Gallotannins

Glucogallin, the simplest gallotannin

Pedunculagin, an ellagitannin

Gallotannins are hydrolyzable tannins (in contrast to the non-hydrolyzable catechin tannins ), chemically they are sugar esters of gallic acid .

properties

In the case of gallotannins, the acid component consists either of gallic acid, but usually of two or three depsidic (ester-like) linked gallic acids, i.e. digallic acid or trigallic acid . Gallic acids can not only have a depsidic bond, but oxidative dimerization can produce hexahydroxydiphenic acid from two gallic acids and then ellagic acid through lactone formation. Sugar esters of these acids are called ellagitannins .

Some gallotannins have microbicidal and anti- tumor effects.

biosynthesis

The biosynthesis of gallotannins starts from UDP-glucose .

Color reactions

Color reactions with gallotannins:

• ${\displaystyle \mathrm {Fe^{3+}} }$ → blue coloring
• ${\displaystyle \mathrm {Ba(OH)_{2}} }$ → green, with high concentrations green precipitation
• Proteins → Precipitation
• Ellagitannins with nitrous acid ( ) → initially carmine red, later indigo blue ${\displaystyle \mathrm {HNO_{2}} }$

Individual evidence

1. ↑ ^{a b} Rudolf Hänsel, Josef Hölzl: Textbook of Pharmaceutical Biology . Springer, 1996, p. 218 ( limited preview in Google Book search).
2. ↑ KT Chung, TY Wong, CI Wei, YW Huang, Y. Lin: Tannins and human health: a review. In: Critical reviews in food science and nutrition. Volume 38, Number 6, August 1998, pp. 421-464, doi: 10.1080 / 10408699891274273 . PMID 9759559 .
3. ^ R. Niemetz, GG Gross: Enzymology of gallotannin and ellagitannin biosynthesis. In: Phytochemistry . Volume 66, Number 17, September 2005, pp. 2001-2011, doi: 10.1016 / j.phytochem.2005.01.009 . PMID 16153405 .