Oleuropein is a natural phenolic substance found in the olive tree, virgin olive oil and olive leaves, important for the (bitter) taste, aroma and health effects of olive oil. Chemically, it belongs to the glycosides and polyphenolic substances of olive oil.

It was discovered in 1908 in olive oil and was named after the botanical (scientific) name of the olive tree(Olea europea). In 1960 it was found that its molecule consists of glucose, a phenolic substance, hydroxytyrosol, and an acid known as oleic acid. This acid was already known (it was obtained from olives by a method patented in the USA) and had been proposed since 1962 as an anti-hypertension drug.

Since the second half of the 20th century, many medical studies have gradually been carried out on the biological activity of oleuropein (as well as other polyphenols in olive oil) and its effect on human health. In particular, the antioxidant, bactericidal and bacteriostatic action, the reduction of platelet aggregation, etc. is being studied. The same substance plays an important role in olive plants, because its protective action (mainly antioxidant, but also due to its bitter taste) defends the olives from pathogenic fungi and insects by various mechanisms.
During the production of olive oil, part of the oleuropein is hydrolysed (i.e. broken down into other molecules) and thus compounds are produced which give olive oil its bitter taste and certain other characteristic flavours and aromas. The antioxidants produced also play an important role in limiting the oxidation of olive oil fats (rancidity). It works synergistically with other olive oil antioxidants such as tyrosol, hydroxytyrosol, squalene, alpha-tocopherol (vitamin E) and oleic acid to reduce oxidative damage and oxidative stress in organisms exposed to oxygen.[1]

In the modern medical literature there are a large number of published studies around oleuropein and its beneficial or potentially beneficial effect on the body as a protective against various diseases such as: Alzheimer's disease[2] cardiovascular disease,[3] fat accumulation in the liver[4] and other conditions[5]
Some of these studies have been done in experimental animals, others in vitro and others are clinical or epidemiological in humans.

1.«Επιμέλεια σελίδας: Βαλαβανίδης Θανάσης, Ευσταθίου Κωνσταντίνος, Η χημική ένωση του μήνα: Ελαιοευρωπεΐνη, Oleuropein. Εργαστήριο Οργαν. Χημείας, Σχολή Χημικών, Πανεπιστήμιο Αθηνών, 2007». Αρχειοθετήθηκε από το πρωτότυπο στις 11 Ιανουαρίου 2016. Ανακτήθηκε στις 30 Δεκεμβρίου 2015.
2.Casamenti F. et al. Oleuropein Aglycone: A Possible Drug against Degenerative Conditions. In Vivo Evidence of its Effectiveness against Alzheimer's Disease. J. Alzheimers Dis. 2015; 45(3):679-88. doi: 10.3233/JAD-142850.
3.Bulotta S. et al., Beneficial effects of the olive oil phenolic components oleuropein and hydroxytyrosol: focus on protection against cardiovascular and metabolic diseases. J Transl Med. 2014 Aug 3;12:219. doi: 10.1186/s12967-014-0219-9.
4.Barbaro B. et al., Effects of the olive-derived polyphenol oleuropein on human health. Int J Mol Sci. 2014 Oct 14;15(10):18508-24. doi: 10.3390/ijms151018508.
5.Sci Pharm. 2010;78(2):133-54. doi: 10.3797/scipharm.0912-18. Epub 2010 Apr 23. Omar SH, Oleuropein in olive and its pharmacological effects. Sci. Pharm. 2010;78(2):133-54. doi: 10.3797/scipharm.0912-18. Epub 2010 Apr 23.