# Flavor Chemistry of Virgin Olive Oil: An Overview
## 3 Factors Affecting the Flavor of VOO
### Interaction Between Food Matrix and VOO Volatile Compounds  
It has been reported that non-volatile compounds present in food, such as proteins, carbohydrates and phenolic compounds, may interact with saliva proteins and volatile compounds affecting the aroma release. These interactions may alter the food-air partitioning (volatility) of the aroma compounds [132; 133; 134; 135]. VOO phenolic compounds, whose total content is typically around 300 mg kg\({}^{-1}\), have been recently shown to affect the release of aroma compounds in saliva-in-oil emulsion with tendency of a lowest headspace release of almost all volatile compounds (significantly for esters, linalool and _trans_-2-hexenal) [126; 136]. In another study, eight volatile compounds were monitored under dynamic conditions, both in vitro and in vivo, in a refined olive oil enriched with phenolic compounds (593 mg kg\({}^{-1}\)) extracted from VOO, in comparison to a blank refined oil without phenolic addition [136]. In the in vitro study it was found that -phenolic compounds can interact with molecules such as hexanal, linalool and 1-hexanol, possibly through non-covalent but reversible bonds. The in vivo study showed that, after swallowing, in the presence of phenolic compounds, the release of 1-penten-3-one, _trans_-2-hexenal, _cis_-3-hexenyl acetate, and ethyl butanoate is lower than the one in the blank sample (Figure 4), thus confirming the results obtained in the previous study [126]. Among the above-mentioned volatile compounds, 1-penten-3-one and _trans_-2-hexenal are the most important active odor aroma compounds contributing to VOO fruity note [19]. 1-penten-3-one is important for its low odor threshold while _trans_-2-hexenal for its usual high concentration in VOO [137; 138]. In fact, in another study, it also emerged that a concentration of polyphenols of 511 mg kg\({}^{-1}\) is responsible for the reduced perception of the positive fruity attribute of about 39% compared to an oil with a lower concentration of polyphenols, of 298 mg kg\({}^{-1}\)[61]. In this sensory study, the higher concentration of phenolic compounds simulated a very bitter VOO while the lower a slightly bitter VOO [49]. Regarding the VOO off-flavors, it has been reported that \"fusty\" defect is perceived less (23%) in an oil with more biophenols. On the contrary, no important effect of VOO phenolic compounds on the perceived intensity of the \"rancid\" defect has been reported although a positive trend has been found in VOO with a higher concentration of polyphenols. The explanation of this effect is attributed to the formation of VOO phenolic compounds-PRPs (Proline Rich Proteins) complexes that could retain some volatile compounds in the hydrophobic cavities and therefore, modifying their release into the mouth cavity. Most of the studies focused on interaction between phenolic compounds and saliva proteins concern tannins, which are responsible of astringency perception [139]. For instance, salivary PRPs have a high affinity for tannins [140]. In addition, smaller polyphenols (propyl gallate and epicatechin) can bind with one phenolic ring stacked against each proline residue, whereas larger polyphenols occupy two or three consecutive prolines [141]. The result of these interactions in wine could be similar to what occurs for VOO perception. In fact, sensory studies showed that the intensities of \"fruity\" and \"floral\" aromas is lower in wine when the level of polyphenols is increased [142]. However, it is expected that the sensory impact of this interaction might be lower compared to the effect of tannins, due to the relatively weak affinity of olive oil phenolics for the different food proteins compared to tann acid [143]. Figure 4: The principle of in vivo study by APCI/MS analysis of the aroma release (time-intensity) in mouth.