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

In this study, heating patterns of multiphase foods during combined microwave and ohmic heating were explored. A continuous flow microwave and ohmic combination heater was designed and fabricated. In order to achieve the maximum energy efficiency and heating uniformity, impedance matching of the microwave cavity was carried out by a vector network analyzer and electric field analysis was conducted via simulation (COMSOL 3.5, COMSOL, Inc., Palo Alto, CA) for ohmic heating module. The heating patterns of solid and liquid phases were studied using mixture of carrot particulates in 0.2% NaCl solution as model food. To enhance the handling of solid particles by the pump, 1.5% of carboxymethylcellulose (CMC) was added to the NaCl solution. Temperatures of liquid particles under individual and combined heating modes were investigated and compared. Preliminary experimental data showed that, during microwave heating, solid particles were heated faster than liquid about 8.1 C. On the contrary, solid particles had a thermal lag of 8.0 C as compared to liquid during ohmic heating. When two heating modes were combined, more uniform heating was achieved and there was no significant temperature difference solid and liquid. The findings opened new and very promising opportunities to thermally process particulate foods with improved uniformity, organoleptic, nutritional quality and reduced food safety problems.