by Emirhan Turan, November 10, 2020
Olea europaea L., known as the olive tree, is an evergreen tree or shrub native to the Mediterranean region, Asia, and Africa. However, the species of the olive tree is cultivated in many different areas and regions as well, including South America, Africa, India, China, Australia, New Zealand, Mexico, and the United States.
Olive was important in history in various civilizations and religions. The olive tree was cultivated first by Semitic people in Syria in 6000 B.C. According to myths, a white pigeon brought a piece of an olive branch as a sign of life to Noah, olive, since then is used as the symbol of peace and togetherness. Olive is mentioned in the Quran, Bible, and Torah in many chapters. In the Babylonian Code of Hammurabi, trimming an olive tree more than 2 times per year was charged with the death penalty.
Olive has healing power and is used for medicinal purposes since the day of Hippocrates. Studies on modern times showed the reason behind it. Olive fruits and olive oil contain some minor constituents, including phenolic compounds, which contribute to antioxidant capacity, bitterness, pungency, and have important biological properties. The phenolic composition is not the same in every fruit and oil as there is a variation due to agronomic, genetic, and environmental factors such as the variety of the olive fruit, the region, and climatic conditions, the agricultural practices applied, the stage of maturity and harvest period, the mode of extraction for olive oil, storage, and packaging.
Chemical Composition of Olive Fruit and Olive Oil
The major phenolic compounds present in olive fruits are anthocyanins (cyanidin glucosides), flavonols (mainly quercetin-3-rutinoside), flavones (luteolin and apigenin glucosides), phenolic acids (hydroxybenzoic, hydroxycinnamic, others), phenolic alcohols (tyrosol, hydroxytyrosol, 3,4-dihydroxyphenylglycol), secoiridoids (oleuropein, demethyloleuropein, ligstroside, nuzhenide), verbascoside, a hydroxycinnamic acid derivative and lignans and Oleoside-11-methylester.
In olive oil, the phenolic composition is different than the olive fruit as synthetic reactions are happening during the process of olive oil. Olive oil contains mainly phenolic acids (hydroxybenzoic, hydroxyphenylacetic, hydroxycinnamic), simple phenols (tyrosol, hydroxytyrosol), derivatives of phenolic alcohols (tyrosol acetate, hydroxytyrosol acetate), glycosides (oleuropein, ligstroside), aglyconic derivatives of glycosides (ligstroside aglycon, oleuropein aglycon), dialdehydic and monoaldehydic forms of decarboxymethyl elenolic acid linked to hydroxytyrosol and tyrosol, lignans, flavonoids (apigenin, luteolin), hydroxy-isochromans, other phenols (vanillin, 4-hydroxy-3-methoxybenzaldeyde, 4-ethylphenol, and nonphenolic compounds (cinnamic acid, elenolic acid, elenolic acid glycoside). Main fatty acids of olive oil are, oleic acid (55.0-83.0%), palmitic acid (7.5-20.0%), linoleic acid (3.5-21.0%), stearic acid (0.5-5.0%), palmitoleic acid (0.3-3.5%).
Health Benefits of Olives
■ Antioxidant and prooxidant effects: Reduction of reactive species in human cells, reduction of oxidative stress, induction of endogenous antioxidant enzymes
■ Inflammation effect: Diminishing of leukosides leukotriene B4, inhibition of pro-inflammatory enzymes
■ Cardiovascular effects: Antihypertensive and potent antioxidant activities, platelet aggregation and endothelial function, anti-atherogenic activity
■ Central nervous system effects: Neuroprotective effects, behavioral effects, others
■ Antimicrobial effects: Antibacterial, antifungal, antiviral properties
■ Gastrointestinal effects: Chemoprevention of peptic ulcers and gastric cancers, ulcerative colitis, Crohn’s disease
■ Anticancer effects: Induction of apoptosis, inhibition of proliferation of tumor cells, inhibition of oxidative DNA damage in human leukocytes
■ Other effects: Immuno-modulatory, endocrine, respiratory effect, anti-aging activity.
Usage
Olive and olive oil is taking an important place in Mediterranean cuisine as well. In Turkey, Spain, Greece, and Italy, olive is used in different products and variously processed end products such as olive pastes, jams, pastry, crackers and snacks, bread, margarine. Different varieties of olives are used in pizzas, salads and in several dishes.
Other products where olives and olive oil can be found are various cosmetics, toothpastes, detergents, soaps, shampoos, foams as well as in dietary supplements and pharmaceutical additives.
Production and Quality of Olive Oils
Production of olive oil consist of 6 phases:
1- Selection, 2- Washing, 3- Chopping, milling, 4- Pressing, 5- Centrifugation, and 6- Filtering, filling.
Olive oil quality is changing according to olive fruits, processing procedure, mode of extraction, and storage. Virgin olive oils are considered the most healthiest for raw consumption while refined olive oils are used for cooking.
Selection, Quality, and Differences of Olive Fruits
The Olive fruit is a drupe and cannot be eaten straight from the tree. The olive contains a bitter compound called Oleuropein which has a strong, bitter taste and although it is harmless, it has to be removed before the olives can be consumed. Therefore, olives are processed to remove the bitterness, to preserve the fruit and enhance the flavour. There are 3 main table olives that are used world-wide:
- Semi-ripen: These are obtained from olives that are picked when their colour is starting to change and harvested before full maturity.
- Green: Green olives are harvested during the ripening cycle when they have reached normal size, but prior to colour change. Colour change should not have begun for good quality of green olives.
- Ripen olives: Ripen olives are harvested when the fruit is close to full ripeness, once it has attained the colour and oil content. The colour and oil content can vary depending on the location and quality attributes.
There are 3 main attributes that show the quality of table olives:
1) Smell: A high standard olive has a clean acceptable aroma and any off-odor is totally unacceptable in quality table olives.
2) Appearance/texture: An olive should have a degree of firmness in the flesh, without being tough or woody. The skin of the fruit should not be too tough, and the flesh should detach from the pit quite readily.
3) Taste: The taste and flavour of an olive product is generally subjective – it depends on what the customer needs. There are different tastes like salty, sour, bitter etc.
References
Boskou, D. (Ed.). (2015). Olive and olive oil bioactive constituents. Elsevier.
Borges, T. H., López, L. C., Pereira, J. A., Cabrera–Vique, C., & Seiquer, I. (2017). Comparative analysis of minor bioactive constituents (CoQ10, tocopherols and phenolic compounds) in Arbequina extra virgin olive oils from Brazil and Spain. Journal of Food Composition and Analysis, 63, 47-54.
Covas, M. I., Fitó, M., & de la Torre, R. (2015). Minor bioactive olive oil components and health: Key data for their role in providing health benefits in humans. In Olive and olive oil bioactive constituents (pp. 31-52). AOCS Press.
Kelebek, H., Kesen, S., & Selli, S. (2015). Comparative study of bioactive constituents in Turkish olive oils by LC-ESI/MS/MS. International Journal of Food Properties, 18(10), 2231-2245.
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