produce, are light in weight, hygrimic and keeps the produce for longer periods at pack temperature. The three containers styles illustrated here are constructed from corrugated fiberboard. The regular slotted containers is fully collapsible and the most economical. Collapsible containers can be flattened and stacked during marketing and transport easily and less expensive, and take much less space to store while empty in the packinghouse. Source: Fibre Box Association Half of full-telescopic containers have the highest stacking strength and protect against bulging but are more costly. The choice of package style will depend on what commodity is to be pack and how to use the container throughout the post harvest system (during cooling, for long-term storage, as a display). 19
  20. 20. The container known as a Bliss box has very strong corners, but is not collapsible. Bliss boxes for fresh fruits and vegetables most commonly have either flaps that meet in the middle of the top or that form an open topped tray, which is covered with a separate lid. Bliss Box A simple wooden tray with raised corners is stackable and allow plenty of ventilation for fragile crops such as ripe tomatoes. Stackable cartons reinforced with wooden corners supports Smaller consumer sized containers can be packed into large container. Individual consumer packages Cartons designed to hold six small containers per layer 20
  21. 21. Adding a fiberboard divider to a carton will increase stacking strength. Wooden inserts, or fiberboard folded into tight triangles and placed in all four corners can be especially useful when a carton needs strengthening. Using a polyethylene liner in a fiberboard carton can help protect produce and reduce water loss in commodities such as peach, plums, pears, citrus, cherries, kiwi fruits etc. Water vapor given off by the product is contained within the liner, increasing the RH around the product and decreasing the rate of water loss. The liner can also reduce abrasion damage that results from fruit rubbing against the inside of the box. It is important to keep produce cool to prevent causing damage in cartons lined with polyethylene due to gas composition changes related to increased respiration rates. When a locally made containers have sharp edges or rough inner surfaces, a simple, inexpensive liner can be used to protect produce from damage during handling. General Dos’ and Don'ts for Packaging High Quality Produce • The packages should be sturdy and capable of standing up to handling, cooling and storage conditions. • Rough packages such as baskets and wooden crates should be lined with cardboard inserts. • Packages used for heavy produce should be reinforced with corner supports or folded dividers. • Avoid using very large packages since the produce suffers more damage during handling of large packages. • For delicate produce such as berries, grapes, summer squash and ripe stone fruits use shallow packages having single layer or double layers. • Avoid overfilling or under filling packages. • For adequate ventilation of packages about 5% of the surface area per side should be vented. • For immobilizing the produce in a package, use packaging materials such as trays, cups, wraps, liners and pads. • To decrease the rate of water loss from produce like cherries perforated plastic film liners should be used. • Take care while using fillers and liners in packages so that the ventilation holes are not blocked. • Labeling containers with your logo or farm name help in creating a brand name for quality produce. • Consumer packages that can be used to display produce during marketing should be considered. • Use large packages to pack 'consumer packages' such as gift packs or display trays for providing better protection to the containers during stacking, transport and marketing. • For reducing produce damage, packages with handles to carry should be considered. D. Post harvest Treatments Fresh fruits are living tissues subject to continuous change after harvest. Some changes are desirable from consumer point of view but most are not. Post-harvest changes in fresh fruit cannot be stopped, but these can be slowed down within certain limits to enhance the shelf life of fruits. The 21
