The objective of this study was to evaluate the effects of ultrasound on the number of Escherichia coli O157:H7 and vegetative cells of Bacillus cereus in brining and beef during the curing processing. The mechanisms of the inactivation for the pathogens were preliminarily explored. The ultrasound intensity (2.39, 6.23, 11.32 and 20.96Wcm-2) and sonication time (30, 60, 90 and 120min) at 10°C were assessed in brine and meat. Plate count data indicated that 20.96Wcm-2 for 120min was the optimal treatment for bacterial reductions. E. coli O157:H7 was more susceptible to ultrasonic treatment in the first 30min than B. cereus in brine. However, a similar reduction percentage with around 40% in both cultures could be achieved when sonicated for 120min. Good fitness of Weibull model (R2>0.98; RMSE<0.12) was obtained with the distinct shape of the curves which predicted microbial inactivation by ultrasound in salt solution (6%). The production of hydrogen peroxide in brine by ultrasound confirmed the effects of ultrasound on the inactivation of microorganisms during the curing processing. The particle size distribution of bacterial and cell fluorescence staining analysis showed that ultrasound could result in the formation of cell fragments through destroying the integrality of the membrane of E. coli O157:H7 and B. cereus. However, the promoting effect of ultrasound on the number of bacteria in beef suggested that the sanitation conditions of equipment and raw meat must be paid attention when applying ultrasound for curing procedure.
Keywords: Bacillus cereus; Cell particle size distribution; Escherichia coli; Hydrogen peroxide; Ultrasound; Weibull modeling.
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