Tannins

Proanthocyanidins from wikipedia represent a group of condensed flavan-3-ols, such as procyanidins, prodelphinidins and propelargonidins, that can be found in many plants, most notably apples, maritime pine bark, cinnamon, cocoa, grape seed, grape skin (procyanidins and prodelphinidins),[2] and red wines of Vitis vinifera (the common grape).

However, bilberry, cranberry, black currant, green tea, black tea, and other plants also contain these flavonoids. The berries of chokeberry, specifically black chokeberry, have the highest measured concentrations of proanthocyanidin found in any plant to date.[3][4] [5]

Proanthocyanidins can also be isolated from Quercus petraea and Q. robur heartwood (wine barrel oaks).[6] Apples contain on average per serving about eight times the amount of proanthocyanidin found in wine, with some of the highest amounts found in the Red Delicious and Granny Smith varieties.[7] A patented extract of maritime pine bark called Pycnogenol bears 65-75 percent proanthocyanidins (procyanidins).[8] Thus a 100 mg serving would contain 65 to 75 mg of proanthocyanidins (procyanidins). Proanthocyanidin glycosides can be isolated from cocoa liquor.[9] The seed testas of field beans (Vicia faba) contain proanthocyanidins[10] that affect the digestibility in piglets[11] and could have an inhibitory activity on enzymes[12].