Changes in antioxidant concentration of virgin olive oil during thermal oxidation

The concentration of α-tocopherol, hydroxytyrosol derivatives and tyrosol derivatives was measured in samples of virgin olive oil during thermal oxidation at 60 and 100 °C. Hydroxytyrosol derivatives are the first antioxidants that are lost during thermal oxidation (until a peroxide value of 20–30 meq/kg). Tyrosol derivatives seem to be the most stable compounds, while α-tocopherol has an intermediate rate of loss at low peroxide values and is destroyed at peroxide values from 20 to 50 meq/kg. This means that hydroxytyrosol derivatives are the first compounds to be oxidized, providing therefore oxidative stability to the oil. α-Tocopherol seems to be oxidized after a significant decrease on hydroxytyrosol derivatives content. Tyrosol derivatives are the antioxidants that decrease with the lowest rate, providing the oil with the less antioxidant activity.