Phenotypic and genetic characterization of a selected set of Lactococcus lactis strains isolated from a starter-free farmhouse cheese

Eleven strains of lactococci isolated from a farmhouse starter-free cheese manufactured from raw cow's milk were analysed in detail for some technolog ically-related properties. Large phenotypic differences were encountered be tween the isolates, some of which could be of practical relevance. Several strains produced lactic acid at a rate and at a final concentration suitabl e for large-scale cheesemaking. The enzymatic capabilities assayed with the API ZYM system showed that all strains possess similar profiles with weak proteinase and moderate leucine-arylamidase and esterase-lipase activities. Interestingly, two related strains presented a strong beta-galactosidase a ctivity Plasmid and chromosomal analyses indicated a high degree of diversi fy among wild strains and showed low homology with some well-known Lactococ cus lactis strains. Under highly stringent conditions only one plasmid from a single strain gave a clear positive hybridization signal with lactococca l-derived probes for the beta-phosphogalactosidase and the proteinase genes . in general wild strains produced more odorous compounds and in higher amo unts than the reference strains. (C) 2000 Academic Press.