Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/20/2011
Publication Date: 7/1/2011
Citation: Luchansky, J.B., Porto Fett, A.C., Shoyer, B.A., Call, J.E., Schlosser, W., Shaw, W., Bauer, N., Latimer, H. 2011. Inactivation of Shiga toxin-producing O157:H7 and non-O157:H7 Escherichia coli in brine-injected, gas-grilled steaks. Journal of Food Protection. 74:1054-1064. Interpretive Summary: In 1994 the USDA Food Safety and Inspection Service (USDA/FSIS) stipulated that E. coli O157:H7 (ECOH) was considered an adulterant in raw ground beef, and in 1999, it modified this policy to also include tenderized, that being “non-intact”, products. As is true for ECOH, any cells of non-O157 Shiga-toxin producing strains of E. coli (STEC) that may be present on the surface of whole muscle meats will be transferred into the deeper tissues by tenderization. At present, restaurants, food service, and retail establishments may blade tenderize and/or inject beef with brine solutions to enhance the tenderness and flavor of the resulting non-intact products, as well as to improve yield. Considering that about 18% of beef products sold at retail are mechanically tenderized/enhanced and considering that such products may be perceived by some individuals as being more like steaks (i.e., “intact”) than ground beef (i.e., “non-intact”) and thus may not be properly cooked, there may be a potential threat to public health attributed to non-intact beef, especially since between 40 to 58% of consumers ordered their steaks medium rare to rare. Thus, a greater understanding of how beef is processed, that being tenderized versus injected versus marinated versus tumbled, as well as how it should be cooked will lead to a more focused, comprehensive, and meaningful comparative risk assessment of intact and non-intact beef. Our data revealed that ECOH and STEC behave similarly with respect to translocation and thermal stability within non-intact subprimals and steaks. Our findings also established that proper cooking appreciably reduces the levels of Shiga toxin-producing E. coli in chemically tenderized meat, but does not completely eliminate the pathogen due to non-uniform heating. Further research is warranted to develop interventions to treat subprimals prior to tenderization and/or to develop brines for injection to lessen the prevalence and levels of ECOH and/or STEC during subsequent storage and cooking of tenderized steaks. Regardless, our findings will be useful to estimate the comparative risk between intact and non-intact meats and to assist in the validation of targeted interventions and the development of potential labeling requirements for such products.
Technical Abstract: We quantified translocation of Escherichia coli O157:H7 (ECOH) and non-O157:H7 verocytotoxigenic E. coli (STEC) into beef subprimals following chemical tenderization and subsequently monitored their viability after cooking steaks cut therefrom. Beef subprimals were inoculated on the lean side with ca. 6.0 log CFU/g of a five-strain cocktail of rifampicin resistant ECOH or kanamycin resistant STEC and then passed once through an automatic brine-injector tenderizer with the lean side facing upwards. Brine solutions (9.9 +/- 0.3% over fresh weight) consisted of 3.3% (w/v) of sodium tripolyphosphate and 3.3% (w/v) of sodium chloride, prepared both with (Lac+; pH 6.76) and without (Lac-; pH 8.02) a 25% (v/v) solution of a 60% potassium lactate-sodium diacetate syrup. For all samples injected with Lac- or Lac+ brine, levels of ECOH or STEC recovered from the top most 1 cm (i.e., segment 1) of a core sample obtained from tenderized subprimals ranged from ca. 4.7 to 6.3 log CFU/g; however, it was possible to recover ECOH or STEC from all six segments of all cores tested. Next, brine-injected steaks from tenderized subprimals were cooked on a commercial open-flame gas grill to internal endpoint temperatures of either 37.8 deg C (100 deg F), 48.8 deg C (120 deg F), 60 deg C (140 deg F), or 71.1 deg C (160 deg F). Regardless of brine formulation or temperature, cooking achieved log CFU/g reductions of 0.3 to 4.1 of ECOH and 0.5 to 3.6 of STEC. However, spurious survivors were recovered even at 71.1 deg C (160 deg F) at a range of 0.01% to 0.83% for ECOH and of 0.06% to 0.43% for STEC. Thus, ECOH and STEC behave similarly relative to translocation and thermal destruction: chemical tenderization transfers both pathogens throughout subprimals and cooking highly contaminated, brine injected steaks on a commercial gas grill to 71.1 deg C (160 deg F) is insufficient to kill all cells due, primarily, to non-uniform heating (i.e., cold spots) within the meat.