Value-Addition-of-Fruits-and-Vegetables.pdf

HORT 381 POST HARVEST MANAGEMENT AND VALUE ADDITION OF FRUITS AND VEGETABLES 2(1+1) POST HARVEST MANAGEMENT Course Overview: This course deals with overall post harvest management of fruits and vegetables from farm to fork. Learning objective: The students are expected to gain know...

HORT 381 POST HARVEST MANAGEMENT AND VALUE ADDITION OF FRUITS AND VEGETABLES 2(1+1) POST HARVEST MANAGEMENT Course Overview: This course deals with overall post harvest management of fruits and vegetables from farm to fork. Learning objective: The students are expected to gain knowledge on various management technologies on pre- harvest and post harvest of fruits and vegetables. Students are also expected to gain knowledge on conventional and modern packaging methods. Outcome of the course Students will acquire knowledge on post harvest management tools and novel paclkaging techniques. Lecture schedule: The Post Harvest Mangement portion is divided into following headings: (i) The Importance of post harvest technology of horticultural crops (ii) Maturity indices, harvesting and post harvest handling of fruits and vegetables (iii) Maturity and ripening process – factors affecting ripening of fruits and vegetables- chemicals used for hastening and delaying ripening of fruits and vegetables. (iv) Pre harvest factors affecting quality on post harvest life of fruits and vegetables – factors responsible for deterioration of harvested fruits and vegetables. (v) Methods of storage-precooling, pre storage treatments, low temperature storage, controlled atmosphere storage, hypobaric storage, irradiation and low cost storage structures. (vi) Various methods of packaging-packaging materials and transport – packaging technology for export. Fabrication of type of containers, cushioning material, vacuum packaging, poly shrink packaging, specific packaging for export of mango, banana, grapes, etc., Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  Chapter 1: IMPORTANCE OF POST HARVEST TECHNOLOGY OF HORTICULTURAL CROPS Horticulture plays a significant role in Indian Agriculture. It contributes 30% GDP from 11.73 % of its arable land area. India is the second largest producer of both fruits and vegetables in the world (52.85 Mt and 108.20 Mt respectively). Fruits and vegetables are of immense significance to man. In India, the fruits have been given a place of honour on being offered to God at every festival and have also been mentioned in our epics like Mahabharata, Ramayana and writings of Sushrutha and Charaka. Being rich source of carbohydrates, minerals, vitamins and dietary fibres these constitute an important part of our daily diet. The dietary fibres have several direct and indirect advantages. Not only this, fruits and vegetables provide a variety in taste, interest and aesthetic appeal. Their significance in human life is being recognised increasingly in Western societies with the objective of minimizing the occurrence of the diseases related with an affluent life style. Their lesser recognized benefits relate to their role in kidney functions, prevention of cancer and cardiac disorders through contribution of ascorbic acid, β-carotene and non-starch polysaccharides besides the biochemical constituents like phenols, flavonoids and alkaloids. A considerable amount of fruits and vegetables produced in India is lost due to improper post-harvest operations; as a result there is a considerable gap between the gross production and net availability. Furthermore, only a small fraction of fruits and vegetables are utilized for processing (less than 1%) and exported (Fruits – 0.5% and Vegetables – 1.7%) compared to other countries. Post harvest losses in fruits and vegetables are very high (20-40%). About 10-15% fresh fruits and vegetables shrivel and decay, lowering their market value and consumer acceptability. Minimizing these losses can increase their supply without bringing additional land under cultivation. Improper handling and storage cause physical damage due to tissue breakdown. Mechanical losses include bruising, cracking, cuts, microbial spoilage by fungi and bacteria, whereas physiological losses include changes in respiration, transpiration, pigments, organic acids and flavour. NATURE AND CAUSES OF POST-HARVEST LOSSES Losses occur after harvesting is known as post harvest losses. It starts first from the field, after harvest, in grading and packing areas, in storage, during transportation and in the wholesale and retail markets. Several losses occur because of poor facilities, lack of know-how, poor management, market dysfunction or simply the carelessness of farmers. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. (a) Extend of post-harvest loss: It is evident that the estimation of post-harvest loss is essential to make available more food from the existing level of production. A recent joint study conducted by the management consultancy firm, McKinsey and Co. and (The Confederation of Indian Industry (CII), at least 50% of the production of fruits and vegetab1es in the country is lost due to wastage and value destruction. The wastage cost is estimated to be Rs.23, 000 crores each year. Swaminathan Committee (1980) reported the post-harvest handling accounts for 20-30% of the losses at different stages of storage, grading, packing, transport and finally marketing as a fresh produce or in the processed form. According to Chadha (2009) India loses about 35-45% of the harvested fruits and vegetables during handling, storage, transportation etc. leading to the loss of Rs. 40,000 crores per year. (b) Important sites of post-harvest losses: Important sites where post-harvest losses are noticed in India are — Farmer’s field (15-20%) Packaging (15_2004). Transportation (30-40%) Marketing (30-40%) (c) Estimated loss of fruits Crop Estimated loss (%) Papaya 40100% Grapes 27% Banana 20-28% Citrus 20-95% Avufado 43% Apple 14% Estimated loss of Vegetables Onion 25-40% Garlic 08-22% Potato 30-40° Tomato 5-347% Cabbage & cauliflower 7.08-25.0% ChIli 4-35,0% Radish 3-5% Carrot 5-9% Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. (d) Causes of post-harvest losses Horticultural crops not only provide nutritional and healthy foods to human beings, but also generate a considerable cash income for growers. However, horticultural crops typically have high moisture content, tender texture and high perishability. If not handled properly, a high- value nutritious product can deteriorate and rot in a matter of days or hours. The causes of post- harvest losses can be divided into different categories: 1. Metabolic All fresh horticultural crops are live organs. The natural process of respiration involves the breakdown of food reserves and the aging of these organs. 2. Mechanical Owing to their tender texture and high moisture content, fresh fruits and vegetables are very susceptible to mechanical injury. Poor handling, unsuitable containers, improper packaging and transportation can easily cause bruising, cutting, breaking, impact wounding and other forms of injury. 3. Developmental These include sprouting, rooting, seed germination, which lead to deterioration in quality and nutritional value. 4. Parasitic diseases High post-harvest losses are caused by the invasion of fungi, bacteria, insects and other organisms. Micro-organisms attack fresh produce easily and spread quickly, because the produce does not have much of a natural defense mechanism and has plenty of nutrients and moisture to support microbial growth. 5. Physiological deterioration Fruits and vegetable cells are still alive after harvest and continue their physiological activity. Physiological disorders may occur due to mineral deficiency, low or high temperature injury or undesirable atmospheric conditions, such as high humidity, physiological deterioration can also occur spontaneously by enzymatic action leading to over-ripeness and senescence, a simple aging phenomenon. 6. Lack of market demand Poor planning pr inaccurate production and market information may lead to over production of certain fruits or vegetables which can’t be sold in time. This situation occurs most frequently in areas where transportation and storage facilities are inadequate. Produce may lie Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. rotting in production areas, if farmers are unable to transport it to people who need it in distant locations. 7. Consumption These losses can be due to inadequate preservation methods at home, methods of cooking and preparation such as peeling, consumption styles etc. 8. Others — Lack of clear concept of packing house operations. — Lack of awareness among the growers, contractors and even the policy makers. — Lack of infrastructure. — Late realization of its importance, — Inadequate technical support. — Wide gap in technologies available and in vogue. — Inadequate post-harvest quality control. — Unorganized marketing. — Absence of pre-cooling and cold storage. — Inadequate market facilities, market intelligence and market information service (MIS) — Poor storage facilities. (e) Impact of post-harvest losses Post harvest losses of horticultural crops affect both the nutritious status of the population and economy of the country. Nutrition Fruits and vegetables are rich source of vitamins and minerals essential for human nutrition. These are wasted in transit from harvest to consumer represent a loss in the quantity of a valuable food. This is important not only in quantitative terms, but also from the point of view of quality nutrition. Economy Careless harvesting and rough handling of perishable bruise and scar the skin, thus reducing quality and market price. Such damaged produce also fails to attract the international buyers, and bring the exporting country less profit and bad name. This ultimately results in huge economic losses to the country. For improving the situation, it is essential to create awareness among growers, farm workers, manager’s traders and exporters about the extent of losses being incurred and their economic consequences. These groups of people involved in the fruit industry also need to learn the basic principles of fruit handling and storage. In addition, the government needs to Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. provide basic infra-structure like storage, handling, grading, packing, transport and marketing facilities and technical expertise. This could be carried out by the public and private sectors. (f)Technologies for minimizing the losses Fruits and vegetables are perishable in nature. Scientific harvesting and handling are the practical way to reduce the losses due to physical damage, spoilages, due to insect damages and microbial growth. Various protocols are standardized and available for adoption to get the best result, which will give economic benefits. Similarly, proper storage conditions, with suitable temperature and humidity are needed to lengthen the storage life and maintain quality once the crop has been cooled to the optimum storage tempera Lure. Greater emphasis need to be given on the training of farmers, creation of infrastructure for cold chain with common facilities for sorting, grading, packing and post harvest treatments in all major markets. Some technologies for extension of shelf life of fruits and vegetables are: 1. Waxing It is used as protective coating for fruits and vegetables and help in reduction in loss in moisture and rate of respiration and ultimately results in prolonged storage life. 2. Evaporative cool storage It is the best short-term storage of fruits and vegetables at farm level. It helps the farmers to get better returns for their produce. In this structure, horticultural crops reduce shriveling and extend their storage life. 3. Pre-packaging This technology controls the rate of transpiration and respiration and hence keeps the commodity in fresh condition both at ambient and low temperature. It can able to bring revolutionary progress in our trade practice and also benefit the consumer and the producer because of its low cost and ready availability. 