  22. 22. post-harvest treatments play an important role in extending the storage and marketable life of horticultural perishables. i) Washing with chlorine solution: Chlorine treatment (100-150 ppm available chlorine) can be used in wash water to help control inoculums build up during packing operations. Maintain pH of wash water between 6.5 and 7.5 for best results. ii) Ethylene inhibitors/Growth regulator/ fungicide treatments: 1-MCP (1-methyl cyclopropene), AVG (Amenoethoxyvinyl gycine), siver nitrate, silver thiosulfate, cycloheximide, benzothiadiazole etc. are some of the chemicals which inhibit ethylene production and / or action during ripening and storage of fruits.The growth regulators or fungicidal application such as GA3 or cytokinius, bavistin, procloraj, imazalil etc. can be effectively used to extend/ enhance the shelf life of fruits. iii) Calcium application: The post-harvest application of CaCl2 or Ca (NO3)2 play an important role in enhancing the storage and marketable life of fruits by maintaining their firmness and quality. Calcium application delays aging or ripening, reduces postharvest decay, controls the development of many physiological disorders and increases the calcium content, thus improving their nutritional value. The post-harvest application of CaCl2 (2-4%) or Ca (NO3)2 for 5-10 minutes dip extend the storage life of pear upto 2 months, plum upto 4 weeks and apple upto 6 months at 0-2O C with excellent colour and quality. Calcium infiltration reduces chilling injury and increase disease resistance in stored fruit. iv) Thermal treatments : a) Hot water treatment: Fruits may be dipped in hot water before marketing or storage to control various post-harvest diseases and improving peel colour of the fruit (Table 2). In mangoes, the hot water treatment is recommended at 50-52O C for 5 minutes to reduce the fungal infection during ripening or storage. This treatment help in attaining uniform ripening within 5-7 days. Fruit should not be handled immediately after heat treatment. Cooling of fruit with water showers or forced air should be provided to help return the fruit to their optimum temperature as soon as possible after completion of the treatment. Table 2: Hot water treatments for different fruits. Commodity Pathogens Temp. (°C) Time (min) Apple Gloeosporium sp. Penicillium expansum 45 10 Grapefruit Phytophthora citrophthora 48 3 Lemon Penicillium digitatum Phytophthora sp. 52 5-10 Mango Collectotrichum gloeosporioides 52 5 Orange Diplodia sp. Phomopsis sp. Phytophthora sp. 53 5 Papaya Fungi 48 20 Peach Monolinia fructicola Rhizopus stolonifer 52 2.5 Source : Lisa Kitinoja and James Gorny, 1998 b) Vapour heat treatment (VHT): This treatment proved very effective in controlling infection of fruit flies in fruits after harvest. The boxes are stacked in a room, which are heated and humidified by injection of steam. The temperature and exposure time are adjusted to kill all stages of insects (egg, larva, pupa and adult), but fruit should not be damaged. A recommended treatment for citrus, 22
  23. 23. mangoes, papaya and pineapple is 43O C in saturated air for 8 hours and then holding the temperature for further 6 hours. VHT is mandatory for export of mangoes. v) Fumigation: The fumigation of SO2 is successfully used for controlling post-harvest diseases of grapes. This is achieved by placing the boxes of fruit in a gas tight room and introducing the gas from a cylinder to the appropriate concentration. However, special sodium metabisulphite pads are also available which can be packed into individual boxes of a fruit to give a slow release of SO2. The primary function of treatment is to control the Botrytis Cinerea. The SO2 fumigation is also used to prevent discolouration of skin of litchis. Fumigation with 1.2% sulphur dioxide for 10 minutes was shown to be effective in reducing skin discolouration in fresh litchis, especially if it is combined with a 2 minute dip in IN HCl acid directly afterwards. Immediately after sulphur dioxide treatment litchi fruit may appear a uniform yellow colour and then turn red again after 1 or 2 days. Some people are allergic to sulphur, particularly those who have chronic respiratory complaints, and it may be necessary to label fruit or boxes of fruit to indicate that these have been fumigated with sulphur. Paper pads or wraps impregnated with biphenyl fungicides are commonly applied to citrus fruits. The chemical vaporizes slowly, protecting the fruit from fungal infection. vi) Irradiation: Ionizing radiation can be applied to fresh fruits and vegetables to control micro- organisms and inhibit or prevent cell reproduction and some chemical changes. It can be applied by exposing the crop to radiations from radioisotopes (normally in the form of gamma-rays measured in Grays (Gy), where 1 Gray = 100 rads. A combination of hot water treatment (55°C for 5 minutes) followed by 30 Gy irradiation was found to be the best treatment for shelf life extension and quality maintenance of mangoes. After this treatment mangoes