ellagitannin

Ellagitannins are a class of hydrolyzable tannins in which one or more hexahydroxydiphenic acid (HHDP) units are esterified to a sugar, typically glucose. Upon hydrolysis, HHDP units are released and readily lactonize to ellagic acid. Many ellagitannins are oligomeric or polymeric, containing multiple HHDP units linked to a glucose core; the gallotannins are a related group in which galloyl units predominate. The structural diversity arises from different HHDP linkages and the degree of polymerization.

Ellagitannins occur in a variety of plants. Pomegranate contains the well-known punicalagin and punicalin, major contributors to its polyphenol content. Other sources include berries such as raspberries and strawberries, walnuts, and certain nuts and seeds. In the context of foods and wines, ellagitannins are also associated with oak wood and influence the phenolic composition of aged wines and spirits, with vescalagin and castalagin among the representative oak-derived compounds.

Biological activity and metabolism: Ellagitannins are potent antioxidants in vitro. In humans, absorption is limited; gut microbiota hydrolyze the compounds to ellagic acid and further metabolize them to urolithins (e.g., urolithin A and B), which may be more bioavailable and biologically active systemically. Experimental studies have explored anti-inflammatory, anti-proliferative, and antimicrobial effects, but clinical evidence remains inconclusive. The health relevance of ellagitannins depends on individual gut microbiota composition and dietary context.