Redgram Harvesting And Storage Introduction Harvesting Dehulling Processing Threshing And Yield Storage Methods Storage Pests

Pigeonpea : Postharvest technology Introduction The area of postharvest technology includes all the operations that commence with the harvesting of grains from the field. These operations, also referred to as the post-production systems, have important effects on the utilization of food crops. Efficient postharvest processing is essential to minimize qualitative and quantitative losses of food crop dietary nutrients. Harvesting, processing green and mature seeds, and storage are all important aspects of post harvest processing in pigeonpea. Each of the above processes involves a set of traditional practices dependant on the region of pigeonpea cultivation and consumption. Developing pods of pigeonpea are harvested and their green seeds shelled and used as a vegetable in India and in some Southern Asian and African countries. Canned or frozen green pigeonpeas are used in Latin American and Caribbean countries and are also exported to North America and Europe. Dry whole seeds of legumes have a fibrous seed coat, also called the husk, hull or skin. This seed coat is indigestible and sometime associated with a bitter taste; its removal improves the appearance, texture, cooking quality, and palatability of grain legumes. Such antinutritional factors as polyphenols are mostly present in the seed coat and are thus removed by dehulling. For use as a human food, dry pigeonpea seeds are consumed after dehulling (or dehusking), and this process is the major postharvest operation before utilization. Like other pulse crops in India, pigeonpea is mainly consumed in the form of dhal which is cooked in water to a desired softness. Processing whole pigeonpea seed into dhal (decorticated dry split cotyledons) is an age-old practice with rural origins, but with the introduction and development of suitable machines, dehulling has been adopted on a large scale by dhal mill industries in urban areas. Storage is an important component of the postharvest operation, and the loss of seed by insect infestation due to improper storage has been reported to be higher in pigeonpea than in the other commonly grown grain legumes in India. Pulses (including pigeonpeas) are commonly stored in over ground structures and are attacked by pulse beetles, this seriously deteriorates grain and makes it unhygienic. Storage of pigeonpeas for long periods under improper conditions adversely affects its dehulling quality, consumer acceptability and nutritive value. In view of the importance of the above-mentioned areas in pigeonpea utilization, this chapter presents the topic in four main categories; harvesting procedures, processing green seeds, dehulling operations, and storage practices. Top Harvesting Green pigeonpea pods are harvested for different purposes. Near cities where they can be readily marketed they are harvested for sale as a vegetable. Fully developed, bright green seed is preferred so pods should be harvested just before they start loosing their green colour. It is important to remember that the appearance of pods at this stage varies between cultivars. Green pods used as a vegetable are commonly picked by hand, but they may be mechanically harvested for large scale processing i.e., for canning and freezing. In the Caribbean countries, this type of harvesting has been mechanised by the successful adoption of mechanical green been pickers. It is possible to continuously harvest green pods for vegetable consumption because pigeonpea is a perennial crop, and the harvesting period can be extended if ratoonable cultivars are grown. Pigeonpeas can be grown as trees or shrubs for 4 to 5 years if irrigation or sufficient rainfall is available and under these conditions, each flush of green pods can be harvested when the pods reach the right stage of maturity. Pigeonpea, picked while it is still green is an excellent vegetable, but is currently an important market commodity in only a few areas of India. There is considerable potential for the increased consumption of vegetable pigeonpea in India because new high quality vegetable cultivars are becoming increasingly available and consumers are learning new ways of eating the crop. The dry seeds of pigeonpea are harvested when the pods are fully ripe and have turned yellow, but before the pods start to shatter. Nearly mature pods continue to ripen even after plants are cut, but very dry pods shatter and heavy crop losses occur when plants are cut. Harvesting is usually done manually by using a sickle to cut plants and vines, but occasionally by machines, and is followed by drying and threshing, Generally, harvested material is dried in the sun in the threshing yard for about a week, depending on the weather conditions. Threshing is done by manually and mechanically. Manual threshing, involves beating vines and pods with sticks to separate out the seeds and in some places animals are allowed to walk on the dried produce to thresh it. In other places mechanical threshers are used. Top