Rates of thermal inactivation of a five-strain mixture of Listeria monocytogenes were determined in ground beef roast and fermented beaker sausage. Studies were also done on ground beef contaminated with L. monocytogenes Scott A from an experimentally infected cow. D-values for the five-strain mixture at 54.4, 57.2, 60.0, and 62.8°C were 22.4, 15.7, 4.47, and 2.56 min, respectively, for ground beef roast. D-values for fermented beaker sausage at 48.9, 51.7, 54.4, and 60.0°C were 98.6, 44.4, 20.1, 11.2, and 9.13 min, respectively. D-values for the single strain of L. monocytogenes mixture in ground beef from the infected cow were about two to four times less at equivalent temperatures than those of the five-strain L. monocytogenes mixture in ground beef roast. Results from the five-strain mixture indicate that L. monocytogenes is about four times more heat resistant that Salmonella in ground beef roast.
1Present address: Department of Food Services, Georgia Experiment Station, University of Georgia, Griffin, GA 30223.