Inactivation of Escherichia coli O157:H7 in Beef Roasts Cooked in Conventional or Convection Ovens or in a Slow Cooker under Selected Conditions

Inactivation of Escherichia coli O157:H7 in beef roasts cooked under selected cooking conditions was evaluated. Eye of round roasts were each inoculated at five sites in the central plane with a five-strain cocktail of E. coli O157:H7 at ca. 6.3 log CFU per site and cooked to center temperatures of 56 to 71 degrees C in a convection oven set at 120, 140, 180, or 200 degrees C, in a conventional oven set at 120 or 210 degrees C, and in a slow cooker set on high or low. Prime rib roasts were each inoculated at 10 sites throughout the roast with the same E. coli O157:H7 cocktail at ca. 6.6 log CFU per site and cooked in the conventional oven set at 140 or 180 degrees C to center temperatures of 58 to 71 degrees C. The number of sites yielding E. coli O157:H7 after cooking decreased with increasing roast center temperature for the eye of round roasts cooked in the convection oven or in the slow cooker at a given setting, but this trend was not apparent for roasts of either type cooked in the conventional oven. Reductions of E. coli O157 in both types of roasts were generally less at the center than at other locations, particularly locations closer to the surface of the meat. When eye of round roasts were cooked to the same center temperature in the convection oven, the reduction of E. coli O157:H7 increased with increasing oven temperature up to 180 degrees C and decreased after that. The reduction of E. coli O157:H7 in replicate roasts cooked under conditions in which the organism was not eliminated during cooking mostly differed by >1 log CFU per site. However, E. coli O157:H7 was not recovered from any of the inoculation sites when eye of round roasts were cooked to 65, 60, 60, or 63 degrees C in the convection oven set at 120, 140, 180, and 200 degrees C, respectively; cooked to 63 or 71 degrees C in the conventional oven set at 120 and 210 degrees C, respectively; or cooked to 63 degrees C in the slow cooker set at high or low. For prime rib roasts, E. coli O157:117 was not recovered from any of the inoculation sites in roasts cooked to 71 or 58 degrees C in the conventional oven set at 140 and 180 degrees C, respectively.