Dehulling In many countries of the world, grain legumes are initially processed by removing the hull and splitting the seed into its dicotyledonous components. In India, dehulling pigeonpea is a primary process that converts the whole seed into dhal. The dehulling operation is usually performed in two steps the first involves loosening the husk from the cotyledons and the second removing the husk from the cotyledons and splitting them using a roller machine or stone chakki (queen). Dehulling Method Dehulling pigeonpea is an age old practice in India. In earlier days hand pounding was common, this was later replaced by stone chakkis. Several traditional methods are used, that can be broadly classified into two categories: The wet method that involves water soaking, sun drying and dehylling and the dry method that involves oil/water application, sun drying and dehulling. A survey of dehulling methods in India indicated that pigeonpea is traditionally dehulled in two ways depending on the magnitude of operation. One is the large scale commercial dehulling of large quantities of pigeonpea into dhal in mechanically operated mills and the other is the small scale home processing method adopted by villagers using a stone chakki. In large scale processing the material is first graded and then passed through a roller machine which causes a mild abrasion - the tempering operation. This tempering causes slight scratches on the seeds and enhances their old and water absorbing efficiency, leading to the loosening of the testa. The material is then treated with oil and water and spread in the drying yard to dry under the sun. If necessary, the material is occasionally stirred. After sun drying, the material is dehusked with a roller machine. Various products i.e., dehusked split (dhal), dehusked unsplits (pearled), and undehusked material of split and unsplit seeds are obtained. These products are separated and if required the whole operation is repeated to obtain more dhal. For small scale dehulling, the basic unit is a chakki comprising two grinding stones. S The treatments given before dehulling in a chakki vary from region to region. For example, in the Indian states of Maharashtra, Uttar Pradesh and Madhya Pradesh soaking pigeonpeas in water for 2-14 h is a common practice. In some other states, villagers prefer to treat the material with oil before dehulling. In some households, pigeonpea is first split using a 'chakki', then treated with oil/water, and finally hand pounded to remove the seed coat. Another procedure, followed in Uttar Pradesh is heating the pigeonpea in an iron pan, with or without sand, before grinding. In recent years, efforts have been made to develop improved methods and machinery to process pigeonpea more economically. Attrition type mills (plate mills) can be used for dehulling if the hull is not firmly attached to the cotyledons. If it is firmly attached, then abrasive type mills are used; these incorporate carborudum to gradually abrade the seed coat from the cotyledon. However, this new technology has not been widely implemented. Top Processing green seeds After green pods are harvested, shelling, canning and freezing are important processing operations. Canning and freezing involve several operations including cleaning, blanching and filling cans and polyethylene bags. Canning In several developing countries, canning pigeonpea for the export market is encouraged as the demand for canned pigeonpeas has increased. Canning green pigeonpea seeds is a common, export oriented business in some Caribbean countries, for example, in the Dominican Republic, about 80 per cent of the annual harvest of green pigeonpea is canned and exported. Although the quality of green seed depends mainly on its maturity and agroclimatic environments, cultivars suitable for canning have been developed. Cultivars with large, uniform, bright green seeds and pods at the canning stage are preferred for canning. Green seeds with a higher soluble sugars content are preferred by the consumer, but genotypes with this trait have not yet been developed. Mature green seeds can better than starchy yellow seeds. Traditional methods of canning pigeonpeas. Harvesting green seeds of similar maturity is an important step in obtaining a high quality canned product, but the nonsynchronized flowering characteristic of pigeonpea makes it difficult to harvest developing pods of similar maturity. Factors such as drained mass, volume, viscosity, and colour of brine and uniformity of colour are all dependent on maturity. Shelling After the developing pods are harvested in the field, they are shelled to separate the green pigeonpeas from their pod walls. The ease with which pigeonpeas can be shelled depends on the characteristics of the cultivar and there are large differences in the shelling recovery of vegetable pigeonpeas. Suggesting that the recovery is higher in some cultivars than others. Shelling recovery is very important to processors and shelling is done mechanically or by hand depending on the volume of product handled by the processor. Hand shelling