2.5.3. Determination of ferric reducing antioxidant
power (FRAP)
The FRAP assay was performed according to the protocol of
Benzie and Strain (1996) with some modifications. The stock
solutions included 300 mM acetate buffer (3.1 g C2H3NaO2·3H2O
and 16 mL of C2H4O2) at pH 3.6; 10 mM TPTZ solution in 40 mM
HCl; and 20 mM FeCl3·6H2O solution. A fresh working solution
was prepared by mixing 25 mL of acetate buffer, 2.5 mL
of TPTZ solution, and 2.5 mL of FeCl3·6H2O solution. Each apple extract (10 μL in 1 mL of distilled water) was allowed
to react with 1.8 mL of the FRAP solution for 10 min at 37 °C.
Results were expressed as μM TE/g FW. Trolox standard solutions
were prepared at concentrations ranging from 800 to
5600 μM.