Research – A Comparison of Three Methods for Determining Thermal Inactivation Kinetics: A Case Study on Salmonella enterica in Whole Milk Powder

Journal of Food Protection

Different methods for determining the thermal inactivation kinetics of microorganisms could result in discrepancies of the resulting thermal resistance values. This study determined the thermal resistance of Salmonella in whole milk powder using three methods (Thermal death time (TDT) disk in water bath, pouches in water bath, and TDT Sandwich). Samples from three separate production lots of whole milk powder were inoculated with a five strain Salmonella cocktail and equilibrated to 0.20 a w . The samples were then subjected to three isothermal treatment methods at 75, 80, or 85 °C. Samples were taken out at six timepoints and enumerated for survivors. The inactivation data were fitted to two consolidated models consisting of two primary models (log-linear and Weibull) and one secondary model (Bigelow). Normality testing indicated that all the model parameters were normally distributed. None of the model parameters for both consolidated models were significantly different (α=0.05). The amount of inactivation during the come-up time phase was also not significantly different among the methods (α=0.05). In terms of magnitude, however, the TDT Sandwich showed less inactivation during the come-up time phase and overall less variation in model parameters. The survivor data from all three methods were combined and fitted to both consolidated models, with the Weibull having lower root mean square error and a better fit according to corrected Akaike’s Information Criterion. These results suggest that the three thermal treatment methods are not significantly different from each other and are interchangeable, at least in the case of Salmonella in whole milk powder. Comparisons with more methods, other microorganisms, and larger varieties of food products using the same framework presented in this study could provide guidance for standardizing thermal inactivation kinetics studies for microorganisms in foods.

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