Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/9/2009
Publication Date: 7/1/2009
Citation: Luchansky, J.B., Porto Fett, A.C., Shoyer, B.A., Phebus, R.K., Thippareddi, H., Call, J.E. 2009. THERMAL INACTIVATION OF ESCHERICHIA COLI O157:H7 IN BLADE TENDERIZED BEEF STEAKS COOKED ON A COMMERCIAL OPEN-FLAME GAS GRILL. Journal of Food Protection. 72(7):1404-1411. Interpretive Summary: We evaluated the cooking of mechanically tenderized steaks on a commercial gas grill to eliminate the human pathogen Escherichia coli O157:H7. About 40,000 cells of this bacterium were placed on the surface of beef subprimals, each of which weighed about 20 pounds. The inoculated subprimals were subsequently passed one time through a mechanical blade tenderizer. Blade tenderization transfers pathogens from the surface of the meat into the relatively sterile interior portions. Next, the tenderized subprimals containing E. coli O157:H7 were cut into steaks and cooked on an open-flame gas grill to a doneness ranging from rare to medium. Regardless of doneness or thickness of the steacks, we observed a reduction in pathogen levels following cooking ranging from about 600 cells to 10,000 cells. These results confirm that mechanical tenderization transfers E. coli O157:H7 from the surface into the interior of subprimals, with the majority of the cells remaining in the top portion, and that cooking on a gas grill is effective at eliminating relatively low levels of cells of the pathogen that may be found in a steak that was mechanically tenderized.
Technical Abstract: Beef subprimals were inoculated on the lean side with ca. 4.0 log CFU/g of a five-strain mixture of rifampicin resistant Escherichia coli O157:H7 strains and then passed once through a mechanical blade-tenderizer with the lean side facing upwards. Another set of inoculated subprimals that were not tenderized served as controls. Two core samples were removed from each of three tenderized subprimals and cut into six consecutive segments starting from the inoculated side: segments 1 to 4 comprised the top four cm and segments 5 and 6 comprised the deepest four cm. A total of six cores were also obtained from control subprimals, but only segment 1 was sampled. Each segment was macerated, and the resulting fluid was surface-plated onto Sorbitol-MacConkey plus rifampicin (10 mg/ml) agar plates (SMACR). The levels of E. coli O157:H7 recovered from the surface of each core sample, that being segment 1, were 3.81 log CFU/g for the control subprimals and 3.36 log CFU/g for tenderized subprimals. The percentage of cells recovered in segment 2 was ca. 25-fold lower than levels recovered from segment 1, but E. coli O157:H7 was recovered from all six segments of the cores obtained from tenderized subprimals. In Phase II, lean side inoculated (ca. 4.0 log CFU/g), single-pass tenderized subprimals were cut into 0.75, 1.0, and 1.25 inch thick steaks that were subsequently cooked on a commercial open-flame gas grill to internal temperatures of 120, 130, and 140 degree F. Each steak was dissected into seven portions that were separately macerated and subsequently surface plated onto SMACR. In general, regardless of temperature or thickness, we observed about a 2.6- to 4.2-log CFU/g reduction in pathogen levels following cooking. These results validate that mechanical blade tenderization transfers E. coli O157:H7 into the interior of subprimals, with the majority of the cells remaining in the top-most 1 cm. In addition, these data validate that cooking on a commercial gas grill is effective at eliminating relatively low levels of the pathogen that may be distributed throughout a blade-tenderized steak.