CHICAGO — Microwave reheating of hot dogs for 75 seconds at high power may decrease risks from pathogens that cause foodborne illness, according to a new study from the Journal of Food Science that was published by the Institute of Food Technologists.

Microwave ovens, due to their speed and convenience, are commonly used to cook and reheat food. But these appliances often provide non-uniform heating, which may produce hot and cold spots within food products being heated. As a result, uneven distribution of heat could lead to the survival of pathogens in contaminated food cooked in microwave ovens.

To date, most studies on the effectiveness of microwave oven heating of foods and its control of pathogens have been solely based on heating frozen meals and cooking meat, chicken or fish. Limited or no information is available about the effectiveness of microwave ovens increasing microbial safety regarding chilled leftovers and ready-to-eat meats, such as frankfurters and deli meats.

During the study, researchers evaluated different power and time combinations of microwave oven heating for inactivation of Listeria monocytogenes on inoculated and stored frankfurters. The frankfurters were formulated with and without antimicrobials, inoculated with Listeria monocytogenes and stored under different conditions.

Findings include:

• The highest reductions of Listeria monocytogenes contamination were obtained when frankfurters were reheated at high power for 75 seconds. Standing time after treatment may also play a role in obtaining a more uniform distribution of heat, by conduction, after the microwave power is off and can improve microbial destruction in food.

• Frankfurters formulated with antimicrobials, which inhibited growth of the pathogen during product storage, displayed a decrease in Listeria monocytogenes counts after microwave treatments at high power for 60-75 seconds, regardless of storage time or packaging condition.

• Regarding frankfurters formulated without antimicrobials and in which counts of Listeria monocytogenes steadily increased during product storage, treatments of medium power for 60 or 75 seconds and high power for 30 or 45 seconds were consistently ineffective in decreasing pathogen numbers. The effectiveness of the 75-second, high-power treatment depended on the contamination level of the pathogen on the frankfurters, which in turn, was related to the length of product storage and packaging condition

"Microwave oven reheating instructions must be designed specifically for each type of product and consider variations in microwave appliance power, amount of food to be reheated, age of the product and the presence of antimicrobial compounds in the formulation of the food," said Patricia Kendall, Colorado State University researcher and I.F.T. member expert.