Phenotypic and genotypic identification and technological characterization of Lactococcus lactis ss lactis isolated from traditional Italian raw milk cheeses

Artisan and traditional Italian cheeses produced in the Alps are manufactured using raw milk, and their fermentation is driven by adventitious microbiota. In many traditional cheeses Lactococcus lactis ss lactis is the most frequently isolated NSLAB species. In the present study, 64 strains of Lc. lactis ss lactis were isolated from dairy products from different Lombardy Alpine areas and identified phenotypically and genotypically, and evaluated for technologically relevant biochemical activities: growth conditions, acid production, redox, lipolytic and proteolytic activities. Phenotype identification was performed on carbohydrate fermentation profile galleries (Api 20 Strep (bioMérieux, France) and Biolog AN Microplate (Biolog, USA)). All the isolates were subjected to PCR amplification specific to Lc. lactis ss lactis to confirm the phenotype identification. Identification was performed by Api 20 Strep and Biolog AN and the results were in agreement in 61 of the considered 64 strains (Biolog AN identified 3 strains as Lc. raffinolactis). PCR with species-specific primers gave different results for 6 strains identified as Enterococci. The strains displayed wide heterogeneity in the biochemical characteristics: 23 strains were able to grow at 45°C, 6 did not grow at 15°C, 9 did not produce acid from maltose and 5 from ribose, while only 1 strain utilized melibiose. Only one isolate fermented raffinose and 20of the 64 produced acid from sucrose. Glucose, fructose and trehalose were fermented by all the isolates, and none utilised melezitose. The technological properties differed within the species, in particular Lc. lactis ss lactis strains isolated from curd showed lower acidifying and higher reducing activity than strains isolated from cheese. The results suggest that the peculiar sensory characteristics of these traditional cheeses are very closely related to the high biodiversity of the indigenous microflora