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

Authors: SHRESTHA, SUBASH - Cargill, Incorporated; RIEMANN, MICHELLE - Cargill, Incorporated; Juneja, Vijay; MISHRA, ABHINAV - University Of Georgia

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2024
Publication Date: 12/28/2024
Citation: Shrestha, S., Riemann, M., Juneja, V.K., Mishra, A. 2024. 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. Journal of Food Protection. https://doi.org/10.1016/j.jfp.2024.100445.
DOI: https://doi.org/10.1016/j.jfp.2024.100445

Interpretive Summary: Slow cooking of foods allows the product to dwell in favorable growth temperatures for pathogens for a longer time. Therefore, the potential for heat-stable enterotoxin production by Staphylococcus aureus during slow cooking poses a food safety concern. We evaluated the growth of S. aureus in slow-cooked beef and turkey products formulated with no antimicrobial and with either lactate diacetate or vinegar. Our results suggest that vinegar in meat formulations minimizes the growth of S. aureus. We demonstrated that commercially available software provide fail-safe but overly conservative predictions. Meat processors can use the information to guard against S. aureus in ready-to-eat products.

Technical Abstract: USDA FSIS recommends meat dwell less than 6 h during cooking from 10 to 54.4C 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%). 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 54.4C 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, 0.9±0.3, and 0.2±0.1 log was observed at 6h in beef with no antimicrobial, lactate diacetate, and vinegar, respectively (p<0.05), and 1.6±0.2, 1.3±0.3, and 0.5±0.3 log CFU/g in the turkey formulations also at 6h (p less than 0.05). The counts decline thereafter (p less than 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 due to their inherent limitations.