4. Cold storage These structures are extensively used to store fruits and vegetables for a long period and employ the principle of maintaining a low temperature, which reduces the rate of respiration and thus delays ripening. 5. Modified atmosphere packaging (MAP) These packaging modify the atmosphere composition inside the package by respiration. This technology is successful to extend the shelf life of (Cavendish banana, carrots capsicum, green chilli and tomatoes by 15, 14, 13, 8 and 15 clays as against 5, 7, 8, 4 and 7 days in control respectively, under ambient conditions. Storage of Papaya can be extended 4 weeks when stored at 10 -12 °C under modified atmosphere (MA) conditions by wrapping them in low Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. density polyethylene (LDPE) bag. Using this technique, the fruit can be transported to different markets in refrigerated sea containers with Temperature Sea at 10-12 °C. Fruits ripen within 3-4 days after arrival when placed at ambient temperature. While using optimum low temperature, storage life of Cavendish banana, capsicum, green chili and tomato can be extended to 42,21,28 and 30 days in comparison to 21, 10,21 and 15 days respectively. 6. Controlled Atmosphere (CA) storage It is based, on the principle of maintaining an artificial atmosphere in storage room, which has higher concentration of CO2 and lower concentration of 02 than normal atmosphere. This reduces the rate of respiration and thus delays aging. This method of storage is very effective when combined with low temperature storage. 7. Cold chain Following cold chain handling system for fresh horticultural crops from (arm to consumer. It helps in reducing wastages and retention of quality of commodities. 8. Irradiation It is the newer technologies that can be gainfully employed during storage to reduce post-harvest losses and extend storage life of fruits and vegetable. When fruits and vegetables expose to ionizing radiation (such as gamma-rays) at optimum dosage delays ripening minimizes insect infestation, retards microbial spoilages, control sprouting, and rotting of onion, garlic and potato during storage. It is also used as a disinfection treatment and controls fruit fly on citrus, mango seed weevil and papaya fruit fly. 9. Edible coatings These are continuous matrices prepared from edible materials such as proteins, polysaccharides and lipids. They can be used as film wraps and when consumed with the food, become an ingredient of the food. They not only minimize the post harvest losses but also need for energy intensive operations and controlled atmosphere storage. They can control migration of gases, moisture, oil, fat, and solutes, as well as retain volatile flavouring compounds. An edible coating improves structural integrity and mechanical handling and carry product so that they help to maintain quality and inhibit microbial growth causing deterioration of the product. 10. Others — Facilities/ services like grading, washing, cleaning, scientific harvesting and the like, in respect of perishables at the farm level. — Cold storage facilities should be extended to tropical fruits and vegetables. Handling protocols should be established for crops other than mango, citrus, grapes and capsicurn to improve the shelf life and export. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. — The issue relating to increasing the shelf life of horticultural products needs to he addressed. — Appropriate packaging material for export of fresh fruits, vegetables and for modified atmosphere packaging should be developed. — Value addition needs to be viewed in a wider perspective than mere processing to ensure better return to the producer/ farmer, besides providing better quality product to the consumer. — Development of natural food columns, fiber, single cell protein and food grade enzymes from processing wastes will be useful. REFERENCES 1. Sudheer, K.P. and V.Indira. 2007. Post harvest technology of horticultural crops. New India Publishing Agency, Nw Delhi. 2. Verma, L.R. and V.K. Joshi. 2000. Post harvest technology of fruits and vegetables – Handling, Processing, Fermentation and Waste Management. Indus Publishing Company. New Delhi. 3. Chadha, K.L. 2009. Handbook of Horticulture. IARI Publications, New Delhi. 4. Thompson, A.K. 1996. Post harvest technology of fruits and vegetables. Blackwell Science Ltd. London. JOURNALS 1. Journal of American Society of Horticultural Sciences. 2. Journal of Agribusiness and Food Industry. e REFERENCES www. Postharvest.ucdavis.edu www.postharvest.ifsa.ufl.edu www.fao.org Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  Lecture 2: MATURITY INDICES, HARVESTING AND POST HARVEST HANDLING OF FRUITS AND VEGETABLES I. MATURITY It is the stage of fully development of tissue of fruit and vegetables only after which it will ripen normally. During the process of maturation the fruit receives a regular supply of food material from the plant. When mature, the abscission or corky layer which forms at the stern end stops this inflow. Afterwards, the fruit depend on its own reserves, carbohydrates are dehydrated and sugars accumulate until the sugar acid ratio form. In addition to this, typical flavour and characteristic colour also develop. it has been determined that the stage of maturity at the time of picking influence the storage life and quality of fruit, when picked immature like mango develop white patches or air pockets during ripening and lacking in normal brix acid ratio or sugar acid ratio, taste and flavour on the other hand if the fruits are harvested over mature or full ripe they are easy susceptible to microbial and physiological spoilage and their storage life is considerably reduce. Such fruits persist numerous problems during handling, storage and transportation. Therefore, it is necessary or essential to pick up the fruits or vegetables at correct stage of maturity to facilitate proper ripening, distant transportation and maximum storage life. Horticultural maturity It is a developmental stage of the fruit on the tree, which will result in a satisfactory product after harvest. Physiological maturity It refers to the stage in the development of the fruits and vegetables when maximum growth and maturation has occurred. It is usually associated with full ripening in the fruits. The Physiological mature stage is followed by senescence. Commercial maturity It is the state of plant organ required by a market. It commonly bears little relation to Physiological maturity and may occur at any stage during development stage. Harvest Maturity It may be defined in terms of Physiological maturity and horticultural maturity, it is a stage, which will allow fruits / vegetables at its peak condition when it reaches to the consumers and develop acceptable flavour or appearance and having adequate shelf life. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. Table 1: Criteria of maturity for harvesting fruits and vegetables Fruit Physical Chemical Mango Olive green colour with clear lenticels, Starch content, flesh colour shoulder development size sp. gravity, days from fruit set. Banana Skin colour, drying of leaves of the plant, Pulp/peel ratio, starch content brittleness of floral ends, angularity of the fruit, and days from emergence of inflorescence. Citrus Colour break of the skin from green to Sugar/acid ratio, TSS orange, size Grapes Peel colour, easy separation of berries, TSS 18-12 Thompson seedless, characteristic aroma 12-14 for Bangalore Blue, 14-16 for Anab-e-shahi Apple Colour size Firmness as measured by pressure tester Papaya Yellow patch or streaks. Jelliness of the seed, seed colour Vegetables are harvested at harvest maturity stage, which will allow it to be at its peak condition when it reaches the consumer, it should be at a maturity that allows the produce to develop an acceptable flavour or appearance, it should be at a size required by the market, and should have an adequate shelf life. Time taken from pollination to horticultural maturity under warm condition, skin colour, shape, size and flavour and abscission and firmness are used to assess the maturity of the produce. Table 2: Time taken from pollination to horticultural maturity S.No. Vegetables Time to harvest Maturity (days) 1. Ridge gourd 5 -6 2. Squash 7-8 3. Brinjal 25 - 40 Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  4. Okra 4-6 5. Pepper (green stage) 45 - 55 6. Pepper (red stage) 60 -70 7. Pumpkin (mature) 65 - 70 8. Tomato (mature green) 35 - 45 9. Tomato (red ripe stage) 45 - 60 10. Peas 30 - 35 Skin colour Loss of green colour in citrus and red colour in tomato. Shape, size and flavour Sweet corn is harvested at immature stage, smaller cobs marketed as baby corn. Okra and cow pea are harvested at mature stage (pre fiber stage). In chilli, bottle gourd, bitter gourd, cluster beans maturity is related to their size. Cabbage head and cauliflower curd are harvested before un pleasant flavour. Abscission and firmness Musk melon should be harvested at the formation of abscission layer. In cabbage and lettuce should be harvested at firmness stage. Factors affecting maturity 1. Temperature: Higher temperature gives early maturity. e.g. Gulabi (Pink) grapes mature in 100 days in Western India but only 82 days are enough in the warmer Northern India. Lemon and guava takes less time to mature in summer than in winter. Sun-scorched portions of fruits are characterized by chlorophyll loss, yellowing, disappearance of starch and other alcohol insoluble material, increase in TSS content, decrease in acidity and softening. 2. Soil: Soil on which the fruit tree is grown affects the time of maturity. e.g. Grapes are harvested earlier on light sandy soils than on heavy clays. 3. Size of planting material: This factor in propagated fruits affects fruit maturity. e.g. In pineapple, the number of days taken from flowering to fruit maturity was more by planting large suckers and slips than by smaller ones. 4. Closer spacing: Close spacing of hill bananas hastened maturity. 5. Pruning intensity: It enhanced the maturity of Flordasun and sharbati Peaches. 