had a storage life of 38 days (at 15°C), 28% rotting and no irradiation injury. Irradiation can also be used to control postharvest diseases of other fresh fruit and vegetables. vii) Waxing: Waxing of fruits or vegetables is a common post-harvest practice. Food grade waxes are used to replace some of the natural waxes removed during harvesting and sorting operations and can help reduce water loss during handling and marketing. It also helps in sealing tiny injuries and scratches on surface of fruits and vegetables. It improves cosmetic appearance and prolongs the storage life of fruits and vegetables. The wax coating must be allowed to dry thoroughly before packing. The commercial available waxes are citrashine, Staryfresh, Sta-fresh 451, Semper Fresh, Carnauba wax etc. Coatings may be applied by either by dipping, brushing or spraying on the fruits & vegetables. Different countries have their own rules and regulations for the use of coatings on horticultural produce. As of now, only coating with beeswax and carnauba is allowed in India. 4. Storage The management of temperature and relative humidity are the most important factors determining storage life of horticultural produce. The natural means like ice, cold water, night temperature have been used for long time for protecting food materials from spoilage and these are still common. However, with the development of innovative technologies, it is possible to achieve optimal environments in the insulated stores. Objective of storage: Regulate the market in an orderly manner. Avoid glut and distress sale in the market, thus prolonging the market period. 23
  24. 24. In long-term storage, making the food available in off-season. Lowering the temperature to the lowest safe handling temperature is of paramount importance for enhancing the shelf life, reducing the losses and maintaining higher quality during marketing. Always, handle produce gently and never store produce unless, it is of the best quality. Damaged produce will lose water faster and have higher decay rates in storage when compared to undamaged produce. Tips for storage of high quality horticultural produce Store only high quality produce, free of damage, decay and of proper maturity (not over-ripe or under-mature). Know the requirements for the commodities you want to put into storage, and follow recommendations for proper temperature, relative humidity and ventilation.; Avoid lower than recommended temperatures in storage, because many commodities are susceptible to damage from freezing or chilling. Do not over load storage rooms or stack containers closely Provide adequate ventilation in the storage room. Keep storage rooms clean. Storage facilities should be protected from rodents by keeping the immediate outdoor area clean, and free from trash and weeds. Containers must be well ventilated and strong enough to with stand stacking. Do not stack containers beyond their stacking strength. Monitor temperature in the storage room by placing thermometers at different locations. Don’t store onion or garlic in high humidity environments. Avoid storing ethylene sensitive commodities with those that produce ethylene. Avoid storing produce known for emitting strong odors (apples, garlic, onions, turnips, cabbages, and potatoes) with odor-absorbing commodities. Inspect stored produce regularly for signs of injury, water loss, damage and disease. Remove damaged or diseased produce to prevent the spread of problems. Storage of compatible groups of fruits and vegetables: Some fruits or vegetables can be stored together due to their common temperature and relative humidity conditions and some can not be stored together. The table3 gives an over view of storage of compatible groups of fruits and vegetables Table 3: Compatibility groups of fruits and vegetables Group Temperature Crops Status of commodities Group 1 0-2o C and 90-95% RH Apple, Apricot, Asian Pear, Grapes, Litchis, Plum, Prunes, Pomegranate, Mushroom Turnip Peach. Produce ethylene. Group 2 0-2o C and 90-95%RH Asparagus, Leafygreens, Broccoli, Peas, Spinach, Cabbage, Carrot, Cauliflower, Cherries. Sensitive to ethylene. Group 3 0-2o C and 65-70% RH Garlic, Onions dry. Moisture will damage these 24
