BEHAVIOR OF CLOSTRIDIUM PERFRINGENS IN PRECOOKED CHILLED GROUND BEEF GRAVY DURING COOLING, HOLDING, AND REHEATING

Abstract

The suitability of handling practices used in school kitchens was evaluated using ground beef gravy that was contaminated with Clostridium perfringens. Cooked gravy was cooled to 110 F (43.5 C) and inoculated with a mixture of vegetative cells and spores of C. perfringens NCTC 8239 to provide approximately 10,000 organisms/g. After inoculation, gravy was packed in bags, refrigerated for 16 h, held for 5 h at 82 F (28 C) or 42 F (5.5 C), and then heated in a compartment steamer for 35 min or until the temperature of the gravy at the center of the pan reached 165 F (74 C). C. perfringens was enumerated at intervals during cooling, holding, and heating of the gravy. The number of viable cells after 16 h of refrigeration at 42 F (5.5 C) was influenced by the first 6 h of cooling when the temperature of the gravy was in the range that permitted growth of C. perfringens (65–122 F; 18.5–50 C). Plate counts of gravy held for 5 h at 82 F (28 C) or 42 F (5.5 C) indicated stablization of the C. perfringens population. When 165 F (74 C) was the final temperature to which the gravy was heated, no viable cells of C. perfringens were found.