2.6. Ferric reducing/antioxidant power (FRAP) assay
The ability of plant extracts to reduce ferric ion to the ferrous
one, (FRAP assay) is another indicator frequently used for assessing
antioxidant power (Benzie & Strain, 1996). Ferrous ion (Fe
2+
) produced in this assay forms a blue complex (Fe
2+
/TPTZ) absorbing
at 593 nm. Briefly, the reagent was prepared by mixing acetate
buffer (300 mM, pH 3.6), a solution of 10 mM TPTZ in 40 mM
HCl, and 20 mM FeCl36H2O at 10:1:1 (v/v/v). Firstly, 300llof
freshly prepared FRAP reagent was heated to 37C and an absorbance (A0) of a blank reagent was read at 593 nm in a Biotek
EL808 microplate reader (Vermont, USA). Then 10ll of 0.1% extract solution in water and 30llH2O were added (final dilution
of samples in the reaction mixture was 1:34) and the absorbance
(A) was recorded every 1 min during the whole monitoring period,
which lasted up to 30 min. The change in the absorbance
(DA593nm) between the final reading andA0 was calculated for
each sample and related to theDA593nm of a Fe
2+
reference solution which was measured simultaneously