Effect of beef product physical structure on Salmonella thermal inactivation

Numerous studies have assessed thermal inactivation of Salmonella in beef. However, the impact of muscle structure has been considered only recently, with several studies reporting enhanced thermal resistance in whole-muscle as compared to ground meat. The functional relationship between meat product physical structure and Salmonella thermal resistance has not been reported; therefore, it is not known whether thermal resistance is affected by the degree of grinding (that is, size of resulting particles). The objective of this study was to evaluate the relationship between thermal resistance of Salmonella and degree of grinding (whole-muscle, coarsely ground, finely ground, and beef puree). Each of the 4 product types was irradiated to sterility and inoculated with a marinade containing an 8-serovar Salmonella cocktail to achieve approximately 10(7.8) CFU/g. Samples (5 g each) were packed into sterile brass tubes, which were sealed, held at 60 degrees C in a water bath, and removed at 30 s intervals. Samples were then serially diluted and plated on Petrifilm aerobic count plates to enumerate surviving salmonellae. All samples had the same composition, thermal history, and initial Salmonella counts; therefore, differences in thermal resistance were due entirely to the degree of grinding. Overall, thermal resistance of Salmonella was highest (P < 0.0001) in whole-muscle (D = 2.7 min), but there were no differences among the 3 ground products (D(mean)= 1.2 min). Therefore, it would be prudent for Salmonella thermal inactivation models to consider whether a product is whole-muscle or ground, but not necessarily the degree of grinding. Practical Application: The results of this study suggest that thermal process validations for ready-to-eat meat products should also consider the structure of the product (which in this study was changed by the physical act of grinding). Salmonella was more resistant to heat in whole-muscle beef than in ground products; however, the degree of grinding did not affect the resistance.