## 3 Results and Discussion
### Evolution of Target Volatile Compounds over the Ageing Experiment  
Table 1 exhibits the results of the target volatile compounds over the ageing time and the corresponding graphical representation to clearly show the behavior over the time. These compounds were chosen as targets from a wide set of volatile compounds in wine spirits [1] because they have different origins and different behaviors during the ageing time according to previous research made on alternative ageing technologies without micro-oxygenation [8; 10]. this alcohol during ageing, particularly glycosidic precursors [33] and terpene diols [34]. The acidic hydrolysis of terpene glycosides result in a molecular rearrangement of the monoterpends, which are then converted into other compounds such as linalool [35; 36]. The higher concentration of oxygen in these MOX modalities (CO30 and CO60) resulted in an increase of electron-deficient oxygen species, such as aldehydes and carboxylic acids [24], contributes to reduce the pH of the medium, and may lead to the degradation of terpene glycosides. A slight decrease over the time of the linalool was observed in all the other modalities. A similar decrease was pointed out during an ageing experiment of two years [10]. The non-saturation characteristic of the double bond relates to the capability to participate in addition reactions, which is enabled by the \(\pi\) bond's weak energy. The cyclization product of monoterpes catalyzed in acidic medium, is well known and can produce the two cineoles, by dehydration and direct cyclization or by the production of \(\alpha\)-terpineol [36]. On the other hand, the high electronic density at the level of a double bond, as well as the accessibility of electrons \(\pi\), means that electrophilic reagents (H\({}^{+}\), R\({}^{+}\), among others) would be the primary cause of attacks. Due to its own reactivity, the double bond is a weak point in the carbon chain, and certain reactions, such as oxidation reactions, can lead to a rupture between two double bonded carbons. The linalool concentration presented in freshly distilled wine spirits supposed to be consumed over time, as there is no way to form it in the reaction mixture, given that primarily sources of terpen are the grapes skins and pulp [35; 37; 38]. Our findings for this compound might suggest further studies to determine whether it can be used as a marker of the authenticity of the wine distillate, as well as of its ageing time, since the longer it ages, the less linalool in its free state should be present. Acetaldehyde, which is linked to a fruity note [13], was present in the unaged wine spirit (Table 1) with an amount of 28.9 mg/L. Indeed, acetaldehyde is a major volatile compound that is produced by yeasts during the wine fermentation process and recovered in the distillate [1], and a by-product of ethanol oxidation metabolism. During the ageing experiment its amount increased over time in all modalities with a slight decrease between 180 and 270 days of ageing. In the first two sampling times (8 and 60 days) there was no significant differences between the five ageing modalities. However, at 180, 270, and 365 days, significant differences between the acetaldehyde concentration in the wine spirits resulting from several ageing modalities was detected (Table 1). The highest amounts were found in wine spirits produced with MOX (CO15, CO30 and CO60) and the lowest ones were found in the wine spirits aged in wooden barrels and with nitrogen. This behavior was expected because the presence of acetaldehyde is related to ethanol oxidation; in more oxidative environments, its higher concentration is not surprising. At the last sampling time, it was possible to discriminate the wine spirit samples proceeding from different alternative modalities based on the acetaldehyde amounts, which were lower in the samples from the nitrogen modality (CN) and higher in CO15 samples. The amount of acetaldehyde found in micro-oxygenation modalities samples should be closely monitored.