## 2 Results
### Effect of Phenolic Compounds on Aroma Volatility in Wines with Different Oral Components  
In a second experiment, the role of phenolic compounds on aroma volatility was investigated using synthetic wines spiked with oral components. Phenolic compounds are quantitatively the most important group of non-volatile wine matrix components, and although their influence on wine aroma volatility has been previously investigated [4; 5; 6; 7; 8], works also considering the presence of oral components and therefore simulating a more realistic scenario of what could happen with aroma compounds in the mouth during wine tasting are quite scarce. For this experiment, the three types of synthetic wines with HS, AS, and BC were prepared and individually spiked with four different types of phenolic compounds: gallic acid (GAc), catechin (Cat), a red wine extract (RWE), and a grape seed extract (GSE). These four types of phenolic compounds exhibited different chemical structures and properties (Figure 2), and likely, a different behavior against aroma compounds and oral components. A control wine of each type (HS, AS, BC) without polyphenols was also prepared. First, to determine the impact of the different types of phenolic compounds on the volatility of the four aroma compounds in the three synthetic wines with oral components (HS, AS, and BC), aroma volatility data (absolute peak areas) from each wine type were separately submitted to one way-ANOVA. In addition, a means comparison test (Tukey test) was also run in order to determine the individual effect of each phenolic compound. Figure 3 summarizes these results. As it can be seen, in the case of guaiacol (Figure 3a), the effect of the type of phenolic compound was only significant in the wines with AS and BC, but not with HS. In wines with AS, the control wine without phenolic compounds and the wine with gallic acid showed the highest headspace amounts of this odorant molecule, but there were not significant differences between them. This reveals that in wines with AS, the monomeric phenol gallic acid did not provoke any effect on guaiacol volatility, which is in agreement with previous studies, in which gallic acid did not show any effect on the volatility of 3-alkyl-2-methoxypyrazynes when added to a model wine at 1 g/L [36]. However, Figure 3a also reveals that wines with AS and supplemented with flavonoid type polyphenols (Cat, GSE, and RWE) exhibited the lowest headspace amount of guaiacol (above 30-40% less compared to the control). In previous works aimed to study the effect of the wine matrix on aroma volatility, interactions between some polyphenols and certain aroma compounds with an aromatic ring through a \(\pi\)-\(\pi\) staking between the galloyl ring of the polyphenol, and the aromatic ring of the odorant molecule, with stability provided by hydrogen bonding, have been described [6]. It has also been shown that this type of interaction can reduce the headspace concentration of aroma compounds in wines [4; 9; 10]. In more recent works using in vivo approaches, it has been suggested a possible interaction of this compound with polyphenols adsorbed to the mucosal pellicle which is the salivary film that covers the oral epithelium and is rich in MUCB and MUC7 [37] explained \(\pi\)-\(\pi\) staking. Thus, the above-proposed mechanism (\(\pi\)-\(\pi\) interactions) might be the reason for the reduction of guaiacol volatility in wines with flavonoid type  
Figure 2: Chemical structure of the phenolic compounds employed in this study. Procyanidins and anthocyanins were the main constituents of the grape seed and red wine extracts, respectively. polyphenols and mucin (AS). As previously described, this large protein should be absent in HS, due to the centrifugation step, explaining the lack of effect of these phenolic compounds on guaiacol volatility in wines with HS. In the wines with BC, a significant effect of phenolic compounds on guaiacol volatility was also observed (Figure 3a).