Thermal inactivation of lactic acid bacteria (Streptococcus thermophilus) phage in milk and milk products [electronic resource].

Includes reference.

The effect of thermal treatments on the viability of three Streptococcus thermophilus (s. thermophilus) phages (0/S0, 10/S0 and 8/S8) in medium, milk with different fat percentages, and yoghurt was investigated by plaquetitration. The thermal resistance was depended on the phage type. Treatments at 90ºC for land 5 min, pasteurization at 72C for 30 second and long-time pasteurization 62ºC for 30 min produced a total inactivation of high titer suspensions qf all studied phages. Additionally. increase the fat percentage from 0.5 to 4.5 % in milk increased the phages stability against the high heat treatment. Mixed phages in milk or yoghurt were more stable when it was subjected to heat treatments. Phage (0/S0 and 10/S0) were more stable against the high heat treatment than (8/S8). The injectivity of phages is affected by freezing at -10 and -20 for 30,60 and 120 min. A complete-inactivation was observed when mixed phages were subjected to freezing at -20 far at least 60 to 120 min. The conditions of yoghurt production (temperature and time of incubation) at 40-42 ºC for 3-4 hrs were suitable for phage propagation, so the phage lyses was incredsed under these conditions. All phages (0/S0. 10/S0 and 8/S8) were resistant at pH ranges from 5.5 to 7.5. No clear inactivation was observed by storage the phages in normal milk or in yoghurt at 4c for 15 days. The rate of S. thermophilus phages inactivation was higher S. thermophilus was in single clilture than in mixed culture containing Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus). Clear differences were observed in phage inactivation of different phages for the same strains. These obtained data of inactivation kinetics of relevant bacteriophages, will make it possible. by specifically setting process parameters. to improve jermentation safety.

Summary in Arabic.

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