Isolation and Partial Characterization of Lactic Acid Bacteria from Natural Whey Starter Culture

Natural whey starter (NWS) cultures are microbial consortia characterized by high microbial diversity in terms of genus and species, as well as strains, accounting for the variety of different characteristics and quality of the artisanal fermented food. By means of a combined approach, using plate counts, bacterial isolation, molecular identification, and genotyping, we analyzed 41 colonies isolated from NWS of cow milk used in the production of caciocavallo, a typical pasta filata Italian cheese. Results revealed that 27 of them were lactic acid bacteria (LAB), including Lactococcus lactis as the dominant species, followed by Streptococcus thermophilus, Enterococcus faecium, Limosilactobacillus fermentum, Lactobacillus helveticus, and Lacticaseibacillus rhamnosus. The remaining isolates were taxonomically identified as non-LAB, probably due to environmental contamination. These results were mostly confirmed by metagenomic analysis, with the exception of only three species. Finally, small-scale fermentation experiments were performed in both standard media and skimmed milk to further characterize the newly isolated LAB strains. Overall, our results show that, except for four of the Lactococcus isolates and one Streptococcus, which show multi-drug resistance, the isolated strains under study exhibit levels of acidifying, metabolic properties, and safety parameters, suggesting their potential as starter cultures in cheese production.