# Flavor Chemistry of Virgin Olive Oil: An Overview
## 3 Factors Affecting the Flavor of VOO
### Human Physiological Factors Affecting Flavour Perception  
Physiological factors such as temperature, saliva, saliva pH, saliva flow, chewing, the speed at which the food is mixed during chewing and the size of the bolus are all factors that could affect VOO perception, and the differences in the sensory impact depending on the individual, as humans show wide variation in these parameters [113]. In addition, the respiration, as well as the dilution effect of the saliva, makes the oral processing a \"dynamic process\", which causes a continuous change in terms of volume, composition and viscosity of the foods. This is the reason for which VOO tasters frequently aspirate the olive oil in the mouth. In fact, this procedure promotes the volatilization by increasing the surface area contact and enhances retro-nasal detection. Saliva is the first digestive fluid that enters in contact with foods in the digestive tract [114], and it exerts several functions [115; 116]. Its action is closely correlated with chewing and swallowing. In humans, the secretion of saliva ranges from 0.5 mL/min without stimulation to over 2 mL min\({}^{-1}\) during meals [117]. The total amount of saliva produced daily is on average around 1-1.5 L, including the moments close to the meals, in which saliva is produced at a higher rate [115]. Several publications have stressed the fact that saliva may partly influence the sensory perception of a food [118; 119]. Salivary amylolytic activity is widely known, but also proteolytic and lipolytic activity has been reported for the saliva [120; 121]. The salivary amylase and mucin play an important role in the phenomena of flocculation and coalescence that occur during the consumption of oil-in-water emulsions. These changes in the structure of the emulsion also have an impact on the product's perception [121]. It is known that mucins have binding sites available to trap volatiles [122],as they can bind specific aroma compounds, mainly aldehydes [122; 123], possibly to form Schiff bases. Studies carried out by [PERSON] and co-workers [124] demonstrated that large concentrations of \(\alpha\)-amylase can lead to a lower flavor release, especially esters, aldehydes and ketones. Mucin influences the release of aroma compounds probably through bonds of a hydrophobic nature. In fact, mucin contains several hydrophobic domains and overall has a negative charge, due to the presence of some sulphate groups. However, also other types of non-covalent bonds cannot be excluded. The presence of other enzymes in the saliva may also be involved in phenomena of oxidation, thus affecting the aroma release especially for high-fat food [121]. Some enzymes involved in the oxidation process of polyunsaturated fatty acids (PUFA), such as acyl hydrolases (AH), lipoxygenase (LOX), hydroperoxide lyases (HPL) and alcohol dehydrogenase (ADH), might be active in the mouth [119] and could lead to the formation of mainly C\({}_{6}\) aldehydes [125]. A possible effect of these enzymes was observed in a study that simulated the conditions of the mouth by using a retro-nasal aroma simulator (R.A.S. ), which simulates the aroma perceived by the retro-nasal route. The result showed an increase in hexanal and _trans_-2-pentenal in the presence of human saliva [126]. Therefore, PUFAs are detectable in humans by multiple sensory systems: gustatory, olfactory and somatosensory signals [68; 121]. Other molecules, mainly esters and linalool, showed a reduction in aroma compounds only in the presence of polyphenols, possibly to be attributed to a direct action of salivary constituents in the saliva-polyphenol interaction [126]. However, saliva may also have an indirect effect on aroma release in the mouth by modifying the rheological properties of food, especially viscosity and spreadability for high-fat foods. It has been reported in an in vitro study that the addition of artificial saliva to dressings increases the viscosity of food changing the aroma release.