Effect of pH on inactivation of Escherichia coli K12 by sonication, manosonication, thermosonication, and manothermosonication.

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.