ABSTRACT
Processing Parameters ................................................................... 331 12.4 Concluding Remarks ................................................................................... 337 Notations ................................................................................................................ 337 References .............................................................................................................. 338
Drying is used conventionally and effectively to maintain the quality of foodstuffs to acceptable levels (i.e., edible). Dried food particles are usually used as ingredients (spices or dairy powders, etc.) or bulk cooking materials (rice, our, etc.). The major motivation for use of drying as a preservation technique is well understood and is illustrated graphically in Figure 12.1. Sun drying is probably the oldest practice and is still popular in some parts of the world today. Water activity (aw) values are extensively used to predict the stability of foodstuff with respect to microbial growth and enzymatic chemical and physical changes (such as glass transition) that can lead to food degradation during storage (Christian 2000). The water activity of the food system indicates how tightly water is bound, structurally or chemically, in the food matrix (Scott 1957, Labuza 1975). In other words, the water activity of the food describes the energetics of water in a food system, and hence its availability to act as a solvent and participate in chemical or biochemical reactions (Labuza 1977). The quality attributes for dried foods may be appearance related (color in particular), denaturation of proteins leading to solubility problem/textural changes, nutrient deterioration, fat crystallization or recrystallization, mechanical property changes, microbial changes, etc. During the conventional drying at higher temperatures, all the quality attributes are usually deteriorating due to thermal and concentration
effects. Therefore, the fundamental question is as to what is perceived/measured to be a good quality of dried materials. Around the world, traded food materials are usually stored and transported in large quantities in dried solid form. Hence drying plays a key role in our world economy and indeed in our life.
