Fate of Listeria monocytogenes in Sweetened Condensed and Evaporated Milk During Storage at 7 or 21 °C

Sweetened condensed and evaporated milks were inoculated to contain ca. 10³ to 10⁷ cells of Listeria monocytogenes (strains Scott A, California, or V7)/ml. Both inoculated products were cooled from 25°C to 21°C in ca. 2 h or to 7°C in ca. 4 h. When inoculated sweetened condensed milk was held at 7°C for 42 d, there was no appreciable decrease in numbers of L. monocytogenes strains Scott A and V7, whereas the population of L. monocytogenes strain California decreased by ca. 1.2 orders of magnitude. Inoculum level had no effect on the magnitude of the decrease. At 21°C, 42 d of storage resulted in a more pronounced decrease in numbers of L. monocytogenes than it did during storage at 7°C, with numbers of the pathogen decreasing by 1.7, 1.6, and 3.4 orders of magnitude for strains Scott A, V7, and California, respectively. All strains of L. monocytogenes not only survived but grew in evaporated milk stored at 7 or 21 °C for 56 or 28 d, respectively.