Olive oil polyphenols, explained: what the number means

1. What they are

Olive oil polyphenols are a family of phenolic compounds the olive makes to defend its fruit, carried into the oil at milling. The ones that matter in oil are hydroxytyrosol and tyrosol and their larger relatives — the secoiridoids oleuropein aglycone, ligstroside aglycone, oleacein and oleocanthal. They are antioxidants: they react with oxygen before the fat does, which is why a high-polyphenol oil stays fresh longer, and they are what you taste as bitterness on the tongue and pungency in the throat.

The amount varies enormously. A late-picked, ripe Arbequina might carry 100 mg/kg; an early-picked Coratina or Picual 600–800; a very early mountain Tsounati with a laboratory certificate, over 1,200. The variety sets the ceiling, the harvest date sets how close the oil gets to it, and time in the bottle brings it down from there.

2. The EU health claim and 250 mg/kg

Regulation 432/2012 lists the health claims a food may make in the EU. One of them reads: “Olive oil polyphenols contribute to the protection of blood lipids from oxidative stress.” It may be used only for an oil containing at least 5 mg of hydroxytyrosol and its derivatives per 20 g, and the label must say the effect is obtained with a daily intake of 20 g. Five milligrams per twenty grams is 250 mg per kilogram — the only externally defined line on the whole polyphenol scale, and the one we use to split the library into bands.

Two things the claim does not say. It does not say more is better: EFSA’s 2011 opinion established a threshold, not a dose-response. And it does not say polyphenols cure anything; the wording is deliberately about blood lipids and oxidative stress. An oil at 300 mg/kg qualifies for the claim exactly as an oil at 1,300 does.

250 mg/kg is a threshold the regulator set. Everything above it is marketing, or taste.

3. Three methods, three numbers

A polyphenol figure means nothing without its method. Three are in common use and they do not give the same answer for the same oil.

Why 600 mg/kg from one laboratory and 450 from another can describe the same bottle. Compare figures only within a method.

This is why every laboratory panel on this site names the method and the laboratory when the producer does, and why we never put a producer’s Folin figure next to a competitor’s HPLC figure as if they were on one scale. When a producer publishes a number with no method, we print it with that caveat.

4. What moves the number

Variety first: Coratina, Picual, Koroneiki, Tsounati and Lianolia are naturally rich; Arbequina, Taggiasca and Manaki are naturally low. Harvest second: green fruit in October carries two or three times the phenols of the same tree’s black fruit in December. Milling third — long, warm malaxation loses phenols to the water phase, which is why serious producers cap it at 25–27 °C and under 45 minutes. Then time: a bottle loses a share of its phenols every month, faster in light and heat, and an unfiltered oil faster than a filtered one.

Water matters too. Irrigated groves give bigger fruit with lower phenol concentration; dry-farmed mountain trees give small, intense fruit. Several of the highest figures in this library — Pamako’s Tsounati at 650 metres, The Governor’s unirrigated Corfu Lianolia — come from exactly that kind of grove.

5. In the library

A spread of published figures from the library, with the methods that make them hard to compare. The full list, with source on every row, is on each oil’s page.