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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 alpha-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 alpha-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 alpha-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 alpha-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 degrees C) was studied by evaluating the loss of alpha-tocopherol and TAA according to a Latin square design. Results indicate that TAA of commercial oils is mainly due to their phenol and alpha-tocopherol content. Heating experiments suggest that polyphenols from EVOO are effective stabilizers of alpha-tocopherol during olive oil heating, thus contributing to the nutritional value of cooked foods.

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In this paper, a novel electrochemical method to evaluate the antioxidant power of lipophilic compounds present in vegetables, such as carotenoids, chlorophylls, tocopherols, and capsaicin, is reported. The method is based on a flow injection system with an electrochemical detector equipped with a glassy carbon working electrode operating amperometrically at a potential of + 0.5 V (vs Ag/AgCl). The proposed method is selective for lipophilic compounds having antioxidant power. When applied to pure compounds, the order of antioxidant power resulted as follows: lycopene > beta-carotene > zeaxanthin > alpha-carotene > beta-cryptoxanthin > lutein > alpha-tocopherol > capsaicin > chlorophyll a > chlorophyll b > astaxanthin > canthaxanthin. Results obtained on five vegetable and two fruit extracts were compared to those obtained by the 2,2'-azinobis(3-ethylbenz-thiazoline-6-sulfonic) acid (ABTS) radical cation decolorization assay, one of the most used methods to evaluate the total antioxidant capacity of foods. A good correlation between the two methods was found, except for spinach, because of the different antioxidant powers assigned by the two methods to chlorophylls. In conclusion, results suggest that the proposed electrochemical method can be successfully employed for the direct, rapid, and reliable monitoring of the antioxidant power of lipophilic food extracts.

Phenols present in wines are responsible for its antioxidant properties. Traditionally the antioxidant power of wines has been measured using in vitro tests principally based on the inhibition of human LDL oxidation and also using the ORAC assay with different reactive species. This work describes a new method to evaluate the antioxidant power of several red and white wines based on a FIA system with electrochemical detection. It represents a significant improvement over other previously reported methods since it is based on the chemical structure of polyphenols and does not require the use of reactive species.