Influence of water activity on inactivation of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in peanut butter by microwave heating

This study evaluated the efficacy of a 915 MHz microwave with 3 different electric power levels to inactivate three pathogens in peanut butter with different a(w). Peanut butter inoculated with Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium and Listeria monocytogenes (0.3, 0.4, and 0.5 a(w)) were treated with a 915 MHz microwave with 2, 4, and 6 kW for up to 5 min. Six kW 915 MHz microwave treatment for 5 min reduced these three pathogens by 1.97 to >5.17 log CFU/g. Four kW 915 MHz microwave processing for 5 min reduced these pathogens by 0.41-1.98 log CFU/g. Two kW microwave heating did not inactivate pathogens in peanut butter. Weibull and Log-Linear + Shoulder models were used to describe the survival curves of three pathogens because they exhibited shouldering behavior. T-d and T-5d values were calculated based on the Weibull and Log-Linear + Shoulder models. T-d values of the three pathogens were similar to D-values of Salmonella subjected to conventional heating at 90 degrees C but T-5d values were much shorter than those of conventional heating at 90 degrees C. Generally, increased a(w) resulted in shorter T-5d values of pathogens, but not shorter T-d values. The results of this study can be used to optimize microwave heating pasteurization system of peanut butter. (C) 2016 Published by Elsevier Ltd.