Stoichiometric and Free Radical-Scavenging Kinetic Studies of Extractable Polyphenols from Pomegranate Husk and Pistachio Hull

In this work, the antiradical activity of fresh and aged skins of two Iranian varieties of pomegranate husk and pistachio hull was measured in order to assess their concentration in antioxidant potential usable in various fields. The radical scavenging capacity (RSC) of pomegranate husks and pistachio hulls samples were studied using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH˙) assay. To determine the RSC and stoichiometric factor of the samplers, the second-order rate constants (k2) and total H-atom-donating capacities (n) for the oxidation of polyphenol extracts by DPPH˙ were evaluated. The resulting k2 values were also compared with those of the natural and synthetic antioxidants. The order of relative second-order rate constants in methanol at 25 °C found to be pomegranate husk > gallic acid > tannic acid > pistachio hull. Furthermore, the RSCs based on the calculation of area under kinetic curve (AUC), total stoichiometric factor of natural phenolics and commercial antioxidants were also compared.