Effect of pH on Inactivation of Escherichia coli K12 by Sonication, Manosonication, Thermosonication, and Manothermosonication

Abstract

The effect of pH on inactivation of Escherichia coli K12 by sonication at 100 kPa/40 degrees C, manosonication (MS) at 400 kPa/40 degrees C, thermosonication (TS) at 100 kPa/61 degrees C, and manothermosonication (MTS) at 400 kPa/61 degrees C at acoustic energy density of 3 W/mL and 6 W/mL was investigated. Five linear and nonlinear kinetic models were used to examine the inactivation kinetics. At all pH levels, the inactivation rates of E. coli K12 in a buffer by TS and MTS were significantly higher than those by sonication and MS. A 5 log reduction of E. coli K12 population by TS and MTS was achieved in 0.5 and 0.25 min, respectively. With an initial count of 10(8) CFU/mL, no colonies were detected at pH 3 after a 0.25-min MTS treatment. The lethal effect of MTS was enhanced at low pH (pHs 3 and 4), whereas at nonlethal temperature of 40 degrees C, no increased killing was observed. Regardless of pH, the treatment by MTS, TS, and MS exhibited a rapid initial reduction followed by tailing-off on the inactivation curves. The biphasic linear, log-logistic, and modified Gompertz kinetic models allowed better fitting of the inactivation data for MTS, TS, and MS treatments than the 1st-order and Weibull models. The survival counts of sonication-treated E. coli K12 at all pH levels fitted well to a 1st-order kinetic model.