## 4 Polyphenols Effects on Aromas Release in Oral Conditions: The Role of Saliva
### Impact of Saliva on Aroma through the Modulation of Polyphenols-VOCs Interactions
The presence of tannins (50 mg/L) corresponded to a higher release of ethyl decanoate, which was significant at the first and fourth minute of monitoring after swallowing [103], in the prolonged aroma release condition, and it was responsible for the aroma persistence [110; 111; 112; 113]. The authors suggested that \"the presence of tannins could have inhibited certain salivary enzymes implicated in the metabolism of aroma compounds, such as ethyl esters, in the mouth\" [103]. Moreover, a modification of VOCs release might be due to competitions between PPhs and VOCs in interacting with salivary proteins. Salivary proteins (e.g., mucus, \(\alpha\)-amylases, etc.) have demonstrated their ability to interact with aroma compounds through hydrophobic and other kinds of non-covalent interactions (electrostatic interactions, Van der Waals forces) [114], modifying their release and perception [87]. However, phenolic compounds have shown to strongly interact with mucin [24; 115], likely competing with aromas in their interaction with saliva. For example, in in vitro conditions and investigating the influence of the presence/absence of saliva on the release of red and white wine VOCs, a lower decrease for some alcohols (i.e., 2-methyl-1-propanol, 3+2-ethyl-1-butanol, 3-methyl-1-pentanol, and 1-hexanol) was found with human or artificial saliva in red wine compared to the white wine [48]. In addition, [PERSON] and co-authors [63] showed a different modulating effect of artificial saliva (with no added enzymes) on some VOCs release in model solutions with added tannins. Following interaction with saliva, the authors observed a lower decrease for isoamyl acetate, ethyl hexanoate, octanoate, decanoate, dodecanoate, 2-methyl-1-butanol, and linalool, in the presence of tannins. However, in the presence of tannins, some VOCs, due to their ability to participate in the formation of large complexes with salivary proteins and wine carbohydrates [63], might be encapsulated, leading to a lower retronasal release. This phenomenon has been observed for some hydrophobic esters (i.e., isoamyl acetate and ethyl hexanote) in different works [100; 101], such as for guiaicol and, to a lesser extent, for \(\beta\)-ionone [101]. These authors suggested an interaction of these VOCs with salivary proteins-PPhs complexes, resulting in a lower immediate release in red wines [100] or in wines added with different types of phenolic extracts [101]. A further aspect possibly affected by the PPhs-VOCs-saliva interactions could be the flavor persistence during wine tasting [103]. Polyphenols are responsible for astringency and bittermess perception, which are two oral sensations characterized by an extended persistence as showed by TDS (temporal dominance of sensations) studies [116]. Based on some evidence, the long time of development and the dynamic persistence might be at least partially linked to the multistage mechanism underpinning PPhs-saliva interactions [20]. The results presented by [PERSON] and co-workers show that polyphenol-protein binding produces a more cross-linked and hydrophobic protein, which could enhance the hydrophobic trapping/inclusion of small molecules such as VOCs. Moreover, specific aroma compounds-mucosa interactions occurring after swallowing could contribute to the formation of a coating on the throat and pharynx, which could increase the liquid/air free surface, thus modulating some VOCs release over time [7], under the expiration flows in specific in vivo conditions. This phenomenon, together with the inhibition by PPhs of salivary enzymes activity in \"metabolizing\" VOCs, could explain the higher ethyl decanoate release over time once the wine was expectorated [103]. In addition, [PERSON] and co-workers [101] have suggested a modification in VOCs behavior over time. After the fourth minute from the expectoration, in prolonged aroma release conditions, the behavior of some VOCs release changed for some individuals.