Grape seed extract (OPC)

Grape seed extract is produced from the ripe seeds of Vitis vinifera L. (Vitaceae), recovered from wine and juice pressing, using food-grade water and ethanol. The standard grade is standardised to not less than 95% total proanthocyanidins by UV-Vis and not less than 75% oligomeric proanthocyanidins (OPC) by HPLC. Chemically the extract is a distribution rather than a single molecule: the flavan-3-ol monomers (+)-catechin and (-)-epicatechin, the dimers procyanidin B1 and B2, oligomers of roughly two to five flavan-3-ol units, and a polymeric tail above DP5. The USP monograph Grape Seeds Oligomeric Proanthocyanidins defines the fraction as containing NLT 75.0% OPC on the anhydrous basis, prepared at a plant-material-to-extract ratio between 70:1 and 10:1 using alcohol, methanol, acetone, ethyl acetate, water or combinations. Specify the method alongside the number. UV assays and HPLC do not return the same figure on the same powder - published comparisons of commercial grape seed extracts put acid-butanol UV results between roughly 70 and 110% and vanillin results in the 28-45% band, against 76-99% total OPC by HPLC on the same materials - so a bare '95%' is not a specification. The CoA carries 95% proanthocyanidins by UV and NLT 75% OPC by HPLC as two separate lines, and either can be nominated as the release assay. Grape seed extract is one of the most persistently adulterated botanical ingredients in the trade. Peanut skin extract and pine bark extract have both been used to inflate the proanthocyanidin number, and in one widely cited survey several samples appeared to consist almost entirely of peanut skin extract - which carries the peanut allergen and is therefore a recall-grade risk, not a potency question. Every lot is fingerprinted by HPLC against authenticated grape seed material to exclude both, and released with an explicit peanut-free statement. The extract is vegan, free from milk, egg, soy, fish, crustacean, tree nut and gluten, and is made without animal-derived processing aids.