Rapid electrochemical method for the evaluation of the antioxidant power of some lipophilic food extracts

In this paper, a novel electrochemical method to evaluate the antioxidant p ower of lipophilic compounds present in vegetables, such as carotenoids, ch lorophylls, tocopherols, and capsaicin, is reported, The method is based on a flow injection system with an electrochemical detector equipped with a g lassy carbon working electrode operating amperometrically at a potential of + 0.5 V (vs Ag/AgCl). The proposed method is selective for lipophilic comp ounds having antioxidant power. When applied to pure compounds, the order o f antioxidant power resulted as follows: lycopene > beta -carotene > zeaxan thin > alpha -carotene > beta -cryptoxanthin > lutein > alpha -tocopherol > capsaicin > chlorophyll a > chlorophyll b > astaxanthin > canthaxanthin. R esults obtained on five vegetable and two fruit extracts were compared to t hose 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 betwe en the two methods was found, except for spinach, because of the different antioxidant powers assigned by the two methods to chlorophylls. In conclusi on, results suggest that the proposed electrochemical method can be success fully employed for the direct, rapid, and reliable monitoring of the antiox idant power of lipophilic food extracts.