  25. 25. crops. Group 4 4-6o C and 90-95% RH Cantaloupes, Guava, Mandarin, Tangerines. Group 5 8-10o C, 85-90% RH Beans, Potatoes (with CIPC treatment), Cucumber, Brinjal, Okra Pepper. Group 6 13-15o C, 85-90% RH Mangoes, Banana, Tomato ripe, Grapefruit Source : Lisa Kitinoja and James Gorny, 1998 Undesirable effect of ethylene: Accelerated senescence Accelerated ripening Loss of green colour Abscission of florets Toughening Poor flavor The symptoms of chilling injury are as follows: If fruits and vegetables are stored at a temperature below their optimum temperature will subject to chilling injury (Table 4). Therefore for maintaining proper quality the produce should be stored at the recommended temperature and relative humidity conditions (Table 5). Table 4: Chilling injury symptoms of different fruits Commodity Lowest safe temperature o C Chilling injury symptoms Apple 2-3 Soft scald, brown core Bananas 12-13 Dull colour when ripened Guavas 4-5 Pulp injury, decay Lemon 11-13 Pitting, membrane staining Mango 10-13 Uneven ripening, grayish skin Ber 7.5 Surface pitting, appearance of brown streaks on the peel Table 5:Recommended Temperature and RH conditions Name of commodity Temp (o C) RH (%) Approximate Shelf-Life Apple -1-4 90-95 1-12 months Apricot 0-1 90-95 1-3 weeks Asian pear 0-1 90-95 2 months Banana 13-15 90-95 1-4 weeks Ber 7.5 90-95 2 weeks Grape -0.5-0 90-95 2-8 weeks Guava 6-8 90-95 2-3 weeks Kiwi ; Chinese gooseberry 0 90-95 3-5 months Lemon 10-13 85-90 1-6 months 25
  26. 26. Loquat 0 90 3 weeks Lychee, Litchi 1-2 90-95 3-5 weeks Mandarin (Kinnow) 4-5 90-95 2 months Mango 13 85-90 2-4 weeks Mushrooms 0 90 7-14 days Nectarine -0.5-0 90-95 2-4 weeks Papaya 7-13 90-95 1-3 weeks Peach 0-1 90-95 2-4 weeks Pear -1.5-0.5 90-95 2-7 months Pineapple 7-13 85-90 2-4 weeks Plum and prunes 0-1 90-95 2-5 weeks Pomegrante 5 90-95 2-3 months Strawberry 0 90-95 7-10 weeks Sweet cherries -1-0.5 90-95 2-3 weeks Asparagus, green 1-2 95-100 2-3 weeks Beans 4-7 90-95 7-10 days Bitter gourd 10-12 85-90 2-3 weeks Broccoli 0 95-100 10-14 days Cabbage 0 90-95 3-6 weeks Carrots 0 90-95 6-8 months Cauliflower 0 90-95 3-4 weeks Eggplant 10-12 90-95 1-2 weeks Garlic 0 65-70 6-7 months Ginger 13 65-70 6 months Lettuces 0 90-95 2-3 weeks Okra 7-10 90-95 7-10 days Onion 0 65-70 1-8 months Peas 0 90-95 1-2 weeks Bell Pepper 7-10 90-95 2-3 weeks Radish 0 90-95 1-2 months Tomato 10-13 90-95 1-3 weeks Turnip 0 90-95 4-5 months Watermelon 10-15 90-95 2-3 weeks Source : Lisa Kitinoja and James Gorny, 1998 Controlled atmosphere (CA) storage The term imply, the addition or removal of gases resulting in an atmospheric composition different from that of normal air. Thus the levels of carbon dioxide, oxygen, nitrogen, ethylene, and metabolic volatiles in the atmosphere may be manipulated. Controlled atmosphere storage generally refers to keeping produce at decreased oxygen and increased carbon dioxide concentrations and at suitable range of temperature and RH. Systems where atmospheric control is accurately controlled are generally called CA storage and where degree of control “less accurately” monitored are called MA (modified atmosphere) storage. In MAP (modified atmospheric packaging) produce is enclosed in polymeric films and is allowed to generate its own atmsophere (passive MAP) or air of known composition is flushed into the bag (active MAP) and depending upon gas / vapour transmission characteristics of the film on appropriate atmosphere develops in the package to prolong shelf life. MAP is ideally combined with temperature control for maximum benefit 26
  27. 27. Benefits of CA storage - Slow down respiration and ethylene production rates, softening and retard senesence of horticultural produce. - Reduce fruit sensitivity to ethylene action - Alleviate certain physiological disorders such as chilling injury of various commodities, russet spotting in lettuce, and some storage disorders including, scald of apples. Harmful effects of CA storage - Initiation or aggravation of certain physiological disorders can occur, such as blackheart in potatoes, brown stain on lettuce, and brown heart in apples and pears. - Irregular ripening of fruits, such as banana, mango, pear and tomato, can result from exposure to O2 levels below 2% or CO2 levels above 5% for more than 2 to 4 weeks. - Off- flavors and off-odours at very low O2 or very high CO2 concentration may develop as a result of anaerobic respiration and fermentative metabolism. Table 6: Recommended CA or MA conditions for selected fruits and vegetables Commodity Temperature (°C) % O2 % CO2 Apple 0-5 1-2 0-3 Banana* 12-16 2-5 2-5 Cherry, sweet 0-5 3-10 10-15 Mango* 10-15 3-7 5-8 Peach, clingstone 0-5 1-2 3-5 Pear, European 0-5 1-3 0-3 Asparagus 1-5 Air 10-14 Beans, green 5-10 2-3 4-7 Broccoli 0-5 1-2 5-10 Brussels sprouts 0-5 1-2 5-7 Cabbage 0-5 2-3 3-6 Cantaloupes 2-7 3-5 10-20 Cauliflower 0-5 2-3 3-4 Okra 7-12 Air 4-10 Onions (bulb) 0-5 1-2 0-10 Pepper (bell) 5-12 2-5 2-5 Radish (topped) 0-5 1-2 2-3 Tomatoes (green) ripe 12-20 10-15 3-5 3-5 3-5 3-5 * CA is especially beneficial during transit (Source : Adel A. Kader, 2002 ) Hypobaric storage or Low-pressure system Hypobaric storage is a form of controlled atmosphere storage in which the produce is stored in a partial vacuum. The vacuum chamber is vented continuously with water saturated air to maintain oxygen levels and to minimize water loss. Ripening of fruit is retarded by hypobaric storage, due to the reduction in the partial pressure of oxygen and for some fruits also to the reduction in the 27
