## 3 Results and Discussion
### Impact on Central Carbon Metabolites  
In order to further assess the impact held by both vitamins on the yeast metabolism, acetaldehyde, acetic acid, D-lactic acid, and glycerol were enzymatically quantified on the endpoint fermentation supernatants for all wines, and ethanol was determined through FT-IR spectroscopy (Tables 4 and 5). Consistent with the evidence that all fermentations managed to achieve a complete consumption of sugars, ethanol did not display any significant dependence (\(p>0.05\)) in regard to the initial concentrations of the vitamins (Tables 4 and 5). Interestingly, amongst all four investigated compounds, solely acetaldehyde and ethanol did not display any significant variation (\(p>0.05\)) regarding the initial thiamine concentration in the medium (Table 5). Such an effect on acetaldehyde does contradict previous knowledge, that established thiamine deficiencies to be associated with higher contents of sulfur-binding compounds, including acetaldehyde [41], as well as the strong dependency manifested by pyruvate decarboxylase (Pdc) towards thiamine [42] for the \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Compound**} & \multicolumn{3}{c}{**Initial Biotin Concentration (\(\mu_{\text{g}}\)/L)**} \\ \cline{2-4}  & **0** & **0.5** & **3** \\ \hline Acetaldehyde (mg/L) & 108.9 \(\pm\) 32.8 \({}^{\text{a}}\) & 144.1 \(\pm\) 19.8 \({}^{\text{a}}\) & 162.4 \(\pm\) 6.5 \({}^{\text{b}}\) \\ Acetic acid (g/L) & 1.4 \(\pm\) 0.2 \({}^{\text{a}}\) & 1.3 \(\pm\) 0.4 \({}^{\text{ab}}\) & 1.0 \(\pm\) 0.2 \({}^{\text{b}}\) \\ D-lactic acid (g/L) & 0.2 \(\pm\) 0.0 \({}^{\text{a}}\) & 0.2 \(\pm\) 0.1\({}^{\text{a}}\) & 0.2 \(\pm\) 0.0 \({}^{\text{a}}\) \\ Glycerol (g/L) & 8.0 \(\pm\) 0.6 \({}^{\text{a}}\) & 7.0 \(\pm\) 0.8 \({}^{\text{b}}\) & 6.5 \(\pm\) 0.3 \({}^{\text{b}}\) \\ Ethanol (\% \(\
u/\
u\)) & 9.6 \(\pm\) 0.1\({}^{\text{a}}\) & 9.6 \(\pm\) 0.1\({}^{\text{a}}\) & 9.4 \(\pm\) 0.3 \({}^{\text{a}}\) \\ \hline \end{tabular} Note: different letters in the same line indicate significant differences between conditions (Scheirer–Ray–Hare and Dunn tests, \(p<0.05\)).  
\end{table} 
Table 4: Central carbon metabolites in the final wines produced in varying initial biotin concentrations. \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Compound**} & \multicolumn{3}{c}{**Initial Thiamine Concentration (\(\mu_{\text{g}}\)/L)**} \\ \cline{2-4}  & **0** & **50** & **250** \\ \hline Acetaldehyde (mg/L) & 126.7 \(\pm\) 37.8 \({}^{\text{a}}\) & 135.8 \(\pm\) 35.8 \({}^{\text{a}}\) & 151.7 \(\pm\) 7.1\({}^{\text{a}}\) \\ Acetic acid (g/L) & 1.1 \(\pm\) 0.4 \({}^{\text{a}}\) & 1.2 \(\pm\) 0.2 \({}^{\text{ab}}\) & 1.4 \(\pm\) 0.2 \({}^{\text{b}}\) \\ D-lactic acid (g/L) & 0.3 \(\pm\) 0.0 \({}^{\text{a}}\) & 0.2 \(\pm\) 0.0 \({}^{\text{b}}\) & 0.2 \(\pm\) 0.0 \({}^{\text{b}}\) \\ Glycerol (g/L) & 6.8 \(\pm\) 0.6 \({}^{\text{a}}\) & 7.0 \(\pm\) 0.8 \({}^{\text{a}}\) & 7.8 \(\pm\) 1.06 \({}^{\text{b}}\) \\ Ethanol (\% \(\
u/\
u\)) & 9.5 \(\pm\) 0.2 \({}^{\text{a}}\) & 9.6 \(\pm\) 0.1 \({}^{\text{a}}\) & 9.5 \(\pm\) 0.3 \({}^{\text{a}}\) \\ \hline \end{tabular} Note: different letters in the same line indicate significant differences between conditions (Scheirer–Ray–Hare and Dunn tests, \(p<0.05\)).  
\end{table} 
Table 5: Central carbon metabolites in the final wines produced in varying initial thiamine concentrations. formation of acetaldehyde from pyruvate. However, some other findings, although recognizing the clear influence of thiamine deficiencies on sulfur-binding ketoacids, did not, opposingly, find any impact of it on acetaldehyde itself [43; 44]. Here, the absence of any effect of thiamine on acetaldehyde contents in wines clearly appeared. Biotin, however, appeared to have a significant effect on acetaldehyde accumulation (\(p<0.05\)) (Table 4). Such a rise in acetaldehyde contents might indirectly result from other influences held by the vitamin on carbon metabolism, although its exact cause remains obscure.