Biodiversità di lieviti isolati da siero-innesto di produzioni casearie italiane

Objectives The dominant species present in the whey starter of PDO and traditional cheeses play a key role, positive or negative, in defining the specific organoleptic characteristics of each cheese. This study provides a view of the composition of the yeast community in natural whey starter for Trentingrana PDO and Provolone Valpadana PDO production. The yeasts isolated from the whey cultures of these two dairy products have been identified, typed and characterized by phenotypic and genotypic methods in order to highlight their biodiversity and metabolic potential. In particular, the strains were evaluated based on some features of technological interest (lipolysis, proteolysis and ability to form biofilms). Methods Thirty-three natural whey starters (21 from 13 Trentingrana DOP dairies and 12 from one Provolone Valpadana DOP dairy) were analyzed for yeast count. The 54 isolates (48 from Trentingrana and 6 from Provolone) were typed by RAPD-PCR and the different biotypes identified by sequencing the D1/D2 domain of the large subunit RNA gene and the internal transcribed spacer regions of the rDNA. They were also technologically characterized (lipolytic activity, proteolytic activity and biofilm production) according to methods reported in the literature. Results The yeast content in whey starters varied between 0.95 and 5.27 log10 UFC/mL, and, in particular, a high variability between samples from processing in Trentingrana DOP was highlighted. The isolates showed good inter- and intra-specific variability and the biotypes identified were found to belong to 9 genera and 15 species, markedly divided according to cheese origin. Almost all strains were lipolytic, while 30% showed proteolytic activity. A marked lipo- and proteolytic potential by Aureobasidium pullulans emerged. Most strains were also able to form biofilm, albeit weakly or moderately. Conclusion The whey starter of Italian PDO cheeses is characterized by a rich biodiversity in terms of yeast species, possessing a metabolic potential that can strongly influence the quality and safety of dairy products.