Stabilities of tocopherols and phenolic compounds in virgin olive oil during thermal oxidation

Abstract

The effects of thermal oxidation at 60 C on tocopherols (a, b, c) and phenolic compounds (hydroxytyrosol and tyrosol) of olive oil were studied. Tocopherols were determined by HPLC and phenolic compounds by HPLC and GC–MS. Peroxide value of olive oil increased with treatment time until it reached to 56.6 meq/kg. aTocopherol, b-tocopherol and c-tocopherol contents of olive oil decreased with treatment time. a-Tocopherol in olive oil was decomposed after 63 days of treatment. bTocopherol in olive oil was depleted after 33 days of treatment. The reduction in c-tocopherol of olive oil was 75% after 63 days of treatment. The degradation of hydroxytyrosol in olive oil was 91% after 63 days of treatment. Tyrosol was more stable than hydroxytyrosol in olive oil. Inverse correlations of peroxide value with hydroxytyrosol, a-Tocopherol, b-tocopherol and c-tocopherol were observed.