Polyphenols in olive oil

What are polyphenols?

Polyphenols are secondary plant compounds found exclusively in plants, in the outer layers of fruit, vegetables and grains. Chemically they are recognised by several aromatic rings (phenol). They include caffeic acid, flavonoids and – particularly relevant in olive oil – hydroxytyrosol, tyrosol, oleocanthal and oleacein.

Why olive oil contains polyphenols

Polyphenols are the olive's protective compounds. They only end up in the oil in significant amounts when the fruit is harvested early, unripe and processed gently:

• Early harvest: green, not yet fully ripe olives contain the highest levels.
• Short time between harvest and mill: ideally a few hours.
• Cold extraction below 27 °C: heat and oxygen break down polyphenols.
• Dark storage: light and heat reduce the content over time.

A high polyphenol content costs yield: early-harvested olives produce significantly less oil per tree. That is the main reason why polyphenol-rich oils are more expensive.

How polyphenols taste

Polyphenols are sensorially perceptible. A polyphenol-rich oil tastes bitter on the tongue, peppery and pungent in the throat (the typical scratch caused by oleocanthal) and grassy-fruity on the nose. In extra virgin olive oil these attributes are not a flaw but a mark of quality. A completely mild, neutral-tasting oil generally contains hardly any polyphenols.

The approved EU claim

There is a single officially approved health claim for olive oil polyphenols: “Olive oil polyphenols contribute to the protection of blood lipids from oxidative stress.” It may only be used if the oil contains at least 5 mg of hydroxytyrosol and its derivatives per 20 g of olive oil – proven by laboratory analysis. The beneficial effect is obtained with a daily intake of 20 g of olive oil. Claims beyond this are not legally permitted.

Polyphenols and shelf life

Polyphenols act as natural antioxidants within the oil itself: they delay rancidity. A polyphenol-rich oil therefore stays fresh longer than a mild oil when stored correctly – dark, cool and tightly sealed.