Evaluation of yeast biodiversity in Iranian traditional Kefir samples

Background and Aim : Kefir is a fermented product with numerous attributed health benefits due to the presence of a mixture of bacteria and yeasts in an exopolysaccharide matrix. Although the bacterial population is dominant in kefir, the presence of yeast plays an important role to develop the flavor and the chemical composition of the kefir product. Moreover, the yeast strains are important for the microbial balance by providing the essential nutrients for a probiotic bacteria population such as vitamins and amino acids and produce some compounds that contribute to the kefir drink taste.Methods : Ten traditional kefir grain samples were acquired from ۳ different cities of Iran (Mashhad, Tehran and Zanjan). Dilutions of the sample were directly plated on Rose Bengal agar and incubated at ۲۵ °C for ۷۲ h. Fungal colonies were subcultured and purified on yeast peptone glucose agar (YPG agar) at the same condition. The morphological and biochemical characteristics of the isolates were determined according to the standard methods. Different morphotypes were identified based on the sequencing of their large subunit rDNA D۱/D۲ domain.Results : ۴۱ yeast strains were isolated from ten different kefir samples and ۱۷ morphotypes were chosen for identification by molecular sequencing. All the selected morphotypes lacked urease activity and showed negative Diazonium Blue B reaction approving them as members of ascomycetes. Molecular identification revealed the morphotypes belongs to Pichia fermentans (۷ strains), Kluyveromyces marxianus (۶ strains), Saccharomyces cerevisiae (۳ strains), and Pichia kudriavzevii (۱ strain). Conclusion : Pichia and Kluyveromyces were found to be the most abundant population in the traditional kefir samples.

Keywords:

Kefir grains , Microbial biodiversity , Molecular identification , Yeast