Air drying is the most commonly employed commercial technique for drying food and chemical products. The basic objective in drying of food products is to removing water in the solids up to a certain level, at which microbial spoilage is minimized.The product quality is strongly affected by the conditions of drying. Thermal damage incurred by a product during drying is directly proportional to the temperature and time.The high temperature and long drying time associated with conventional hot air drying often causes heat damage and adversely affects texture, color,flavor and nutritional value of products.The loss of nutritional quality during processing and storage of foods has become an important problem. Since
the discovery of the basic vitamins and their many forms, efforts have been made to retain them in foods during post-harvest handling, commercial processing,distribution, storage and preparation.