Safety Assessment and Preliminary In Vitro Evaluation of Probiotic Potential of Lactococcus lactis Strains Naturally Present in Raw and Fermented Milk

The present study was conducted to find the potential of Lactococcus lactis strains naturally present in raw and fermented milk as probiotics and to evaluate their safety and some technological characteristics. There are numerous studies that evaluated probiotic properties of lactococci, nevertheless, limited studies on the probiotic potential of lactococci isolated from raw milk or dairy products were performed. Strains isolation from raw milk or dairy products and their characterization is important when selection of starter strains for the production of functional dairy foods is performed. Depending on aroma production and acidifying activity, 33 L. lactis strains were selected out of 169 and evaluated for safety, technological and probiotic properties. These strains were screened for antibiotic sensitivity, enzymatic activity, hemolytic and gelatinase activities. The strains were also assessed for resistance to bile salts and acid, growth in bile acids and cholesterol, cell surface hydrophobicity. Based on the obtained results, two strains with the best probiotic potential were selected. These two L. lactis strains, with 51% and 67% survival at low pH and more than 80% resistance to various bile salt concentrations, proved their resistance in vitro to gastric conditions. Also these strains proved to be good acidifiers (the pH of milk was reduced by at least 1 unit in 6 h at 30–37 °C) and can be used in the development of functional dairy foods as starter cultures.