Changes of diversity and population of yeasts during the fermentations by pure and mixed inoculation of Saccharomyces cerevisiae strains

Mixed inoculation of Saccharomyces cerevisiae strains is used in winemaking for achieving high sensory quality of the wine. However, information on the diversity and population of yeasts during inoculated fermentation is very limited. In this study, we evaluated the effect of mixed inocula with different inoculation timing on the yeast community during fermentations of Cabernet Sauvignon. Grape must was inoculated with pure cultures of S. cerevisiae RC212 or S. cerevisiae R312, and simultaneous and sequential inoculation of both strains. Wallersterin Laboratory Nutrient (WLN) medium and sequence of the 26S rDNA D1/D2 domain were used to compare the diversity of yeast species. Five species, including Candida diversa, Hanseniaspora opuntiae, H. uvarum, Issatchenkia orientalis and I. terricola, were identified in the grape must, with Issatchenkia sp. being predominant (67.5 %). Three to four species were involved in each fermentation treatment. The fermentations by mixed inocula presented more yeast species than by pure inocula. Interdelta sequence typing was used to identify S. cerevisiae strains. Ten genotypes were identified among 322 isolated S. cerevisiae strains. Their distribution varied among different stages of fermentations and different inoculation treatments. The inoculated strains were not predominant, while indigenous genotypes I, III, and V showed strong competitiveness during fermentation. In general, this study provided information on the change of population structure and genetic diversity of yeasts in fermentations inoculated with pure and mixed S. cerevisiae strains.