Botanical Name / Family
Olea europaea L. (family Oleaceae)
Plant Parts Used
Fruit and leaf.
Olive oil is made from the fruit and widely used in cooking. This review will focus on olive oil and olive leaf extracts.
Olive oil contains high levels of monounsaturated fatty acids (chiefly oleic acid) and is also a source of at least 30 phenolic compounds including oleuropein, hydroxytyrosol and tyrosol and also flavonoids, squalene, beta-carotene, and alpha-tocopherol.
Olive leaf extract also contains a variety of phenolic compounds, most importantly oleuropein, hydroxytyrosol and tyrosol, and also rutin, luteolin, catechin and apigenin, and various nutrients such as selenium, chromium, iron, zinc, vitamin C, beta-carotene and a wide range of amino acids. Unlike the olive fruit, olive leaf does not contain significant amounts of monounsaturated fatty acids, oleic acid or squalene.
It is important to note that not all olive products contain the same concentration of phenolic compounds. Olive leaf extract and extra virgin olive oil (acidity <1%) are considered superior sources of phenolic compounds, with extra virgin olive oil containing higher amounts than refined virgin olive oil. Of these, olive leaf extract is the most concentrated. According to one test, total phenol levels ranging from 6360 to 8190 mg/L were identified in olive leaf extract compared to 200-800 mg/L for extra virgin olive oil (unpubl data, Department of Primary Industries Laboratory).
The olive tree is among the oldest known cultivated trees in the world. Several biblical references to olive suggest its use dates back to ancient times and victors in the early Olympic Games were crowned with its leaves. Olives and its associated products have been used widely as folk medicines in countries such as Spain, Italy, France, Greece, Israel, Morocco, Tunisia, Turkey and the Mediterranean islands. Today, the olive plant is most well known for its fruit crop and oil. The Mediterranean region produces approximately 98% of the world’s total olive crop (~11 million tons), although the plant is also widespread on the Arabian peninsula, the Indian subcontinent and Asia. More recently, olive plantations have been developed in Australia and research is now being undertaken to identify the best species suited to the subtropical climate.
Olive: Main Actions
Most of the pharmacological effects for olive oil and olive leaf extract can be attributed to their main phenolic constituents, in particular oleuropein, hydroxytyrosol and tyrosol; however, several other biologically active constituents are also present.
Numerous olive phenolics have strong free radical scavenging capacity and show a synergistic behaviour when combined, as occurs naturally in the fruit and leaf. According to in vitro tests, the flavonoids, rutin, catechin and luteolin exert antioxidant effects almost 2.5-fold those of vitamin C and E and are comparable to that of lycopene.
ANTI-INFLAMMATORY AND ANTITHROMBOTIC
Several constituents within olive oil and/or leaf have demonstrated anti-inflammatory properties, chiefly oleuropein, hydroxytyrosol, oleic acid, luteolin and apigenin.
Oleuropein and hydroxytyrosol are found in both the oil and leaf and inhibit leukotriene B4 generation, which is involved in a wide range of pro-inflammatory pathways. These polyphenols are able to inhibit platelet aggregation and lipoxygenases and eicosanoid production.
Olive oil also contains large amounts of oleic acid, which is an omega-9 monounsaturated fatty acid that is converted to eicosatrienoic acid, which is then converted to leukotriene A3, which is a potent inhibitor of leukotriene B4 synthesis.
The oleic acid component modifies the vascular response to pro-atherogenic chemicals (such as high levels of cholesterol and the advanced glycation end-products of diabetes) and inhibits endothelial adhesion molecule expression, according to test tube studies.
Oleuropein has antimicrobial activity against a variety of viruses, bacteria, yeasts and fungi; however, one study suggests that hydroxytyrosol has stronger broad-spectrum effects.
Studies have identified the Mediterranean diet, as an entity, and the olive oil in particular, as significantly reducing arterial blood pressure in humans.
The hypotensive effect of olive leaves has been well documented in vivo. One of the more recent studies tested a specially prepared olive leaf extract (EFLA 943) and confirmed dose-dependent hypotensive activity when given orally to animals.
Olive leaf extract has demonstrated hypoglycaemic activity in animal models and one of the compounds responsible for this activity is oleuropeoside, which produced antidiabetic activity in animals with alloxan-induced diabetes. The researchers have suggested potentiation of glucose-induced insulin release and increased peripheral uptake of glucose as the most likely mechanisms of action.
Olive: Other Actions
Traditional texts describe the leaves as astringent and antiseptic and useful when boiled in water to create a decoction for the treatment of obstinate fevers. The oil is described as a nourishing demulcent with laxative properties. Oleuropein is the phenolic constituent responsible for the typically bitter and pungent aroma associated with olives, olive oil and leaf.
Luteolin possesses antimutagenic and antitumorigenic properties.
In vivo tests report that olive leaf extract has a hypo-uricaemic effect in treated animals.