In Vitro Screening and Characterization of Kefir Yeast for Probiotic Attributes

Renuka Basavaiah, Geethakumari, Madhukar Nagesh, Murali Harishchandra Sripathy, Harsh Vardhan Batra*

The yeasts constitute a large and heterogeneous group of microorganisms, currently attracting increased attention from scientists and industry as probiotics. Till date only Saccharomyces boulardii has been extensively studied for its probiotic effects. Therefore, the current study aims to characterize the probiotic potential of yeast isolated from kefir, a fermented beverage. Out of 22 yeast isolates screened, 13 isolates could survive (>75%) in simulated conditions similar to the gut (pH 2.0 and 1.0% bile salt). The isolates showed high auto-aggregation (>85%) ability and cell surface hydrophobicity (>75%) have also expressed high in-vitro adherence (>90%) to HT-29 cells. A simulation of transit tolerance in the upper human gastrointestinal tract together with auto-aggregation, hydrophobicity, and adherence to HT-29 cells have been vital in reducing the number of yeast strains to 7 promising probiotics. The probiotic yeast strains showed resistance to commonly used antibiotics and exhibited a broad spectrum of antagonistic activity against pathogenic microorganisms (E. coli, S. typhimurium, S. paratyphi-A, S. aureus, S. sonnei, B. cereus and Y. enterocolitica). The results obtained were compared with the reference culture, Saccharomyces cerevisiae ATCC 7745. Based on 5.8S rRNA gene sequencing the isolates were identified as Pichia kudriavzevii, Candida xylopsoci, Saccharomyces cerevisiae and Issatchenkia orientalis. Overall these results demonstrated the possible use of these isolates in the development of novel functional foods with potential probiotic properties.