Thermal Resistance of Listeria monocytogenes in Dairy Products.

The thermal resistance of Listeria monocytogenes strain Scott A that had been associated with a recent milkborne outbreak of listeriosis was determined in whole and skim milk, heavy cream, and ice cream mix. L. monocytogenes suspended at concentrations of approximately 1 × 10 cells/ml was heated at temperatures ranging from 52.2 to 79.4°C at various contact times. The D values computed for milk samples ranged from 0.9 to 2.7 s. The D value in ice cream mix was 0.5 s. The z value for fluid products ranged from 5.8 to 7.1°C; the z value for ice cream mix was 7.0°C. The L. monocytogenes suspensions would not survive a proper pasteurization process given to raw dairy products.