Dielectric properties directly influence microwave drying characteristics of food products. A knowledge ofdielectric properties of foods as a function of moisture content and temperature is essential in the design and control ofmicrowave drying systems. Dielectric constant and loss factor of Red Delicious apples (Malus domestica Borkh.) weremeasured over a moisture content range of 4% to 87.5% at 22C and 60C. At high moisture content (>70%), free waterdispersion and ionic conduction accounted for the dielectric behavior. At medium moisture (23%), ionic conduction playeda major role. At low moisture contents (4%), bound water accounted for the major dispersion mechanism. A decrease inmoisture content resulted in a decrease in and . Based on this study, we expect a strong moisture leveling effect whendrying apples from 50% to 4% at elevated temperatures in 915 MHz or 2.45 GHz microwave drying systems.
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Feng et al. (2002) studied this question.