Evaluation of non-isothermal inactivation on survivals of pathogenic bacteria by predictive models

Abstract

This study was conducted to examine thermal resistances of Escherichia coli O157:H7, Cronobacter sakazakii, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes upon exposure to non-isothermal inactivation at various heating rates (HRs) between 1.0 degrees C and 9.0 degrees C/min. Bacterial cultures were re-suspended in tryptic soy broth without dextrose and treated with non-isothermal inactivation processing (to maximally 60 degrees C) at different HRs. Predictive models were used to determine fundamental kinetic parameters that describe characteristic behaviors of these bacteria under dynamic environments. At a HR of 9.0 degrees C/min, viable numbers of these organisms declined below the detection limits (< 1.0 log CFU/ml). In contrast, E. coli O157:H7, C. sakazakii, and S. Typhimurium survived at levels of < 2.5 log CFU/ml at HRs of 1.5-6.0 degrees C/min. Under non-isothermal processing, the thermal tolerances increased with slow HRs. Lag time (LT) and delta from the modified Gompertz and the Weibull survival functions were significantly (p < 0.05) higher at the lower HRs. The Weibull distribution showed reliable goodness-of-fits ranging from 0.889 to 0.999, indicating that this equation model was shown to be effective in predicting survival kinetics of these bacteria under non-isothermal inactivation conditions at different HRs. In conclusion, slow HRs resulted in higher thermal tolerances of these bacteria under non-isothermal processing.