Grape seed extract, concentrated from the seeds of grape (Vitis vinifera L.), has a high content of compounds known as oligomeric proanthocyanidins (OPCs), which are made up of proanthocyanidin monomers. In grape seed extract there are basically two proanthocyanidin monomers called catechin and epicatechin. Each of them binds at either the alpha or beta position on their molecular structures to form oligomers or polymers. In addition, catechin and epicatechin can also form numerous esters from gallic acid as well as various glycosides and peptides.