# Flavor Chemistry of Virgin Olive Oil: An Overview
## 2 VOO Flavor Perception
### Triglycerides and Fatty Acids  
The main constituents of VOOs are triglycerides (glycerol esters), diglycerides and few free fatty acids. The latter, when found in large quantities, contribute to increasing the acidity value with the consequent higher oxidation rate of the oil. The percentage composition of fatty acids in extra virgin olive oil varies according to climatic and agronomic conditions, as well as the olive drupe variety; however, oleic acid (C18:1\(n\)-9) is the most abundant (monounsaturated) fatty acid present in extra virgin olive oil in a range of 60-80% [10]. Oleic acid, like other fatty acids present in the lipid fraction of olive oil as constituents of the triglyceride molecules, does not exert a direct flavour impact.  
Oils and fats have been shown to reduce cortical response in several brain areas related to flavor processing and reward [62]. Viscosity, greasiness and food moisture level are initially the main factors responsible for fat sensory impact. Texture perception of a creamy or fat food is strongly correlated to lipid chemic-physical properties [63; 64].  
It has been reported that the level of fat can be perceived sensorially, and it was suggested that this might be related to the greasiness, a tactile attribute of fats [65]. These characteristics can be linked to triglycerides, which are the predominant form of dietary fat. However, they are of such size and structure that binding to cell surface receptors or passageway through the cell membrane channels is quite unlikely [66]. However, there is now more and more evidence supporting an important role of the taste system in the perception of fat [67; 68; 69]. Functional magnetic resonance showed that the neural representations in the brain of the properties of fat differ significantly with faster status [70].  
Sensory studies have highlighted the important influences of sensory signals in the identification of fat taste in terms of free fatty acids [68]. The results of the tests, performed using different fatty acids, reported that linoleic acid, oxidized linoleic acid, oleic acid, and stearic acid are detectable in the oral cavity, with retro-nasal perception thresholds greater than the ortho-nasal one. Free fatty acids are main factors responsible for fat taste perception, once the triacylglycerllycerols have been hydrolyzed by the salivary lipase. This has been demonstrated through the use of orlist, a tasteless substance and potent inhibitor of lipases [71]. A recent study suggested that the lipolytic activity of the human lipase is able to produce fatty acids within the necessary range of concentration necessary to activate the oral sensors [72]. There are different classes of putative receptors of fat food that have been identified in rodents [73; 74; 75], including the glycoprotein CD36 [76].  
Recently, the long fatty acid receptors CD36 and GPR 120 on the surface of the circumvallate and foliate taste buds have been found in humans [77]. This indicates that long-chain fatty acids (LCFAs) play an important role, as primary taste, in the oral fat sensitivity, in addition to their potential role in the regulation of metabolic needs, as recently discovered but still to be fully investigated [78].  
Fat sensitivity has been linked by some authors to fat intake, which eventually might affect the calory intake and thus the body mass index (BMI) of humans. In fact, [PERSON] and coauthors [69; 72] determined that subjects hyposensitive to fatty acids perception consumed significantly higher amounts of fat and energy, as well as highly saturated fats like butter, meat and dairy products compared to hypersensitive subjects. It thus appears that the inability to perceive low concentrations of fats in foods is associated with a higher consumption of fatty foods [69]. The hyposensitive subjects had a genetic variant in the FA translocate gene CD36 and lipase inhibition [79; 80] that could explain their lower sensitivity to fatty acids.