A Comparison of Methods For Quantifying Oligomeric Proanthocyanidins From Grape Seed Extracts

Abstract

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