  28. 28. ethylene levels. A reduction in pressure of air to 10 kilopascals (0.1 atmosphere) is equivalent to reducing the oxygen concentration to about 2 per cent at normal atmospheric pressure. Hypobaric stores are expensive to construct because of the low internal pressures required, and this high cost of application appears to limit hypobaric storage to high value produce such as cut flowers. Secondly control of gases during the storage cannot be manipulated. 5. Ripening of Fruits Ripening is a dramatic event in the life of a fruit during which structure and composition of unripe fruit is so altered that it becomes acceptable to eat. Ripening marks the completion of development of a fruit and the commencement of senescence and it is normally an irrevesible event. Categories of fruits : On the basis of ability to ripen after harvest, sharp rise in respiration rate during onset of ripening and production and/or response to ethylene , the fruits are divided into 2 categories. First group produce very small quantity of ethylene and do not respond to ethylene treatment (except in terms of degreening), and these fruits should be picked when fully ripe to ensure good flavour and quality. For example Citrus, cherry, litchi, pineapple, pomegranate, berries etc. Second group produce much larger quantities of ethylene during ripening and exposure to ethylene treatment will result in faster and uniform ripening. For example apple, pear,stone fruits, mango, papaya guava etc A) Ripening facilities i) Ripening room : Fruit are ripened in specially built rooms that must be gas tight, have systems for controlling humidity and concentrations of carbon dioxide and ethylene, and have equipment to control product temperature. Ripening rooms are usually insulated but they typically operate at temperature 15-210 C. The ripening process is always done at relative humidity above 85%. ii) Temperature : Ripening is controlled on the basis of fruit pulp temperature. It should be measured during each cycle with a calibrated pulp thermometer. Simultaneously, room air temperature must also be regularly monitored with calibrated thermometer. iii) Relative humidity : The refrigeration system must be designed to contain 85-95% RH. Humidity below this range causes excessive product weight loss . Humidifiers are needed to add moisture to the air in rooms. Air humidity should be periodically monitored with a wet and dry bulb psychrometer. iv) Air flow : Air flow is needed to distribute ethylene gas to the product and to add or remove heat from the product during ripening cycle. Boxes must be stacked with space between them to allow good air flow around each box. Boxes or pallet bins should be vented to allow air flow. If packaging materials are placed in the boxes they should not block vents. Poor venting will cause high fruit temperatures and non-uniform ripening. After product has reached ripening temperature ethylene gas is added. The gas can be added with three systems. 1) A patented ethylene generator produces ethylene from ethyl alcohol. It produces a relatively constant flow of gas for atleast 24 hours. 2) pure ethylene can be purchased in small pressurized cylinders holding three cubic feet of gas. The cylinder is opened in the room providing a rapid release of gas, which will provide an adequate level during the process, if the room is fairly gas tight. 3) For larger operations use ethylene gas available in larger cylinders and use flow meters to measure a prescribed amount into the room. 28
