Thermal resistance of bacteriophages attacking flavour-producing dairy Leuconostoc starter cultures

Seventy-seven dairy Leuconostoc phages were tested for their thermal resistance. Of these, 49 were Leuconostoc pseudomesenteroides phages isolated from whey, brine, cheese, butter cream and buttermilk samples obtained from ten dairies or from dairy products collected from the local market, while 28 were Ln. pseudomesenteroides and Leuconostoc mesenteroides phages obtained from two starter culture manufacturers. Heat inactivation experiments in skim milk and water indicated that milk had a protective effect against the destruction of Leuconostoc phages. After 1 min heating at 85 °C, 19 of the 77 phages were still active. For one of the most thermo-resistant Ln. pseudomesenteroides phages (phage P793), inactivation kinetics were determined in a temperature range from 65 to 85 °C for different holding times (0–90 min) and lines of equal effects for 3-log and 9-log reduction were calculated. These data clearly showed that pasteurization was insufficient for a 3-log inactivation of thermo-resistant Leuconostoc phages.