Identification of yeast genes involved in Sauvignon Blanc aroma ...

3.4 Supplementing grape juice with elevated amounts of lysine and the effects on key wineparameters 633.4 Supplementing grape juice with elevated amounts oflysine and the effects on key wine parametersTo determine the effect on key wine parameters, samples from the 10x lysine supplementedferments (Figure 3.3) were analyzed on a WineScan FT 120 spectrophotometer(Section 2.16). Figures 3.4 and 3.5 illustrate the outcome of these measurements. Threeseparate effects were observed.First of all, the most obvious differences in Figures 3.4 and 3.5 were due to strain effectsbetween wine yeast VL3 (right side of each graph) and the laboratory yeast BY4743 (leftside of each graph). Increased ethanol (d = 35) was accompanied by an expected decreaseof residual sugar (d = -26) levels in samples of the wine strain background. In addition,glycerol levels increased (d = 12) and a reduction could be observed for methanol (d =-5), citric acid (d = -3), tartaric acid (d = -8), malic acid (d = -6) and volatile acidity (d =-9).Secondly, a lysine effect could be observed. This was mostly apparent in the threelysine deletions strains lys12, lys1 and lys14 fermented in 10x lysine grape juice: the concentrationof ethanol, glycerol and ethyl acetate increased (Figure 3.4), while the amountof residual sugar, methanol and tartaric acid decreased (Figure 3.5). Wine samples fermentedwith BY4743-wt, gap1, lyp1 and wine yeast VL3 showed only minor changesacross the eleven measured parameters between the two lysine treatments of each yeaststrain (Figures 3.4 and 3.5).Thirdly, a key driver of changes of the wine parameters was the fermentation rate of theparticular yeast strain, which is dependent on the yeast strain and, in the case of the lysineauxotrophic yeast strains, can be influenced by varying levels of lysine. BY4743-lys14,the strain with the smallest increase in fermentation rate, shows consistently the smallestchange in the six wine parameters as shown in Figure 3.6. Summarizing the results, itseems that the observed changes in the lys deletion strains supplemented with 10x lysinecompared to the 1x lysine addition are consistent with a direct effect on the increasedfermentation rate.