Abstract
An improved decolorization method for measuring the antioxidant activity of food samples using N, N-dimethyl-p-phenylenediamine (DMPD) is developed. DMPD radical cation (DMPD.+) is generated through a reaction between DMPD and potassium persulfate and is subsequently reduced in the presence of hydrogen-donating antioxidants. This assay has a clear edge over the previous DMPD assay (the DMPD/FeCl3 assay) for the determination of antioxidant activity on a number of counts. The chemistry involves the generation of a more stable DMPD radical mono-cation by a reaction with potassium persulfate. The DMPD radical cation generator does not involve Fe(II) ions, which through Fenton's Reaction could cause negative deviation in the antioxidant activity of food extracts. The assay can equally be applied to the determination of antioxidant capacity of both hydrophilic and lipophilic antioxidants. The experimental procedure is rapid, inexpensive and ensures sensitivity along with reproducibility in the measurement of antioxidant activity of hydrophilic and lipophilic compounds and thus has a promising aspect of use in screening large number of fruit samples. The effectiveness of new DMPD decolorization assay was verified by evaluating the antioxidant capacity of different fruit samples.