Purpose: To evaluate the effect of fat on the survival of Salmonella in a whey protein isolate (WPI) model food system at 50, 60,70 and 80°C at water activities of 0.18, 0.26, 0.34, 0.42, and 0.57.
Methods: Peanut oil was homogenized with whey protein isolate to achieve 20 and 50% (w/w) fat concentration and was equilibrated to target water activity levels. A dried cocktail including Salmonella Typhimurium, Tennessee, Agona, and Montevideo was inoculated and treated at 50 and 60°C for up to 28 d and at 70 and 80°C for up to 48 h. Survivors were recovered at various times using supplemented Tryptic Soy Agar. Log CFU/g of surviving Salmonella in 0, 20 and 50% peanut oil at each time point were compared using a two-way ANOVA.
Results: Survival differed with water activity at 70°C and was affected by fat content at 50, 70 and 80°C (P = <0.0001, α = 0.05). At 60°C, survival was not affected by fat content or water activity (P = 0.8253). There was 4.0 log greater survival at 50% fat level compared to no added fat after 48 h at 80°C.
Significance: An understanding of the role of fat in the survival of Salmonella in low-water activity foods will improve the ability to predict and control the behavior of Salmonella in these foods.