Nanoceria-based reactive species scavenging activity of antioxidants using N,N-dimethyl-p-phenylenediamine (DMPD) probe

Abstract

The aim of this work was to develop a fast and low-cost method to measure the reactive species formed in an aqueous suspension utilizing nanoceria as a peroxidase-like catalyst. Nanoceria was produced with a green synthesis using Thymbra spicata L. (Zahter) extract in conjunction with {Ce(III) + aqueous NH₃} as a heterogeneous catalyst to generate reactive species (RS) from hydrogen peroxide. DMPD reagent was used as a colorimetric probe due to its absorbance increase at 515 nm accompanying a color change from transparent to red-violet in the presence of RS. The developed method was used to determine the percentage RS scavenging activity of synthetic antioxidant samples and herbal infusions with regard to their bleaching action on the DMPD radical cation. For validating the proposed method, the cupric reducing antioxidant capacity (CUPRAC) reactivity of the {nanoceria + H₂O₂} suspension before and after reaction with antioxidants was measured, and the difference between the CUPRAC absorbances was converted to RS scavenging, where the excess of H₂O₂ was decomposed with catalase. Both DMPD and CUPRAC methods showed a similar order of RS scavenging activities for a number of antioxidant compounds. As a result, it can be concluded that the combination of nanoceria, hydrogen peroxide and DMPD provided a fast detection system to investigate the RS scavenging antioxidant activity of food and plant samples, as confirmed by the CUPRAC assay.