Effects of high intensity ultrasound on the inactivation profiles of Escherichia coli K12 and Listeria innocua with salt and salt replacers

This study investigated the efficacy of power ultrasound (US) for the inactivation of Escherichia coli and Listeria innocua in the presence of sodium salt and salt replacers. Inoculated bacteria suspensions were treated at ultrasonic frequencies of 33 or 20 kHz alone or in combination, and in the presence of 5% NaCl, 5% KCl or 5% NaCl/KCl. Inactivation curves were fitted to the Weibull and the Biphasic models. The goodness of the fit for each model was evaluated based on R2 and RMSE, while AIC and BIC values were used to choose the best model predictor. The Weibull and the biphasic models showed high regression coefficient (R2 > 0.99) and low RMSE (<0.03) values. According to the results, inactivation up to 6 log for E. coli K12 and to 4 log for L. innocua could be achieved within one hour of ultrasound treatment. However, the presence of NaCl, or its substitution with KCl did not affect the degree of inhibition for both microorganisms. The results of this study suggest that power ultrasound treatment may be employed for the inactivation of microorganisms when low salt or salt substitutes are employed.