Effects of Microwave Power Level and Time on Escherichia coli P511 in Microwavable Foods

Introduction: Microwave heating utilizes electromagnetic waves of certain frequencies to produce heat energy in food materials while minimizing thermal degradation of the food components. Using proper microwave heating techniques (i.e., correct power level and time) microwave heating has potential in inhibiting foodborne pathogens.

Purpose: It is the purpose of this study to determine the survivability of Escherichia coli P511 after microwave treatments. 

Methods: Microwavable foods were microwaved with different treatments at 270 W for 60 s, 950 W for 150 s and 300 s. Twenty-five g of the treated samples were tested for total coliform counts, aerobic plate counts, presumptive coliform test, E. coli and Salmonella. Survivability (challenge tests) of E. coli P511 were determined in microwavable food samples at 300, 600 and 900 W at 60, 90, 120, 150 and 180 seconds.

Results: Total bacterial count for all microwavable food samples were below detection limit. Challenge tests showed that the microbial count of E. coli P511 can be reduced from an initial 9.47 log CFU/g to 2.67 log CFU/g at 600 W for 120 s with an average internal temperature of 60.09±0.82°C. E. coli counts were reduced to below detection limit when treated at 600 W for 150 s and 900 W for 90 s with an average internal temperature of 68.20±2.92°C and 65.44±3.56°C. Microwave power level at 300 W and 180 s were not sufficient to inhibit the growth of E. coli and the average internal temperature was 52.21±3.63°C. 

Significance: Microwave heating show potential in decontaminating microwavable food at high power level and short treatment time and can be applied as part of the hurdle technology in food industry to inhibit foodborne pathogens.