Purpose: Research was performed to test the survival of several serotypes of Salmonella in low moisture foods at various temperatures.
Methods: The serotypes used (Salmonella Agona, Salmonella Montevideo, Salmonella Tennessee, Salmonella Typhimurium phage type 42, and Salmonella Weltevreden) were associated with outbreaks in low moisture foods. Dried carrots, dried onions, black pepper, and flour samples were inoculated and stored at 25°C, 35°C, and 42°C. For ten weeks, samples were plated weekly on XLD agar.
Results: Salmonella in low moisture foods generally demonstrates biphasic death curve; an initial exponential reduction which tapers off over time. This trend was observed with samples stored at 25°C. The survival of samples stored at 35°C varied depending on the product. Onion and flour samples showed the expected biphasic trend, while the pepper and carrot samples did not. Carrot and pepper samples stored at 35°C showed a greater reduction of 6 logs in the thirty days compared to the onion and flour samples, which showed a 4-log reduction in thirty days. This more rapid decrease continued until no growth occurred at the limit of detection (< 5 CFU/g). All products held at 42°C fell below the limit of detection before samples at other temperatures. A 7-log reduction for samples held at 35°C and 42°C was observed. Once a sample fell below the limit of detection, a qualitative ELISA test showed the presence of Salmonella in the samples.
Significance: These results question the biphasic model of survival of Salmonella in some low moisture foods at varying temperatures.