The FRAP assay was done according to Benzie and Strain (1996). The FRAP 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 FeCl3•6H2O at 10:1:1 (v/v/v) and then warmed at 37 °C before using. Plant extracts (15 μl) were
allowed to react with 285 μl of the FRAP reagent for 30 min in the dark condition. The absorbance of
the mixer was taken at 593 nm, using FRAP reagent solution as blank. The standard curve was linear
range 25 - 800 mM Trolox. Absorbance values were converted to μmol trolox equivalent per gram of
dry weight (μmol TE/g dw). Additional dilution was needed if the FRAP value measured was over the
linear range of the standard curve. Each composite sample was analyzed in triplicate and each leaf
parts was replicated at least three times.