2.5 Ferric reducing/antioxidant power assay (FRAP)
The total reducing capacity was determined by
using FRAP assay. FRAP assay was performed according
to the method of Benzie and Strain (21) with some modification.
The stock solution of FRAP reagent was initially
prepared consisting of 300 mM acetate buffer (pH 6.3), 20
mM 2,4,6-Tris (2-pyridyl)-s-triazine (TPTZ) solution in
40 mMHCl and 20 mM FeCl3.6H2O solution. The fresh
working solution was warm at 37๐C in oven prior to use.
Briefly, 300μl of peel extract was allowed to react with
2.7 ml of the FRAP reagent in test tubes for 30 min in the
dark condition. Readings of the colored product were then
taken at 593 nm by using spectrophotometers. The total
reducing capacity by FRAP assay were calculated from
ascorbic acid (0.01-0.05 mg/ml)standard, and concentrations
was expressed as mg of ascorbic acid equivalent
(AAE) per gram dry weight (mg AAE/ g DW).