Thermal Inactivation of Escherichia coli O157:H7 Inoculated at Different Depths of Non-Intact Blade-Tenderized Beef Steaks



Abstract:  Studies evaluated thermal inactivation of Escherichia coli O157:H7 inoculated at different depths of simulated blade-tenderized non-intact steaks. Fresh beef slices (0.3 or 0.6 cm thick) were stacked on top of each other to form 2.4 or 1.2 cm thick steaks. Steaks were blade-tenderized and then inoculated with rifampicin-resistant Escherichia coli O157:H7 (8 strain mixture; 4 log CFU/cm2) on the surface or between slices, vacuum-packaged, and stored at 4 or –20 °C for 5 d before cooking. Steaks were cooked by pan-broiling or roasting to a geometric center temperature of 60 °C. Frozen samples were either cooked from the frozen state or after thawing to approximately 4 or 25 °C. In steaks inoculated on the external surface and cooked by pan-broiling, pathogen survivors recovered from thinner (1.2 cm) steaks were greater (P < 0.05) than those recovered from thicker (2.4 cm) steaks. Cooking steaks from a frozen state or after thawing (4 or 25 °C) did not (P≥ 0.05) affect extent of pathogen inactivation. Survivors after pan-broiling of 2.4 cm thick steaks increased (P < 0.05) from 0.3 to 1.3 log CFU/cm2 for surface-inoculated steaks to 2.5 to 3.2 log CFU/cm2 for samples inoculated at the center (1.2 cm depth). In comparison, overall thermal destruction of the pathogen in steaks cooked by roasting was less, and survivor counts were generally not different (P≥ 0.05) at each depth of inoculation. These data should be useful in development of lethality guidelines to ensure safe consumption of non-intact meat products.

Practical Application:  Results of this study should be useful for developing cooking guidelines, for foodservice establishments and consumers, to ensure safe consumption of non-intact meat products.