Spectral analysis allows using the DPPH* UV–Vis assay to estimate antioxidant activity of colored compounds

Abstract

An accurate measurement of antiradical activity to samples, such as herbal extract and natural or synthetic pure compounds, is essential to estimate its scope as antioxidant, for example, in functional foods. The 2,2-diphenyl-1-picrylhydrazyl (DPPH*) UV–Vis assay is the most widely used method for this aim. Nevertheless, it can drive to erroneous results if the spectroscopic properties of each substance, in the reaction medium, are not considered. To overcome this limitation, we present a new methodology based on spectral analysis which, instead of reading at fixed wavelength, uses the UV–Vis spectra of selected compounds, as well as simple algebraic operations and fitting by residual sum of squares. The proposed methodology was assayed successfully to determine the antiradical activity of three compounds: naringin, which does not present absorbance in the absorption band of DPPH*, naringin-Cu(II) complex, with moderate absorbance at this range, and naringin-Fe(III) complex, which shows intense absorption at the studied range. The proposed methodology is simple with a broad scope, since it allows to study the free radical scavenging activity on samples with high color that could not be analyzed, by UV–Vis spectrophotometry, up to the moment.