polyphenols

Polyphenols are a broad group of plant-derived compounds characterized by the presence of multiple phenol units. They are widespread in the plant kingdom and contribute to color, flavor, and defense against pathogens and ultraviolet radiation. Major classes include flavonoids (such as quercetin, kaempferol, catechins, and anthocyanins), phenolic acids (like ferulic and caffeic acids), stilbenes (notably resveratrol), lignans, and tannins (condensed tannins). More than 8000 individual polyphenols have been identified.

In plants, polyphenols serve various roles, including pigmentation, structural support, and protection against pathogens and abiotic stress. They often accumulate in fruits, flowers, leaves, and seeds, imparting red, purple, or blue hues and contributing to taste and bitterness.

Dietary sources of polyphenols are abundant and include fruits (berries, apples), vegetables, tea, coffee, red wine, cocoa and chocolate, nuts, seeds, and whole grains. Intake varies considerably with diet and cultural patterns; processed foods can alter polyphenol content.

Bioavailability and metabolism: Polyphenols are absorbed to varying extents in the gastrointestinal tract and undergo extensive phase II metabolism (glucuronidation, sulfation, methylation) in the liver. The gut microbiota also metabolizes many polyphenols into smaller compounds that may be biologically active. Overall bioavailability is generally low to moderate and is influenced by the chemical structure, food matrix, and processing.

Health aspects: Polyphenols exhibit antioxidant activity in vitro and can modulate inflammatory pathways, lipid metabolism, and cell signaling in experimental settings. Observational studies link higher polyphenol intake with reduced risks of some chronic diseases, but randomized trials yield mixed results, and causality remains unproven. High intakes can interfere with mineral absorption in some cases. Ongoing research aims to clarify effective doses, bioavailability, and mechanisms.