3.2. Determination of Ferric Reducing Antioxidant Power (FRAP)

The FRAP assay is based on the reduction of the Fe(III)-TPTZ complex to the ferrous form at low pH. This reduction was monitored by measuring the absorption change at 593 nm [4]. One millilitre of the working reagent was mixed with 20 μL of the extract, and the absorbance at 593 nm was recorded exactly after 4 min of incubation at room temperature. The absorption of 1000 μM ferrous sulphate standard was also measured. FRAP values are expressed as mmol of Fe(II) equivalent per 100 g rice.