## 3 Results and Discussion
### Odonant Compounds of Aged Wine Spirits  
At the end of the ageing experiment (365 days), the odorant compounds of the aged wine spirits were quantified. The ethyl isovalerate is not quantifiable and the \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Odorant Compound** & _Significance Level_ & **Control** & \multicolumn{4}{c}{**Aged Wine Spirits after 365 Days of Ageing Modality**} \\ \cline{3-6}  & & **CB** & **CO15** & **CO30** & **CO60** & **CN** \\ \hline Isobutyl acetate & _0.002_ & 2.36 & 1.81 b & 0.55 a & 0.0 a & 0.0 a & 1.34 b \\ Ethyl hexanoate & _0.009_ & 1.20 & 1.89 c & 1.72 b & 1.72 b & 1.80 b,c & 1.58 a \\ Guaiacol & _0.001_ & 0.00 & 0.11 a & 0.51 b & 0.45 b & 0.46 b & 0.48 b \\
4-Methylylgaiaicol & _0.004_ & 0.00 & 0.05 a & 0.31 b & 0.28 b & 0.25 b & 0.28 b \\ Eugenol & _0.021_ & 0.00 & 0.33 c & 0.28 a,b & 0.30 b,c & 0.28 a,b & 0.23 a \\
4-Methylsyringol & _0.000_ & 0.00 & 0.36 a & 1.24 c & 1.24 c & 1.26 c & 1.09 b \\ Vanillin & _0.014_ & 0.00 & 7.74 b & 7.52 b & 7.14 b & 8.21 b & 4.97 a \\ Acetovanillone & _0.003_ & 0.00 & 0.34 a & 0.80 b,c & 0.81 b,c & 0.97 c & 0.77 b \\ \hline Ethyl acetate & _0.003_ & 459.88 & 472.54 c & 389.74 b & 374.85 a,b & 382.28 b & 335.22 a \\ \hline \hline \end{tabular}  
* For each compound of aged wine spirit samples, means within the same row followed by different uppercase letters (e, b, c) are significantly different (_p_ < 0.05).  
\end{table} 
Table 2: Concentration (mg/L) of odorant compounds quantified in wine spirits sampled from different ageing modalities at the end of the ageing experiment (365 days) and the summary of one-way ANOVA. ethyl-2-methylbutanoate, \(\beta\)-methyl-\(\gamma\)-octalactone, diethyl malate, 4-propylguaiacol and 4-ethylphenol were not detected in these samples. The ANOVA results (Table 2) pointed out a significant effect of the ageing modality on the contents of twelve compounds, which include the four previously mentioned and discussed (linalool, acetic acid, syringol and ethyl acetate). On the other hand, the concentrations of other 17 odorant compounds were not affected (Table S1-Suplementar material). Regarding isobutyl acetate, which is related to fruity notes [48], higher concentrations were found in samples from wooden barrels (CB) and from nitrogen modality (CN) while in MOX samples the amounts were lower or quite null. These results are not in accordance with those reported by [PERSON] et al. [25], whose found the highest values of this ester in wine spirits aged through an alternative ageing system (staves combined with micro-oxygenation using a single flow of oxygen; 2 mL/L/month) in comparison with wooden barrels. Since esters are roughly as reactive as carboxylic acids, this reaction is highly reversible. Higher isobutyl acetate concentrations need excess concentration of acetic acid, which was not found in MOX samples. According to [PERSON]'s theory, higher concentration of acetic acid would shift the equilibrium toward ester production, which is confirmed by higher concentrations of isobutyl acetate and acetic acid in samples from wooden barrels (CB) at the conclusion of the ageing experiment (365 days). The concentrations of isobutyl acetate in CO30 and CO60 MOX samples may be indicating that the wide availability of oxygen induces significant chemical content variation over the time, resulting in an increase of electrophilic species, among these phenolic aldehydes and acids such as: syringaldehyde, coniferaldehyde, anispaldehyde, ellagic, and syringic acid, previously confirmed for the same MOX samples [24].