Ferric reducing-antioxidant power (FRAP)
The ferric reducing-antioxidant power test was conducted according
to Benzie and Strain (1996). Acetate buffer (0.3M, pH 3.6) was prepared
by dissolving 3.1 g C2H3O2Na·3H2O and 16 ml of acetic acid in 1 l of
distilled water. TPTZ (2,4,6-tripyridyl-S-triazine) solution was prepared
by dissolving 23.4mg of TPTZ in 7.5 ml of 40 mM HCl solution. Ferric
solution (20 mM) was prepared using FeCl3·6H2O. The final working
FRAP reagent was prepared freshly by mixing acetate buffer, TPTZ and
ferric solutions at a ratio of 10:1:1, and was warmed to 37 °C. Aliquots
(200 μl) of each extract were mixed with 1.8 ml of FRAP reagent and the
absorbance of the reaction mixture was measured at 593 nm after
incubation at 37 °C for 10 min. Aqueous standard solutions of FeSO4·7H2O
(0–1000 μmol/l) were used for the calibration curve. The results were
expressed as μmol Fe2+/100 g sample dw.