Novel Approach to Study Oxidative Stability of Extra Virgin Olive Oils:  Importance of α-Tocopherol Concentration

The stability of extra virgin olive oils is mainly due to their relatively low fatty acids unsaturation and to the antioxidant activity of some of the unsaponifiable components. We studied the activity of α-tocopherol in extra virgin olive oil in its natural state, using new and simple oxidizing conditions in “thin layer” and “bulk phase”. Oxidation time course was monitored at 37 °C or 75 °C. A storage test was also performed. Two parameters were evaluated: depletion of α-tocopherol and formation of PUFA hydroperoxides, measured as conjugated dienes (CD) and peroxide value. The value of complex polyphenols was also measured. α-Tocopherol concentration decreased in function of time and temperature and showed a strong inverse correlation with the increase of CD. When α-tocopherol reached a “threshold value” of 60−70 mg/kg, a significant increase of CD formation was observed, together with a good correlation between CD and peroxide value. The initial amount of α-tocopherol is one of the components that influences oil oxidative susceptibility. Keywords: α-Tocopherol; conjugated dienes; olive oil; oxidation; polyphenols