Raw milk as a source of Bacillus spp. responsible for the spoilage of milk products
2007
Mijacevic, Z.(Univerzitet u Beogradu, Beograd (Serbia). Fakultet veterinarske medicine) | Bulajic, S.(Univerzitet u Beogradu, Beograd (Serbia). Fakultet veterinarske medicine)
Bacillus spp. are often present as contaminants in raw milk. Due to thermo resistance of their spores, bacilli survive after the heat treatment in milk industry. The proteolytic activity of bacilli leads to spoilage of milk and milk products and according to that influenced the durability of milk product. The material of investigation consisted of 243 samples of raw milk, 40 samples of pasteurized milk and corresponding 40 samples of raw milk during the milk pasteurization and 60 samples of pasteurized milk on expiry date. The proteolytic activity of bacilli was determined according to modified method that is established by Hill and Gasson (1986). The level of Bacillus spp. contamination of raw milk was 2.76+/-0.72 log(10) cfu/ml, 1.74+/-2.52 log(10) cfu/ml for pasteurized during production process, and level of Bacillus spp. contamination of final product-pasteurized milk was 2.38+/-0.47 log(10) cfu/ml. It was determined the presence of following species: B. licheniformis 46.15%, B. pumilus 15.38%, B. subtilis 15.38%, B. brevis 11.54%, B. sphaericus 7.69%, B. cereus 3.85% in raw milk and B.subtilis 71.42%, B. pumilus 14.28% and B. licheniformis 14.28% in pasteurized milk during production process. Isolated strains of Bacillus spp. showed significant proteolytic activity which have influenced the durability of pasteurized milk.
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