## 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 contradictory results available in the current literature could be at least partially due to the different approaches that were used (i.e., model solutions or real wines, artificial or real human saliva, different aromas and polyphenols concentrations, different analytical methods), so that it is difficult to get general conclusions on causes and effects of aromas-saliva-polyphenols interactions. Therefore, as already observed [100], the effect of polyphenol-salivary proteins interactions on aroma release is little known. Some hypotheses have been presented as possible causes of the different VOCs release behaviour in retronasal conditions compared to orthonasal ones, in the presence of different polyphenols at different concentrations. In the PPhs-VOCs-saliva systems, not only dilution, interaction, and salting-out effects can occur, but also the balance among the following phenomena should be considered: inhibition by PPhs of salivary enzymes activity in \"metabolizing\" VOCs; competitions between PPhs and VOCs in interacting with salivary proteins; hydrophobic VOCs inclusion in PPhs-saliva complexes. These phenomena have been argued based on results from in vivo trials and mainly observed on wine volatile esters. Saliva contains several enzymes (e.g., esterases, aldehyde dehydrogenase, aldose reductases, peroxididases, etc.) originating from salivary glands, oral tissues, and microbiota [104; 105]. These enzymes may be able to catalyze biochemical reactions, metabolizing certain classes of aromas (e.g., esters, aldehydes, ketones, alcohols, thiols) by transforming them into different odorants. Oral enzymes can also hydrolyze odorless aroma precursors (glycosidic or aminoacid) with the consequent production of odorous aglycones [94; 95; 96; 98; 99; 106; 107]. In the presence of phenolic compounds, it has been shown that some enzymatic activities may be inhibited [108; 109]. In the specific case of esters, it has been hypothesized that the activity of carboxyl esterase involved in their metabolism might be inhibited in the presence of phenolic compounds, thus leading to a lower hydrolysis of esters in solutions and, consequently, to a higher concentration of molecules that can be released. This hypothesis is supported by results obtained in both in vitro [48] and in vivo [83] conditions. [PERSON] and co-workers investigated the influence of human and artificial saliva on the release of white and red wine VOCs by SPME/GC-MS analyses using a model mouth system called retronasal aroma simulator (RAS). In the experiment with human saliva, containing salivary enzymes, the authors observed a significant lower decrease of some VOCs concentrations (i.e., ethyl butanoate, 3-mehtylbutyl acetate, ethyl hexanoate, hexyl acetate, and ethyl dodecanoate) in red wine headspace compared to the white one. Successively, interesting results have been pointed out in a more recent study involving a panelists' group that was classified as a lower releaser based on their real-time breathing profile monitored by a tailor-made retronasal aroma trapping device (RATD) that allowed entrapping the exhaled breath of the panelists and consequent GC-MS analysis [83]. The authors have shown a higher release of ethyl hexanoate during the consumption of a young-red wine, which was characterized by the highest polyphenic content, in comparison with a white, an aged-red, a sparking,and a sweet wine [83]. Since the same effect was not observed on the other analyzed ester (i.e., isoamyl acetate), the presence of tannins could have played an inhibition activity on certain salivary enzymes implicated in the metabolism of ethyl esters in the mouth. Similar phenomena have been observed by using a more innovative in vivo PTR-ToF-MS approach monitoring the nasal cavity of nine subjects after they rinsed their mouths with three different samples (a control wine and the same wine with two different commercial oenological tannins added).