Comparison of the yeast flora of freeze-dried, water-soaked and daily transferred kefir grains (Georgia, Russia)

Yeast flora of three kinds of Georgian kefir grains was investigated. They were freeze-dried grains (FDG), water-soaked grains (WSG), and daily transferred active grains (DTG). Strains of three well-known yeast species, Saccharomyces unisporous, Candida kefyr, and Candida holmii were isolated from DTG. Only Saccharomyces unisporus strains were isolated from FDG and WSG. Furthermore, strains of Candida valida were contaminated at a ratio of 1 : 3 in WSG. These results would indicate that C. kefyr and C. holmii are less tolerant to freeze-drying compared with S. unisporus. Freeze-drying seems to damage the cells of C. kefyr and C. holmii by cold shock and a concentration of lactic acid produced by lactic acid bacteria in the kefir production. C. holmii is nutritionally exacting and grows slowly. The role of this species has not been clear, but some effects will be expected for stimulation of other microorganisms. Preservation of the kefir grain was discussed from the viewpoint of yeast flora.