Antioxidant capacity of edible plants: extraction protocol and direct evaluation by cyclic voltammetry

Reactive oxygen-derived species are produced in cells under physiological conditions and in response to stress. Among the various antioxidant systems responsible for protection against these species, the low-molecular-weight antioxidants (LMWA), such as ascorbate, play an important role. Cyclic voltammetry (CV) has been proposed as a tool for quantitation of the total antioxidant capacity of plasma. It has also been shown that biological oxidation potentials, as determined from the anodic current waves of the CV tracings, are specific characteristics of the various LMWA components, and that the amplitude of each wave can be used for quantitation of the specific component. The adaptation of CV for evaluation of the total antioxidant capacity of edible plants is demonstrated here. The area under the anodic current wave is proposed as a better indicator for the content of LMWA, compared with the amplitude. This distinction could prove valuable when more than a single molecule contributes toward a specific anodic wave and when the identities of the components of a wave are not known. Vegetables and fruits that are commonly consumed in the U.S. diet were used. They were extracted with either water, aqueous acetic acid (30%), or a mixture of water, acetic acid, and acetonitrile (40:30:30). The LMWA contents were evaluated by CV. In three to five steps the LMWAs were completely extracted from the edible foods, and their amounts were translated into equivalents of ascorbate.