SPONTANEOUSLY FERMENTED PRODUCTS—MICROBIAL RESERVOIR FOR ISOLATING NEW POTENTIAL PROBIOTIC YEAST STRAINS

The growing interest of consumers in minimally processed and health-promoting foods prompts researchers to find alternative probiotics, especially yeast strains, that are able to withstand industrial and gastrointestinal stress, are not associated with horizontal gene transfer of antibiotic resistance and display broad environmental tolerance.

Our study aims at determining the probiotic potential of nine newly identified yeast strains isolated from household spontaneously fermented food products (pickled cucumbers, homemade borscht, wine wort and pickled cabbage in brine) from the Bucharest-Ilfov region, Romania. The taxonomic identification using PCR-RFLP and ITS1-5.8S-ITS2 rDNA sequencing showed that the yeast isolates belong to Saccharomyces, Torulaspora, Debaryomyces and Metschinikowia genera. The safety profiling was performed by screening for the production of extracellular enzymes known to damage human cells, including hemolysins, gelatinases, caseinases, DNases, amylases and phospholipases. None of the strains produced all the tested enzymes, suggesting an acceptable safety profile. Functional characterization revealed promising probiotic traits: wine wort isolates showed strong auto-aggregation (up to 75%) and hydrophobicity (up to 80%), which indicates good adhesion potential. The strains from brine-based products exhibited high tolerance to bile salts, while those from borscht and wine wort tolerated low pH (pH 2) and showed increased biomass production in the presence of pancreatic enzymes. Antimicrobial activity was observed for the strains Debaryomyces hansenii V I and Torulaspora delbrueckii III 2 based on the production of killer toxins which were effective against common foodborne pathogens and clinically relevant Candida strains. Additionally, Metschinikowia pulcherrima M3 showed high antimicrobial potential via iron competition, inhibiting food spoilage microorganisms.

The results highlight the untapped potential of naturally fermented foods as an isolation source for potential probiotic yeasts. The nine newly characterized yeast strains exhibit key probiotic traits, recommending them as promising candidates for further testing for the development of functional food products.