Dehydration is a versatile, widespread technique in the food industry; it is the oldest and most frequently used method of food preservation. The main objective of drying is the removal of moisture so as to reduce the water activity and hence the associated microbial and enzymatic activity and product quality deterioration. Drying methods have been applied to extend the shelf life of the product; however, they often affect the quality of the final product.
The most common quality defects associated dehydrated products are poor reconstitution, loss in texture, loss in the nutritive and sensory properties such as flavor and color. These are mainly due to the exposure of the product to high temperatures and long drying times mostly in the presence of air (Lenart, 1996; Lin et al., 1998). A new interest has recently arisen in finding new ways to improve the quality of dried food products.
Many alternatives have been recognized such as the use of vacuum so that lower temperatures could be used, use of freeze drying which is done under conditions below the triple point of water facilitating sublimation thereby protecting the product texture and other quality factors, use of rapid drying techniques which would reduce the drying time, use of novel heating sources like microwave and radio frequency heating (significant reducing in drying time), use of various treatments which promote better mass transport phenomena etc.
Osmotic dehydration is acknowledged to be an excellent energy saving method as moisture is efficiently removed from a food product without a phase change (Bolin et al., 1983). Since the water activity of the product is decreased, microbial growth is largely inhibited. However, the product is not shelf-stable since relatively large proportion of moisture still exists (up to 50%).
The main theme of Dehydration
Additionally, complementary treatments such as freezing (Tregunno and Goff, 1996), freeze drying (Donsì et al., 2001), vacuum drying (Rahman and Mujumdar, 2007), air drying, osmo-convective drying (Islam and Flink, 1982; Corzo et al., 2008) and microwave drying (Orsat et al., 2007) are necessary in order to provide shelf stability to the product.
Osmotic dehydration is a time-consuming process; therefore, supplementary methods are needed to increase the mass transfer without affecting the product quality (Rastogi et al., 2002). One of the distinctive aspects of osmotic dehydration in compar- Azarpazhooh, Ramaswamy.
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