Olive leaf is the leaf of the olive tree (Olea europaea). Although olive oil is well known for its flavor and possible health benefits, the leaf and its extracts remain under preliminary research with unknown effects on human health.
The silvery green leaves are oblong, measuring 4–10 centimetres (1.6–3.9 inches) long and 1–3 centimetres (0.39–1.18 inches) wide. When consumed, leaves have an astringent bitter taste.
Olive phenolics are much more concentrated in the leaves compared with olive fruit or olive oil: 1450 mg total phenolics/100 g fresh leaf vs. 110 mg/100 g fruit and 23 mg/100 ml extra virgin olive oil. The primary active compounds in unprocessed olive leaf are oleuropein and hydroxytyrosol, as well as polyphenols and flavonoids, including luteolin, rutin, caffeic acid, catechin and apigenin. Elenolic acid is a component of olive oil and olive leaf extract. It can be considered as a marker for maturation of olives. Oleuropein, together with other closely related compounds such as 10-hydroxyoleuropein, ligstroside and 10-hydroxyligstroside, are tyrosol esters of elenolic acid. The phenolic composition of olive leaf extract varies according to plant variety, harvesting season and method, leaf maturity, storage conditions and extraction method.
Historically the benefits of olive leaves have been used in traditional medicine practices as folk remedies for the treatment of various illnesses. However, scientific evidence for health effects of using olive leaf extract has been deemed insufficient by the European Food Safety Authority to prove any cause-and-effect relationship.
Plants in the Mediterranean have developed high levels of polyphenols as a protection mechanism against environmental stressors. Some of these compounds display antioxidant properties in vitro.
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