67 Virgin Olive Oil Benefits erties. In recent decades, a considerable number of studies (in vitro and in vivo) have shown the protective effects of some phenolic compounds on illness, particularly those associated with oxidative stress, such as cardiovascular and metabolic diseases. In some research, benefits of the phenolic compounds on infections, cancer, adipogenesis modulation, autoimmune and neurodegenerative processes have also been described. Tocopherols, commonly known as vitamin E, act as cellular antioxidants because their hydrophobic lateral chain allows them to cross biological membranes. They prevent the lipid peroxidation chain reaction thus avoiding oil rancidity. α-Tocopherol accounts for90-95% of total tocopherols, whilst β-tocopherol and γ-tocopherol represent less than 10% (and δ-tocopherol is found in an even smaller proportion). The olive oil triterpenoids with well-characterized biological activity include the pentacyclic triterpenes and phytosterols. Pentacyclic triterpenes are made up of thirty carbons grouped into five or six membered rings with different substituents. They are secondary plant metabolites excreted for protection and, thus, particularly present in the stem and the cuticular waxes found on leaves and fruit surfaces. The most well-known are the triterpenic acids - maslinic, oleanolic, and ursolic, and the alcohols - erythrodiol and uvaol. As they have been attributed several healthy properties, they are frequently used in dietetic supplements. Phytosterols are the main compounds of the unsaponifiable fraction in vegetal oils. Their skeleton is composed of four rings (three six-carbon rings in a non-linear structure joined to a five-carbon ring) with a flexible lateral chain. They can be free or sterified. The main sterols in olive oil are β-sitosterol, Δ5-avenasterol, stigmasterol, and campesterol. Phytosterols contribute to plasma cholesterol regulation, the control of cell membrane permeability, and the regulation of enzyme responses. Undoubtedly, each and every one of these compounds in the relative proportion in which they are found (and their antagonistic and synergistic actions) will be responsible, to a greater or lesser extent, for the properties of an extract or an oil; therefore, correctly determining them is key to explain many of the interesting properties that EVOO exhibits.
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