Modeling the Influence of Macronutrients on the Heat Resistance of Salmonella in Milk Powder

Multiple Salmonella outbreaks linked to milk powders call for the need for effective pasteurization processes. Understanding the thermal inactivation kinetics of Salmonella in milk powder is crucial; however, the influence of macronutrient content (protein, fat, and carbohydrate) on these kinetics remains unclear. This study investigated the effects of common reconstitution temperature (45, 70, and 99 °C) on Salmonella survival in infant milk powder to raise public awareness about contamination risks. Seven milk powders with varying macronutrient compositions were used as model systems. After equilibrating to a uniform water activity (a_w = 0.2), the thermal resistance of Salmonella was determined at 75, 80, and 85 °C. The goodness-of-fit of two primary models (log-linear and Weibull) was compared, and secondary response surface models were developed to predict the combined effects of temperature and macronutrient composition on Salmonella inactivation. Results showed that Salmonella could proliferate or be resuscitated when contaminated milk powder was reconstituted at conventional preparation temperatures (45 °C and 70 °C). Across the seven formulations, Salmonella thermal resistance (D-value) increased with protein content (10.44-90.18%) and decreased with carbohydrate content (0.35-63.24%). A significant protein-temperature interaction was observed, whereby the effect of protein content on the Salmonella D-value decreased as temperature increased from 75 to 85 °C. Fat content did not significantly affect thermal inactivation (p > 0.05). The log-linear model provided a better fit than the Weibull model in this study. Overall, this research quantifies how macronutrient composition impacts Salmonella thermal resistance and offers predictive models to improve pasteurization strategies for milk powder.