Improving radio frequency heating uniformity in cauliflower by changing density in different zones

Radio frequency (RF) treatment is one of the most promising approaches for disinfesting, drying, and pasteurizing agricultural products. However, the inhomogeneous heating of RF treatment is the primary barrier for practical applications. To improve the RF heating uniformity, a 27.12 MHz, 6 kW pilot-scale RF system was applied to heat the cauliflower by changing its density in different zones of a rectangular container. The results proved that the RF heating rate and the average mass change rate of the cauliflower decreased with increasing electrode gap and bulk density of the cauliflower. The RF heating uniformity of the cauliflower was improved by increasing the electrode gap and the bulk density of the cauliflower during RF heating. With increasing of the bulk density of sample at the edges in the container, the RF heating rate and heating uniformity index of the sample firstly decreased and then increased when the sample density at the center and the corners were 405.5 and 516.8 kg/m3, respectively. The mass change rate of the sample presented an inverse relationship with the heating rate and heating uniformity index during RF treatment. The best heating uniformity and highest mass change rate were obtained when the bulk density of the cauliflowers at the center, edges, and corners in the container was 405.5, 461.1, and 516.8 kg/m3, respectively. The results of this study can offer effective method for improving the RF heating uniformity in high moisture products.