Purpose: To determine the influence of food composition and temperature dependence of aw on thermal resistance of Salmonella in a multicomponent food system.
Methods: Food matrices, comprised of rice flour, soybean oil and soy protein powder, were formulated to contain high-carbohydrate (67.3%), high-protein (85.8%) and different levels (55.9% and 87.0%) of fat content. Each matrix was inoculated with Salmonella Agona then stored under controlled humidity to equilibrate aw. Samples, ~0.7g, were loaded into aluminum test cells, which were heated at 85oC in a water bath. Samples were cooled, diluted in buffered peptone water, and enumerated on tryptic soy agar supplemented with yeast extract. D-values were calculated and results analyzed by t-test.
Results: Thermal resistance of Salmonella was lower in formulations where aw increased and higher in the formulation where aw decreased at elevated temperature. D-values for Salmonella in the high-carbohydrate and high-protein formulations (3.09±0.11 min and 3.13±0.10 min) were significantly lower (p<0.05) than in the 55.9% fat matrix (7.22±0.31 min). The D-value of Salmonella in the 87% fat formulation (11.08±0.36 min) was significantly higher (p<0.05) than in other formulations.
Significance: Since significantly higher D-values for Salmonella in low aw foods may result at elevated temperature, food composition and temperature dependence of aw should be considered when validating thermal inactivation processes.