Purpose: To determine the D- and z-values to inactivate a Salmonella cocktail in high-fat raw materials from animal processing by-products subjected to thermal rendering conditions.
Methods: A cocktail of 5 Salmonella strains isolated from cattle or associated with human illness were used to prepare an inoculum (8 log CFU/ml). Samples of high-fat beef trim and fat rendering raw material were obtained from local sources, mixed, and inoculated with the Salmonella cocktail. The samples were packed in aluminum bags and immersed in an oil bath in the established temperatures range from 60°C to 121°C. Surviving Salmonella were enumerated by plating serial dilutions in duplicate onto XLD plates with a thin-layer overlay of TSA for recovery of injured cells and incubated at 37°C for 24 h. The D-value of Salmonella at each temperature was calculated from the negative inverse slope of the log (CFU/g) vs. time plot. The z-value was determined from the negative inverse slope of the log (D) vs. temperature plot.
Results: The thermal death time curves indicate D-values for 60 to 121°C ranging from 2.17 to 0.099 min in the high-fat rendering raw material. The z-values were 38.61 and 40.82°C, for low and high temperature treatments.
Significance: Thermal lethality data for Salmonella reductions in high-fat rendering raw materials will assist renderers to design adequate thermal processes to support critical control points to ensure safety in products used as ingredients in pet food.