Ferruzzi M.G., Lobo J.K., Janle E.M., Cooper B., Simon J.E., Wu Q.L., Welch C., Ho L., Weaver C., Pasinetti G.M. (2009) Bioavailability of gallic acid and catechins from grape seed polyphenol extract is improved by repeated dosing in rats: implications for treatment in Alzheimer's disease. J Alzheimers Dis 18:113-24 PubMed (19625746)

Compound Mean content
Gallic acid 91 mg/g dry weight
(+)-Catechin 147 mg/g dry weight
(+)-Epicatechin 164 mg/g dry weight