Exploring the heating patterns of multiphase foods in a continuous flow, simultaneous microwave and ohmic combination heater

Abstract

A continuous flow, simultaneous microwave and ohmic combination heater was designed and fabricated to heat treat particulate foods without leaving solids under-processed. Heating uniformity of the combination heater was examined by numerically analyzing the electric field distribution under microwave and ohmic heating. In addition, to minimize the reflection of microwave power, impedance matching of the microwave cavity was conducted with a vector network analyzer. Performance of the heater was studied using food mixtures containing sodium chloride solutions (0.2–0.5%) and carrot particulates. Heating patterns of liquid–particle mixtures were investigated and compared under individual and combination heating modes. Energy efficiencies were also determined for corresponding heating methods. The results showed that maximum solid–liquid temperature differences under microwave and ohmic heating were about 8.1 and 8.0°C, respectively. However when microwave and ohmic heating techniques were applied simultaneously, there was no significant temperature difference between solid and liquid phases. Energy efficiency of combination heating was higher than microwave heating and a maximum increase in energy conversion of 12.8% was obtained. The findings opened new and very promising opportunities to thermally process particulate foods with improved uniformity, organoleptic, and nutritional quality in addition to reduced food safety problems.