Thirty seven samples of grape seed extract (GSE) from various producers were evaluated by RP HPLC for procyanidin composition. Reverse phase chromatography resolves epicatechin (1), catechin (2) and individual oligomers with a degree of polymerization (DP) 2 to 4 but does not resolve procyanidins with a DP>4. The composition of the extracts varied dramatically, falling into three broad categories: a) very low levels of both monomers and oligomer peaks, b) significant levels of monomers and low levels of oligomers, c) significant levels of both monomers and oligomers. In the final category the extracts show a similar set of peaks dominated by seven oligomeric procyanidins. Some of the highest levels of oligo-procyanidins were detected in Activin® (San Joaquin Valley Concentrates). Subsequently, the dominant procyanidins were isolated and structurally characterized. The content of procyanidins 3-9 in the GSE samples reflects to a large degree the quality of the production process. Thus, the combined percentage of these seven oligomers can be used as a measure of the quality of GSE. We found that the sum of the percentages by weight of 3-9 in eight lots of Activin® varied from 5.2% to 7.7%. For a comparison, the same lots of Activin® were subjected to quantification using normal phase HPLC providing a breakdown of procyanidins according to their DP. In such a mode, a series of bands elute, beginning with the monomers (DP1) and followed sequentially by the bands with DP2 and higher.
