## 3 Results and Discussion
### Effect of Blending on the Total Phenolic Index and Low Molecular Weight Compounds Contents of WSs
sensitivity towards oxidation for these coumarins because the direct supply of oxygen through MOX (alternative ageing technology) favours the oxidation reactions involving several phenolic compounds [16]. Scopoletin seems to be more prone to oxidation than umbelliferone; for this reason, lower contents existed in the WSs from alternative ageing. Despite their very low levels in WSs, some sensory attributes, namely bitterness [61], and benefits for human health due to specific biological activities [62; 63] have been ascribed to these minority phenolic compounds, and therefore a similar effect as mentioned above for syringaldehyde is plausible. So, these results also support the appropriateness of natural blending towards a more sustainable WS production. Figure 6 shows the results of ANOVA for the furanic aldehydes contents in the WSs under study. None of these compounds were significantly influenced by the blending technology, that is, the effects of natural blending and blending operation were similar, regardless of the ageing technology. Among furanic aldehydes, furfural stood out from HMF and 5-methylfurfural due to its higher concentration. Indeed, this aldehyde already exists in the wine distillate [16] as a consequence of the thermal degradation of wine pentoses in the distillation process [64], and greater amounts are also extracted from the wood (in which it exists in the free form due to degradation of hemicelluloses during the heat treatment in cooperative; this polysaccharide is more thermosensitive than cellulose that gives rise to HMF and 5-methylfurfural [65]) by the WS. Higher furfural concentrations were determined in the WSs produced by the alternative technology than by the traditional one (91.95-101.28 vs. 26.62-42.17 mg/L), as observed during their ageing process [17]. Our work on the ageing chemistry [16] revealed that furfural content mainly depended on the wood extraction and less on the oxidation reactions (triggered by the level of oxygen supplied) and other subtractive phenomena occurring during ageing, which can explain such an accumulation in these WSs. According to [PERSON] et al. [17], a significant interaction between the ageing technology and kind of wood and a synergistic effect between chestnut wood and the alternative ageing technology were detected. Since chestnut wood promoted greater extraction of furfural, the outcomes of the present work suggest that (i) natural blending did not change this distinctive behaviour, and (ii) chestnut wood had more marked influence on the blends than the Limousin oak wood, despite the same amount used (50:50 ratio). It should also be emphasized the relationship between furanic aldehydes and the 'dried fruits' and 'caramel' sensory attributes of these WSs, which were of the utmost importance for their differentiation [17]. Figure 6: Average values of furanic aldehydes concentrations of WSs from natural blending and from the blending operation in each ageing technology. Bars not marked with letters indicate non-significant differences between the average values (\(p>0.05\)). Hence, given that the furanic aldehydes contents were preserved by the natural blending, it also preserved the WSs quality and therefore it is a reliable technology for the improvement of the WS' production process.