The reducing power of the test samples was determined by the method of Yen and Duh (1993). Different
concentrations of grape seed extracts (167, 334 and 500
mg/ml) in 1 ml methanol were mixed with 2.5 ml of
phosphate buffer (0.2 M, pH 6.6) and 2.5 ml of 1%
The reducing power tests were run in triplicate. 5000
potassium ferricyanide in 10-ml test tubes. The mixtures
were incubated for 20 min at 50? C. At the end of the
incubation, 2.5 ml of 10% trichloroacetic acid was
added to the mixtures, followed by centrifuing at
nm.
rpm for 10 min. The upper layer (2.5 ml) was mixed
with 2.5 ml of distilled water and 0.5 ml of 0.1% ferric
chloride and the absorbance was measured at 700 Increase
in absorbance of the reaction mixture indicated the
reducing power of the samples.