not only requires a low capital investment, but also helps produce a much better looking product. It also results in higher yields than machine shelling. Fresh pigeonpeas that are sold packed in polythene bags, are invariably shelled by hand and some frozen product packers also prefer hand shelling. Cleaning An appropriate cleaning procedure is followed depending on whether the shelling operation is by hand or machine. During hand shelling for the fresh market and before freezing small quantities, the product is cleaned and inspected so that damaged seeds and foreign matter can be rejected. Hand shelled pigeonpeas for freezing, are cleaned by placing them in containers of cold water before blanching, so as to keep the blanching water as clean as possible. Fresh market produce is not washed, and cleaning is done by the shellers themselves. Mechanically shelled seeds are transferred to conveyors for cleaning and washing. Small pieces of pod and damaged and small seeds are removed by air blast. The seeds then drop onto a large mesh screen that allows them to drop through while the screen retains pieces of pod and other extraneous material. As a part of the cleaning operation, the seeds are washed with cold running water in various combinations and types of flotation washers. Blanching Blanching is an essential heat treatment operation in the canning and freezing process. Blanching is primarily done to; fix the colour, improve the flavour, reduce the volume and improve the texture to permit a large mass of peas to fit into the can, remove mucous substance(s) and free starch so as to obtain a clearer brine, and to remove intercellular gases from the seeds to lessen can strain during heating. Two methods of blanching have been reported. In the most commonly used method, to obtain a clear brine, seeds are heated at 185°F (85°C) for 5 min in hot water, and then cooled immediately in cold water to about 80°F (26.7°C). The other method involves steam blanching, which causes less shrinkage and lower nutrient losses, but is more expensive because of the energy costs involved and hence is an unacceptable alternative in developing countries. After blanching and cooling, seeds are inspected to remove any off coloured ones that did not appear before blanching and to ensure complete removal of foreign matter before canning or freezing, all the above mentioned steps are similar for both canning and freezing process. Filling, Closing and Cooling cans After blanching and cooling, cans of different sizes are filled with seeds and a 2 per cent brine solution at 195oF (90.5°C to 93.3°C). No sugar or any other additives are added. To close small cans, the brine is maintained almost at boiling point and no mechanical exhaust is required. However, for large cans, the near boiling brine does not create a sufficient vacuum before the cans are closed, so an additional means of creating a vacuum is needed. Closed cans are thermally processed as soon as possible for closure to inhibit the growth of thermophillic bacteria that may spoil the product later if it is stored at high temperatures. Freezing Freezing is by two methods, an automatic continuous system, and a labour intensive batch system. In the automated system, blanched and cooled seeds are transported by conveyor to a fluidised bed freezer. In this process, that operates at a temperature well below freezing (-10°F to -20°F) (-23.3°C to -28°C) the seeds are individually quick frozen. Once frozen, the seeds are hand packed into cartons that have been especially wax treated to prevent dehydration of the product and are then store d at 0°F (-17.8°C). In the batch system, blanched seeds are dropped into cooled water tanks as they come out of the hot water blanches. After cooling, they are hand packed into polyethylene bags, and placed in trays for freezing in a batch freezer (-10°F to -20°F) (-23.3°C to -28.9 °C) for 4 to 10 ha depending on the freezer design, package size, and the initial temperature of the product. Frozen bags are then placed in corrugated containers for storage at 0°F (-17.7 °C). Top Harvesting and threshing Redgram is an intermediate growth type and thereby the growth is continued with reproductive phase. The best time of harvesting of the crop is when over 75 per cent of pods turn brown. Harvesting may be done with the help of sickle in Karnataka. After harvesting, plants are left in the sun for drying. Threshing may be done by beating the pods with sticks. Threshing may also be done with the help of small threshers. Storage er threshing, grain should be dried in the sun so that moisture content is reduced to around 10 per cent. Dried grains should be stored in dry clean stores or gunny bags. Yield Pure crop: 12-15 qts/ha Mixed crop: 2-3 qts/ha Top Methods of Storage The methods of storage play an important role in reducing storage losses. It is often observed that farmers adopt various methods to prevent losses but they are only partially successful because of poor storage conditions, particularly store construction. At the farm level, storage structures made of