Nutrient broth, skimmilk, and evaporated milk at pH 5.0, 5.5, or without pH adjustment and with and without 2,000 and 3,000 ppm sorbic acid were evaluated at 7, 13, and 37 C for their effects on Salmonella typhimurium. The combination of 3,000 ppm sorbic acid and acetic acid at pH 5.0 most effectively inactivated S. typhimurium in all media and at all temperatures. Complete inactivation by this treatment required from 12 hr or less in nutrient broth at 37 C to 55 days in evaporated milk at 7 C. In some instances, treatment with 3,000 ppm sorbic acid combined with lactic acid at pH 5.0 was equally effective. Reduction of sorbic acid concentration to 2,000 ppm or raising the pH of the substrate to 5.5 increased the time needed for inactivation of S. typhimurium. Inactivation of S. typhimurium was most rapid in nutrient broth at 37 C and required progressively more time either as the temperature was reduced or as more complex foods were substituted for the broth. Growth of S. typhimurium occurred at 37 and 13 C in plain nutrient broth, in nutrient broth at pH 5.0 or 5.5, and in nutrient broth with 2,000 or 3,000 ppm sorbic acid (pH not adjusted). Growth in skimmilk occurred under similar conditions except when the pH was reduced to 5.0 with acetic acid. In evaporated milk, growth at both temperatures was possible only in untreated samples and in those acidified to pH 5.5. In some instances, a lag period of 25–29 days occurred at 13 C before growth was evident.
Amplicon sequencing for the quantification of spoilage microbiota in complex foods including bacterial spores
