Antioxidant activity of grape seed extracts was determined using the thiocyanate method (Yen & Hsieh,
1998). The linoleic acid emulsion was prepared by
homogenizing 0.28 g of linoleic acid, 0.28 g of Tween-40
as emulsifier and 50 ml of phosphate buffer (0.2 M, pH
7.0). Test samples were prepared in MeOH: water mix-
ture (6:4 v/v). Different test samples (0.5 ml) were mixed
with 2.5 ml of linoleic acid emulsion and 2.5 ml of
phosphate buffer (0.2 M, pH 7.0) and incubated at 37? C
for 120 h. The mixture prepared as above without test
sample served as control. Aliquots (0.1 ml) were drawn
from the incubation mixture at an interval of 20 h and
mixed with 5.0 ml of 75% ethanol, 0.1 ml of 30%
ammonium thiocyanate and 0.1 ml of 20 mM in ferrous
chloride in 3.5% HCl and allowed to stand at room
temperature for 3 min. The colour developed was measured at 500 nm. The degree of linoleic acid peroxidation was calculated at 100 h using the following formula
(Pin-Der Duh, 1998).