The total reducing capacity of gac juice was determined
using FRAP assay (Benzie & Strain, 1996). The FRAP
reagent was initially prepared including 300 mM acetate
buffer, pH 3.6, 10 mM TPTZ solution in 40 mM HCl and
20 mM FeCl3.6H2O solution. The fresh working solution
was warmed at 37ºC prior using. 20 µl of gac juice were
mixed with 180 µl of the FRAP solution and incubated for
4 min. The absorbance was then recorded at 593 nm using
a spectrophotometer. The FRAP values were calculated
by standard curves prepared with known concentrations
of FeSO4 and expressed as µmol FeSO4/ml sample.