Yeast Microflora of Dairy Products Sold in Russia

The yeast microflora of various dairy products sold in Russia was studied using RFLP analysis of the 5.8S-ITS rDNA fragment and sequencing of the D1/D2 domain of 26S rDNA. Most of the fermented milk products studied were dominated by lactose-utilizing yeasts Kluyveromyces and Debaryomyces and by lactose-negative yeasts Saccharomyces, Monosporozyma, Pichia, Geotrichum, and Yarrowia. The yeast Kluyveromyces marxianus was present in most of the fermented milk products studied, while the related species K. lactis was found only in some samples of ayran, curds, and cheese. The dominance of K. marxianus is apparently associated with their physiological characteristics (thermo- and osmotolerance), which provide these yeasts with better adaptation to industrial fermentation conditions. The dominant species in mixed-fermentation dairy products, Saccharomyces cerevisiae and Monosporozyma unispora, were completely absent in cheeses and lactic acid fermentation products. In general, the species composition of yeasts largely depended on the fermented milk product, the type of milk, and the specific manufacturer.