6. Girdling: Process of constricting the periphery of a stem which blocks the downward translocation of CHO, hormones, etc. Beyond the constriction which rather accumulates above Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. it. In Grape vines it hastens maturity, reduces the green berries in unevenly maturity cultivar and lowers the number of short berries. It is ineffective when done close to harvest. CPA has an additive effect with girdling MATURITY INDEX Maturity index The factors for determining the harvesting of fruits, vegetables and plantation crops according to consumer’s purpose, type of commodity, etc and can be judged by visual means (colour, size, shape), physical means (firmness, softness), chemical analysis (sugar content, acid content), computation (heat unit and bloom to harvest period), physiological method(respiration). These are indications by which the maturity is judged. Various index are as Follows; 1. Visual indices It is most convenient index. Certain signals on the plant or on the fruit can be used as pointers. E.g. drying of top leaves in banana, yellowing of last leaf of Peduncle in jackfruit. Flow of sap from cut fruit stalk of mango slows down if the harvest is done after maturity but in immature fruits, exudation is more and comes with force in a jet form. in papaya, the latex becomes almost watery. The flow gets reduced on maturity in Sapota. In fruits like banana and Sapota, floral ends become more brittle and shed with a gentle touch or even on their own. In Sapota, the brown scurf on the fruit skin starts propping. In mango, lenticels become more prominent and the waxy bloom gradually disappears. Grapes develop translucent bloom. Other changes like angularity in banana, development of creamy wide space between custard apple segments and the flattening of the eyes in pineapple and tubercles in litchi serve as reliable maturity indices. 2. Seed development It can also be used as an index of fruit maturity, e.g. endocarp hardening for stone and fiber development for dessert in mango. 3. Start of bud damage Occasionally it can be used as an index of fruit maturity in mango. 4. 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. This approach relies on a reproducible date for the time of the flowering and a relative constant growth period from flowering through to maturity. Time of flowering is largely dependent on temperature, and Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. the variation in number of days from flowering to harvest can be calculated for some commodities by use of the degree- concept. 5. Heat units Harvest date of newly introduced fruits in a widely varying climate can be predicted with the help of heat unit. For each cultivar the heat requirement for fruit growth and development can be calculated in terms of degree days: Maturity at higher temperature is faster as the heat requirement is met earlier. This heat unit helps in planning, planting, harvesting and factory programmes for crops such as corn, peas and tomato for processing. MATURITY OF FRUITS AND VEGETABLES Banana The fruit is harvested when the ridges on the surface of skin change from angularity to round i.e. after the attainment of 3% full stages. Dwarf banana are ready for harvest within 11- 14 months after planting while tall cultivars takes about 14-16 months to harvest. Peel colour change from dark green to light green the remaining style ends were dry, and brittle and fruits were less angular in shape. Guava TSS acid ratio, specific gravity and colour are determined the maturity in guava. For e.g. Allahabad safeda - 35.81 Apple colour guava - 26.39 Chittidar guava - 28.13 Lucknow - 49 -34.25 Specific gravity - Less than I Colour - Light green to yellow. Ber In ber maturity is judged by colour (yellow), specific gravity (less than 1) and TSS Pomegranate Sugar percentage should be 12-16% and acid percentage 1.5—2.5%, variety Ganesh harvest when seed colour becomes pink. In this stage TSS 12.5% and sugar acid ratio 19.5%. Bael It takes one year for fruiting after flowering. It is the fruit which ripen after one year of flowering. April start harvesting and may end it start in flowering. Mango Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  This can be judged when one or two mangoes ripen on the tree are fall on the ground of their own accord. This process of fallen is known as tapaca specific gravity 1,01—1.02 and TSS 10-14%. Table 3 Maturity indices of vegetable crops Root, bulb and tuber crops Maturity indices Radish and carrot Large enough and crispy Potato, onion and garlic Tops beginning to dry and topple clown Yams, bean and ginger Large enough FRUIT VEGETABLES Cowpea, snap bean, sweet pea, Well filled pods that snap readily winged bean Lima bean and pigeon pea Well filled pods that are beginning to lose their greenness. Okra Desirable size reached and the tips of which can be snapped readily Snake gourd Desirable size reached and thumbnail can still penetrate flesh readily Egg plant, bitter gourd, slicing Desirable size reached but still tender cucumber Tomato Seeds slipping when fruit is cut, or green colour turning pink Muskmelon Easily separated from vine with a slight twist leaving clean cavity (full slip stage). Watermelon Dull hollow sound when thumped FLOWER VEGETABLES Cauliflower Curd compact Broccoli Bud cluster compact II. HARVESTING The goals of harvesting are to gather a commodity from the field at the proper level of maturity with a minimum of damage and loss, as rapidly as possible and at a minimum cost. This is achieved through hand-harvesting in most fruit, vegetable and flower crops. 1. Hand Harvesting Hand harvesting has a number of advantages over machine harvest. People can accurately determine product quality, allowing accurate selection of mature product. This is Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. particularly important for crops that have a wide range of maturity and need to be harvested several times during the season. Properly trained workers can pick and handle the product with a minimum of damage. Many fresh-market products have a short shelf life if they are bruised or damaged during harvest and handling. The rate of harvest can easily be increased by hiring more workers. Hand- harvesting also requires a minimum of capital investment. The main problem with hand harvesting is labor management. Labor supply is a problem for growers who cannot offer a long employment season. Labor strikes during the harvest period can be costly. In spite of these problems, quality is so important to marketing fresh- market commodities successfully that hand harvesting remains the dominant method of harvest of most fruits and vegetables and for all cut flowers. Effective use of hand labor requires careful management. New employees must be trained to harvest the product at the required quality and at an acceptable rate of productivity. Employees must know what level of performance and must be encouraged and trained to reach that level. 2. Mechanical Harvesting Mechanical harvest is currently used for fresh-market crops that are roots, tubers, or rhizomes and for nut crops. Vegetables that are grown below ground (radishes, potatoes, garlic, carrots, beets and others) are always harvested only once and the soil can be used to cushion the product from machine caused mechanical injury. Tree nuts and peanuts are protected by a shell and easily withstand mechanical handling. A number of products destined for processing such as tomatoes, wine grapes, beans, peas, prunes, peachesand some leafy green vegetables are machine harvested because harvest damage does not significantly affect the quality of processed product. This is often because the product is processed quickly after harvest. These crops have also been amenable to new production techniques and breeding that allow the crop to be better suited to mechanical harvest. The main advantage of mechanical harvest equipment is that machines can often harvest at high rates. Tree nut harvesters, for eg. attaching a shaking mechanism to the tree and remove most of the nuts in few seconds. The nuts are either caught on a fabric- covered frame or picked up from the ground by other machines. This allows an orchard to be harvested very quickly compared to handshaking with poles. Machine harvest also reduces management problems associated with workers. The commodity must be grown to accept mechanical harvest. Demerits of Mechanical Harvesting Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  Machines are rarely capable of selective harvest. Mechanical harvesting will not be feasible until the crop or production techniques can be modified to allow one time harvest. Harvesting machines often causes excessive product perennial crops eg. Bark damage from a tree shaker. The harvesting machines are quite expensive. III. POST HARVEST HANDLING Being living organs, fruits and vegetables continue to respire even after harvesting when they have a limited source of food reserves. In addition to degradation of respiratory substrates, a number of changes in taste, colour, flavour, texture and appearance take place in the harvested commodities which make them unacceptable for consumption by the consumers if these are not handled properly. Post harvest technology starts immediately after the harvest of fruits and vegetables. The whole process of processing the commodities is categorized as Handling of fresh produce. Post harvest Technology of fresh fruits and vegetables combines the biological and environmental factors in the process of value addition of a commodity. 1. Precooling Precooling (prompt cooling after harvest) is important for most of the fruits and vegetables because they may deteriorate as much in 1 hr at 32°C. In addition to removal of field heat from commodities, precooling also reduces bruise damage from vibration during transit. Cooling requirement for a crop vary with the air temperature during harvesting, stage of maturity and nature of crop. There are many methods of precooling viz, cold air (room cooling, forced air cooling), cold water (hydrocooling), direct contact with ice (contact icing), evaporation of water from the produce (evaporative cooling, vacuum cooling) and combination of vacuum and hydrocooling (hydrovac cooling). Some chemicals (nutrients/growth regulators/ fungicides) can also be mixed with the water used in hydrocooling to prolong the shelf life by improving nutrient status of crop and preventing the spread of post harvest diseases. 2. Washing, Cleaning and Trimming Before fresh fruits and vegetables are marketed various amounts of cleaning are necessary which typically involves the removal of soil dust, adhering debris, insects and spray residues. Chlorine in fresh water is often used as disinfectant to wash the commodity. Some fungicides like Diphenylamine (0.1 - 0.25%) or ethoxyquin (0.2 - 0.5%) may be used as post harvest dip to control the disorders. Eg. Apple superficial scald. For cleaning of some fruit type vegetables (melons, brinjals, tomatoes, cucumber) they should be wiped with damp cloth. Many vegetable need trimming, cutting and removal of unsightly leaves or other vegetative parts. 3. Sorting, Grading and Sizing Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  Sorting is done by hand to remove the fruits which are unsuitable to market or storage due to damage by insects, diseases or mechanical injuries. The remainder crop product is separated into two or more grades on the basis of the surface colour, shape or visible defects. For eg, in an apple packing house in India 3 grades viz. Extra Fancy, Fancy and standard may be packed for marketing. The fourth “cull” grade is meant for processing. After sorting and grading, sizing is done either by hand or machine. Machine sizers work on two basic principles: weight and diameter. Sizing on the basis of fruit shape and size are most effective for spherical (Oranges, tomato, certain apple cultivars) and elongated (Delicious apples and European pears or of non-uniform shape) commodities, respectively. 4. Curing Curing is an effective operation to reduce the water loss during storage from hardy vegetables viz, onion, garlic, sweet potato and other tropical root vegetables. The curing methods employed for root crops are entirely different than that from the bulbous crops (onions and garlic). The curing of root and tuber crops develops periderms over cut, broken or skinned surfaces wound restoration. It helps in the healing of harvest injuries, reduces loss of water and prevents the infection by decay pathogens. Onions and garlic are cured to dry the necks and outer scales. For the curing of onion and garlic, the bulbs are left in the field after harvesting under shade for a few days until the green tops, outer skins and roots are fully dried. 