According to the CDC, Salmonella is a leading cause of gastroenteritis in humans and continues to be significant in relation to public health concerns for the food industry. This may be attributed to inadequate heating/cooking. The lowest temperature and holding time the USDA recommends in Appendix A to achieve a 6.5-log₁₀ reduction in Salmonella is 54.4°C for 112 min. To date there is limited research in utilizing lower temperatures for ribeye rolls to increase juiciness and perceived tenderness. This study evaluated the reduction of Escherichia coli in strip loins, top rounds and ribeye rolls cooked to internal temperatures of 54.4°C or lower to determine if temperatures less than 54.4°C would achieve a 6.5-log₁₀ reducation in accordance with Appendix A.

A local company provided their proprietary brine and rub ingredients and raw meat materials for the experiment. A cocktail of five stains of Escherichia coli (ATCC BAA-1427, 1428, 1429, 1430, 1431) were utilized. These strains are approved by the USDA as surrogates for Salmonella for inplant verification studies. Ribeye rolls were dip inoculated with E. coli to achieve a 7.5-log₁₀ CFU per gram inoculation level on the meat. Ribeye rolls were pumped 15% with a brine solution and then rubbed with the rub. They were then placed into cook-in bags and vacuum-sealed. Packages were placed on a smokehouse trolley in the smokehouse. The combination of temperatures and times held were 54.4°C for 2 and 3 h, 51.7°C for 3 and 5 h, and 48.9°C for 10 and 12 h. Times were determined utilizing a model from the North American Meat Institute. Internal temperatures were continuously monitored utilizing Type-K Thermocouples. Inoculations were prepared by inoculating TSB with each E. coli strain and allowed to grow at 37°C for approximately 24 h. Once removed from the smokehouse 1-kg samples were taken from each ribeye roll and were vacuum-packaged for E. coli enumeration. Samples were taken to Food Safety Net Services for enumeration. MacConkey Sorbital Agar was utilized to determine E. coli survival. The experiment consisted of three replications with 2 samples per replication. Data were analyzed using excel and the GLM procedure of SAS (SAS Inst. Inc., Cary, NC) to determine average reduction of E. coli in top rounds.

Ribeye rolls had a 6.3-log₁₀ reduction (var = 0.1) at 54.4°C when held for 2 h and a 6.5-log₁₀ reduction (var = 0.01) when held for 3 h. When held at an internal temperature of 51.7°C a 6.08-log₁₀ reduction (var = 0.74) was achieved when held for 3 h and a 5.43-log₁₀ reduction (var = 0.22) when held for 5 h. The lower reduction when held at for a longer period of time may have occurred due to a sample having a higher inoculation level or contamination during sampling. Ribeye rolls that were cooked to 48.9°C and held for 10 h resulted in a 5.3-log₁₀ reduction (var = 1.07) and when held for 12 h achieved a 6.1-log₁₀ reduction (var = 0.36).

Results suggest that lower temperatures may possibly achieve a 6.5–7.0-log₁₀ reduction in accordance with Appendix A if the product was held at the temperature for the correct time. This information is useful for companies that wish to use other temperature/time relationships than those stated in Appendix A.