The FRAP assay is a method of measuring the ability of reductants
(antioxidants) to reduce Fe3+–Fe2+. The formation of bluecoloured
Fe2+-TPTZ complex (Fe2+ tripyridyltriazine) increases the
absorbance at 593 nm. The method of Kubola and Sirithon (2008)
was used with some modifications. The stock solutions included
300 mM acetate buffer, pH 3.6, 10 mM TPTZ solution in 40 mM
HCl, and 20 mM FeCl36H2O solution. The fresh working solution
was warmed at 37 C before using. Rice extracts (300 ll) were allowed
to react with 1.7 ml of the FRAP solution. The absorbance
at 593 nm of the mixture was measured after 60 min of reaction.
The results were calculated by standard curves prepared with
known concentrations of FeSO4, and were expressed as lmol
FeSO4/g fresh weight.