Zygosaccharomyces bailii: A Promising Probiotic Candidate for Functional Food Development.

The growing interest in functional foods is accompanied by the need to select new probiotic microorganisms. Artisanal fermented foods serve as excellent sources for identifying probiotics, particularly yeasts. In this work, two strains isolated from kombucha were identified: Zygosaccharomyces bailii (UVI60) and Z. lentus (UVI61). Strain UVI61 did not grow at 37 °C, so the evaluation of probiotic properties was carried out with strain UVI60. Z. bailii UVI60 showed excellent survival (98%) under adverse conditions involving synthetic gastric and duodenal juices. The self-aggregation capacity (97% after 4 h), cell surface hydrophobicity (85% after 48 h) and, in particular, adhesion to Caco-2 cells demonstrated its ability to adhere to the intestinal epithelium. Additionally, the strain exhibited strong antioxidant activity (86%), ability to hydrolyze bile salts and excellent coaggregation capacity (64-92%) with pathogens. Using Caenorhabditis elegans as an animal model, Z. bailii demonstrated a potential geroprotective effect by extending the mean lifespan of the worm by 12.5%. Moreover, intracellular extracts and supernatants obtained from Z. bailii showed remarkable cytotoxic activity against colon, ovarian and melanoma tumor cell lines. Z. lentus UVI61 also presented this activity, thus suggesting its potential as a postbiotic. The results confirm that the studied strains contribute to the probiotic and functional properties of kombucha and highlight the potential use of Z. bailii as a promising probiotic. Finally, Z. bailii UVI60, together with the strain Brettanomyces bruxellensis UVI56, which was previously characterized as a putative probiotic, exhibited excellent viability in different foods based on various plant food matrices, confirming its suitability for the development of new functional foods.