Oleacein is an antioxidant compound in fresh extra virgin olive oil that forms from oleuropein and carries a hydroxytyrosol unit. It is often one of the most abundant phenolic compounds in early harvest oil. Because it contains hydroxytyrosol, it counts toward the EU-authorised claim that olive oil polyphenols protect blood lipids, including LDL cholesterol, from oxidative stress. In laboratory studies it is a strong free radical scavenger.

What is oleacein?

Oleacein is a secoiridoid, the class of compounds found only in the olive family. Its full chemical name is long, so researchers use the short one. It is a dialdehyde: a hydroxytyrosol unit joined to a small, reactive two-aldehyde fragment.

Oleacein is the twin of oleocanthal. Both form during milling, when crushing the olive releases enzymes that cut up larger parent compounds. Oleuropein becomes oleacein. Ligstroside becomes oleocanthal. The only structural difference is one hydroxyl group on the ring. That small difference makes oleacein the stronger antioxidant of the pair.

Oleacein contributes to the bitterness and pungency of a fresh oil. Its taste is less distinctive than oleocanthal's throat sting, so it tends to be overshadowed. In many fresh Greek oils, though, it is present in similar or larger amounts.

How it works in the body

Oleacein's catechol ring, inherited from hydroxytyrosol, lets it donate electrons and neutralise free radicals. That is the core of its antioxidant action. It works in fatty settings, which matters for LDL particles. Oxidised LDL is the form that builds up in artery walls, so slowing that oxidation is a meaningful target.

Oleacein is not just a scavenger. In cell studies it reduces the release of inflammatory signals from immune cells. Once digested, it also releases hydroxytyrosol, which is well absorbed. So part of its effect in the body is likely delivered through hydroxytyrosol and its metabolites.

What the research shows

The EU health claim. EFSA concluded that olive polyphenols protect LDL particles from oxidative damage, with a minimum of 5 mg of hydroxytyrosol and its derivatives per 20 g of oil (EFSA NDA Panel, EFSA Journal, 2011). The EU then authorised this claim (Commission Regulation (EU) No 432/2012). Oleacein is one of these hydroxytyrosol derivatives, so it is part of the measured total behind the claim.

Human evidence on oil phenolics. In the EUROLIVE trial, 200 healthy men took three olive oils that differed only in phenolic content (Covas et al., Annals of Internal Medicine, 2006). Markers of lipid oxidation fell as phenolic content rose. The trial measured total phenolics, not oleacein alone. It shows the effect of the compound family to which oleacein belongs.

Antioxidant strength. A laboratory comparison found that oleacein was at least as strong an antioxidant as oleuropein, its parent compound, across several test systems (Czerwinska et al., Food Chemistry, 2012). This supports the idea that conversion during milling preserves, and may sharpen, antioxidant activity.

Cell signalling. Cell studies have reported that oleacein reduces inflammatory signals from immune cells and slows growth pathways such as STAT3 and mTOR in some cancer cell lines (preclinical). These results explain the scientific interest. They are not evidence of any effect in people.

How much is in olive oil and in Phenolia

Oleacein is absent from refined oil and varies widely between extra virgin oils. Older or late harvest oils may contain very little. Fresh, early harvest oils can contain from tens to several hundred mg/kg.

The same three factors drive it as for oleocanthal. Green olives contain more oleuropein to convert. The Greek Koroneiki cultivar is rich in secoiridoids. Careful, cold milling and dark, cool storage slow its breakdown. Oleacein is reactive, so it declines over months after bottling.

Pomoni measures phenolic compounds by HPLC (high-performance liquid chromatography). HPLC separates oleacein from oleocanthal and the other compounds before measuring each one. Learn more in HPLC vs NMR.

Pomoni High-Phenolic Olive Oil is pressed from early harvest Koroneiki olives. Phenolia Daily combines high-phenolic olive oil (powdered), olive leaf extract and Greek Mountain Tea. Its compound profile differs from fresh oil. The current batch certificate on testing and certifications lists the measured figures. For the heart connection, see our cholesterol page.

Related compounds

• Oleocanthal
• Hydroxytyrosol
• Oleuropein
• Tyrosol
• The science of polyphenols
• HPLC vs NMR testing

Frequently asked questions

These statements have not been evaluated by the Food and Drug Administration. Pomoni products are not intended to diagnose, treat, cure or prevent any disease.

Sources

1. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles from oxidative damage. EFSA Journal. 2011;9(4):2033. doi:10.2903/j.efsa.2011.2033
2. Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods. Official Journal of the European Union. 2012. eur-lex.europa.eu
3. Covas MI, Nyyssonen K, Poulsen HE, et al. The effect of polyphenols in olive oil on heart disease risk factors: a randomized trial. Annals of Internal Medicine. 2006;145(5):333-341. doi:10.7326/0003-4819-145-5-200609050-00006
4. Czerwinska M, Kiss AK, Naruszewicz M. A comparison of antioxidant activities of oleuropein and its dialdehydic derivative from olive oil, oleacein. Food Chemistry. 2012;131(3):940-947. doi:10.1016/j.foodchem.2011.09.082