Relative Survival of Four Serotypes of Salmonella enterica in Low-Water Activity Whey Protein Powder Held at 36 and 70℃ at Various Water Activity Levels

摘要

Salmonella enterica is not able to grow at water activity (a_w) levels below 0.94, but it can survive in low-a_w foods for long periods of time. Temperature, a_w, substrate, and serotype affect its persistence. The aim of this study was to evaluate the influence of temperature and a_w on the relative persistence among four serotypes of Salmonella enterica in low-a_w whey protein powder. Whey protein powder was equilibrated to a_ws 0.18 ± 0.02 and 0.54 ± 0.03, inoculated with a cocktail of Salmonella serovars (Agona, Tennessee, Montevideo, and Typhimurium), vacuum sealed, and stored at 36℃ for 6 months and at 70℃ for 48 h. Presumptive Salmonella colonies (30 to 32) were randomly picked from each plate at the end of each survival study. PCR multiplex serotyping was used to identify the isolates. A multinomial mixed logistic model with Salmonella Tennessee as a reference was used to test for significant differences in frequency distribution of the surviving serotypes. Salmonella Tennessee and Salmonella Agona were the most prevalent surviving serotypes, followed in decreasing order by Salmonella Montevideo and Salmonella Typhimurium. Statistical analysis indicated that temperature (P = 0.003) and a_w (P = 0.012) influenced the relative prevalence of the Salmonella serotypes. If other environmental conditions are equal, Salmonella Tennessee is better able to survive than Salmonella Montevideo and Salmonella Typhimurium at higher temperatures and higher a_w levels in low-a_w whey protein powder held at 36 and 70℃. The relative prevalence of Salmonella Agona to Salmonella Tennessee did not change with increasing temperature (P = 0.211) or a_w (P = 0.453). These results should be considered in risk assessment and when developing predictive models for survival of Salmonella in low-a_w, foods.