Radio frequency heating of corn flour: Heating rate and uniformity

Non-uniform heating is a major challenge for using radio frequency (RF) heat treatment in pasteurization of low moisture food products. The objective of this study was to evaluate the effect of different electrode gaps, moisture content (MC), bulk density and surrounding materials on RF heating uniformity and rate in corn flour. Additionally, the dielectric and thermal properties of corn flour were determined as affected by MC, temperature (degrees C), and frequency (MHz). Changes in MC, water activity (a(w)) and color in the sample after RF heating were measured to evaluate treatment effect on food quality. A precision LCR meter and a liquid test fixture were used to study DP of the sample at RF frequency ranging from 1 to 30 MHz. The RF heating uniformity and temperature profiles of corn flour as exposed to RF heating were obtained with an infrared camera and a data logger connected to a fiber optic sensor. The DP values increased with increasing MC and temperature, but decreased with frequency. The heating rate increased from 3.5 to 6.8 degrees C min(-1) with increasing MC (from 10.4 to 16.7%), but decreased from 12.7 to 5.2 degrees C min(-1) with increasing electron gap (from 11 to 15 cm). The corner and edge heating were observed at all layers of the samples for all the distances, and the hottest and the most uniform layer were determined as the middle layer at an electrode gap of 15 cm. Glass petri dish provided better uniformity than those of polyester plastic petri dish. Covering by foam led to more uniform RF heating uniformity in corn flour, and better moisture and a(w) distribution. This study provided useful information to develop an effective RF process as an alternative of conventional thermal treatments for pasteurization of low moisture products. Industrial relevance: This paper describes a novel methodology based on Radio Frequency heating to pasteurize food powder while maintaining the quality. The study addresses the ever-increasing global demand from consumers for safe food products.