Effect of surrounding medium on radio frequency (RF) heating uniformity of corn flour

Abstract

Radio frequency (RF) heat treatment holds great potential for packaged food powder pasteurization by providing rapid and volumetric heating with a high penetration depth. Edge and corner overheating create high temperature differences throughout the product, which is a major drawback in its industrial applications. In this study, the effect of the surrounding media (air, DI water, and soybean oil), medium level, heating mode, electrode gap, and heating time on the heating uniformity was investigated by determining the thermal distributions, heating uniformity index, and heating rate at the top and middle layers of RF heated corn flour. The thermal images indicated that less edge and corner overheating occurred when corn flour container was immersed in soybean oil. A higher heating rate (7.77 and 9.86 °C/min at the top and middle layers, respectively) and a better heating uniformity (as indicated by lower heating uniformity indices: 0.047 and 0.037 at the top and middle layers, respectively) were obtained for the corn flour heated in soybean oil with an 11 cm electrode gap compared to those heated in air. The study proposed a method for improving the heating uniformity of RF heated food powders which can be easily implemented in industrial applications of RF treatment.