## 2 Results and Discussion
### Amino Acids Involved in CoA Biosynthesis
#### 2.2.1 Stimulation of Ester Production by \(\beta\)-Alanine.
Significantly increased concentrations of MCFAs (hexanoic acid 1522-1732 \(\mathrm{\SIUnitSymbolMicro\text{g}}\cdot\)L\({}^{-1}\)_vs._ 681 \(\mathrm{\SIUnitSymbolMicro\text{g}}\cdot\)L\({}^{-1}\); octanoic acid 3826-5119 \(\mathrm{\SIUnitSymbolMicro\text{g}}\cdot\)L\({}^{-1}\)_vs._ 1804 \(\mathrm{\SIUnitSymbolMicro\text{g}}\cdot\)L\({}^{-1}\); decanoic acid 545-1195 \(\mathrm{\SIUnitSymbolMicro\text{g}}\cdot\)L\({}^{-1}\)_vs._ 174 \(\mathrm{\SIUnitSymbolMicro\text{g}}\cdot\)L\({}^{-1}\)) were observed in fermentations spiked with 50 and 100 mg\(\cdot\)L\({}^{-1}\)\(\beta\)-alanine or with all four amino acids compared to the control wine (Figure 5). Therefore, the increase in ethyl ester production may be linked to an increase in the production of MCFAs rather than an increase in activation of existing free fatty acids via an increase in CoA concentration. The lack of any significant difference in hexanoic and octanoic acid content between the wines produced after the addition of four amino acids and those made after \(\beta\)-alanine addition alone may reflect the lower volatility of the MCFAs, compared to the ethyl esters, which reduces their loss from the wine in the two-day time difference between the completions of the fermentations. However, this was not the case for decanoic acid, which was found in significantly lower concentrations when all four amino acids were added compared to those spiked with \(\beta\)-alanine alone (Figure 5C). Figure 4: The concentration of (**A**) ethyl hexanoate, (**B**) ethyl octanoate and (**C**) ethyl decanoate in model wines produced after the addition of amino acids as indicated on the x-axis. The number in brackets represents the concentration added in mg\(\cdot\)L\({}^{-1}\). Histograms represent the mean values (n = 3) and error bars show standard errors. Different letters (e.g., a, b, c) denote significant differences between treatments at \(p<0.05\) using ANOVA followed by [PERSON]’s _post hoc_ test. The concentration of three abundant acetate esters was also determined in the model wines produced after amino acid additions to the model must (Figure 6). Both ethyl acetate and phenylethyl acetate  
Figure 5: The concentration of **(A)** hexanoic acid, **(B)** octanoic acid and **(C)** decanoic acid in model wines produced after the addition of amino acids as indicated on the x-axis. The number in brackets represents the concentration added in mg\(\cdot\)L\({}^{-1}\). Histograms represent the mean values (n = 3) and error bars show standard errors. Different letters (e.g., a, b, c) denote significant differences between treatments at \(p<0.05\) using ANOVA followed by [PERSON]’s _post hoc_ test. production was higher in the wines produced after \(\beta\)-alanine addition to the musts, either alone or in combination with the other three amino acids, compared to control wine. However, isoamyl acetate concentrations were not significantly higher in the wines produced after \(\beta\)-alanine addition compared to the control. This suggests that isoamyl alcohol concentrations may be limiting production of the corresponding acetate ester, but the concentration of the alcohol moiety of the acetate ester is not limiting for ethyl acetate and phenylethyl acetate production. Presumably, increased CoA synthesis caused by the presence of \(\beta\)-alanine in the must can then increase production of these acetate esters during fermentation. Figure 6: The concentration of (**A**) ethyl acetate, (**B**) isoamyl acetate and (**C**) phenylethyl acetate in model wines produced after the addition of amino acids as indicated on the x-axis. The number in brackets represents the concentration added in mg\(\cdot\)L\({}^{-1}\). Histograms represent the mean values (n = 3) and error bars show standard errors. Different letters (e.g., a, b, c) denote significant differences between treatments at \(p<0.05\) using ANOVA followed by [PERSON]’s _post hoc_ test.