5. Waxing Quality retention is a major consideration in modem fresh fruit marketing system. Waxes are esters of higher fatty acid with monohydric alcohols and hydrocarbons and some free fatty acids. But coating applied to the surface of fruit is commonly called waxes whether or not any component is actually a wax. Waxing generally reduces the respiration and transpiration rates, but other chemicals such as fungicides, growth regulators, preservative can also be incorporated specially for reducing microbial spoilage, sprout inhibition etc. However, it should be remembered that waxing does not improve the quality of any inferior horticulture product but it can be a beneficial adjunct to good handling. The advantages of wax application are: - Improved appearances of fruit. - Reduced moisture losses and retards wilting and shrivelling during storage of fruits. - Less spoilage specially due to chilling injury and browning. - Creates diffusion barrier as a result of which it reduces the availability of 02 to the tissues thereby reducing respiration rate. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  - Protects fruits from micro-biological infection. - Considered a cost effective substitute in the reduction of spoilage when refrigerated storage is unaffordable. - Wax coating are used as carriers for sprout inhibitors, growth regulators and preservatives. The principal disadvantage of wax coating is the development of off- flavour if not applied properly. Adverse flavour changes have been attributed to inhibition of O 2 and CO 2 exchange thus, resulting in anaerobic respiration and elevated ethanol and acetaldehyde contents. Paraffm wax, Carnauba wax, Bee wax, Shellac, Wood resins and Polyethylene waxes used commercially. 6. Packaging Proper or scientific packaging of fresh fruits and vegetables reduces the wastage of commodities by protecting them from mechanical damage, pilferage, dirt, moisture loss and other undesirable physiological changes and pathological deterioration during the course of storage, transportation and subsequent marketing. For providing, uniform quality to packed produce, the commodity should be carefully supervised and sorted prior to packaging. Packaging cannot improve the quality but it certainly helps in maintaining it as it protects produce against the hazards of journey. Striking developments have been in the field of packaging of horticultural produce and the gunny bags, grasses and stem leaves used so far for packaging are now being replaced by a variety of containers such as wooden boxes, baskets woven from bamboo or twigs, sack/jute bags and corrugated fibre board (CFB) boxes. 7. Storage A number of storage techniques (ground storage, ambient storage, refrigerated storage, air cooled storage, zero energy storage, modified atmospheric storage, hypobaric storage and controlled atmosphere storage) are being used for fruits and vegetables depending upon the nature of the commodity and the storage period intended. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  MATURITY AND RIPENING PROCESS MATURITY It is the stage of fully development of tissue of fruit and vegetables only after which it will ripen normally. During the process of maturation the fruit receives a regular supply of food material from the plant. When mature, the abscission or corky layer which forms at the stern end stops this inflow. Afterwards, the fruit depend on its own reserves, carbohydrates are dehydrated and sugars accumulate until the sugar acid ratio form. In addition to this, typical flavour and characteristic colour also develop. it has been determined that the stage of maturity at the time of picking influence the storage life and quality of fruit, when picked immature like mango develop white patches or air pockets during ripening and lacking in normal brix acid ratio or sugar acid ratio, taste and flavour on the other hand if the fruits are harvested over mature or full ripe they are easy susceptible to microbial and physiological spoilage and their storage life is considerably reduce. Such fruits persist numerous problems during handling, storage and transportation. Therefore, it is necessary or essential to pick up the fruits or vegetables at correct stage of maturity to facilitate proper ripening, distant transportation and maximum storage life. FRUIT RIPENING Fruit ripening is a genetically programmed stage of development overlapping with senescence. The fruit is said to be ripe when it attains its full flavour and aroma and other characteristics of the best fruit of that particular cultivar. The words “mature “and “ripe” are essentially synonymous when used to describe these fruits that ripe on the plants known as non-climacteric. However, in case of climacteric fruits a mature fruit require period before attaining a desirable stage of edibility. Table 1. List of climacteric and non-climacteric fruits Climacteric Non-climacteric Apple Carambola Apricot Cherries Avocado Citrus Banana Grape Ber Litchi Cherimoya Loquat Fig Olive Guava Pineapple Kiwifruit Pomegranate Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  Mango Strawberry Melons Pear Peach Plum Persimmon Papaya Tomato Sapota Passion fruit Changes during Fruit Ripening 1. Cell Wall Changes Cell wall consists of pectic substances and cellulose as the main components alongwith sma1amounts of hemicellulose and non-cellulosic polysaccharides. In cell wall, the changes particularly in the middle lamella which is rich in pectic polysaccharides are degraded and solubilised during ripening. During this softening, there is a loss of neutral sugars (galactose and arabinose-major components of neutral protein) and acidic pectin (rhamnogalacturonan) of all cell wall. The major enzymes implicated in the softening of fruits are pectine1asterase, polygalacturonase cellulase and β- galactosidase. 2. Starch During fruit ripening sugar levels within fruit tend to increase due to either increased sugar importation from the plant or to the mobilization of starch reserves within the fruit, depending on the fruit type and whether it is ripened on or off the plant. With the advancement of maturity, the accumulated starch is hydrolysed into sugars (glucose, fructose or sugars) which are known as a characteristic event for fruit ripening. Further breakdown of sucrose into glucose and fructose is probably mediated by the action of invertase. In vegetables like potato and peas on the other hand, the higher sucrose content which remains high at fresh immature stage, converts into starch with the approach of maturity. 3. Organic Acids With the onset of fruit ripening there is downward trend in the levels of organic acids. The decline in the content of organic acids during fruit ripening might be the result of an increase in membrane permeability which allows acids to be stored in the respiring cells, formation of salts of malic acid, reduction in the amounts of acid translocated from the leaves, Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. reduced ability of fruits to synthesize organic acids with fruit maturity, translocation into sugars and dilution effect due to the increase in the volume of fruit. 4. Colour With the approach of maturation, the most obvious change which take place is the degradation of chlorophyll and is accompanied by the synthesis of other pigments usually either anthocyanins or carotenoids. They can give rise to a wide range of colours (from red to blue). The chloroplasts in green immature fruit generally lose chlorophyll on ripening and change into chromoplasts which contain carotenoid pigments. Carotenoids are normally synthesized in green plant tissue a major product being 3-carotene. However, in many fruits additional - carotene and lycopene is synthesized during ripening. 5. Flavouring Compounds Although fruit flavour depends on the complex interaction of sugars, organic acids, phenolics and volatile compounds but the characteristic flavour of an individual fruit or vegetable is derived from the production of specific flavouring volatile. These compounds are mainly esters, alcohols, aldehydes, acids and ketones. At least 230 and 330 different compounds in apple and orange fruits have been indicated respectively. 6. Ascorbic Acid L-ascorbic acid (Vitamin C) is the naturally occurring ascorbic acid in fruits. A reduced amount of ascorbic acid is noticed in pome, stone and berry fruits at the time of harvest. An increase in ascorbic acid content with the increase in fruit growth has been and the levels declined with the advancement of maturity and onset of fruit ripening in pear, sweet potatoes, potato, asparagus and okra during the course of post harvest handling. 7. Phenolics The phenolic content of most fruits declines from high levels during early growth to low levels when the fruit is considered to be physiologically mature and thereafter susceptible to the induction of ripening. 8. Amino Acids and Proteins Decrease in free amino acid which often reflects an increase in protein synthesis. During senescence the level of free amino acids increases reflecting a breakdown enzymes and decreased metabolic activity. 9. Ethylene Production and Respiration Physiological events responsible to ripening process are as follows (1) Ethylene production (2) Rise in respiration Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. Ethylene production In climacteric fruits such as mango, banana, ethylene production increase and causes: Rise in respiration Rise in temperature Rise in activity of hydrolytic enzymes. Ethylene is produced from an essential amino acid — methionine. Following the steps as below: SAM — Methionine S adenosyl methionine (ACC synthase) Amino cyclo propane (ACC oxidase) Carboxylic acid (ACC) Ethylene Perception by ethylene receptor Signal transduction Switching or ripening genes Rise in respiration Respiration is required for releasing energy and the substrate for synthesis of several organic compounds required in the ripening process. During ripening in climacteric fruits, there is rise in respiration called climacteric. The clirnacteric peak is obtained very fast when temperature is relatively high. Respiration is a most deteriorating process of the harvested fruits and vegetables which leads to the oxidative breakdown of the complex materials (carbohydrates or acids) of cell into simpler molecules (CO 2 and water) with the concurrent production of Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. energy required by the cell for the completion of chemical reactions. In brief, the process of respiration can be summed up with the following reaction: C 6 H12 0 6 +6O 2 6 CO 2 + 6 H2 0 + energy USE OF CHEMICALS FOR INCREASING SHELF LIFE OF FRUITS AND VEGETABLE (A) Ethylene absorbent Ethylene is responsible for decreasing shelf life. Putting KMNO 4 @ 100 ppm soaked filter paper can minimized ripening and increase shelf life. In Banana this method is very useful. (B) Antifungal Agents SOPP: Sodium orthophenylphenate Diphenyl wraps protection against moulds, stem-end rot. Dibromoletrachloroethane and esters give better flavour. (C) Use of Inhibitors Treatment Crop Chemical Concentration Post-harvest Mango MH 1000-2000 ppm After fruit formation Apple 2-Dimethyl-hydrazide 10,000 ppm (D) Use of Auxins Also helpful to advance in ripening and may increase shelf life. Chemical Concentration Crop Stage 2,4-D 5 ppm Grape Pre-harvest 2,4,5-T 25 ppm Fig Pre-harvest 2,4,5-T 100 ppm Mango After harvesting E) Vegetables can be preserved by lactic acid and may increase the shelf life. F) Post harvest dipping of papaya fruits either in l00 ppm GA3 or CaCl 2 al 2% extended shelf life up to 9 days without any decline in quality. