Automatic control of a microwave heating process for in-package pasteurization of beef frankfurters

A microwave heating system equipped with a proportional–integral–differential (PID) control device was developed for in-package pasteurization of ready-to-eat meats. Frankfurters, inoculated and vacuum-sealed in plastic packages, were subjected to microwave or water immersion heating, with the package surface temperature increased to and maintained at 65, 75, or 85 °C, for different periods of time, ranging from 2 to 19 min in total heating time.During microwave heating, the surface temperature of frankfurter packages increased linearly with the heating time until it reached a set point. The concentration of Listeria monocytogenes decreased linearly with heating time. The observed rate of bacterial inactivation was 0.41, 0.65, and 0.94 log (CFU/pk)/min at the surface temperature of 65, 75, or 85 °C. When compared with water immersion heating at the same surface temperatures, the overall rate of bacterial inactivation was 30%–75% higher with microwave in-package pasteurization. This study demonstrated the feasibility of a PID-controlled microwave heating process for in-package pasteurization of frankfurters.