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Polyphenolic compounds (meaning the presence of more than one phenol group per molecule), often referred to as polyphenols, are plant-derived polyhydroxylated (meaning has more than one hydroxyl (OH), or alcohol, group attached) phytochemicals. Polyphenols are divided into three classes and include tannins, phenylpropanoids and flavonoids.

Tannins are astringent (meaning a substance that contracts bodily tissues), bitter-tasting polyphenols that bind and precipitate proteins. Historically, tannin chemistry originated with the tanning of animal hides into leather. Tannins may be further subdivided into hydrolyzable tannins and condensed tannins (proanthocyanidins). Foods that contain tannins include fruits, teas and wine. Tannins are metal chelators and, if ingested in large quantities, can inhibit the absorption of minerals in the body.

Flavonoids are responsible for the pigmentation found in flowers, fruits and vegetables. Flavonoids may be further divided into several subclasses, including flavones, isoflavones, flavan-3-ols and anthocyanidins. Flavonoids are also commonly referred to as bioflavonoids. Dietary sources of flavonoids include citrus fruits, onions, tea, wine and dark chocolate.

Phenylpropanoids are synthesized from the amino acid phenylalanine. Resveratrol, a compound found in varying amounts in the skin of red grapes, is a phenylpropanid.

About the Author

Walter Jessen is a senior writer for Highlight HEALTH Media.