A comparison of methods for quantifying oligomeric proanthocyanidins from grape seed extracts

Grape seed extract (GSE) has become popular in recent years as a nutritiona l supplement that possesses antioxidant activity. These extracts contain a heterogeneous mixture of monomers, oligomers, and polymers composed of proa nthocyanidin (or flavan-3-ol) subunits. The common colorimetric methods for analyzing the procyanidin concentration and/or composition of grape seed e xtracts and products containing it can give only crude information on the d istribution of the sizes of the components. A normal phase HPLC method has proven to be very applicable to analyzing grape seed extract material and p roducts thereof, and monomer, oligomer (2-7 subunits) and polymeric (8-24 s ubunits, and similar to 24+ subunits) fractions can be discriminated. Value s ranged from 5% to 30% for monomers, 17% to 63% oliogomers, 11% to 39% pol ymers and 2% to 50% for the large (24+) polymers. When specific attributes can be defined for particular size fractions, this method can provide the i nformation needed to compare different samples for their relative potential effect.