Thermal resistance of Yersinia enterocolitica and Listeria monocytogenes in meat and potato substrates

The heat resistance of a wild type and nalidrxic acid resistant strain of Yersinia enterocolitica and Listeria monocytogenes, was measured in meat (minced beef and minced beef homogenate) and potato substrates over the temperature range 50-60C. Comparisons of hear resistance were determined using D-values calculated using a linear survival model. The results showed that the wild-type strain of Y. enterocolitica was more heat resistant than the mutant (P<0.05). Under mast conditions, the use of a nonselective/overlay recovery medium resulted in higher D-values compared to a selective recovery medium (P<0.05). Analysis of the data using a nonlinear survival model (D-1 and D-2-values) suggested the presence of heat resistant subpopulations and was particularly evident for the mutant strain, and in potatoes compared to minced beef.