Survival of Escherichia coli O157:H7 in Ground Beef after Sublethal Heat Shock and Subsequent Isothermal Cooking

摘要

Heat shock of Escherichia coli O157:H7 in broth media reportedly leads to enhanced survival during subsequent heating in broth medium or ground beef. Survival of E. coli O157:H7 during slow cooking thus may be enhanced by prior exposure to sublethal heat shock conditions, thereby jeopardizing the safety of slow-cooked products such as beef roasts. This study examined the effect of heat shocking E. coli O157:H7-inoculated lean (6 to 9% fat) ground beef on the survival of the pathogen in the same ground beef during a subsequent 4-h, 54.4℃ cooking process. Six different combinations of heat shock temperature (47.2, 48.3, or 49.4℃) and time (5 or 30 min) were applied to a five-strain cocktail of microaerophilically grown cells in 25 g of prewarmed ground beef, which was followed by cooking at 54.4℃. Temperature during a 30-min heat shock treatment did not significantly affect E. coli O157:H7 survival during subsequent isothermal cooking (P > 0.05). Survival after a 5-min heat shock was higher when the heat shock temperature was 48.3 or 49.4℃ (P < 0.05) than when it was 47.2℃. The D-values at 54.4℃ (130℉) (D_(54.4)-value) of the process significantly increased only when cells were exposed to a heat shock combination of 5 min at 49.4℃. Mean (n = 3 trials) reductions in E. coli O157:H7 during the 4-h, 54.4℃ isothermal cooking process ranged from 4.3 to 7.5 log CFU/g. Heating E. coli O157:H7-contaminated beef at the high end of the sublethal temperature range for 5 min could increase survival of E. coli O157:H7 during subsequent slow-cooking processes.