polyphenol

Polyphenols are a diverse group of plant secondary metabolites characterized by multiple phenolic structures. They occur in most plants and contribute to color, flavor, and defense against pathogens. In the human diet they are abundant in fruits (berries, apples), vegetables, tea, coffee, red wine, cocoa, nuts, and whole grains. Most polyphenols are present in foods as glycosides or esters; during digestion they are hydrolyzed to aglycones and undergo extensive metabolism.

Classification: Major classes include phenolic acids (hydroxybenzoic and hydroxycinnamic acids), flavonoids (subclasses such as flavonols, flavones, flavanones, flavan-3-ols, isoflavones, anthocyanins), stilbenes (notably resveratrol) and lignans. Flavonoids share a common structure of two benzene rings (A and B) linked by a three-carbon C ring; this framework yields numerous compounds such as quercetin and catechin.

Biosynthesis and functions: In plants, polyphenols derive from the phenylpropanoid pathway and participate in UV protection, pigmentation, and defense. In humans, they can act as antioxidants and modulators of cell signaling and inflammation.

Health and metabolism: Dietary polyphenols exhibit antioxidant and anti-inflammatory activities in vitro, but in vivo effects depend on absorption, conjugation (glucuronidation, sulfation), and gut microbial metabolism. Observational studies associate high polyphenol intake with reduced risk of cardiovascular disease and some cancers, yet randomized trials show mixed results.

Processing and safety: Heat, light, and processing alter polyphenol content; fermentation can modify availability. They are generally safe at dietary levels, though high-dose supplements may interact with drugs or cause adverse effects.