Purpose: To evaluate the effects of rehydration on survival rates and heat resistance of S.enterica serotypes in PB.
Methods: Relative heat resistances of serotypes S. Typhimurium, S. Enteritidis and S. Tennessee were compared individually and as a 3-strain cocktail at 90°C and 126°C in two PB formulations adjusted to aw 0.2, 0.4, 0.6 and 0.8. Scanning electron microscopy was used to monitor morphological changes of cells in peanut oil. D-values were calculated using Bigelow model and compared using ANOVA.
Results: Increased aw in PB significantly reduced the heat resistance of desiccation-stressed cells treated at 90°C (P < 0.05). Differences in heat resistance were observed among the three serotypes and between the two PB formulations. When treated at 126°C, differences in heat resistance among different serotypes and adjusted water activities were less notable (P > 0.05). Based on the Weibull model, an average of 52-132 min was required to achieve a 5-log reduction of the 3-strain cocktail at 90oC in PB with aw of 0.2. When aw was increased to 0.6, only 23-27 min was required to achieve the same 5-log reduction. Under scanning electron microscope, minor morphological changes were apparent in cells during desiccation and rehydration processes in peanut oil having a similar aw to that of PB.
Significance: Results from this study collectively suggest that water activity plays a key role in determining S. enterica heat resistance in PB. The variability of heat resistance among different serotypes, PB formulations and water activities should be taken into consideration for developing and validating effective intervention and mitigation strategies.