  29. 29. B) Ripening Techniques i) Ripening with ethephon / Ethrel : Ethephon (2-choloroethyl-phosphonic acid) is commercially available and is registered for pre-harvest use on a variety of crops for controlling developmental processes or inducing ripening. This chemical is approved for post-harvest use on fruits crops for enhancing ripening. For post-harvest treatments, the known quantity of ethephon is diluted in water and fruits are dipped in the solution for a specified period. This substance ensures that there is uniform ripening of fruits. This technique provides a safe and effective method of ripening of fruits compared to the conventional technique of using calcium carbide. ii) Ripening with Ethylene gas: In this technique, the fruits are exposed to low level of ethylene gas (10-100ppm) in an air-tight ripening chamber for 24 to 72 hours so as to induce ripening. The most important thing in this technique is temperature and relative humidity control inside the ripening chamber, which should range between 15-250 C and 90-95% relative humidity, depending upon the fruit type. Several methods are used to provide proper ethylene concentration in the ripening room. a) Gas Cylinders: Ethylene is available in large steel cylinders where it is stored under pressure. As it is highly flammable, the use of pure gas is discouraged. Therefore, it is usually used diluted with nitrogen or other inert gases. Typical mixtures are 95 per cent nitrogen and 5 per cent ethylene or 95.5 per cent nitrogen and 4.5 per cent ethylene. The measured quantities of ethylene are introduced in ripening room at regular intervals or continuously and the flow is regulated through metering devise or flow meter. Any piping leading into the ripening room should be grounded to prevent possible electrostatic ignition of ethylene gas. b) Shot system: On small scale, commodities can be treated using shot method with ethylene liberated from ethephon. A calculated amount of ethephon in stainless steel bowl is placed around the room. The fruits are stacked in the room and sodium hydroxide is added to ethephon and all ventilation to the room is then blocked. When sodium hydroxide reacts with ethephon, ethylene gas is released that ripens the fruits, Precaution should be taken while handling sodium hydroxide and ethephon as these are corrosive. Safety glasses and rubber gloves should be used while their handling. c) Ethylene generator: This is a device that is portable and placed inside the ripening room. A liquid (ethyl alcohol) is filled into the tank fitted with ethylene generator and it is connected to an electric power source. The ethyle alcohol gets heated in a controlled manner in the presence of a catalyst that produces ethylene gas. Gas is maintained inside the ripening room until colour break occurs in the fruits. Table 7 : Ripening conditions for some fruits Commodity Ethylene concentration (ppm) Ethylene exposure time Ripening temperature Predicted storage after treatment Apple(Grany Smith) 10 ppm 6 days 25°C Less than 4 months at 0°C Banana 100-150 ppm 24-48 hours 14-18°C Less than 7 days at 14°C Mango 100 ppm 12-24 hours 15.5-25°C Less than 7 days at 10- 13°C Tomato (mature green stage) 100 ppm 3-3.5 days to reach breaker stage and 5-16 days, depending on temperature, to reach full red stage 18°-20°C (65°- 68°F) with 90- 95% RH 7 days after reaching the red stage (Source : Adel A. Kader, 2002 ) 29
  30. 30. iii) Calcium carbide : In India and many other developing economies, the banana and mango are are ripened with the use of calcium carbide, which releases acetylene and ethylene on interaction with moisture coming from fruits. This chemical is harmfull to human health and its use for ripening of fruits is band in India under section 44-AA of PFA rules 1954. References 1. Dhatt, A.S., Mahajan, B.V.C., Sandhu, K.S., Garg, A and Sharma, S.R. (2007) Handbook on Post harvest Handling of Fruits and Vegetables. 3rd edition, PHPTC, PAU, Ludhiana 2. Friend Manufacturing Corporation, Prospect Street, P.O. Box 385, Gasport, New York 14067, USA. 3. Kader Adel A (2002). Post harvest Technology of Horticultural Crops. 3rd Edition, University of California, Agricultural and Natural Resources. 4. Kader Adel A and Merita Cantwell (2006). Produce Quality Rating Scales and Color Charts. Postharvest Horticulture Series No 23. Post harvest Technology Research & Information Center University of California, Davis 5. Kitinoja, L and Gorny, J. (1998) Post-harvest technology for fruits and vegetables Produce marketers: Economic opportunities. Quality and Food Safety by, Department of Pomology, University of California, Davis. A joint publication of UC Post harvest Outreach Program and Punjab Horticultural Post harvest technology Centre, USAID/ACE 6. Thompson A.K. (1996) Post harvest Technology of Fruits and Vegetables. 1st Edition, Blackwell Science, Inc. USA. 7. Wardlaw, C.W. and Leonard, E.R. (1936). The storage of West Indian Mangoes, Low Temperature Research Station Memoir 3, 47 pp. 8. Wills, R; McGlasson, B; Graham, D and Joyce, D (1998) Post harvest: An Introduction to the Physiology and Handling of Fruit, Vegetables and Ornamentals. 4th Edition, CAB International,UK. 9. Von Loesecke, H.W. (1949). Bananas. Wiley Inter-sciences, London. 30