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 aw. Peanut butter inoculated with Escherichia
coli O157:H7, Salmonella enterica serovar Typhimurium and Listeria monocytogenes (0.3, 0.4, and 0.5 aw)
were treated with a 915 MHz microwave with 2, 4, and 6 kWfor 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 0.41e1.98 log CFU/g. Two kW microwave
heating did not inactivate pathogens in peanut butter. Weibull and Log-Linear þ Shoulder models were
used to describe the survival curves of three pathogens because they exhibited shouldering behavior. Td
and T5d values were calculated based on the Weibull and Log-Linear þ Shoulder models. Td values of the
three pathogens were similar to D-values of Salmonella subjected to conventional heating at 90 C but T5d
values were much shorter than those of conventional heating at 90 C. Generally, increased aw resulted in
shorter T5d values of pathogens, but not shorter Td values. The results of this study can be used to
optimize microwave heating pasteurization system of peanut butter