A procyanidin is a type of of condensed tannins, otherwise known as oligomeric proanthocyanidin compounds (OPCs). This is a specific class of flavonoids that are synthesized when epicatechin and catechin are combined together. When conditions become oxidized, procyanidins can produce cyanidin if they become depolymerized. Although these condensed flavan-3-ol compounds are naturally present in various plants, they are especially plentiful in the bark of pine trees from southern France and several other geographic locations. Other significant food sources of procyanidins include cinnamon, grape seeds, grape skins, cocoa beans and apples to name several. Our collection of dimeric procyanidin reference material are useful analytical standards in the field of food supplements, as quantitative reference substances