Suitability of ccRSM as a tool to predict inactivation and its kinetics for Escherichia coli, Staphylococcus aureus and Pseudomonas fluorescens in homogenized milk treated by manothermosonication (MTS)

The application of ultrasound (US) technology (i.e. sonication) has been used as an alternative to thermal technologies to reduce the microbial population of foods and beverages. This approach can be used on its own or combined with pressure and temperature (i.e. manothermosonication (MTS)). Microbial inactivation kinetics by sonication remains unclear. In the present study, a central composite response surface model (ccRSM) was used in order to study the effects of temperature (20-52°C), acoustic intensity (60-120W/cm²) and treatment time (40-240s) at a constant pressure (225kPa) by MTS processing on microbial inactivation. Reductions of up to c. 1.6logCFU/ml were achieved for Escherichia coli and Pseudomonas fluorescens. Lower inactivation values were reported for Staphylococcus aureus (1.05logCFU/ml). These inactivation values were achieved using conditions of 36°C, 90W/cm² and 240s. Inactivation of E.coli by MTS (R²=0.90) was described by an exponential curve, whereas inactivation of S.aureus and P.fluorescens by MTS (R²≥0.73) were described by a linear trend. The coefficient of determination values were obtained following validation between the theoretical model and the experimental values. Statistical analysis showed that treatment time was the factor with greatest influence on microbial inactivation for all three microorganisms. The present study confirms the suitability of using ccRSM as a tool for investigating and predicting the inactivation of E.coli, S.aureus and P.fluorescens as a function of temperature, acoustic power and treatment time, and may also be useful for predicting inactivation of other microorganisms commonly found in raw milk.