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. Published by Elsevier Ltd.