gallotannins

Gallotannins are a class of hydrolyzable tannins consisting of gallic acid units esterified to a sugar core, most commonly glucose. They form polymers in which multiple galloyl groups are attached to the glucose molecule, yielding compounds such as tetragalloylglucose, pentagalloylglucose, and higher oligomers. On hydrolysis, gallotannins release gallic acid and glucose.

Chemical structure and differentiation from related tannins: Gallotannins are distinguished from ellagitannins by the absence of hexahydroxydiphenic (HHDP) units; ellagitannins contain HHDP groups that can lactonize to ellagic acid. Gallotannins thus represent gallate-based hydrolyzable tannins with a relatively simple gallic acid polyester framework.

Occurrence and biosynthesis: Gallotannins are widely distributed in plants, with notable concentrations in gall nuts, sumac, chestnut, and various hardwoods. They arise from the biosynthesis of gallic acid and its esterification to a sugar core. They can be released by hydrolysis under acidic or basic conditions to yield gallic acid and glucose.

Properties and applications: Gallotannins are water-soluble polyphenols with astringent taste and the ability to bind proteins. They contribute to the tanning of hides and skins and are sources of antioxidant phenolics in some plants. In research, they are examined for biological activities such as antimicrobial or anti-inflammatory effects, as well as for analytical roles in quantifying total tannins.

Analytical notes: Total gallotannin content can be estimated by hydrolysis to gallic acid followed by quantification, and by HPLC or mass spectrometry for structural characterization alongside broader tannin analyses. See also ellagitannins and hydrolyzable tannins.