Antioxidant kinetics of plant-derived substances and extracts.

The antioxidant activity (AA) of substances present in several plant species has been widely studied which reflects their fundamental role in the protection of skin tissue against the harmful action of reactive oxygen species. Given the importance of effective and long-lasting protection against ultraviolet radiation, we studied the AA of several plant derivatives and extracts over time. Several chemical in vitro methods may be used to evaluate antioxidant capability, among which the 1,1-diphenyl-2-picrylhydrazyl (DPPH) method stands out, despite its unspecificity, as the most cited and described method in the literature. In this work the AA was evaluated by measuring their capacity to reduce DPPH in 30 min, which is suggested in the literature, and additionally at different times up to 8 h from the baseline reading. The methodology used to evaluate the AA over time was validated. It is important to emphasize that this study proposes to modify the conventional DPPH method, although considered to be non-specific, to be used to test new antioxidant agents. This represents a considerable advantage because some substances show no significant activity during the first 30 min of reaction. Among other plant products, we tested a proantocyanidin-rich grapeseed extract, a hesperidin derivative, a rutin-containing ginkgo extract, a polyphenol-containing yerba maté extract and tocopheryl acetate, all of which were properly standardized. As they have different antioxidant profiles, each ingredient showed a specific behaviour over time, which may promote the selection of anti-radical compounds capable of offering protection against external agents. Combining extracts and plant derivatives that present fast, medium and slow antioxidant kinetic it is possible to create complexes capable of offering an effective protection from the moment of application up to several hours later. It is a perfectly feasible method, and such combinations prove to be more effective and have more durable effect.