Inactivation of Staphylococcus aureus and Escherichia coli O157:H7 under isothermal-endpoint pressure conditions

Temperature variations during high pressure processing (HPP) can induce uncertainty in process characterization, particularly for determination of microbial inactivation kinetics. Ultra-high temperature (UHT) whole milk inoculated with Staphylococcus aureus ATCC 12600 or Escherichia coli O157:H7 ATCC 43895 was exposed to 600 MPa at 4, 21 and 45 °C. An isothermal-endpoint HPP procedure led to constant process temperature during pressure increase and so minimized temperature change involved in HPP. Three nonlinear models: the Weibull, log-logistic and modified Gompertz methods, were fitted to survival data. Goodness-of-fit of these models were compared using mean square error. Overall, S. aureus and E. coli O157:H7 showed less inactivation at 4 °C than at 21 and 45 °C. The log-logistic model was a better fit for E. coli O157:H7 inactivation data. In contrast, either the modified Gompertz or the Weibull models, depending on the process temperature, were more appropriate to describe S. aureus inactivation.