Improving radio frequency (RF) heat treatment performance of peanuts based on dielectric loss mechanisms and frequency coupling

Abstract

Radio frequency (RF) technology is being recognized and widely used in food, chemical industries due to its efficiency and sustainability. Revealing the dielectric loss mechanisms is crucial to improving energy utilization in food, especially moisture-induced ionic loss. In this study, the dielectric loss mechanism of peanut was analyzed using the Debye model, and then the conversion efficiency of RF energy was investigated at various moisture contents, loss tangents and frequencies. The results indicated that protein, fat, and sucrose exhibited typical polar losses but with lower loss intensities, and the free-water induced ionic conductivity loss was the dominant factor affecting changes in the dielectric loss tangent. Multi-physics field simulation results showed that: the heating rate decreased from 3.97 °C/min to 1.01 °C/min when the initial moisture content was constant but the loss tangent increased from 1 to 7. Combined with the electromagnetic loss density analysis, maximum electromagnetic-thermal conversion efficiency was achieved with a loss tangent close to 1. Additionally, samples with lower dielectric constants reduced the attenuation effect on electric field intensity, thereby increasing the heating rate. Furthermore, since ideal RF heating performance was difficult to achieve at 13.56 MHz and the lower penetration depth at 40.68 MHz limited loading, 27.12 MHz was deemed more suitable for peanut RF heating treatment. This research provides a theoretical foundation for improving the performance of RF heating by considering sample dielectric loss and RF frequency selection.