A New Automated Microwave Heating Process for Cooking and Pasteurization of Microwaveable Foods Containing Raw Meats

Authors: Huang, Lihan; Sites, Joseph

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2009
Publication Date: 2/1/2010
Citation: Huang, L., Sites, J.E. 2010. A New Automated Microwave Heating Process for Cooking and Pasteurization of Microwaveable Foods Containing Raw Meats. Journal of Food Science. 75:E110-E115.

Interpretive Summary: Escherichia coli O157:H7 is a life-threatening foodborne pathogen that has caused multiple foodborne illness outbreaks in the United States. It can cause foodborne poisoning if not completely inactivated in foods. The objective of this research was to develop a new microwave heating process to ensure the destruction of E. coli O157:H7 in microwaveable foods. If adopted by the industry and consumers, this technology can significantly reduce the incidences of foodborne poisoning caused by microwaveable foods.

Technical Abstract: A new microwave heating process was developed for cooking microwaveable foods containing raw meats. A commercially available inverter-based microwave oven was modified for pasteurization of mechanically tenderized beef, inoculated with Escherichia coli O157:H7 (~ 5 log cfu/g) and packaged in a 12 oz CPET tray containing 150 ml de-ionized water. The new microwave heating system was equipped with an infrared sensor and a proportional feedback mechanism to allow temperature controlled microwave heating. A two-stage heating strategy was adopted to cook the product. In the primary heating stage, the sample surface temperature was increased to an initial temperature set-point (ITSP, 65, 70, 75, or 80C). In the secondary heating stage, the heating was continued with a small fraction of microwave power. The effect of ITSP, hold time (0 to 3 min), and sample elevation (0, 0.03, and 0.07 m above turntable) on inactivation of E. coli O157:H7 and background flora was evaluated. It was observed that only a small number (~ 1.3 logs) of E. coli O157:H7 and background flora were inactivated in the primary heating stage. The elevation 0.07 m, which was in the proximity of the geometric center of the metal cavity, was more effective in inactivating both E. coli O157:H7 and background flora. Substantially more bacteria were inactivated in the secondary heating stage. Complete inactivation of E. coli and background flora was observed with heating at temperatures above 70C for more than 1 min. This study demonstrated a new approach for ensuring the safety of microwavable products containing raw meats.