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

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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°C cooking process. Six different combinations of heat shock temperature (47.2, 48.3, or 49.4°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°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°C (P < 0.05) than when it was 47.2°C. The D-values at 54.4°C (130°F) (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°C. Mean (n = 3 trials) reductions in E. coli O157:H7 during the 4-h, 54.4°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.

Document Type: Research Article

Affiliations: 1: Department of Food Science, University of Wisconsin–Madison, 1605 Linden Drive, Madison, Wisconsin 53706, USA 2: Division of Food Safety, Wisconsin Department of Agriculture, Trade and Consumer Protection, P.O. Box 8911, Madison, Wisconsin 53708, USA

Publication date: August 1, 2009

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    The Journal of Food Protection (JFP) is a refereed monthly publication. Each issue contains scientific research and authoritative review articles reporting on a variety of topics in food science pertaining to food safety and quality. The Journal is internationally recognized as the leading publication in the field of food microbiology with a readership exceeding 11,000 scientists from 70 countries. The Journal of Food Protection is indexed in Index Medicus, Current Contents, BIOSIS, PubMed, Medline, and many others.

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