| Salmonella, which is often been inactivated by heat-based processes in the food industry, has greater thermal resistance at a lower water activity (aw). Scientists slowly discover a shallow understanding that aw is temperature dependent and may effect by macronutrients. However, these influences on Salmonella inactivation in low aw multicomponent foods is not well understood and often been ignored in process validation. This thesis project initiated with an objective to determine the influence of macronutrient composition and temperature dependence of aw on thermal resistance of Salmonella in a multicomponent food system.;Food matrices, comprised of rice flour, soybean oil, and soy protein powder, were formulated to contain different levels of carbohydrate, protein and fat content, respectively. Moisture equilibrated food matrices were then been put into a conventional oven for heat treatment, while the high-temperature sensor was monitored aw changes.;Salmonella inactivation has validated with selected food matrices based on water activity changes during the elevated temperature. Each matrix was been inoculated individually with Salmonella Agona inoculum and then stored under controlled humidity to equilibrate a w. Samples, ~0.7g, were loaded into aluminum test cells and thermally treated at 85 °C in a water bath then immediately cooled in ice water before diluted in BPW broth and enumerated on TSAYE. Enumeration data was then used to calculate as D-values and Weibull model and results analyzed by t-test.;Results from water activity measurement revealed that in this multicomponent food system aw did not change appreciably with increasing temperature when formulated at 55.9% fat. However, aw increased in high-protein and high-carbohydrate formulations and decreased in high-fat formulations. At food matrix with 55.9% fat content, the D-value was 7.22 +/- 0.31 min. As expected, D-values for high-carbohydrate and high-protein formulations (3.09 +/- 0.11 min and 3.13 +/- 0.10 min) were significantly lower (p < 0.05), while a significantly higher D-value of 11.08 +/- 0.36 min (p < 0.05) was observed for the high-fat formulation.;Because aw is typically measured at 25°C, lethality may be overestimated since significantly higher D-values for Salmonella at elevated temperature result in foods that contain a high percentage of fat. Thus, matrix composition and temperature dependence of aw should be considered when validating thermal inactivation processes for low aw foods. |
