Kombucha as a Reservoir of Probiotic Yeasts Tailored for Plant-Based Fermentations

Kombucha is a reservoir of health-promoting yeast strains. In this study, molecular characterization of the Kombucha microbiota led to the identification of 52 distinct yeast isolates, highlighting a complex community, where Brettanomyces anomalus was identified as the dominant yeast species. Other key species were identified, such as Pichia membranifaciens, Torulaspora delbrueckii, Zygosaccharomyces bailii, Starmerella bacillaris, and Meyerozyma guilliermondii. These isolated yeasts were screened for essential probiotic requirements, demonstrating excellent functional traits showing over 80% survival rate under simulated gastric and gastrointestinal conditions. Regarding the surface properties, wide cell hydrophobicity and auto-aggregation capabilities were seen. Broad antioxidant ability and robust antimicrobial activity against Escherichia coli and Staphylococcus aureus were observed, highlighting a protective function. Two strains of T. delbrueckii and one strain of Z. bailii stood out as probiotic candidates and were technologically evaluated in different culture combinations: yeast formulation pools using a specialized "probiotic pool" (PP) and a broader "yeast pool" (YP) both yielded successful analytical and sensory profiles. A strain of Lachancea thermotolerans, isolated from a distinct natural matrix, was employed as a technological booster to drive a yeast-based, bacteria-free kombucha. This study confirmed that specialized kombucha yeasts were not just fermentation drivers, but sustainable assets for developing novel functional plant-based probiotic beverages.