2.3. Determination of antioxidative activity
2.3.1. Reducing power
The reducing power was based on the method described
previously by Yildirim, Mavi, and Kara (2001). Different concentrations
of extracts and BHT (SigmaeAldrich GmbdH,
Germany) (50e200 mg/mL) in 1 mL of methanol were mixed
with 2.5 mL of phosphate buffer (0.2 mol/L, pH 6.6) and
2.5 mL of 10 g/L potassium ferricyanide. The mixture was
incubated at 50 C for 30 min. An aliquot (2.5 mL) of 100 g/L
trichloroacetic acid was added to the mixture, which was
then centrifuged at 3000 rpm for 10 min. Finally, 2.5 mL of
the upper layer solution was mixed with 2.5 mL of distilled
water and 0.5 mL of 1 g/L FeCl3, and the absorbance of the
resulting solution was measured at 700 nm.
2.3.2. b-Carotene linoleate model system
The antioxidant activity of rambutan peel and seed extracts
was determined according to the method of Jayaprakasha et al.
(2001). First, 0.2 mg of b-carotene in 1 mL of chloroform,
20 mg of linoleic acid and 200 mg of Tween-40 were mixed.
Chloroform was removed using nitrogen gas and the resulting
mixture was topped up to 50 mL using oxygenated water and
mixed well. Aliquots (5 mL) of the emulsion were pipetted