Resistance of 17 mesophilic lactic Streptococcus bacteriophages to pasteurization and spray-drying

For 17 phages active against Streptococcus cremoris, Str. lactis and Str. lactis subsp. diacetylactis, the killing efficiency of pasteurization (log No/N) at 72 degrees C for 15 s in skim-milk showed large variations from greater than 6 to 0; the efficienty of killing during spray-drying ranged from 3.7 to 0.2 and phages survived well storage of milk powder at room temperature. Destruction in a heat exchanger was found to be greater than that calculated from biphasic curves obtained by heating phages in sealed ampoules. No relationship was established between lytic classification of phages and their heat resistance.