Screening for promising yeast strains for sherry wine production using genetic and enological markers

Flor yeast is a special group of wine-making microflora used in the production of biologically aged wines. In the process of biological aging, flor yeast, cultivated on the surface of dry, alcohol-based wine materials, switches its metabolism from enzymatic to oxidative, which leads to deep biochemical changes in the wine with the formation of unique features of the bouquet and aroma of sherry wines. Genetic, biochemical and physiological features of flor yeast associated with their adaptation to specific conditions of sherry winemaking have been studied in sufficient detail. Earlier, the use of comparative genomic analysis methods allowed us to identify a number of genetic markers specific for flor strains, convenient for searching for strains that are promising for producing sherry-type wines. This work presents the results of using a combined approach based on primary molecular genetic screening followed by analysis of physiological, biochemical and oenological properties for the selection of strains promising for sherry winemaking in a sample of 47 strains from the Magarach Winemaking Microorganism Collection and 96 natural isolates from samples of grapes in different climatic zones in the Republic of Crimea and in the Rostov region. At the first stage, the selection of promising strains was carried out on the basis of the results of genotyping by the presence of alleles of the loci ITS, YDR379C-A , and FLO11 characteristic of flor strains. According to the genotyping data, the flor allele of the ITS locus was identified in 41 strains, the flor allele of the YDR379C-A gene was identified in 41 strains, and a deletion of 111 nt in the promoter of the adhesin FLO11 gene, typical of flor strains, was found in only 12 strains. A total of 59 studied strains had the flor allele of at least one of the three loci. Further study of oenological properties showed that the presence of the ITS flor locus can serve as a marker for the selection of strains with high oxidative capacity. Film formation in most strains (11 samples out of 12) with a flor variant of the FLO11 gene promoter confirmed the main role of this adhesin gene in determining the ability of strains to surface growth on wine material. The most informative was the use of the YDR379C - A marker. Of the 12 strains for which the presence of only this flor locus was determined, three collection and two natural strains (I-133, I-492, I-616, No. 49, No. 78) showed the presence of all flor characteristics. The formation of a continuous film with a reproducibility of 100 % was observed in two collection strains from this group - I-133 and I-492. Nine strains (75 %) synthesized aldehydes in an amount exceeding 100 mg/l, 6 strains (50 %) formed a film with varying degrees of formation from islands on the surface to continuous growth and film reproducibility from 33 to 100 %. Aldehyde aroma and oxidation taste were determined for 58 % of the samples. Analysis of the oenological properties of six strains with three flor loci showed that all of them formed a continuous film on the surface of the fermented wort at optimal times, and five strains synthesized aldehydes during alcoholic fermentation above 100 mg/l. Tasting laboratory samples of fermented wort revealed the presence of sherry tones in aroma and taste. According to the results of genotyping and oenological sherry characteristics, these strains were close to the control strain I-329. As a result, according to the results of the screening and production check, the collection strain I-271 can be recommended for sherrying wine materials from the Aligote grape variety, traditionally used for these purposes, as well as blended wine materials from the Rkatsiteli and Sauvignon green grape varieties, new for sherry wines, which opens up the prospect creation of new brands of this type of wine. Thus, the study showed that during the initial selection of new flor strains of S. cerevisiae yeast, testing them for genetic markers ITS, YDR379C-A , and FLO11 allows you to quickly and reliably identify the most promising strains for the technology of sherry wine production. Of 143 strains of wine yeast, according to the results of genotyping, taking into account oenology, strain I-271 with great potential for sherrying wine materials was identified.