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Aware and Thorat - Solar Drying of Fruits and Vegetables more than the immediate consumption needs, resulting in wastage of food surpluses during the short harvest periods and scarcity during post-harvest period (Ekechukwu and Norton, 1997). Hence, a reduction in the post-harvest losses of food products should have considerable effect on the economy of these countries (Sodha et al., 1986). More than 80% of food is being produced by small farmers in developing countries (Murthy, 2009). These farmers dry food products by sun drying, an advantage being that solar energy is available free of cost, but there are several disadvantages which are responsible for degradation and poor quality of the end product. Certain variety of food products are not supposed to be dried by sun drying because they lose certain basic desirable characteristics (Jairaj et al., 2009). Drying and dehydration of fresh fruits and vegetables is one of the most energy intensive processes in the food industry, good understanding of the drying processes plays a vital role in increasing the drying efficiency as well as in maintaining product quality resulting in significant reduction in postharvest losses. Convective hot air drying is still the most popular method applied to reduce the moisture content of fruits and vegetables (Lewicki, 2006). Fruits and vegetables are dried to enhance storage stability, minimize packaging requirement and reduce transport weight. Energy consumption and quality of dried products are critical parameters in the selection of drying process (Al-Juamily et al., 2007). An optimum drying system for the preparation of quality dehydrated products should be cost effective with low drying time and should cause minimum damage to the product. To reduce the energy utilization and operational cost new dimensional solar dryers are good options for drying of fruits and vegetables. 2.2. FRUITS AND VEGETABLES Fruits and vegetables are the fresh agriproduce having high moisture content and are perishable in nature; fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state, such as apples, oranges, grapes, strawberries, juniper berries and bananas. Vegetable usually means an edible plant or part of a plant other than a sweet fruit or seed. This typically means the leaf, stem, or root of a plant. Some vegetables can be consumed raw, some may be eaten, cooked, some must be cooked in order to be edible and some are dried to increase the shelf life. Fruit drying has a long tradition. Inhabitants living close to the Mediterranean Sea and in the Near East traded fruits that had been dried in the open sun. Dried fruit is a delicacy, because of the nutritive value (66– 90% carbohydrate) and shelf life. Today, the production of dried fruits is widespread. Nearly half of the dried fruits in the international market are raisins, followed by dates, prunes, figs, apricots, peaches, apples, pears, and other fruits. Significant amounts of sour cherries, cherries, pineapples, and bananas are also dried. The selection of fruit for drying depends on local circumstances. Fruits can be dried whole, in halves, or as slices, or alternatively can be chopped after drying. The residual moisture content varies from small (3–8%) to large (16–18%) amounts, according to the type of fruit (Josef, 2006). A wide range of dried fruits and vegetables are available in the market in whole, sliced, or ground form. Reduction in moisture during drying of high-moisture materials, 54 Drying of Foods, Vegetables and Fruits
Aware and Thorat - Solar Drying of Fruits and Vegetables like fruits and vegetables, induces changes in shape, density, and porosity. Product quality plays a major role in food drying operation. Upon rehydration, dried vegetables should exhibit desirable sensory and nutritional quality. Numerous processing techniques have been practiced for drying of vegetables. However, it should be noted that water should be removed in such a way that dehydrated products can easily be rehydrated to regain their structure (Jasim, 2011). In fruits and vegetables drying, diffusion transport mechanism has a significant role, especially during the falling rate period, which is controlled by the mechanism of liquid and vapor diffusion. This behavior indicates an internal mass transfer-type drying with moisture diffusion as the controlling step. The water diffusion coefficient reflecting the whole complexity of water transport is referred to as an effective coefficient. Generally, it is difficult to predict the effective mass diffusion coefficient values theoretically; therefore, experimental techniques based on sorption/desorption kinetics, moisture content distribution, or porosity can be used (Bialobrzewski and Markowski, 2004). For vegetables with significantly high moisture content, like celery, it is often assumed that mass diffusion is determined by external conditions of mass transfer. The rate of moisture movement during drying is well described by effective diffusivity (D eff) value (Jasim, 2011). 2.2.1. Fruits Fruits are mainly fleshy and compound in nature with high moisture content (Table 2.1), All these are as follows, Table 2.1. Types of Fleshy fruit and Compound fruit True berry Pepo Hesperidium Aggregate fruit Multiple fruit Accessory fruit Blackcurrant, Redcurrant, Gooseberry, Tomato, Eggplant, Guava, Lucuma, Chili pepper, Pomegranate, Kiwifruit, Grape, Cranberry, Blueberry Pumpkin, Gourd, Cucumber, Melon Blackberry, Raspberry, Boysenberry Orange, Lemon, Lime, Grapefruit Pineapple, Fig, Mulberry, Hedge apple Apple, Rose hip, Strawberry Fleshy fruit, which includes: Berry – simple fruit and seeds created from a single ovary Pepo – Berries where the skin is hardened, like cucurbits Hesperidium – Berries with a rind and a juicy interior, like most citrus fruit Compound fruit, which includes: Aggregate fruit – with seeds from different ovaries of a single flower Multiple fruit – fruits of separate flowers, merged or packed closely together Accessory fruit – where some or all of the edible part is not generated by the ovary Drying of Foods, Vegetables and Fruits 55
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PREFACE Drying using solar radiatio
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Index Chapter No Title / Authors Pa
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Visavale - Principles, Classificati
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