Purpose: To determine the thermal inactivation parameters (D- and z-values) for Salmonella spp. in whole-grain bread dough, and to validate a representative commercial baking process as an effective pathogen kill-step during bread production.
Methods: Whole-grain flour was inoculated with a 7-strain cocktail of Salmonella spp. [four food production facility isolates, and three ATCC strains (Senftenberg 775W 43845, Newport 6962, and Typhimurium 14028], formed into dough, and either baked at 190.6°C for 35 minutes simulating a commercial baking process or transferred to thermal death time disks and heated in hot water baths at 50, 52, or 55°C for 30 to 80 minutes. Surviving Salmonella spp. populations were determined by plating on injury recovery and selective agars. Three replications were conducted with randomized complete block design. D- and z-values were determined by linear regression.
Results: Salmonella spp. populations were undetectable after enrichment (>6 log CFU/g reductions) following 16 minutes of baking. D-values of the 7-strain Salmonella spp. cocktail in bread dough were 59.6, 20.0, and 9.7 at 50, 52, and 55°C, respectively. The z-value of Salmonella spp. was 6.5°C. No significant differences (P > 0.05) in Salmonella spp. recovery were observed between the injury recovery and selective agars.
Significance: Baking at 190.6°C reduces Salmonella spp. populations in bread by >6 log CFU/g to non-detectable populations, thus providing an effective kill-step for Salmonella spp. during typical commercial baking processes. Established D- and z-values in whole-grain bread dough will assist bakers in process lethality determinations and modeling.