Role of moisture content, temperature, and frequency on dielectric behaviour of red lentil and Kabuli chickpea in relation to radio frequency heating

Abstract

Dielectric constant (ε′) and loss factor (ε″) of lentil (grain and flour) and chickpea (split and flour) were determined over four moisture content (MC), seven temperature, and seven frequency using a computer-controlled precision LCR meter built for measurements at low frequencies. Both properties increased with MC and temperature but decreased as frequency increased. The decrease was prominent at high MC and temperature as frequency increased from 5 to 30 MHz for all samples. At 13.56 MHz, penetration depth of lentil grain and flour ranged from 1.77 to 34.25 m and 1.78 to 61.07 m, while for split chickpea and chickpea flour, it ranged from 0.99 to 31.79 m and 1.29 to 105.75 m, respectively. The resulting penetration depth indicated that thick layer of samples can be processed with adequate heating uniformity using radio frequency heating as an innovative option in industrial processing of grains. Regression models generated in this study could be used to predict ε′ and ε″of grains at low frequencies (5 to 30 MHz) and temperature of up to 90°C, and for modeling and simulation of radio frequency heating.