LAUSR

Abstract Fifty three bacteriophages of three lactic acid bacteria species (i.e., Lactococcus lactis , Leuconostoc pseudomesenteroides, Streptococcus thermophilus ) isolated from whey powders and whey powder formulations, were tested for their thermal stability. Complete inactivation of Ln. pseudomesenteroides and S. thermophilus phages required 1 min heating at 85 °C and 90 °C, respectively. L. lactis phages exhibited the highest heat resistance and 16% of them were still detectable after heat treatment at 95 °C for 1 min. The most thermo-resistant phages of L. lactis (P956), Ln. pseudomesenteroides (P973) and S. thermophilus (P1008) were selected to determinate their kinetic parameters and lines of equal effects for 9-log inactivation. High D-values of 105 min (phage P956), 74 min (P973) and 25 min (P1008) were determined for thermal treatments at 75 °C, confirming previous findings that pasteurisation conditions are insufficient for adequate inactivation of thermo-resistant dairy phages.