Effect of microwave drying on the dielectric properties of Jiangnan rice cakes

Jiangnan rice cakes were used as the object in this study, and a network analyzer was used to determine the effects of frequency (915~2450 MHz), moisture content of rice cakes (16~48%), and temperature (25~60) on the relative permittivity Ε' and dielectric loss factor Ε. The microwave penetration depth was calculated and the impacts of frequency, moisture content, and temperature on the microwave penetration depth were analyzed. A relationship model between dielectric parameters of rice cakes and the main factors at some frequencies was established to examine the accuracy and feasibility of moisture content prediction based on the dielectric parameters. The results showed that in the frequency range of 915~2450 MHz, Ε' of rice cakes decreased and Ε increased with increasing frequency; both Ε' and Ε increased with increasing moisture content, but decreased with increasing temperature. The value of energy penetration depth decreased with increasing moisture and frequency, and increased with increasing temperature. The relationship between dielectric parameters and the main influencing factors could be described by binary cubic functions, and the coefficients of determination of all models were greater than 0.99. These findings would have an important guiding significance on understanding the dielectric properties of rice cakes and developing moisture detectors. © 2015, Editorial Board of Modern Food Science and Technology. All right reserved.