Inactivation kinetics of inoculated Escherichia coli and Listeria innocua in fresh-cut Chinese cabbage using sweeping frequency ultrasound

Sweeping frequency ultrasound washing is a recent technology of applying varying ultrasound frequencies in the decontamination of fresh produce. Ultrasound inactivation of Escherichia coli and Listeria innocua inoculated on fresh-cut Chinese cabbage was investigated at sweeping frequencies of 28 +/- 2 to 68 +/- 2 kHz for washing time of 5-40 min. The survival ratio of E. coli and L. innocua decreased with the time of exposure to ultrasound washing and varying frequencies. E. coli were more sensitive to ultrasound washing than L. innocua, achieving >3.0 log reductions after 10 min of washing with 40 +/- 2 kHz. A nonlinear Weibull model was used to describe the experimental data, and the fitness of the model was evaluated by the coefficient of determination (R-2) and the root mean square error (RMSE). The model used provided a good fit with R-2 >= .98 for both bacteria and RMSE values in the range of 0.03-0.21 and 0.02-0.32 for E. coli and L. innocua, respectively. Practical Application Ultrasound decontamination is an alternative nonthermal technology that has been applied in recent years to improve the microbial safety of fresh produce. The bacterial inactivation is predominantly attributed to cavitation, an occurrence that interrupts cellular arrangement and function. With the known significance of sanitization in the processing of vegetables, it is imperative to develop and appraise novel approaches that contribute to the microbial safety of these fresh produce. Largely, the results of our study could guide the design of new ultrasonic fresh produce wash systems in addition to current industrial practice related to frequency selection and use of ultrasound during fresh produce sanitation.