Direct Analysis of Total Antioxidant Activity of Olive Oil and Studies on the Influence of Heating

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Abstract
Aim of this study was to evaluate the total antioxidant activity (TAA) of extra virgin olive oil (EVOO) and the effect of heating on the α-tocopherol content and TAA in relation to the presence of polyphenols, heating time, and temperature. Experiments included the measurement by ABTS decolorization assay of antioxidant capacity of α-tocopherol and 14 simple phenolic compounds present in EVOO, either dissolved in ethanol or added to refined olive oil, and the evaluation of TAA, total phenols, and α-tocopherol of six commercial EVOO and three olive oils. Finally, four experimental oils were prepared from refined olive oil containing a fixed amount (300 ppm) of α-tocopherol and increasing amounts of polyphenols (25, 125, 225, and 326 ppm) extracted from EVOO. The thermal stability of experimental oils under domestic heating conditions (heating time from 30 to 120 min, heating temperature from 160 to 190 °C) was studied by evaluating the loss of α-tocopherol and TAA according to a Latin square design. Results indicate that TAA of commercial oils is mainly due to their phenol and α-tocopherol content. Heating experiments suggest that polyphenols from EVOO are effective stabilizers of α-tocopherol during olive oil heating, thus contributing to the nutritional value of cooked foods. Keywords: Olive oil; antioxidant activity; thermal oxidation; polyphenols; α-tocopherol; hydroxytyrosol