Development of a dual cylindrical microwave and ohmic combination heater for minimization of thermal lags in the processing of particulate foods

- A microwave and ohmic combination heater was designed for uniformity heating.
- There were found few typical cold or under-processed spots in particulate foods.
- Controllable ranges of key parameters was formulated using the graphical model.

Dual cylindrical microwave chambers equipped with ohmic heating tubes were designed to maximize the electric field strength for thermal treatment of particulate foods. Temperature profiles of particle-liquid mixtures containing sodium chloride solution (Cs, 5-20 g/L), chicken, and potato particulates at different mass fractions (Mf, 10-15 g/100 g) were collected and compared for individual and combination heating modes. Results indicated that particle size (Sp, 0.5 and 1 cm cubes) and salt concentration affected temperature variations between solution and particulates in ohmic heating. For microwave heating, the solution temperature lagged behind the particle temperature up to 12.5 g/L salt concentrations, regardless of particle size and mass fraction; however, an opposite tendency was observed in the food mixtures including 20 g/L salt concentration. The maximum temperature differences between particles and solution obtained by individual microwave and ohmic heating were 7.1 ± 1.7 and 11.9 ± 2.9 °C, respectively, while the combination heating exhibited little significant temperature gaps (maximum difference < 3.08 °C) at 12.5 g/L salt concentrations. 3D block diagrams constructed using the controllable ranges of Cs, Sp, and Mf estimated by empirical equations could be used to describe temperature similarities between particles and solution when the combination heating was applied.