Development of a new chromium reducing antioxidant capacity (CHROMAC) assay for plants and fruits

A chromium reducing antioxidant capacity (CHROMAC) assay was presented to measure antioxidant capacity of selected plants and fruits and compared its performance with other commonly used antioxidant capacity methods of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and cupric reducing antioxidant capacity (CUPRAC). The assay is based on the spectrophotometric measurement of colored a chelate complex of Cr(III) and diphenylcarbazone formed by the reaction of Cr(VI) and 1,5-diphenylcarbazid in acidic medium. Phenolic compounds react with excessive amounts of Cr(VI) at low pH values, causing reduction of Cr(VI) to Cr(III) and conversion of phenols to oxidized products. The assay comprises of the antioxidant with a chromium(VI) solution, a 1,5-diphenylcarbazid in acidic medium and subsequent measurement of the developed absorbance at 540 nm after 50 min. The color development is stable for phenolic compounds in plant and fruit. The selectivity of the assay for phenolic compounds was improved by adjusting pH to 2.8 and reduction potential between 0.2 and 0.9 V. The developed assay was successfully applied to the measurement of antioxidant capacity of three plants and one fruit (Prunus divaricata Ledeb.subsp. divaricata) samples and comparable results were obtained by ABTS and CUPRAC assays.