P2-160 Impact of Temperature Dependence of Water Activity on Salmonella Inactivation in a Multicomponent Food System

Tuesday, July 11, 2017
Exhibit Hall (Tampa Convention Center)
Nathan Anderson , U.S. Food and Drug Administration , Bedford Park , IL
Yuqi Luo , Illinois Institute of Technology , Bedford Park , IL
Elizabeth Grasso-Kelley , Illinois Institute of Technology , Bedford Park , IL
Introduction: Salmonella, which is often inactivated by heat-based processes, has greater thermal resistance at low water activity (aw). Prior research revealed that aw did not change appreciably with increasing temperature in a multicomponent food system formulated with 55.9% fat; however, aw increased in high-protein and high-carbohydrate formulations and decreased in high-fat formulations. Though aw is temperature dependent and impacted by food composition, the influence of these factors on Salmonella inactivation in low aw multicomponent foods is not well understood and often ignored in process validation. 

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.