Impact of Candida railenensis during fermentation on the aromatic profile of Vidal blanc icewine.

Mixed culture fermentation with non-Saccharomyces yeasts and Saccharomyces cerevisiae as multi-starters has more advantages than spontaneous fermentation, and wine products with distinctive and pleasant aromas can fulfill the diverse demands of consumers. This study was carried out to illuminate the effect of sequential inoculation of indigenous Candida railenensis and S. cerevisiae on alcoholic fermentation behavior and chemical and aromatic characteristics of Vidal blanc icewine. During the mixed culture fermentation, C. railenensis was present in the initial and middle stages but was absent after 14 days. The results of basic chemical parameters showed that the glycerol content in the mixed culture-fermented icewine was higher than that of the pure fermented icewine, but the acetic acid content was the opposite. In terms of volatile aroma compounds, C. railenensis in the mixed culture fermentation reduced some metabolites such as lower alcohols, 1-hexanol, 3-methylthiopropanol, and their unpleasant notes and increased the production of some desired volatile aroma compounds such as benzaldehyde, ß-damascenone, 2-furanmethanol, and 5-methyl furfural associated with rose, honey, nut, and caramel characteristics. Furthermore, C. railenensis also changed the sensory performance of icewine by participating in the fermentation of S. cerevisiae. These findings suggest that C. railenensis with positive enological properties has the ability to be used in icewine production, which has never been reported before.

Impact of Torulaspora delbrueckii During Fermentation on Aromatic Profile of Vidal Blanc Icewine.

Non-Saccharomyces yeasts usually have a positive effect on improving the diversity of wine aroma and increasing the differentiation of wine products. Among these non-Saccharomyces yeast species, Torulaspora delbrueckii is often studied and used in winemaking in recent years, but its application in icewine has not been reported yet. In this study, indigenous T. delbrueckii strains (TD1 and TD2) and Saccharomyces cerevisiae strains (commercial yeast SC1 and indigenous icewine yeast SC2) were sequentially inoculated for icewine fermentations; meanwhile, pure S. cerevisiae (SC1 and SC2) fermentations were used as the control; TD1, TD2, and SC2 strains used were screened from spontaneous fermentations of Vidal blanc icewine. The aim was to investigate the effect of T. delbrueckii on the aroma complexity of icewine, which is of great significance to the application of T. delbrueckii in icewine production. The results showed that T. delbrueckii was completely replaced by S. cerevisiae at the middle and later fermentative stages in mixed culture fermentations. Compared with the icewine fermented with pure S. cerevisiae, mixed culture fermented icewines contained lower acetic acid and ethanol, and higher glycerol. The inoculation of T. delbrueckii greatly impacted the levels of several important volatile compounds, and more 2-phenylethyl alcohol, isoamyl acetate, linalool, D-limonene, p-cymene and cineole were produced, and the fruity, flowery, and sweet characteristic was intensified. Moreover, the relevance of strain-specificity within T. delbrueckii to aroma compound differences was shown. To our knowledge, this study is the first to investigate the application of T. delbrueckii in Vidal blanc icewine fermentation, and volatile aroma compounds in the icewine fermented by T. delbrueckii and S. cerevisiae.

Characterization of tolerance and multi-enzyme activities in non-Saccharomyces yeasts isolated from Vidal blanc icewine fermentation.

This work aim to study the tolerance and aroma-related enzymes activities of the non-Saccharomyces yeasts in Vidal blanc icewine from the Huanren region of China. The strains were identified by sequencing internal transcribed spacer (ITS) region and the 26S rDNA D1/D2 domain genes and all representative non-Saccharomyces yeasts were belonged to genera Metschnikowia, Hanseniaspora, Torulaspora, Candida, and Debaryomyces. A total of 28 strains were carried out for tolerance experiments and results suggested that most of them could tolerate 500 g/L glucose, 4% ethanol, 20 g/L tartaric acid, and 350 mg/L SO2 . Finally, a total of 17 strains with better tolerance were carried out for the ß-glucosidase, ß-xylosidase, and pectinase activities experiments. The results showed that Candida railenensis HC08 and the strains of Hanseniaspora genus have satisfactory multi-enzyme activities, which can be used to design mixed fermentation to produce characteristic icewine. PRACTICAL APPLICATIONS: Non-Saccharomyces yeasts produces a series of hydrolytic enzymes that are thought to have a significant contribution to the aroma complexity of wines, however, are poorly explored in icewine. In this work, most of the non-Saccharomyces yeasts screened from Chinese icewine can adapt well to the high-sugar and high-acid environment of icewine, and can secrete hydrolase. The application of these strains in mixed fermentation could provide a prospect for the production of characteristic icewine.