steel, mud, wood, plastic and concrete and jute bags are frequently used to store pigeonpea. Mud bins are most commonly used by farmers. Storage in jute bags is common in markets and urban dhal mills. There is little difference in the storage structures meant for seeds or grains for consumption. Seed treatments to reduce storage losses are becoming increasingly important. Toxic chemicals are used to protect seed stocks against insects and seed borne pathogens. Contact insecticides such as DDT, BHC and malathion are commonly applied as seed treatments. The use of ethylene dibromide as a fumigant and malathion mixed with tricalcium phosphate at 0.2 per cent have been found quite effective (Vimala and Pushpamma, 1985), but fumigation with toxic chemicals causes considerable loss of viability, probably because the chemicals react with enzymes in the seeds. The coating of stored pulses with a thin film of edible oils to protect them against insect infestation is an age-old traditional practice in the villages of India. Oil treated pigeonpea seeds were not preferred by pulse beetles, and suggested that oil treatment could be useful for the safe storage of pigeonpea. Use of mustard, sunflower, safflower, castor, cotton, neem (Azadirachta indica), and karanj or honge (Pongamia glabra) oils to check infestations of pulse beetle in pigeonpea, and observed that honge and neem oils at 1.0 per cent were effective as surface protectants against attack by C.chinensis. According to this study, there was complete protection from infestation for 319 days honge oil and 161 days using neem oil. There is less pulse beetle infestation if pigeonpea is stored in the form of dhal. In order to avoid storage losses, and to make consumable stocks safer because the use of chemicals can be avoided, pigeonpea seeds should be preferably processed and stored as dhal. Top Storage pests Pulse beetles popularly known as dhoras are important storage pests of pigeonpea in India. These include three bruchid species; Collosobruclus chinensis (L.)., C.maculatus (F.) and C.analis (F.) of which C.maculatus is the most important. Sometimes these insects begin their infestation when the pods are in the ripening stage in the field, and are subsequently carried with the grain into the stores after harvesting, resulting in considerable losses. Howe and Currie (1964) gave a detailed account of the development rate, mortality and oviposition of several species of Bruchidae breeding in stored pulses, and observed that C.maculatus and C.chinensis completed their life cycles in a weeks at 30oC and 70 per cent relative humidity in stored pigeonpea. Noticeable differences in susceptibility of pigeonpea cultivars to pulse beetle attack have been observed. Among several cultivars of pigeonpea, seed infestation due to C.maculatus ranges between 7.0 and 28.7 per cent beetle incidence was highest in JA 8 and lowest in ICPL 7 of the cultivars he tested. The relative susceptibility of 33 cultivars of pigeonpea to C.chinensis was studied under laboratory conditions, ICPL 148 and ICPL 151 were found to be the least susceptible and H 79-74 and ICPL 289 were the most susceptible. None of the cultivars was completely resistant to the attack, although susceptibility varied significantly among the cultivars studied. In different pulses, seed surface, seed coat thickness and seed size have been linked with the mechanism of resistance to different species of Callosobruchus. According to another study, both C.maculatus and C.chinensis showed ovipositional preferences for whole grains over dhal indicating that the seed coat provided the ovipositional stimulus. However, seed characters such as size, colour and texture were not related to beetle preferences, but seed coat thickness influenced beetle incidence. Storage losses Storage losses can be broadly categorized as losses in mass, quality and nutritive value and hygienic deterioration. About 90 per cent of the total postharvest losses of pulses are estimated to occur during storage. Over 50 per cent of such losses are due to storage pests and insects. According to a recent literature survey, more losses occur in pigeonpea than other legumes that damage in pigeonpea was 32.6 per cent, cowpea 18.5 per cent and bean 14.9 per cent, mung bean 9.9 per cent and chickpea 4.8 per cent. Pigeonpea storage losses due to insect infestation varied from 14 to 64 per cent studied the growth and development of C.maculatus, and observed that pigeonpea supported more pest growth than cowpea and chickpea. There are various biological and physical factors that influence storage losses. The extent of losses at the farm level depends on the temperature, humidity and moisture content of the stored pigeonpea, the air concentration in storage structures, hygienic conditions and use of pesticides. The three essential physical variables to be controlled in stored grain are temperature, moisture and oxygen content. Of the biological factors, insect, moulds, bacteria and yeast are important and cause considerable losses. Top

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