title: Survival of Escherichia coli O157:H7 in ground beef after sublethal heat shock and subsequent isothermal cooking.
abstract: 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 degrees C cooking process. Six different combinations of heat shock temperature (47.2, 48.3, or 49.4 degrees C) 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 degrees C. 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 degrees C (P < 0.05) than when it was 47.2 degrees C. The D-values at 54.4 degrees C (130 degrees F) (D54.4-value) of the process significantly increased only when cells were exposed to a heat shock combination of 5 min at 49.4 degrees C. Mean (n = 3 trials) reductions in E. coli O157:H7 during the 4-h, 54.4 degrees C 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.
authors.affiliation: Department of Food Science, University of Wisconsin-Madison, 1605 Linden Drive, Madison, Wisconsin 53706, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Wiegand
authors.forename: S C
authors.initials: SC
authors.lastname: Ingham
authors.forename: B H
authors.initials: BH
authors.lastname: Ingham
mesh_terms: D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D003296:Cooking / Q000379:methods*; D019453:Escherichia coli O157 / Q000254:growth & development*; D005516:Food Microbiology; D006358:Hot Temperature; D006801:Humans; D008461:Meat Products / Q000382:microbiology*; D013997:Time Factors