Grape tannins

Procyanidins are members of the proanthocyanidin (or condensed tannins) class of flavonoids. They are oligomeric compounds, formed from catechin and epicatechin molecules. They yield cyanidin when depolymerized under oxidative conditions.

Procyanidins, including the lesser bioactive / bioavailable polymers (4 or more catechines) represent a group of condensed flavan-3-ols that can be found in many plants, most notably apples, maritime pine bark, cinnamon, aronia fruit, cocoa beans, grape seed, grape skin, 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, as do cocoa beans. Procyanidins can also be isolated from Quercus petraea and Q. robur heartwood (wine barrel oaks).Açaí oil, obtained from the fruit of the açaí palm (Euterpe oleracea), is rich in numerous procyanidin oligomers.

Apples contain on average per serving about eight times the amount of procyanidin found in wine, with some of the highest amounts found in the Red Delicious and Granny Smith varieties.

The seed testas of field beans (Vicia faba) contain procyanidins that affect the digestibility in piglets and could have an inhibitory activity on enzymes.Cistus salviifolius also contains oligomeric procyanidins.

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Wikipedia