Thermal Inactivation of Shiga Toxin-producing Escherichia coli within Cubed Beef Steaks Following Cooking on an Electric Skillet

Introduction: Cubed steak is an eye round steak that has been mechanically tenderized to make it more desirable for the consumer. Since it is a non-intact product, it should be cooked like ground beef due to possible bacterial translocation into the deeper tissues of the meat as a result of the tenderization process. However, no studies have addressed the viability of Shiga toxin-producing Escherichia coli (STEC) in non-intact beef processed via mechanical cubing.    

Purpose: Quantify thermal inactivation of STEC within knitted/cubed steak following cooking on an electric skillet.

Methods: For each of three trials, commercially-processed eye round steaks (ca. 114 g; ca. 1.5 cm thick) were surface inoculated (ca. 6.6 log CFU/g) with a rifampicin-resistant cocktail comprised of single strains from each of eight target serogroups of STEC (STEC-8; O111:H-, O45:H2, O103:H2, O104:H4, O121:H19, O145:NM, O26:H11, and O157:H7). Next, inoculated steaks were passed once through a mechanical tenderizer, and then two tenderized steaks were knitted together by passing them concomitantly through the tenderizer two additional times. Following tenderization, knitted/cubed steaks were individually cooked on a flat-surface electric skillet set at ca. 191.5°C for up to 3.5 minutes per side.

Results: The longer the cooking time, the higher the final internal temperature, and the greater the inactivation of STEC within cubed steaks. The average final internal temperature of knitted/cubed steaks cooked for 1.0 to 3.5 minutes ranged from 40.3° to 82.2°C. Cooking cubed steaks on an electric skillet set at ca. 191.5°C for 1.0, 1.5, 1.75, 2.0, 2.5, 3.0, and 3.5 minutes per side resulted in average total reductions of ca. 1.0, 2.1, 2.2, 2.8, 4.1, 5.2, and 6.3 log CFU/g in pathogen numbers, respectively. 

Significance: These data validated that cooking cubed steaks on an electric skillet at 191.5°C for at least 3 minutes per side was sufficient to achieve a 5.0-log reduction of STEC-8.