These phenols exhibit significant biological effects in many diseases, participating in various cellular and biochemical processes. Oleocanthal can protect and prevent against the Alzheimer disease, demonstrates acute antiplatelet effects, which has a vital role against cancer, and can act like ibuprofen. Oleacein has antioxidant and anti-inflammatory activities and helps against atherosclerosis. Moreover, it acts as an antiaging factor and as a 5-lipoxygenase inhibitor. Ligstroside aglycon implicates to mechanisms against breast cancer, while oleuropein aglycon shows activities against the Alzheimer disease and breast cancer. […]
[…] 3.1 Phenols in EVOO: structure, chemistry, and biosynthesis
About 98% of EVOO consists of triacylglycerols (TGAs), a group of glycerol esters containing different fatty acids. Oleic acid is the major fatty acids, while there are also palmitic acid, linoleic acid, stearic acid, and palmitoleic acid. Moreover, there are minor compounds that are lipophilic or amphiphilic like phytosterols such as β-sitosterol, campesterol, and 4-methylsterols and hydrocarbons such as squalene and β-carotene. There are also fatty alcohols, triterpenic alcohols, and triterpenic acids, like erythroidol, oleanolic, and maslinic acids. There are, also, tocopherols such as α-tocopherol and pigments. Other minor components of EVOO are sterol esters, glyceroglycolipids, phosphatides, waxes, sterol esters, and mono- and diacylglycerols.
Another group of molecules present in EVOO, of a high impact in diet, are the phenolic compounds or as usually are called, polyphenols, such as tyrosol and hydroxytyrosol and their derivatives. The phenolic cluster of EVOO can be further divided into several subclasses. There are the lignans like taxifolin, luteolin, apigenin, and other molecules . EVOO contains simple phenols that include tyrosol, hydroxytyrosol, and phenolic acids. Another subgroup is the secoiridoids that are derivatives from tyrosol, hydroxytyrosol, and elenolic acid, like the dialdehydic form of elenolic acid linked to hydroxytyrosol (3,4-DHPEA-EDA or oleacein) and tyrosol (p-HPEA-EDA or oleocanthal). The secoiridoids subgroup includes also the oleuropein and ligstroside aglycons (3,4-DHPEA-EA, p-HPEA-EA, respectively) and their isoforms oleomissional and oleokoronal.
The majority of EVOO phenols belong to the secoiridoids tyrosol and hydroxytyrosol subgroup, contributing to the bitter taste and the throat burning sensation. In plants, the production of secondary metabolites is initiated by the mevalonate (MVA) and 2-C-methyl-d-erythritol 4-phosphate (MEP) pathways. These two pathways lead to the production of sterols and terpenoids. Secoiridoids are produced by the MEP pathway but presumably derived from tyrosine proceeding via tyrosol. Arogenate decarboxylated is the precursor of tyrosine in the phenylpropanoid metabolism, while hydroxytyrosol is synthesized from tyrosine that is produced through the dopamine pathway. Flavonoids, lignans, and verbascoside are products of the phenylpropanoid pathway, while verbascoside could be a product of tyramine via dopamine or coming from tyrosol via hydroxytyrosol.
Phenols are organic molecules characterized by the existence of a hydroxyl group attached directly to the benzolic group of the compound. Secoiridoids are the primary phenolic compounds present in EVOO, and their molecules are based on a phenylethanoid structure, such as oleuropein and ligstroside.
In EVOO these compounds are present as esters of hydroxytyrosol and tyrosol, respectively, as their initial forms are hydrophilic and are the most predominant phenols. The biosynthesis of all secoiridoid derivatives in EVOO has as start point these two compounds: oleuropein and ligstroside, the predominant phenols in olives. During the process steps in EVOO production and in particular in the crushing and malaxation steps, these molecules are transformed due to β- glucosidase, into their aglycon forms.
The aglycon forms of oleuropein and ligstroside are very unstable, and they further transform to closed-ring monoaldehydic or open-ring dialdehydic forms. At the malaxation step, the dialdehydic forms undergo demethylation and decarboxylation leading to the production of oleacein and oleocanthal. […]