Evaluating the Growth of Staphylococcus aureus During Slow Cooking of Beef and Turkey Formulations from 10 °C to 54.4 °C for an Extended Time

USDA FSIS recommends meat dwell ≤6 h during cooking from 10 to 54.4 °C to limit the growth of Staphylococcus aureus and prevent its production of heat-stable enterotoxins. This study evaluated the growth of S. aureus in irradiated beef and turkey formulations with no antimicrobial, lactate-diacetate (2.5% w/w), or vinegar (1.98% w/w). Individual experimental units consisting of a 5 g portion of meat in a plastic bag were inoculated with 3 log CFU/g of S. aureus and then spread thin within the bag. Units were heated from 10 to 54.4 °C in 9.3 h in a water bath, representing a process deviation case in a commercial establishment. S. aureus populations were enumerated on Baird-Parker agar plates from five inoculated units before cooking, and three units each at 4.5, 6.0, 7.0, 8.0, and 9.3 h. Likewise, two uninoculated units each were evaluated at 0, 6, and 9.3 h to verify the absence of competition from background microflora. Data from three trials were reported as mean ± SD. Beef formulations had pH, moisture, and salt content of 6.41 ± 0.25, 74.1 ± 0.5%, and 0.6 ± 0.1%, respectively, whereas turkey had 6.74 ± 0.08, 76.4 ± 0.6%, and 0.6 ± 0.1%, representing the most optimum condition for growth present in the commercial products. Maximum growth of 1.1 ± 0.2 (p < 0.05), 0.9 ± 0.3 (p < 0.05), and 0.2 ± 0.1 (p > 0.05) log CFU/g was observed by the 6th h in beef with no antimicrobial, lactate diacetate, and vinegar, respectively, and 1.6 ± 0.2 (p < 0.05), 1.3 ± 0.3 (p < 0.05), and 0.5 ± 0.3 (p > 0.05) log CFU/g in the turkey formulations also by the 6th h. The counts declined thereafter (p < 0.05) in all formulations, reaching below the inoculation level by 9.3 h. In comparison, UW Therm 2.0 and DMRI Staphtox Predictor, after adjusting for their temperature limitations per USDA FSIS guidelines, estimated a 4.2 and 3.3 log increase, respectively, in beef with no antimicrobial, and 4.3 and 3.7 log increase in turkey. The models provide fail-safe but overly conservative predictions of S. aureus growth in beef and turkey.