## 3 Results and Discussion
### Relevance for the Production of Volatile Compounds during Alcoholic Fermentation
#### 3.3.2 Thiamine Influence on Wine Volatile Compounds
Such a phenomenon appears consistent with the thiamine-dependency exhibited by the Tk11/2 transketolase of the pentose phosphate pathway (PPP), as well as the decarboxylation step (Aro10, Pdc1/2/5) of the Ehrlich pathway [42]. The Ehrlich pathway precursor phenylpyruvate is, indeed, a product of the shikimate pathway, itself deriving from the PPP through phosphoenolpyruvate, and further converted to phenyl ethanol. It is, however, most surprising that the other higher alcohols do not display a similar behavior and dependency in regard to thiamine, since isoamyl alcohol and isoamyl acetate did not express any significant effect of the initial vitamin on their contents (Figure 2E), consistent with the absence of any influence of the initial thiamine on isoamyl alcohol, as found by [PERSON] using _S. cerevisiae_[38]. Amongst those compounds, both isovaleric acid and phenyl ethanol were found in concentrations above their olfactory detection thresholds of, respectively, 7 and 14 mg/L [52]. It also appears relevant to note that the ratio between superior alcohols and the total esters (calculated as the sum of the individual esters quantified here) was significantly (\(p<0.05\)) impacted by the initial thiamine in the medium, and diminished against thiamine doses, suggesting that, although the vitamin stands as a cofactor in the initial steps of the Ehrlich pathway, it overall favors the production of esters in the final wine. Significant (\(p<0.05\)) increases in the total esters were indeed found in regard to the initial thiamine, rising from 42.5 \(\pm\) 0.9 to 71.6 \(\pm\) 1.8 mg/L when increasing thiamine from 0 to 250 \(\upmu\)g/L. This first evidence of an influence held by the vitamin on ester production in wines suggests that sufficient thiamine doses, therefore, might contribute to expanding the ester profiles of wines, and, as such, possibly take part in the definition of the aromatic signature of the wine, since most esters are associated with fruity, pleasant notes [41]. Although the individual esters reported here were mostly under their detection thresholds, and therefore individually might not play any role in the sensory profiles of wines, their synergistic, combined effect might prove significant [41]. Central Carbon Metabolism-Derived Compounds  
In addition to what was observed in volatiles from the fatty acid metabolism and the Ehrlich pathway, thiamine appeared to have a significant influence on only one carbon metabolism-derived compound out of the four quantified here (Figure 2F). As such, ethyl benzaldehyde rose from 2.89 \(\pm\) 0.35 \(\upmu\)g/L to 3.49 \(\pm\) 0.33 \(\upmu\)g/L when similarly increasing thiamine from 0 to 250 \(\upmu\)g/L, which might be originating from the dependency held by benzaldehyde lyase (BAL) towards thiamine pyrophosphate for the synthesis of acetoin from benzaldehyde and acetaldehyde [56], although benzaldehyde itself, interestingly, did not present any significant differences in regard to initial thiamine. This might, however, be rather dependent of acetaldehyde contents, since those appear to have decreased in an opposite fashion to ethyl benzaldehyde. It could be envisioned, as such, that since the conversion of benzaldehyde and acetaldehyde towards acetoin cannot be as efficiently performed in case of thiamine limitation, the esterification of benzaldehyde towards ethyl benzaldehyde could preferentially occur.