Tanning agents, vegetable

Natural tanning agents consisting of water-insoluble, slightly acidic phenolic substances that interact with the collagen of the skin.

Due to their chemical structure, vegetable tanning agents can be divided into 4 main groups:

Hydrolysable tanning agents

• Gallotannins: Here, gallic acid or its derivatives (tannic acid) are esterified with sugar or sugar alcohols.
• Ellagitannins (ellagic tanning agents). Here, the gallic acid is replaced by ellagic acid

Non-hydrolyzable tanning agents (condensed tanning agents):

• Non-hydrolyzable tanning agents contain instead of gallic or ellagenic acids mainly catechins like catechin and isomers like epicatechin. Treatment with diluted acids leads to polymerization of the basic components.

Complex tannic acids:

• These contain structural elements of both hydrolyzable and non-hydrolyzable tanning agents.

Derivatives ofcaffeic acid and phloroglucine:

• This independent group of substances has a weaker astringent effect. Chlorogenic acid and rosemary acid belong to this group.

Natural tanning agents are found, for example, in the leaves, wood, bark, fruits and roots of Pinaceae, Rosaceae(Tormentillae rhizoma), Hamamelidaceae (Hamamelidis cortex s.u. Hamamelis), Lamiaceae and others. Furthermore, they are found in bananas, horse chestnuts (Castaneae folium), in oak bark (Quercus cortex) in tea varieties such as black and green tea. Tannins can also be found in plant decomposition products such as peat.

Natural tanning agents are widely used for medicinal purposes (see below tanning agent drugs)

Tannins in wine: Wines contain tannins as components from the stems, seeds and berries of the vine plant, which contribute to the taste of the wine.

Other use of natural tannins: Some tannins form stable colour complexes with metal salts, mainly iron salts. These complexes were formerly used for the production of writing ink.

The term tannin is often colloquially equated with the vegetable t.tanning agents

1. de Jesus NZ et al (2012) Tannins, peptic ulcers and related mechanisms. Int J Mol Sci 13:3203-3228.
2. Sieniawska E (2015) Activities of Tannins--From In Vitro Studies to Clinical Trials. Nat Prod Commun 10:1877-1884.