## 2 Results and Discussion
### Amino Acids Involved in CoA Biosynthesis
#### 2.2.2 \(\beta\)-Alanine Concentrations in Grapes are Sufficient to Stimulate Ester Production
Ethyl hexanoate production in the fermentations was stimulated to the same degree by the addition of \(\beta\)-alanine, pantothenate or both compounds to the MGJM (Figure 8A). This was also observed for ethyl decanoate, although ethyl octanoate concentrations were not significantly different to the control when only pantothenate was added to the must (data not shown). Hexanoic acid concentrations were significantly greater in the wines produced from all three treatments compared to the control (Figure 8B). Figure 8: The concentration of (**A**) ethyl hexanoate, (**B**) hexanoic acid and (**C**) ethyl acetate in model wines produced after the addition of \(\beta\)-alanine (\(\beta\)-Ala), pantothenate (Panto) or both compounds (\(\beta\)-Ala/Panto) as indicated on the x-axis. 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. and octanoic and decanoic acid responded in the same manner to the supplementation of the must (data not shown). Of the acetate esters, ethyl acetate production was significantly increased in response to the addition of pantothenate to the model must, but even greater production was observed when \(\beta\)-alanine was added (Figure 8C). When isoamyl acetate and phenylethyl acetate were examined, only those wines produced after the addition of \(\beta\)-alanine to the must had greater amounts of these esters compared to the control (data not shown). In general, both \(\beta\)-alanine and pantothhenate could stimulate ester production in the model fermentation system used in these experiments. However, in some cases, \(\beta\)-alanine was more efficient than pantothenate at increasing ester concentrations. This observation seems counterintuitive given that pantothenate is produced from pantoate and \(\beta\)-alanine during CoA biosynthesis (Figure 3). However, there may be differences in the ability of yeast to transport these compounds into the cell which in turn could influence CoA and ester production. It is known that pantothenate is transported by the Fen2p symporter, whereas \(\beta\)-alanine is transported mainly by the general amino acid permease Gap1p, although other transporters are involved [42]. The redundancy in the \(\beta\)-alanine transport system may make its transport more efficient and hence the concentration in the yeast cytoplasm may be greater than that of pantothenate when both are at the same concentration in the media. Alternatively, \(\beta\)-alanine may be used in other metabolic pathways that can also stimulate ester production independent of CoA biosynthesis. A survey of pantothhenate concentrations in grapes grown in the Pacific northwest of the USA found that they ranged from 0.18 to 1.26 mg\(\cdot\)L\({}^{-1}\)[43]. This is lower than the values reported for \(\beta\)-alanine (this manuscript, [39]) which would suggest that \(\beta\)-alanine may have a more important role in CoA production during fermentation of grapes than pantothenate.