Validation of D- and z-values for Salmonella, Listeria monocytogenes, and Shiga toxin-producing Escherichia coli in processed meat products

The objectives of this study were to validate experimentally derived D- and z-values for Salmonella, Listeria monocytogenes, and Shiga toxin-producing Escherichia coli (STEC) in a pilot plant-scale meat system in 3 commercial products: deli-style uncured roast beef, uncured turkey breast, and cured ham, and to evaluate the efficacy of United States Department of Agriculture (USDA), Food Safety and Inspection Service (FSIS) guidelines (e.g., Appendix A for cooked beef, roast beef, and experimentally derived Time-Temperature Tables for Cooking Ready-to-Eat Poultry Products). Each product-pathogen combination was inoculated with 8.0 log colony-forming units (CFU)/g of the designated pathogen cocktail, stuffed into 10.61cm diameter casings, and cooked using either a step-up steam (roast beef, turkey breast) or wet-bulb/ dry-bulb (ham) thermal process. Validation experiments confirmed that heating to 71.1°C was sufficient to inactivate >6.5 log of all 3 pathogens in each of the products tested. Shiga toxin-producing Escherichia coli and Salmonella also had >7.0-log reductions in roast beef when heated to 62.8°C and held for 5 min. Less than 4.0 log CFU/g of Salmonella or STEC were inactivated in roast beef heated to 54.4°C and held for 2 h. A series of follow-up experiments confirmed that ≥ 4 h were needed to achieve a 5.0-log reduction of Salmonella in roast beef held at 54.4°C. The D54.4°C of 23.3 min for Salmonella in samples of roast beef with a slow come-up time was significantly greater (P < 0.05) than the D54.4°C of 10.3 min in control samples that were not subjected to a slow heating process, suggesting that extended come-up times during cooking can enhance thermotolerance of Salmonella. These results support the continued use of USDA, FSIS Appendix A guidelines for controlling Salmonella, L. monocytogenes, and STEC in deli-style roast beef, turkey breast, ham, and similar product types using cook processes with endpoint internal temperatures ≥ 62.8°C.