Occurrence and thermoresistance of thermophilic streptomycetes spores in milk.

200 samples of raw milk and 100 samples of pasteurized milk were tested for the presence of thermophilic streptomycetes. One ml of raw and pasteurized milk contained mean 8.42 and 14.95 thermophilic streptomycetes, respectively. The isolated strains belonging to the species Thermoactinomyces vulgaris Tsiklinsky 1899 and Micromonospore sp. (Agre et al., 1972) were identified. To determine the survival of spores of these thermophiles after pasteurization, samples of milk were heated at 63.5 degrees C/30 min and at 75 degrees C/15 s. Ampouls with this milk, dairy pasteurized milk and raw milk were heated for the same time intervals at 100, 105, 110 and 120 degrees C. Thermophilic streptomycetes spores contained in the investigated milk samples survived the both of pasteurization temperatures. A relative high number of thermophilic streptomycetes spores survive the heat treatment at 100 degrees C. The heat resistance at 105, 110 and 120 degrees C is distinctly lower. The most resistant in the range of the testet temperatures proved spores of the species Thermoactinomyces vulgaris Tsiklinsky 1899.