## 4 Polyphenols Effects on Aromas Release in Oral Conditions: The Role of Saliva  
When considering PPhs-VOCs interactions in oral modality, the effects described above for orthonasal conditions can change. During wine tasting, and in general during food consumption, aroma compounds are transported to the nasal cavity by following the retronasal route (nasopharynx). Along this path, there is a dilution and a change in VOCs repartition between the condensed and the gas phases due to the mixing of wine with saliva and their interaction with the oral/pharyngeal cavity during the transfer to the olfactory receptors through the breath airflow. Several factors (e.g., anatomical, physicochemical, physiological, mechanical, etc.) can be implicated in VOCs release and perception in retronasal conditions [80]. Individual oral physiology characteristics, such as salivary flow rate, protein content and composition, antioxidant capacity, temperature, mucosa, swallowing and tongue force, oral volume, respiratory flow, and other oral physiological components could vary amongst individuals and with matrix composition, affecting wine aromas release [49; 81; 82; 83; 84; 85]. However, among all, saliva can be considered as a main factor so that its effects on food and beverages flavor perception have been frequently investigated in the last decades.  
Saliva can directly play a modulating role on polyphenols perception (PPhs-saliva interactions) and on aroma release and perception (VOCs-saliva interactions) during wine tasting, so we can argue that saliva could play a further indirect role by affecting PPhs-VOCs interactions [7; 8; 89; 90; 82; 24; 98]. While the first evidence on the molecular mechanisms explaining astringency as the sensation elicited by the interaction and precipitation of salivary proteins by tannins was published around 50 years ago [16], the direct impact of saliva on VOCs release and perception has started to be shown more recently [91; 92; 93; 94; 95]. Numerous phenomena have been proposed to explain the changes in release amount, kinetic, and nature of VOCs in the presence of saliva. Salivary proteins have binding sites available to trap volatiles. In fact, mucin and other salivary proteins can directly bind specific aroma compounds through covalent and non-covalent interactions (hydrophobic and electrostatic interactions, Van der Waals forces, formation of Schiff bases), inducing a modification in their release [7; 92; 93; 96; 97]. Salivary enzymes present in human saliva can catalyze reactions, are able to transform some volatile molecules into other odorants, and can hydrolyze bound volatiles from non-volatile precursors [7; 98; 99; 94; 96; 98]. Moreover, saliva can directly impact VOCs dilution, affecting their release to the oral cavity, since the repartition of molecules within the system wine-saliva-air is different compared to the wine-air system [7]. The first works hypothesizing a role played by saliva on PPhs-VOCs interactions during white and red wine tasting have been conducted using model mouth systems, in in vitro conditions, with either human saliva, artificial saliva, or comparing both types [48; 63]. In recent years, the development of procedures and methodologies allowing the quantification of aroma release in real in vivo conditions has improved results useful to understand how saliva-polyphenols interactions could impact the release and the perception of wine aroma. Different innovative approaches were used, such as the application of retronasal trapping devices that allowed entrapping the exhaled breath of the panelists [83], or intra-oral SPME (Solid Phase Micro Extraction) procedures [100; 101; 102], or the monitoring of the nasal cavity exhalations through PTR-ToF-MS (Proton Transfer Reaction-Time of Flight-Mass Spectrometry) (during real wine tasting sessions [103].