Abstract

HART, R.S.; NDIMBA, B.K.  and  JOLLY, N.P.. Characterisation of thiol-releasing and lower volatile acidity-forming intra-genus hybrid yeast strains for sauvignon blanc wine. S. Afr. J. Enol. Vitic. [online]. 2017, vol.38, n.2, pp.144-155. ISSN 2224-7904.  http://dx.doi.org/10.21548/38-2-1322.

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 thiol-releasing 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.

Keywords : Acetic acid; iTRAQ; metabolomic; Orbitrap LC-MS/MS; proteomics; SPE GC-MS/MS; volatile thiols.

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