Research and optimization on the effect of radio frequency heat treatment on the uniformity of hot air drying of jujube slices

The non-uniformity during the radio frequency (RF)-assisted hot air (HA) drying process can seriously affect the quality of jujube slices, leading to problems such as nutrient degradation, color deterioration, and prolonged processing time. Existing research mainly focuses on the comparative study of the uniformity of material drying after processing by different drying methods, lacking research on the changes in uniformity during the drying process, their influencing mechanisms, and optimization schemes. In this study, coupled models of mass and heat transfer were respectively constructed for four drying processes: HA, RF applied in the early stage (E-HA + RF, 0–1.5h), middle stage (M-HA + RF, 1.5-3h) and late stage (L-HA + RF, 1.5-3h) of HA. By using software such as MATLAB, the non-uniformity coefficient K was introduced to characterize the moisture distribution characteristics of jujube slices. The temperature distribution characteristics of jujube slices were characterized by the "overheated zone" and the temperature rise rate at the center of the jujube slices. After optimizing the radio frequency application mechanism through the coefficient of variation method, the quality indicators were experimentally verified. The results showed that M-HA + RF achieved the best drying effect. Compared with HA drying, the drying time of jujube slices was shortened by 43.75%, ∆E was reduced by 21.3%, and the VC content was increased by 18.6%. This study clarified the uniformity changes in RF-HA drying, their influencing mechanisms and optimization schemes, providing feasible strategies for improving the processing efficiency and product quality of agricultural products.