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  Lecture 4. Factors affecting ripening can be physiological, physical, or biotic. Physiological factors relate to fruit maturity or environmental factors, which affect the metabolism of fruit and banana. Physical factors include mechanical damage, or relate to dimensions of the fruit. Biotic factors include attack from pests and diseases. Fruit maturity. The more mature fruit is at harvest, the shorter the ripening period. Studies show that banana harvested 100 days after flowering ripened in 11 days. When the same cultivar was harvested 90 days after flowering, the ripening period increased to 15 days, and further increased to 22 days when the fruit was harvested at 80 days. Farmers have to match the date of harvest with the transportation time to the market. However, an early harvest reduces yield. As fruits mature, the cross-sectional diameter increases. Fruit angularity also changes during growth and maturation. As fruits approach full maturity, fruit angles become less acute Fruit angularity can be used to predict the optimum harvest date of banana. Temperature. Physiological studies on bananas show that storage life Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. decreases as external temperature increases over the range 15-35ºC. A 1ºC reduction increases storage period by 1-2 days. The relationship between ripening period and temperature is due to fruit respiration. Fruit respiration depends on many enzymatic reactions, and the rate of these reactions increases exponentially with increase in temperature. Studies show that ripe fruits respire at approximately 4 times the rate of unripe fruits. Consequently, ripe fruits lose sugar resources at a higher rate than unripe fruits. This explains why ripe fruits deteriorate quickly. The relationship between temperature and respiration is described mathematically by van't Hoff's temperature quotient (Q10). van't Hoff showed that the rate of respiration approximately doubles for each 10ºC rise in temperature. Water loss and humidity. Where fruit is sold on a weight basis, loss of water means economic loss. Additionally, water loss reduces visual quality. Water loss causes fruit to lose its firmness, the peel becomes soft and shriveled, and ripening period reduces. Studies on fruits show a curvilinear or power relationship between fruit weight loss and ripening period. For a 2% change from 2% to 4% weight loss per day, ripening period reduced by 9 days or 50%. Therefore, at a low rate of weight loss, a small increase in weight loss has a critical effect on ripening. The rate of water loss depends on the ambient relative humidity (RH). RH is the amount of water vapor present in the air, relative to the maximum amount of water vapor that can be held in the air, at a given temperature, saturated air being 100% RH. When a water-containing material such as fruit is placed in an enclosed space, for example, a sealed container, the water content of the air within the container increases or decreases until it is in equilibrium with the fruit. The water equilibrium principle applies when fruit is stored. The rate of water loss depends on the ambient RH. At an ambient RH of 95-100%, Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. fruit loses little or no moisture, and ripening period is unaffected. However, as humidity decreases, the rate of water loss increases, and ripening period reduces. Excessive wetting can also be a problem. When fruit is stored in wet conditions, such as in moist coir (coconut fiber), the uptake of water from the coir to the fruit leads to peel splitting. Sunlight. Exposure to direct sunlight reduces the ripening period of fruits. Sunlight increases fruit temperature above ambient temperature, which increases respiration, and possibly the rate of water loss. The solar radiation that falls upon foods held in direct sunlight increases the temperature above the ambient temperature. The amount of increase in temperature depends on the intensity of the radiation, the size and shape of the food' and the duration of exposure to the direct rays of the sun. The intensity of solar radiation depends upon latitude, altitude, season of the year, time of day, and degree of cloud cover. Altitude. Within a given latitude the prevailing temperature is dependent upon the elevation when other factors are equal. There is on the average a drop in temperature of 6.5°C for each Km increase in elevation above sea level. Storing food at high altitudes will therefore tend to increase the storage life and decrease the losses in food provided it is kept out of the direct rays of the sun. Atmosphere. The normal atmosphere contains by volume, approximately 78% nitrogen, 21% oxygen, 1% argon, 0.03% carbon dioxide' various amounts of water vapor and traces of inert gases. Modifying the atmosphere can improve the shelf life and reduce wastage of certain foods. One type of controlled atmosphere storage (CA) is refrigerated storage in which the level of oxygen is reduced to about 3% with the carbon dioxide content being raised to 1 to 5%, depending on the commodity. This CA storage may double the storage life over that of regular cold Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. storage for certain varieties of apples and pears by slowing down the natural rate of respiration. Ethylene (C2H4) is a gaseous plant hormone which determines the time between harvest and senescence. The time from harvest to the climacteric respiratory response is called the 'green life' or preclimacteric period. Ethylene shortens the preclimacteric period; at high concentrations, ethylene causes rapid initiation of the climacteric respiratory response and accelerates ripening. When nonclimacteric fruits are exposed to ethylene, fruits show an increased rate of respiration. However, respiration rate falls when ethylene is removed. A rise in respiration rate may occur more than once in nonclimacteric fruits. However, for climacteric fruits, the climacteric is autocatalytic, that is, once started, the process cannot be stopped until the fruit is ripe. Poor storage methods allow a build up of ethylene, stimulate the climacteric response, and reduce the ripening period. For example, plastic sheets placed over stacks of fruit for shade increase the level of ethylene within the fruit stack and increase the rate of ripening. Therefore, store fruit in thatched or ventilated areas to prevent the build up of ethylene. Also, do not store unripe fruits with ripe fruits. During the preclimacteric period, fruits are less susceptible to physical damage and pathological attack. This is the best time for handling, transportation, and marketing. Mechanical damage. Mechanical damage is a physical factor affecting ripening. Fruit damage during handling generates ethylene. If ethylene production is sufficient to start the climacteric respiratory response, fruit immediately starts to ripen. Damage can also reduce ripening period by causing moisture loss. The effect of damage can easily be measured by recording fruit weight loss over time. Cuts and abrasions on the surface membrane cause the most weight loss. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. After harvest, fruits lose the ability to repair ruptured peel. Harvesting techniques which damage fruit reduce storability. Studies show that an abrasion affecting 5-10% of the peel can reduce the ripening period by 40%. Damage can also lead to secondary infection, which increases the rate of water loss and further reduces quality. Surface to volume ratio. The ratio between surface area and volume determines the rate of water loss. The greater the surface to volume ratio, the shorter the postharvest life. A leaf which has two large surfaces with little volume loses moisture faster than a fruit. Large fruits lose less water than small fruits. Peel thickness. Fruits with thin peel lose more water. A higher peel permeability leads to a higher rate of water loss and a faster ripening rate. Also, fruits with thick peel, for example melons, withstand damage better than fruits with thin peel, such as tomatoes. Stomatal density. A higher density of stomata may cause a higher rate of water loss, which accelerates ripening. Biotic stress. Fungi, bacteria, viruses, and insects also account for a considerable proportion of total postharvest loss. Pests and diseases reduce both ripening period and overall quality. However, attack by pests and diseases is often secondary because a pest exploits a damaged area of the fruit. Careful fruit handling often prevents such attacks. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. Chapter 5: PRE HARVEST FACTORS AFFECTING QUALITY ON POST HARVEST LIFE OF FRUITS AND VEGETABLES – FACTORS RESPONSIBLE FOR DETERIORATION OF HARVESTED FRUITS AND VEGETABLES Quality of post harvest product Post harvest quality represents market quality, edible quality, transport quality, table quality, nutritional quality, internal quality and appearance quality. Quality means a combination of characteristics, attributes and properties that gives the values to human and enjoyments. Consumers consider good quality in relation to colour, flavour and nutrition. Quality of the produce is the final manifestation of inter-relation between the commodity and its environment. The genetic characteristics and physiological status of the commodity determine the typical post-harvest behavior and quality of the produce and these two are the major bases for the interaction. Pre-harvest factors viz, environmental factors such as temperature, relative humidity, water potential, light, cultural practices and pest management techniques determined the inherent quality of the produce. However, the ultimate quality is the final manifestation of inter relation between the commodity and its environment. Several pre-harvest and post-harvest factors affect the quality of horticultural crops. Some of these factors are related to plant, others are related to environment or to cultural practices. A. Pre-harvest factors a) Related to plants  Crops: Quality of the fruit and vegetables are varies from crop to crop e.g. jackfruit, bael, potato, onion, pumpkin, garlic etc. having good quality in relation to shelf life, while apple, mango, cherry, strawberry, tomato, capsicum, okra, brussels sprout, chinese cabbage, carrot, radish attract more to consumers due to their attractive appearance.  