Although the conventional techniques used for food drying are well established, there is still need to develop new and innovative drying techniques (Kudra and Mujumdar, 2009; Mujumdar and Wu, 2008). Major reasons to trigger attempts for development of advanced drying techniques are: making the process cost effective, reducing the energy consumption, intensifying the drying rates (in turn reducing the size of the dryer required), improving the quality of dried food products, reducing the carbon foot print, increasing safety in operation and making the drying process easy to control.
There are few facts that need to be highlighted with respect to food products. The drying of fruits mainly falls in the falling rate period hence it becomes a diffusion control process. However, higher temperatures cannot be implemented to enhance diffusion which may lead to thermal deterioration of the product. Higher temperature can also lead to unacceptable quality changes such as case hardening, flavor loss, nutritional loss and color degradation.
Presence of microorganisms in drying medium can also lead to unfavorable quality of dried product; hence it needs to be filtered before using for drying. Freeze drying Jangam, Mujumdar – Basic Concepts and Definition Drying of Foods, Vegetables and Fruits 25 is the best way to dehydrate most of the food products; however, it is associated with tremendous cost and cannot be applied for low value fruits and vegetables. Loss of volatiles is another important issue in drying of high valued fruits, spices, etc and needs to be handled properly but in a cost effective manner.
There have been numerous efforts from all around the world to come up with new ideas to achieve aforementioned goals in an innovative way. Table 1.8 summarizes some of the advanced drying techniques developed for food products with their advantages and limitations. Some of these techniques will be discussed in detail in the chapters to follow.
However, all the advanced techniques will not be covered as the main aim of the book is to provide knowledge about food drying to the readers from developing and underdeveloped countries where applying some of these techniques may not be feasible. Kudra and Mujumdar (2009) have discussed most of the new and advanced drying concepts, many of which are still at the laboratory and pilot scale.
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