Diversity among lactococci isolated from ewes' raw milk and cheese

摘要

The technological and genetic characteristics of lactococci present in ewes' raw milk and 1-d-old ewes' raw milk cheeses sampled over a 1-year period were investigated. The proportion of lactic acid bacteria isolates from milk samples able to decrease milk pH by more than 1.25 units after 6 h incubation at 30 deg C reached 14.5% in spring vs 10.7% in summer, 8.3% in autumn and 3.0% in winter. In 1-d-old cheese samples, the proportion of lactic acid bacteria able to lower milk pH by more than 1.25 units increased up to 32.3% in spring vs 23.4% in summer, 8.0% in autumn and 10.3% in winter. Fast acid-producing lactic acid bacteria mainly belonged to the genus Lactococcus. Using polymerase chain reaction protocols, fast acid-producing lactococci were grouped as 61 Lactococcus lactis subsp. lactis, 13 L. lactis subsp. cremoris and 14 L. lactis subsp. lactis biovar diacetylactis. Randomly amplified polymorphic DNA (RAPD) fingerprinting of fast acid-producing lactococci, using two primers, resulted in 21 differen RAPD patterns for L. lactis subsp. lactis isolates, nine RAPD patterns for L. lactis subsp. cremoris isolates and three RAPD patterns for L. lactis subsp. lactis biovar diacetylactis isolates. Up to 19 different RAPD patterns were found for L. lactis isolates from cheeses made in a particular month.