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Validation of a nut muffin baking process and thermal resistance characterization of a 7-serovar Salmonella inoculum in batter when introduced via flour or walnuts

Channaiah, Lakshmikantha H., Michael, Minto, Acuff, Jennifer C., Lopez, Keyla, Phebus, Randall K., Thippareddi, Harshavardhan, Milliken, George
International journal of food microbiology 2019 v.294 pp. 27-30
Salmonella, baking, batters, detection limit, heat tolerance, ingredients, inoculum, mists, muffins, ovens, temperature, walnuts, wheat flour
This study was conducted to validate a commercial nut muffin baking process and to compare the survival of a 7-serovar Salmonella cocktail when contaminated via inoculated flour or walnuts. Enriched wheat flour or walnut pieces were mist inoculated with the Salmonella cocktail and dried back to the pre-inoculation weight, resulting in a Salmonella population level of 6.9 and 8.4 log CFU/g, respectively. Nut muffin batters were prepared separately using inoculated flour or walnuts, followed by baking at 375 °F (190.6 °C) oven temperature for 21 min and post-bake ambient air-cooling (B + C). During baking, >5-log CFU/g reductions in the Salmonella population in nut muffins was achieved in 17 min, and Salmonella was not detected by direct plating (<0.2 log CFU/g detection limit) but was recovered by enrichment at the end of 21 min of baking and B + C. In a separate baking study using an extended baking time (24 min) at 375 °F, Salmonella was detected after 24 and 22 min using enrichment plating of nut muffins prepared from inoculated flour and walnuts, respectively. The D-values of the Salmonella cocktail in nut muffin batters prepared from inoculated flour were 24.0, 4.0 and 0.6 min at 60, 65 and 70 °C; whereas, corresponding D-values in batters prepared from inoculated walnuts were 22.0, 3.6 and 1.7 min. The z-values of the Salmonella cocktail in nut muffin batters were 6.1 and 9.0 °C for inoculated flour and walnuts, respectively. This simulated commercial nut muffin baking study utilizing an oven temperature of 190.6 °C for at least 17 min validates that the process will eliminate Salmonella populations by ≥5 log CFU/g if pre-baking contamination occurs via flour or walnut ingredients.