Investigation on dielectric heterogeneity and radio frequency differential heating of corn kernels based on multicomponent structure

Germ and endosperm are key components of corn kernels for processing by-products. Knowledge of their dielectric properties is essential for understanding the interaction between corn kernels and electromagnetic fields, and assists in developing RF thermal procedures of high-quality corn kernels. In this study, an impedance analyzer was used to determine the dielectric properties of corn kernel, germ and endosperm with real density. A 27.12 MHz free-running oscillator RF system was preformed to evaluate the temperature evolution of corn kernels with various moisture contents (0.15-0.35 d.b.). Results showed that dielectric constant (e') and loss factor (e") of corn kernel, endosperm and germ increased with increasing moisture content and temperature at 27.12 MHz, which could be quantified by cubic polynomials. e' and e" of germ were much larger than those of endosperm, which was a reasonable explanation that the temperature of germ was higher than that of endosperm. Such preferential heating of germ was most prominent in corn kernels with moisture content of 0.25 d.b. instead of 0.15 d.b. and 0.35 d.b., because the e" of germ was closest to the e". This study of dielectric properties provides a good understanding of the RF heating behavior of corn kernel and its components.