Purpose: The purpose of this study is to evaluate the response of Salmonella enterica to two stressors commonly encountered in low-aw food processing, desiccation and heat.
Methods: Five serotypes of S. enterica were desiccated in three food matrices with varying aw: peanut oil (aw = 0.560), peanuts (aw = 0.330) and chia seeds (aw = 0.585) to identify survival characteristics in low-aw environments. Oil-desiccated cells were subsequently used in heat experiments to identify cross-protective mechanisms. In these assays, tolerance to lethal heat at 70°C following six-day oil desiccation was evaluated. Survival at 70°C following exposure to a sub-lethal heat of 45°C was also assessed.
Results: S. enterica exhibited serotype-specific differences in survival capabilities in the low-aw foods. Serotypes Hartford and Tennessee demonstrated an aggressive phenotype across all three low-aw foods, while Typhimurium was identified as the least aggressive serotype. Interestingly, persistent serotypes survived to upwards of 90 days in peanut oil. Exposure to 70°C following six-day oil desiccation revealed significantly (P < 0.05) higher concentrations in all serotypes compared to non-desiccated controls. Moreover, significantly (P < 0.05) higher concentrations were observed following pre-adaptation to 45°C.
Significance: These results indicate that S. enterica is capable of long-term desiccation in low-aw foods and can lead to enhanced resistance to heat treatments. These are problematic to the food industry, which often use these two hurdles in tandem to reduce Salmonella contamination.