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United States Department of Agriculture

Agricultural Research Service

Research Project: PATHOGEN PERSISTENCE AND PROCESSING OPTIMIZATION FOR ELIMINATION IN FOODS

Location: Food Safety and Intervention Technologies

Title: Shiga-toxin producing 0157:H7 and non-0157:H7 Escherichia coli cells within refrigerated, frozen, or frozen then thawed ground beef patties cooked on commercial open-flame gas or clam-shell electric grills

Authors
item Luchansky, John
item Porto Fett, Anna
item Shoyer, Brad
item Phillips, John
item Chen, Vivian -
item Kause, Janelle -
item Eblen, Denise -
item Cook, Victor -
item Mohr, Timothy -
item Esteban, Emilio -
item Bauer, Nathan -

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 2, 2013
Publication Date: March 20, 2013
Citation: Luchansky, J.B., Porto Fett, A.C., Shoyer, B.A., Phillips, J.G., Chen, V., Kause, J., Eblen, D., Cook, V.L., Mohr, T.B., Esteban, E., Bauer, N. 2013. Shiga-toxin producing 0157:H7 and non-0157:H7 Escherichia coli cells within refrigerated, frozen, or frozen then thawed ground beef patties cooked on commercial open-flame gas or clam-shell electric grills. Journal of Food Protection. 76:1500-1513.

Interpretive Summary: There is little debate that serotype O157:H7 strains of Escherichia coli (ECOH) and non-O157:H7 Shiga toxin producing strains of E. coli (STEC) can be recovered from raw beef, or that raw ground beef has been implicated more often than other foods as a vehicle for human ECOH infections, and more recently STEC infections. There have also been several publications detailing the response of ECOH and STEC to elevated temperatures in food systems, including several on their thermal inactivation in ground beef. However, further studies are warranted to validate the comparative response of STEC and ECOH within inoculated beef patties in response to freezing or freezing/thawing and subsequent cooking due to the higher volume produced and the wide spectrum of individuals who consume such products. Our data confirmed that ECOH and STEC behaved similarly with respect to their thermal stability in fresh and frozen ground beef patties (with or without thawing) cooked on commercial grills. Our data also confirmed that although uneven heating and the occasional presence of cold spots within patties can allow for recovery of fortuitous survivors, cooking ground beef patties that were refrigerated, or frozen, or frozen and then thawed to the recommended internal temperatures of 71.1 deg C was effective for eliminating ca. 100,000 to 10,000,000 cells of ECOH and STEC.

Technical Abstract: We evaluated the possible effect of both fat and grill type on the fate of serotype O157:H7 strains of Escherichia coli (ECOH) and non-O157:H7 Shiga toxin producing strains of E. coli (STEC) in cooked ground beef patties. Both high fat and low fat ground beef (percent lean:fat = ca. 70:30 and 93:7, respectively) were inoculated with a 5-strain cocktail of ECOH or a 6-strain cocktail of STEC (ca. 7.0 CFU/g). Patties were pressed (ca. 2.54 cm thick, ca. 300 grams each) and then either refrigerated (4C, 18-24 h), or frozen (-20 deg C, 3 weeks), or frozen (-20 deg C, 3 weeks) and then thawed (4 deg C for 18 h or 21 deg C for 10 h) before being cooked on a commercial open-flame gas grill or on a clam-shell electric grill to internal temperatures of 60, 65.5, 71.1, or 76.6 deg C. For ECOH, regardless of the type of grill or the fat level, cooking refrigerated patties to 71.1 or 76.6 deg C decreased ECOH numbers from an initial level of ca. 7.0 log CFU/g to a final level of equal or less than 1.0 log CFU/g, whereas decreases to a final level of ca. 1.1 to 3.1 log CFU/g were observed when refrigerated patties were cooked to 60.0 or 65.5 deg C. For patties that were frozen or frozen then thawed and cooked to 71.1 or 76.6 deg C, ECOH numbers decreased from an initial level of ca. 7.0 log CFU/g to a final level of ca. 1.7 to equal or less than 0.7 log CFU/g. Likewise, pathogen numbers decreased from an initial level of ca. 7.0 log CFU/g to a final level of ca. 0.7 to 3.7 log CFU/g in patties that were frozen or frozen then thawed and cooked to 60.0 or 65.5 deg C. For STEC, regardless of the type of grill or the fat level, cooking refrigerated patties to 71.1 or 76.6 deg C decreased pathogen numbers from an initial level of ca. 7.0 log CFU/g to a final level of equal or less than 0.7 log CFU/g, whereas decreases to a final level of ca. 0.7 to 3.6 log CFU/g were observed when refrigerated patties were cooked to 60.0 or 65.5 deg C. For patties that were frozen or frozen then thawed and cooked to 71.1 or 76.6 deg C, STEC numbers decreased from an initial level of ca. 7.0 log CFU/g to a final level of ca. 1.5 to equal or less than 0.7 log CFU/g. Likewise, pathogen numbers decreased from an initial level of ca. 7.0 log CFU/g to a final level of ca. 0.8 to 4.3 log CFU/g in patties that were frozen or frozen then thawed and cooked to 60.0 or 65.5 deg C. These results validated that cooking ground beef patties that were refrigerated, or frozen, or frozen and then thawed to internal temperatures of 71.1 and 76.6 deg C was effective for eliminating ca. 5.1 to 7.0 log CFU/g of Shiga toxin-producing E. coli and, in turn, lessening the threat of illness associated with this food borne pathogen due to ingestion of undercooked ground beef.

Last Modified: 7/31/2014