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

Eleven strains of lactococci isolated from a farmhouse starter-free cheese manufactured from raw cowʹs milk were analysed in detail for some technologically-related properties. Large phenotypic differences were encountered between the isolates, some of which could be of practical relevance. Several strains produced lactic acid at a rate and at a final concentration suitable 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 β -galactosidase activity. Plasmid and chromosomal analyses indicated a high degree of diversity among wild strains and showed low homology with some well-known Lactococcus lactis strains. Under highly stringent conditions, only one plasmid from a single strain gave a clear positive hybridization signal with lactococcal-derived probes for the β -phospho- galactosidase and the proteinase genes. In general, wild strains produced more odorous compounds and in higher amounts than the reference strains.