The amount of total favanols was assayed colorimetrically by the vanillin method using catechin as a
standard (Price, Scoyoc & Butler 1978). 5.0 ml of 0.5%
in vanillin in MeOH was added to 1.0 ml of methanolic
grape seed extracts and mixed well. Similarly, a blank
was prepared by adding 5.0 ml of 4% HCl in methanol
to 5.0 ml of 0.5% vanillin in MeOH. The absorbances
of sample and blank were measured at 500 nm after 20
min in the dark at room temperature. The absorbance
of the blank was subtracted from the absorbance of the
sample. The content of total flavonols in the grape seed
extracts was expressed as catechin equivalents per 100 g
of extracts. The content of procyanidins was calculated
as the difference between total flavanols and monomeric
flavanols and is shown in Table 2 (Saito et al., 1998).
The estimation of procyanidins and monomeric flavanols in these fractions was carried out in triplicate and
the results were averaged.