Cultivars: The quality of seed or plant material is an important factor that controls the quality of the fruit and vegetable produced. Several parameters of quality are controlled genetically. Cultural practices: All cultural practices have direct effect on the final quality of the produce. Planting period: Many plants are very sensitive to environmental conditions, and thus quality will not be optimized when crop is produced under adverse conditions. Producing summer plants during the winter or vice-versa will not be appropriate, unless protection practices are implemented. Planting density: It affects both the quantity and quality of the produce. High density planting increases competition between plants, reduces light availability, and thus may decrease Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. quantity. Low density planting lead to large size, better colored fruit or vegetable which may have shorter shelf life. Larger fruits are commonly more sensitive to physiological disorders. Irrigation: Irregular watering usually reduces fruit size, increases splitting, physiological disorders, reduces water content in the plant or plant part, etc. Fertilization: Poor management of fertilizers will increase physiological disorders due to deficiencies of some minerals or increase of other leading to toxicity. In both cases, quality will be negatively affected. Pruning: It reduces the load and increases the growth of fruit and chemical use after harvest. Thinning: This operation reduces the competition between fruits or plants and thus promotes a good balance between the vegetative and fruit parts and improves quality. Protection: Pathogens and insects have a very negative effect on quality. Poor management of plant protection programmes can lead to very poor quality and reduced yield. b) Related to environments Temperature is the most important environmental factor that affects quality, very low or very high temperature may injure sensitive crops. Adequate high intensity and quality is important for the formation of some colour. Wind and rain may cause negative effects on some crops. c) Related to chemicals Many hormones and growth regulators are used in agriculture and they can affect quality in different ways. B) During harvest factor Season: Quality of produce are greatly influenced by season e.g. Winter season harvest having more shelf life as compared to other season, while off season fruits and vegetables give more remunerative price. Harvesting during or immediately after rains should not be carried out since it creates most favourable conditions for multiplication of micro-organisms. Citrus fruits become susceptible to damage if harvested during rains as their rind becomes turgid and prone to easy bruising, sun-scald etc. Time: Fruits and vegetables should always be harvested when temperature is mild. Because, higher temperature leads to faster respiration. Morning harvest of horticultural crop prefer for local market because they are fully fresh and turgid and having dew drop in this time. Evening harvesting is preferred for distant market due to higher accumulation of reserved carbohydrates and less amount of moisture which give the better quality of the produce to consumer. Leafy vegetables harvested in the latter part of the morning or late in the afternoon, the petioles of these vegetables break less easily and their leaves are more resistant to tearing, since they Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. have lost water through transpiration and therefore are less brittle. Cucumber is harvested in the late morning when it to be transported under less than ideal condition because it is less prone to injury when it contains less water. Method of harvesting: Selection of suitable method for harvesting of the produce is necessary otherwise bruises or injuries during harvesting may later manifest as black or brown patches making them unattractive. Latex coming out of stem in mango should not be allowed to fall on fruits as it creates a black spot. Injury to peel may become an entry point for microorganisms, causing rotting. Some harvesting gadgets have been developed, e.g. mango harvester in Lucknow (CISH). Stage of harvesting: Fruits and vegetables must be harvested at right stage of maturity. A very common cause of poor product quality at harvest and rapid deterioration thereafter is harvesting immature vegetables. Vegetables harvested immature or over mature usually do not keep long. Fruit vegetables harvested too early lose water fast and are more susceptible to mechanical damage and microbial attack. An over mature vegetable is more susceptible to decay, has passed its best eating quality, and deteriorates fast. Consumer demand: Harvesting time and harvest maturity can be altered by the requirement of the consumer’s demand which may affect the quality of the produce at some extent. c) Post-harvest factors: Curing: Curing is done immediately after harvesting. It strengthens the skin. The process is induced at relatively higher temperature and humidity, involving suberization of outer tissues followed by the development of wound periderm which acts as an effective barrier against infection and water loss. It is favoured by high temperature and high humidity. Potato, sweet potato, colocasia, onion and garlic are cured prior to storage or marketing. Potato tubers are held at 18°C for 2 days and then at 7°—10°C for 10—12 days at 90% relative humidity. Curing also reduces the moisture content especially in onion and garlic. Drying of superficial leaves of onion bulbs protects them from microbial infection in storage. Degreening: It is the process of decomposing green pigment (Chlorophyll) in fruits usually applying ethylene or similar metabolic inducers to fruit. It is applicable to banana, citrus and tomato. Degreening is carried out in special treating rooms with controlled temperature and humidity in which low concentration of ethylene (20 ppm) is applied. Pre-cooling: High temperatures are detrimental to keeping quality of fruits and vegetables, especially when harvesting is done during hot days. Pre-cooling is a means of removing the field heat. It slows down the rate of respiration, minimizes susceptibility to attack of micro- Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. organisms, and reduces water loss. Peas and okra which deteriorate fast need prompt pre- cooling.  Washing and drying: Most of the fruits and vegetables are washed after harvesting to improve their appearance, to prevent wilting and to remove primary inoculum load of microorganism. Hence, a fungicide/bactericide should be used in washing water. Washing, improves shelf life of bananas by delaying their ripening. After washing, excess of water should be removed which would otherwise encourage microbial spoilage. Sorting and grading: Fruits and vegetables require sorting and grading for uniform packing at field level. Sorting is done on the basis of size and colour while grading practice is performed as per the defect or on the basis of marketable and unmarketable produce. Disinfection: Papaya, mango, melon and other fruits are susceptible to fruit fly attack. Disinfection is done either by vapour heat treatment (VHT) at 43°C with saturated air with water vapour for 6-8 hr by Ethylene dibromide fumigation. Waxing: Fruits and vegetables have a natural layer on their outer surface which is partly removed by washing. An extra discontinuous layer of wax applied artificially with sufficient thickness and consistency to prevent anaerobic condition within the fruits provides necessary protection against decay organism. Waxing also improves the appearance and glossiness, making them more acceptable. Packing: It means more than carrying multiples of an object. Packing not only protects the horticultural produce but also makes a favourable impression on the buyers and May able to fetch higher income. Delivery: Moving the harvest produce from the farm to the customer in good condition is important. All efforts upto delivery can be invalid if the fresh fruits and vegetables reach the destination in poor condition. Care should be taken to protect the produce and it becomes necessary when mixing load of fruits and vegetables to prevent violating the compatibility factors. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  LECTURE 6. FACTORS RESPONSIBLE FOR DETERIORATION OF HARVESTED FRUITS AND VEGETABLES A- Primary causes of loss: Those are directly affect the food Enzymic changes Enzymes which are endogenous to plant tissues can have undesirable or desirable consequences. Examples involving enzymic changes include:  the post-harvest spoilage of fruit and vegetables  oxidation of phenolic substances in plant tissues by phenolase (leading to browning)  sugar - starch conversion in plant tissues by amylases  post-harvest demethylation of pectic substances in plant tissues (leading to softening of plant tissues during ripening, and firming of plant tissues during processing). The major factors useful in controlling enzyme activity are: 1. temperature 2. water activity 3. pH 4. chemicals which can inhibit enzyme action Chemical changes Sensory quality The two major chemical changes which occur during the processing and storage of foods and lead to a deterioration in sensory quality are lipid oxidation and non-enzymatic browning. Chemical reactions are also responsible for changes in the colour and flavour of foods during processing and storage. - Lipid oxidation rate and course of reaction is influenced by light, local oxygen concentration, high temperature, the presence of catalysts (generally transition metals such as iron and copper) and water activity. Control of these factors can significantly reduce the extent of lipid oxidation in foods. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. Non-enzymic browning is one of the major causes of deterioration which occurs during storage of dried and concentrated foods. Colour changes Almost any type of food processing or storage causes some deterioration of the chlorophyll pigments. This reaction is accelerated by heat and is acid catalysed. Flavour changes In fruit and vegetables, enzymically generated compounds derived from long-chain fatty acids play an extremely important role in the formation of characteristic flavors. In addition, these types of reactions can lead to significant off-flavors. The permeability of packaging materials is of importance in retaining desirable volatile components within packages, or in permitting undesirable components to permeate through the package from the ambient atmosphere. Nutritional quality The four major factors which affect nutrient degradation and can be controlled to varying extents by packaging are 1. Light 2. oxygen concentration 3. temperature 4. water activity. 2.3- Physical changes One major undesirable physical change in food is the absorption of moisture as a consequence of an inadequate barrier provided by the package; this results in caking. It can occur either as a result of a poor selection of packaging material in the first place, or failure of the package integrity during storage. In general, moisture absorption is associated with increased cohesiveness. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. Biological changes Microbiological Micro-organisms can make both desirable and undesirable changes to the quality of foods depending on whether or not they are introduced as an essential part of the food preservation process or arise unintentionally and subsequently grow to produce food spoilage. The two major groups of micro-organisms found in foods are bacteria and fungi, the latter consisting of yeasts and moulds. Bacteria are generally the fastest growing, so that in conditions favourable to both, bacteria will usually outgrow fungi. Foods are frequently classified on the basis of their stability as non- perishable, semi-perishable and perishable. The protection of packaged food from contamination or attack by micro- organisms depends on the mechanical integrity of the package (e.g. the absence of breaks and seal imperfections), and on the resistance of the package to penetration by micro-organisms. Macrobiological Insect Pests Warm humid environments promote insect growth, although most insects will not breed if the temperature exceeds about 35 C° or falls below 10 C°. Also many insects cannot reproduce satisfactorily unless the moisture content of their food is greater than about 11%. Rodents Rats and mice carry disease-producing organisms on their feet and/or in their intestinal tracts and are known to harbour salmonella of serotypes frequently associated with food-borne infections in humans. B- Secondary causes of loss: Those lead to conditions that encourage a primary cause of loss such as: 1- Inadequate harvesting, packaging and handling skills. