Is it possible to use the DPPH and ABTS methods for reliable estimation of antioxidant power of colored compounds?

Negative impact of radicals on humans and animals is responsible for growing research interest in antioxidant properties of substances, which protect living organisms from the damaging influence of these reactive species. Among numerous methods for antioxidant activity estimation, DPPH and ABTS are the most popular and commonly used ones due to their ease, speed, sensitivity and the usage of stabile radicals. The paper shows and discusses the antioxidant properties of a few compounds exhibiting different extinction of the wavelength used to monitor colored radical depletion in spectrophotometric measurements—e.g. 516 and 744 nm in DPPH and ABTS assays, respectively. As results from the presented data, the difference between true and spectrophotometrically estimated IC50 values for colored antioxidants depends not only on extinction coefficient of the monitored wavelength by the antioxidant but also on its remaining concentration in the measuring system. The presented results seems to be helpful for the researches examining coloured antioxidants and plant extracts containing substances having spectra in Vis region.