Inactivation of a composite of five serotypes of salmonellae was monitored in autoclaved ground beef exposed to constantly rising temperatures increased at rates similar to those used in beef cookery. Rising temperature rates of 6.0 C/h, 8.5 C/h and 12.5 C/h and constant temperatures of 55, 57, 61 and 63 C were examined. Survival of Salmonella typhimurium TM-1 was compared to survival of the composite. D and z values were compared for constant and rising temperature rates. The D50 C for constant temperature data was 30.2 min, and the D50 C for changing temperature data was 78.6 min (6.0 C/h), 82.4 min (8.5 C/h), and 49.8 min (12.5 C/h). Neither serotype nor heat treatment of ground beef had a major influence on apparent heat resistance of salmonellae. A comparison of these results to previous rising temperature work with Clostridium perfringens suggested that controlling C. perfringens will result in control of salmonellae. On the basis of these results, the July 18, 1978, USDA processing ruling appears adequate to control salmonellae in precooked beef roasts.
1Paper No. 10,505, Scientific Journal Series, Minnesota Agricultural Experiment Station. St. Paul, MN 55108.