INSIGHTS ON THE ROLE OF GENES ON AROMA FORMATION OF WINES

Abstract

Yeast secondary metabolism is a complex network of biochemical pathways and the genetic profile of the yeast carrying out the alcoholic fermentation is obviously important in the formation of the metabolites conferring specific odors to wine. The aim of the present research was to investigate the relative expression of genes involved in flavor compound production in eight different Saccharomyces cerevisiae strains.

Two commercial yeast strains Sc1 (S.cerevisiae x S.bayanus) and Sc2 (S.cerevisiae) and six indigenous S. cerevisiae strains (Sc3, Sc4, Sc5, Sc6, Sc7, Sc8) isolated during spontaneous fermentations were inoculated in Assyrtiko and Vidiano grape must. The fermentation kinetics, content of organic acids and gly- cerol production was monitored daily throughout the experiment. Transcript profiling of yeast genes in- volved in aroma formation and volatile composition of the must/wine was performed through real-time RT-PCR and SPE/GC–MS respectively, at four different time points of the fermentations. Specifically, a total of 28 volatile compounds were determined and the relative expression levels of 46 genes coding for acetyl-CoA synthetases, amino acid permeases, transaminases, reductases, decarboxylases, alcohol and aldehyde dehydrogenases, alcohol acetyltransferases, acyltransferases, esterases and glycosidases were recorded.

The relative expression levels of the genes implicated in amino acids, higher alcohols, ethyl esters, and terpenes metabolism, such as EEB1, EHT1, EXG1, ARO8, ARO9, PDC5, PDC6, ADH6, ADH3, AAD14, AAD16, were higher at the first three time points studied, since the most active period of aroma compound accumulation appears to occur in earlier fermentation stages. Additionally, the transcriptome data revealed substantial changes in expression patterns of genes between the different strains tested. In terms of the volatile characterization of the wines, the concentration levels of total esters and total alcohols appeared to be clearly distinct between the wines, which confirms that the production of volatile compounds is strain depended. Remarkable differences in the gene expression levels were observed when comparing the different strains which resulted in different aroma profiles.

This study enhances our understanding on yeast aroma metabolism-related gene expression and regulation. This knowledge can be a tool to modulate aroma production and orient the fermentation process towards a desirable wine aromatic profile.