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South African
Wine Lab Association:

Charaterisation of Thiol-releasing and Lower Volatile Acidity-forming Intra-genus hybrid Yeast strains for Sauvignon blanc wine

R.S. Hart1,2*, B.K. Ndimba1, N.P. Jolly1

A single Saccharomyces cerevisiae wine yeast strain produces a range of aroma and flavour metabolites
(e.g. volatile thiols), as well as unfavourable metabolites (e.g. volatile acidity [VA]), during the alcoholic
fermentation of white wine, especially Sauvignon blanc. The former contribute to the organoleptic
quality of the final wine. Previous research showed that yeast-derived enzymes (proteins) are involved in
the release of wine quality-enhancing or quality-reducing metabolites during fermentation. Small-scale
winemaking trials were initiated to evaluate the protein expression and metabolite release of S. cerevisiae
hybrid yeasts producing tropical fruit aroma. Commercial ‘thiol-releasing’ wine yeasts (TRWY) were
included in winemaking trials as references. Improved hybrids were identified that showed enhanced thiolreleasing
abilities, specifically 3-mercaptohexanol (3MH), and lower VA formation during the production
of Sauvignon blanc wines compared to some commercial TRWY references. It is noteworthy that the
hybrid NH 56 produced wines with the second highest 3MH levels after hybrid NH 84, and with the lowest
acetic acid of all strains included in this study. This yeast was also the only strain to have downregulated
proteins linked to amino acid biosynthesis, the pentose phosphate pathway, glycolysis, and fructose and
galactose metabolism during the lag phase. Furthermore, differences in protein expression were reflected
in the variation in metabolite release by different strains, thereby confirming that enzymes (proteins) are
the final effectors of metabolite release.

acetic acid, iTRAQ, metabolomic, Orbitrap LC-MS/MS, proteomics, SPE GC-MS/MS, volatile thiols

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