Purpose: The aim of this study was to determine the heat resistance, decimal reduction times (D-values), and thermal resistance constants (z-values) for Escherichia coli AW1.7 and Salmonella enterica ATCC 43845 in ground beef.
Methods: Ground beef was inoculated (107/g) with E. coli AW1.7 or Salmonella enterica ATCC 43845, formed into patties (200 g), and cooked to an internal temperature of 71°C. After heating, samples were immediately cooled on ice and plated onto LB agar for enumeration of cells. Inoculated ground beef (10 g) was vacuum packed, immersed in a heated, circulating water bath, and held at 55, 57.5, 60, 62.5, 65, 67.5, and 70°C for different time intervals prior to plating as above. All experiments were done in triplicate. A linear regression model was used to calculate the D- and z-values.
Results: In ground beef patties cooked to 71°C, E. coli AW1.7 and Salmonella enterica ATCC 43845 were reduced by 2.9 and 4.0 log CFU/g, respectively. Average D-values for E. coli AW1.7 and Salmonella ATCC 43845 at a temperature range of 55 to 70°C were 33.70 to 0.10 min and 21.14 to 0.14 min, respectively. Calculated z-values for E. coli AW1.7 and Salmonella ATCC 43845 were 5.8 and 6.4, respectively.
Significance: The results of this study can be used by producers to help to assess their process and predict the survival of heat resistant organisms in ground beef products.