Modeling the survival of Salmonella in low-moisture foods
Santillana Farakos, Sofia Maria
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Salmonella can survive in low-moisture foods (aw<0.7) for long periods of time. The interaction of cells with water is often related to aw. Little is known about the role of water mobility. The aim of this study was to determine how the physical state of water in low-moisture foods influenced the survival of Salmonella and to use this information to develop mathematical models that predict the behavior of Salmonella in these foods. Whey protein powder of differing water mobilities was produced and equilibrated to various aw levels (<0.6). Powders were inoculated with a four-strain cocktail of Salmonella and stored at temperatures ranging from 21 °C to 80 °C. Survival data was fitted to primary inactivation models. Secondary linear models relating the time required for first decimal reduction (δ) and shape factor values (β) to temperature, aw and water mobility were fit using multiple linear regression. The models were validated in dry non-fat dairy and grain products, as well as low-fat peanut and cocoa products. The Weibull model provided the best description of survival kinetics for Salmonella. Water activity significantly influenced the survival of Salmonella at all temperatures, survival increasing with decreasing aw. Water mobility did not significantly influence survival independent of aw. Secondary models were useful in predicting the survival of Salmonella in various low-moisture foods, providing more accurate predictions for survival in non-fat food. When tested against published literature data, the secondary models were fail-safe and provided acceptable prediction performances. Serotype and product composition showed to be global influencing factors on Salmonella survival. The presence of NaCl did not influence the kinetic parameters for Salmonella in whey protein powder. Significant differences in prevalence were found among Salmonella serotypes surviving storage treatments. The models can quantitatively support a hazard analysis and critical control point system and provide an accurate quantification of the risk of Salmonella in low-moisture foods. Future studies should incorporate compositional factors such as fat content as well as the Salmonella serotype to improve the developed predictive models.