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al., 2018), maslinic acid and oleanolic acid. In a more recent record, Talhaoui et al., (2018) listed the association of olive oil as the main dietary fat with diverse beneficial health effects, such as antihypertensive, antiviral, antiinflammatory, hypoglycemic, neuroprotective and anticancer properties.
The phytochemistry of olive
Phytochemical research carried out on O. europaea led to the isolation of many classes of compounds. These include the iridoids, lignans, phenols, flavonoids, glycosides and terpenoids. It was noted that the polar fractions, such as n-butanol and water soluble fractions, could offer an important scope for further studies (Muhammad Ali Hashmi et al., 2015). The major constituents of the fruits oil would consist of the galactolipids and triacylglycerols. Advanced research in biotechnology would include the analysis of the different fatty acid compositions of volatiles from the fruits of various olive cultivars.
Meanwhile, the leave which was considered as a waste by-product in the olive industry, in turn, could be employed to yield natural biophenol, particularly the oleuropein (Figure 2) (Cifá et al., 2018;
Sahin et al., 2018). This observation was made, followed by the utilisation of the ultrasound technology, in comparison to the conventional maceration method, during the extraction procedures.
Oleuropein (C25H32O13, molecular weight: 540.514 g/mol) is recognised as a non-crystalline, intensely bitter biophenol, which is soluble in water and alcohol. It is not soluble in ether, due to its glucoside moiety. Being a polar compound, much more oleuropein could be obtained from olive mill waste water than that of non-polar olive oil (Sahin et al., 2018). Oleuropein is also a heterosidic ester of 𝛽- glucosylated elenolic acid and hydroxytyrosol. Therefore, oleuropein is responsible for the existence of hydroxytyrosol, another valuable natural antioxidant (Figure 2). In addition, elenolic acid can be considered as a marker for maturation of olives (Esti et al., 1998).
Other oleuropein related compounds in olive oil would include the oleocanthal, a tyrosol ester and oleacein (Figure 3). By using proton Nuclear Magnetic Resonance spectroscopy (H-NMR) (Angelis et al., 2018), both chemical compounds could be quantitatively measured in the olive oil samples (Karkoula et al., 2012). These authors observed the phenolic group in oleocanthal would resonate at δH 5.3 ppm. Meanwhile, the aldehyde protons in oleocanthal would resonate at δH
9.7 – 9.8 ppm. However, an additional phenolic group in oleocein would resonate as δH 8 - 9 ppm.
Therefore, the presence of o-dihydroxy substitution (catechol) in the ring structure of hydroxytyrosol could be recognised by NMR, due to the occurrence of intramolecular hydrogen bonds (Charisiadis et al., 2014).
Oleuropein Elenolic acid
Hydroxytyrosol or 4-(2-hydroxyethyl)-1,2-benzenediol Figure 2: The structure of oleuropein from olive leaves and fruits (Cifá et al., 2018; Sahin et al.,
2018). The ester part consists of elenolic acid and hydroxytyrosol.
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Oleocanthal Oleacein
Figure 3: The structure of oleocanthal and oleacein from olive oil.
CONCLUSION
A number of articles mentioned the benefit of the oil from O. europaea. The phytochemical investigations on Olea should be further extended in order to explore the therapeutic potential of this plant, particularly in vivo studies. It is hoped that this sacred medicinal plant can also be utilised for clinical therapy.
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