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. 2- Lack of adequate containers for the transport and handling of perishables. 3- Storage facilities inadequate to protect the food. 4- Transportation inadequate to move the food to market before it spoils. 5- Inadequate refrigerated storage. 6- Inadequate drying equipment or poor drying season. 7- traditional processing and marketing systems can be responsible for high losses. 8- Legal standards can affect the retention or rejection of food for human use. 10- Knowledge of management is essential for maintaining tool in good condition during marketing and storage. 11- Bumper crops can overload the post-harvest handling system or exceed the consumption need and cause excessive wastage. Sites of losses Losses may occur anywhere from the point where the food has been harvested or gathered up to the point of consumption. Losses can occur during one of the following processes: 1- Harvest. The separation of the commodity from the plant that produced it. 2- Preparation. The preliminary separation or extraction of the edible from the non- edible portion. 3- Preservation. The prevention of lose and spoilage of foods. For example, the sun-drying of fruit, the use of refrigeration and the use of fungicides to inhibit mold growth in fruits. 4- Processing. The conversion of edible food into another form more acceptable or more convenient to the consumer, for example, the manufacture of fruit juice and the canning of fruits and vegetables. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. 5- Storage. The holding of foods until consumption. Most storage is common storage (ambient temperature) but there are extensive storage capacities that can hold food under refrigerated or controlled atmosphere conditions. 6- Transportation. All forms of transportation are used to convey foods from the point of production to the ultimate point of consumption. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  Lecture 7: Chemicals used in Ripening Chemicals for hastening and delaying ripening of fruits and vegetables Hastening ripening: These some times stimulate ripening of gathered fruits. It seems that the treatment is effective especially when the application is made very early soon after the picking. Stems of bananas immersed in solution containing 1000ppm sodium 2,4-D, 2,4,5 -T or Para- chloro- phenoxy acetic acid showed that ripening was accelerated.2, 4,5 -T and to some extent 2,4-D when sprayed in a wax emulsion delayed the development of yellow colour in the rind of lemons during storage increases the storage life.. Application of ethephon promotes degreening and early ripening in grape, tomato, coffee, pear, plum, peach and citrus. Smoking is commercially employed to hasten de-greening and ripening of banana and mango. Calcium carbide release acetylene which on hydrolysis hasten ripening process. ABA at 1ppm, thio- urea at 20%.CCC 4000ppm,ethrel 200-300ppm sprays one week before harvest hastens ripening. Delaying ripening: Auxins may slow down (generally) or even sometimes accelerate ripening process. Ethylene formation is inhibited by auxin and therefore auxins have to be broken down by peroxidases (IAA Oxidases) to control fruit ripening. Ripening in accompanied by a rise in auxin degrading enzymes. Gibberellins also stop colour changes in fruits like banana. Accumulation of abscisic acid (ABA) is also associated with ripening. Chemials that delay ripening are (1) Kinetin, (2) GA, (3) Auxin, (4) Growth retardant (MH), (5) Alar, (6) CCC. (7)CIPC. (8)Metabolic Inducers- (a)Cycloheximide, Actinomycin-D(b)Vitamin-k,(c)Maleic acid, (d)Ethylene Oxide, (e)NA-DHA, (f)Carbon monoxide,(9) Ethylene absorbents- (a)KMno4(b)Fumigants like methyl bromide(c)Reactants Volatiles: Non-ethylinic volatiles can stimulate ripening. Air purification with activated carbon, H2SO4 and NaOH slowed down the ripening of pre- climacteric apples in a recirculation system. Carbon (activated) reduces the effect in both the cases. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. Growth regulators: These some times stimulate ripening of gathered fruits. It seems that the treatment is effective especially when the application is made very early soon after the picking. Stems of bananas immersed in solution containing 1000ppm sodium 2,4-D, 2,4,5 -T or Para- chloro- phenoxy acetic acid showed that ripening was accelerated.2, 4,5 -T and to some extent 2,4-D when sprayed in a wax emulsion delayed the development of yellow colour in the rind of lemons during storage. The storage life increases. Application of ethephon promotes degreening and early ripening in grape, tomato, coffee, pear, plum, peach and citrus. Smoking is commercially employed to hasten de-greening and ripening of banana and mango. Calcium carbide release acetylene which on hydrolysis hasten ripening process. ABA at 1ppm, thio- urea at 20%.CCC 4000ppm,ethrel 200-300ppm sprays one week before harvest hastens ripening. Auxins may slow down (generally) or even sometimes accelerate ripening process. Ethylene formation is inhibited by auxin and therefore auxins have to be broken down by peroxidases (IAA Oxidases) to control fruit ripening. Ripening in accompanied by a rise in auxin degrading enzymes. Gibberellins also stop colour changes in fruits like banana. Accumulation of abscisic acid (ABA) is also associated with ripening. The shelf life of fruits like apple, banana and others can be improved by storing the fruit in low oxygen tension (203%) or by absorbing ethylene with a suitable absorbent like alumina or silica gel impregnated with potassium permanganate. MH,GA(10-6M), IAA(10-6M) sprays one to two weeks before harvesting and post harvest dip of cycocel, Alar, GA(150ppm), Vit K3, KMNO4,Ca Cl2,Waxol delays ripening. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. Chapter 8: METHODS OF STORAGE-PRECOOLING, PRE STORAGE TREATMENTS, LOW TEMPERATURE STORAGE, CONTROLLED ATMOSPHERE STORAGE, HYPOBARIC STORAGE, IRRADIATION AND LOW COST STORAGE STRUCTURES Pre-cooling is the key component in the preservation of quality for perishable fresh produce in post-harvest systems. It is likely the most important of all the operations used in the maintenance of desirable, fresh and salable produce. Precooling is defined as the removal of field heat from freshly harvested produce in order to slow down metabolism and reduce deterioration prior to transport or storage. One of the most important factors affecting the postharvest life and quality of fruits and vegetables is temperature. Quality loss after harvest occurs as a result of physiological and biological processes, the rates of which are influenced primarily by product temperature. As the maintenance of market quality is of vital importance to the success of the horticultural industry, it is necessary not only to cool the product but to cool it as quickly as possible after harvest. Pre-cooling rapidly lowers the temperature of freshly harvested produce and is done immediately following harvest to minimize spoilage. It is the first operation in the cold chain and is essential for produce (fruits and vegetables) as they are perishable in nature. Although produce may be pre-cooled in a cold storage facility, pre-cooling differs from cold storage. In cold storage, the temperature is simply maintained at a predetermined low temperature. If the cold storage facility is to double as a pre-cooling facility, higher refrigeration capacity is required as well as appropriate provisions for pre-cooling and handling of the produce. The main beneficiary of precooling is the grower as it allows him to sell the produce at the most appropriate time and at the competitive price. Consumers and general economy also benefit through adoption of proper post harvest handling procedures through improved shelf quality, lower real costs for fruits and vegetables through the reduction of losses and spoilage. Proper pre-cooling preserves product quality by  inhibiting the growth of decay producing microorganisms  restricting enzymatic and respiratory activity  inhibiting water loss  reducing ethylene production The importance of precooling (i) Importance of lag time between harvest and cooling Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc.  Field heat can cause rapid deterioration of some horticultural crops and therefore it is desirable to remove this heat as quickly as possible after harvesting. When it comes to produce quality, every minute counts and that precooling is among the most cost-effective and effcient quality preservation methods available to commercial crop produces. For example, strawberries experience increasing deterioration losses as delays between harvesting and cooling exceeds 1 h and the effects of the delay on cooling of strawberries is shown in Fig.1. Fig.1. Effect of delay before cooling on the quality of Shasta strawberries From this it can be seen that even after a short time of 2 h at 30 0C, only 80% of the strawberries are considered marketable fruit, which represents an apparent loss of approximately 10% by not cooling the produce immediately after picking. Furthermore, precooling slows down the deterioration and the rotting process by retarding the growth of decay organisms, and it reduces wilting since transpiration and evaporation occurs more slowly at low temperatures. (ii) Influence of precooling on the respiration rate The rate of deterioration after harvest is closely related to the respiration rate of the harvested product, therefore the reduction of respiration rate is essential to preserving market quality. Since the rate of respiration is influenced by temperature , precooling to remove the field heat before storage will reduce the respiration rate and hence deterioration will decline accordingly. For example reduction in temperature of 9.50C in grapes halved the rate of respiration and doubled their keeping quality. (iii) Influence on metabolism The increase in the rate of deterioration is related to the metabolic processes of the crop. Within the plants temperature range, the rate of deterioration increases logarithmically with increasing temperature. Metabolic rates double for each 100C rise in temperature. From these Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. reports, it can be seen that the quicker the temperature is reduced the less losses that can occur. Hence, precooling is essential in order to reduce metabolic changes such as enzyme activity, and to slow the maturation of perishable produce. (iv) Effects of rapid cooing on ethylene The reduction in temperature has the added advantage of reducing the production and sensitivity of the produce to ethylene that accelerates ripening and senescence. Therefore, the faster and more promptly the field heat and hence temperature is reduced after harvest, the quicker these deteriorative processes are retarded and hence the more of the initial quality can be maintained. Methods for Precooling Produce There are seven principal methods of pre-cooling fresh produce: 1) Room cooling 2) Forced-air cooling 3) Hydro-cooling 4) Ice cooling 5) Vacuum cooling 6) Cryogenic cooling 7) Evaporative cooling Considerable loss in quality and shelf life can occur as a result of holding harvested produce in the field before pre-cooling. All methods require sufficient refrigeration capacity to reduce the temperature of the produce within the required time plus the ability to remove the normal heat gain in the facility. 