Abstract
Yeast influences the development of red wine colour during winemaking and its stability during bottling and storage. Thus, understanding the yeast genetic mechanisms regulating such phenomena will contribute to consistent wine quality. A sequenced set of 96 progeny derived from a genetic cross of two commercial wine strains was used to unravel the genetic basis of yeast-derived colour modulation of model red wine. Colour differences have been genetically linked by Quantitative Trait Loci (QTL) mapping to regions of chromosomes 8 and 15. Further work is required to characterise the identified genes which may modulate wine colour through the adsorption of red pigment on yeast biomass.
Summary
This project sought to genetically map the genes responsible for yeast-derived modulation of colour in a model red wine. A set of 96 hybrid wine yeast derived from a genetic cross between two commercial wine strains (Enoferm M2 and Zymaflore F15) were evaluated for fermentation performance in synthetic red juice, and their effect on the resultant ‘wine’. The biochemical and colour data were collected by Drs Michelle Walker and Tommaso Liccioli (University of Adelaide) and correlated to the genome sequences of the 96 wine strains by Dr Miguel Roncoroni and Professor Richard Gardner (University of Auckland).
The key findings are listed below:
The genomes of the 96 hybrid wine yeast have been previously sequenced, and the allelic variations in the corresponding genes, originating from the two parents, Enoferm M and Zymaflore F15 identified (Roncoroni 2014)
Laboratory-scale (100 mL) fermentations were conducted in batches of 96 (totalling ~350) using an automated fermentation platform which allowed continual on-line monitoring of fermentation progress
Spectrophotometric determination of CIELab coordinates (L*, a*, b*), was used to define the colour in clarified fermented juice and re-suspended yeast biomass. Colour differences were calculated mathematically between the parental strains and hybrids, and the data ‘mapped’ to the 96 genomes
Two QTLs, associated with specific regions of chromosome 15 and chromosome 8 were identified as being strongly correlated with variation in wine colour and pigmented yeast biomass. The region on chromosome 15 was linked to L*, a* and b*, whilst that of chromosome 8, to L* and b*
A minor QTL on chromosome 6 was also identified, specifically linked to b* for only yeast biomass
Strong correlations between visual determination of colour (CIELab) and physical and biochemical determination of colour using the Somers Method
Computational ‘mapping’ of the biochemical data (anthocyanins, organic acids, glycerol, ethanol) to the 96 genomes is in progress
A manuscript on QTL mapping of traits related to wine making is in preparation (Roncoroni et al). Colour data generated as part of this project will contribute to the results disseminated in the paper
These findings related to colour modulation will be used as support of new funding applications to further investigate several genes identified in this preliminary study as affecting colour in model red wine through possible adsorption on yeast cells