Submitted to: Journal of Food Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2006
Publication Date: 10/1/2006
Citation: Huang, L., Sites, J.E. 2006. Automatic control of microwave heating for in-package pasteurization of beef frankfurters. Journal of Food Engineering. 80:226-233.
Interpretive Summary: Listeria monocytogenes is a life-threatening foodborne pathogen frequently complicating ready-to-eat (RTE) foods in U.S. A new technology was developed in this research using an automatically controlled microwave heating process to kill this organism in RTE frankfurters. This study demonstrated that microwave heating can kill L. monocytogenes at a faster rate than water immersion heating, but would lead to slight changes in the physical dimension. If further developed, this technology may be used in the food industry to reduce or eliminate the risk of foodborne listeriosis.
Technical Abstract: 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, surface-inoculated with a 4-strain cocktail of freshly grown and harvested Listeria monocytogenes and vacuum-sealed in plastic packages at a level of approximately 9 log(CFU) per package, were subject to microwave heating or water immersion heating with the package surface temperature increased to and maintained at 65, 75, or 85C, for different periods of time, ranging from 2 to 19 min in total heating time. Results indicate that the surface temperature of frankfurter packages increased linearly with heating time until it reached a set point during PID-controlled microwave heating. The concentration of L. monocytogenes in frankfurter packages decreased linearly with heating time under a constant surface temperature. The observed rate of bacterial inactivation during microwave heating was 0.41, 0.65, and 0.94 log(CFU/pk) per min at the surface temperature of 65, 75, or 85C. When compared with water immersion heating at the same surface temperatures, the overall rate of bacterial inactivation was 30-75 percent higher with microwave in-package pasteurization. Although microwave heating may be more effective in killing L. monocytogenes in frankfurter packages, product deformation due to shrinkage in the longitudinal direction and expansion in the radial direction, both by approximately 10 percent, was observed in the microwave-treated frankfurters. However, this study demonstrated the feasibility of a PID-controlled microwave heating process for food pasteurization. When further developed, this technology may be used to pasteurize foods and eliminate foodborne listeriosis caused by ready-to-eat meats.