Developing a rotation device in radio frequency systems for improving the heating uniformity in granular foods

A major obstacle for industrial radio frequency (RF) treatments is non-uniform and thermal runaway heating. This study aimed to improve the RF heating uniformity in granular products using a rotation device with sample mixing. After the run-out error of the rotation device met the allowable tolerance range, the RF heating uniformity was evaluated for mung bean, coix seed, peanut kernel and almond kernel under different rotating speeds, volume ratios and moisture contents (MCs). The results showed that the RF heating uniformity index decreased and then increased with increasing rotation speed, whereas the volume ratio presented the opposite effect. The RF heating uniformity index raised with increasing MCs. The heating uniformity in mung beans was the best because of their smallest particle size among the four selected samples. Therefore, the laboratory-scale rotation device applied in the RF system could provide a solid foundation for further large-scale industrial applications. •A rotation device in RF systems was developed to improve the sample mixing.•RF heating uniformity was evaluated for 4 granular products.•The heating uniformity index decreased with decreasing moisture content and particle size.•Best heating uniformity was obtained at rotating speed of 16 r/min and volume ratio of 75% for coix seed.