1) Room cooling Precooling produce in a cold-storage room or precooling room is an old well-established Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. practice. This widely used method involves the placing of produce in boxes (wooden, fiberboard or plastic), bulk containers or various other packages into a cold room, where they are exposed to cold air. It is used for produce sensitive to free moisture or surface moisture. Because this type of cooling is slow, room cooling is only appropriate for very small amounts of produce or produce that does not deteriorate rapidly. Fig.2. Room cooling Typically the cold air is discharged into the room near the ceiling, and sweeps past the produce containers to return to the heat exchangers. The cooled air is generally supplied by forced or induced draft coolers, consisting of framed, closely spaced and finned evaporator coils fitted with fans to circulate the air over the coils. Therefore, as to achieve fast and efficient cooling, care should be taken that the correct packaging (well vented) or containers and stacking patterns are used. Air velocities around the packages should be at least 60 m/min to provide the necessary turbulence to achieve heat removal and therefore attain adequate cooling. As much of the cooling is achieved by conduction, room cooling gives a slow and variable temperature reduction, therefore perishable produce used in this method must be tolerant of slow heat removal. A conventional cold store is unsuited for this operation because as much as three-quarters of the refrigerator capacity may be required simply to remove field heat and the cooling rates are frequently no better than 0.50C/h. The rooms commonly used for highly perishable fruit are designed to have an airflow rate of about 170 to 225 m 3/min for a room with a capacity of 15,000 kg and sufficient refrigeration so as to cool the fruit to 50C in approximately 12 h. Containers are stacked individually so that cold air from the ceiling blows over or around the produce to contact all surfaces of the containers. Produce will dry out if a high relative humidity (90-95 percent) is not maintained. Containers should be well vented so as much air as possible can circulate through them. Spacing between the containers and walls must be from 6 to 12 inches, and between the boxes and ceiling, 18 to 24 inches. Room cooling is not recommended for bulk bins because they contain a much greater mass of produce than smaller containers. Proper design of the cooling room and refrigeration equipment is necessary for room cooling to work efficiently. The refrigeration equipment must be capable of cooling down fresh produce within 24 hours and of maintaining the storage temperature of the produce. Normally, much larger refrigeration equipment is needed to cool down the produce than to maintain the produce at a cool temperature. Room cooling has become increasingly difficult as more commodities are being handled in larger quantities and are packaged immediately after harvest due to better Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. mechanization. These difficulties coupled with its slow and variable cooling extend the cold chain and therefore reduce the product life in subsequent storage. 2) Forced air cooling Forced air cooling was developed to accommodate products requiring relatively rapid removal of field heat immediately after harvest. Forced air or pressure cooling is a modification of room cooling and is accomplished by exposing packages of produce to higher air pressure on one side than on the other. This technique involves definite stacking patterns and the baffling of stacks so that the cooling air is forced through (rather than around) the individual containers. For successful forced air cooling operations, it is required that containers with vent holes be placed in the direction of the moving air and packaging materials that would interfere with free movement of air through the containers should be minimized. A relatively small pressure difference between the two sides of the containers exists, resulting in good air movement and excellent heat transfer and hence faster cooling. Produce can be cooled by a variety of different forced air cooling arrangements. These include (a) air circulated at high velocity in refrigerated rooms, (b) by forcing air through the voids in bulk products as it moves through a cooling tunnel on continuous conveyors, and (c) by encouraging forced airflow through packed produce by the pressure differential technique. Each of these methods is used commercially, and each is suited for certain commodities when properly applied. The product cooling rate is affected by numerous variables and, therefore, the overall cost of the forced air cooling will vary. These variables include product size and shape; thermal properties; product configuration (bulk or packaged); carton vent area; depth of product load during cooling; initial product temperature; final desired product temperature and airflow rate, temperature, and relative humidity. The cooling rate in a given system depends primarily on the velocity of the cold air flowing through it, and this is the only controlling factor, since no change can be made in certain fixed factors such as size, shape and thermal properties of the produce. In addition, the temperature of the cold air cannot be reduced below a certain safe point to avoid chilling injury. In general, the cool air necessary for this type of cooling can be generated from (a) direct expansion refrigeration system, (b) ice bank cooling system and (c) water cascade. Forced air coolers utilise centrifugal (commonly known as squirrel cage) or axial fans which push the cold air around the system. Fans are selected based on the criteria of required airflow and static pres-sure. These requirements are influenced by the type of produce and quantity being cooled, the arrangement of the produce (bulk, boxes or stacking) and the cooling rate required. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. Differential pressures in use are approximately 0.6 to 7.5 mbar with air flows ranging from 0.001 to 0.003 m 3/s kg product. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. Fig.3. Forced horizontal air flow Fig.4. Forced vertical air flow The air can be channeled to flow either horizontally or vertically. In a horizontal flow system, the air is forced to flow horizontally from one side of the pallet load to the other through holes in the sides of the pallet bin or containers. Only two sides that are opposite can be open in the pallet bin or containers. In stacking containers, the side holes must line up for the air to pass from one side of the stack to the other. In this system, the top and bottom of the pallet or containers must be sealed to prevent air from by passing the produce. In a vertical flow system, the air is forced to flow vertically from the bottom to the top of the pallet through holes in the bottom of the pallet, and containers if used, then out the top. In this system, the sides must be sealed to prevent the air from bypassing the produce. Also, if containers are used, the holes in the tops and bottoms of the containers must line up, so the air can travel vertically from one container to the next. This method is faster than room cooling because a flow of chilled air is in direct contact with the produce. In these systems, condensation on the produce can be minimized by a simple cover placed on top of the stack of containers, which prevents the entry of ambient air during handling. The key to forced-air cooling is moving the cold air through the container and its contents. Important factors in container ventilation are location of container vents, stacking of containers, and size of the vents. Container vents should be aligned whether the containers are straight-stacked or crossstacked, to maximize air flow through the containers. If vents are too small or too few, air flow is slowed. If there are too many, the container may collapse. In this method, containers are stacked close together (tight). Five percent vent-hole space per side and/or end is best. Liners, bags, wrappers, or dividers can slow the flow of air through the container, so precooling produce is usually recommended prior to additional packing. The following are forced-air cooling alternatives. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. Cold Wall A permanent false wall or air plenum contains an exhaust fan that draws air from the room and directs it over the cooling surface. The wall is at the same end of the cold room as the cooling surface. The wall is built with a damper system that only opens when containers with openings are placed in front of it. The fan pulls cold room air through the container and contents, cooling the produce. Fig.5. Cold Wall Forced-air Tunnel An exhaust fan is placed at the end of the aisle of two rows of containers or bins on pallets. The aisle top and ends are covered with plastic or canvas, creating a tunnel. An exhaust fan draws cool room air through the container vents and top. The exhaust fan may be portable, creating a single forced-air tunnel where needed, or it may be part of a stationary wall adjacent to the cooling surface, with several fans that create several tunnels. Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. Fig.6. Forced-air Tunnel Serpentine Cooling A serpentine system is designed for bulk bin cooling. It is a modification of the cold-wall method. Bulk bins have vented bottoms with or without side ventilation. Bins are stacked several high and several deep with the fork lift openings against the cold wall. Every other forklift opening—sealed with canvas—in the stack matches a cold wall opening. The alternate unsealed forklift opening allows cold air to circulate through the produce. Cold room air is drawn through the produce via the alternate unsealed openings in the stack and the top of the bin. Fig.7. Serpentine Cooling Because the cooling air comes in direct contact with the product being cooled, cooling is much faster than with conventional room cooling. Cooling by the forced air method was usually Visit www.iaritoppers.com For Agri.Study Material, JRF Mock Tests, PDF Books etc. 4 to 10 times faster than room cooling but that hydrocooling and vacuum cooling was 2 to 23 times faster than forced air cooling. Another aspect of forced air cooling is that converting existing facilities is often simple and inexpensive, provided that sufficient refrigeration capacity and cooling surfaces are available. When very rapid cooling is required forced air cooling is more costly than other precooling methods, and therefore this may limit its application to some produce which needs to be cooled extremely quickly. Another drawback of forced air cooling is that it requires a definite stacking pattern hence this technique requires skilled operators so as to achieve the required loading pattern to ensure satisfactory cooling rates. 3) Hydrocooling Hydrocooling essentially is the utilization of chilled or cold water for lowering the temperature of a product in bulk or smaller containers before further packing. Hydrocooling is achieved by flooding, spraying, or immersing the product in/with chilled water. There are several different hydrocooler designs