Purpose: This study validated a typical commercial muffin baking process as an effective kill-step using a Salmonella cocktail of Newport (ATCC 6962), Senftenberg 775W (ATCC 43845) and Typhimurium (ATCC 14028). D- and z-values in muffin batter were also determined to address variances of baking process parameters.
Methods: Muffins were prepared using inoculated flour (~7 log CFU/g), baked at 190.6°C (oven temperature) for 21 min (mimicking industrial processes), and analyzed by plating samples on selective and injury-recovery media at regular time intervals to determine Salmonella reductions. “Breakpoint” time (when no salmonellae were recovered after enrichment) was determined using an extended baking process. D-values of the salmonellae cocktail in muffin batter were determined using thermal-death-time disks. Randomized complete block designs were used for baking and D-value studies, with three replications as blocks using a = 0.05.
Results: After 21 min of baking, salmonellae counts in the muffins decreased by 6.1 log CFU/g; however, a 5-log reduction was achieved by 17 min. The breakpoint of salmonellae in muffins was 27 min. D-values of the Salmonella cocktail in muffin batter were 62.2, 40.1 and 16.5 min at 55, 58 and 61°C, respectively; the z-value was 10.4°C.
Significance: Baking standard muffins at an oven temperature of 190.6°C for 21 min ensures a >5-log reduction of salmonellae that might be present from contaminated raw ingredients. Presence of inclusions such as fruits, nuts and/or chocolate might impact lethality determinations, prompting additional research. The D- and z-values determined in this study will help processors design appropriate baking parameters to control salmonellae if pre-baking contamination occurs.