Tannin

The tannins ( from the French tanin tannin, also known as condensed proanthocyanidins ) are vegetable tanning agents, which are widely used in dicotyledonous perennials, shrubs and tree leaves and other plant parts particularly in the tropics and subtropics and are taken up by herbivorous mammals. These compounds have a molecular weight of 500-3000 Da.

Tannins belong to the so -called quantitative secondary plant substances. You have as opposed to qualitative ingredients ( alkaloids ), another defense spectrum against herbivores ( herbivores ), as they are likely mainly affect the digestive system by disabling proteins.

Composition and properties

Chemically, it is polyhydroxyphenols. They are soluble in water, ethanol and acetone, and contain sufficient ortho phenolic hydroxyl groups to form crosslinks between the macromolecules, such as proteins, cellulose and pectin can. Such cross-linking may inhibit the activity of plant enzymes and organelles and care in the production of leather for durability and protection against microorganisms ( tanning ).

The vegetable tannins vary significantly in their chemical structure and biological activity. Tannins with strong absorption features are generally found in the vacuoles, separated from the protoplasm of the plant. The physiological activity results from the selective binding capacity of tannins to proteins, particularly for large and proline-rich molecules with an open conformation.

Tannins are divided due to their chemical properties into two groups

The former can be hydrolyzed to glucose, other polyhydric alcohols, gallic acid or ellagic acid. As an example of a hydrolyzable tannin which is corilagin. Condensed tannin is made of another polymerized flavonoid phenols such as catechins, epicatechin, anthocyanins, etc. are in accordance with polymers whose monomeric phenolic units consist of flavans, usually catechin ( flavan-3 -ol).

Tannins can inactivate a variety of viruses.

Occurrence

Tannins are among the most anti - nutrients, protect with which various nutrient-rich plants, which are also used in the human diet ( legumes such as lima beans ), from predators.

They are found in the wood and the bark of oak, birch and chestnut, in the pericarp of walnut, the pods of the divi-divi tree ( Caesalpinia coriaria ) in Sumachgewächsen, in the fruit of the persimmon tree, cherry plums, Trillo, Valonea, bloodroot, in grapes, quince and in plant galls. These substances are also produced by acacias as the Gummiarabikumbaum to deter potential predators. Monomers groups of tannins are also included in the hop as well as in black and green tea, in tea as the catechin.

Tannins in foods

Wine

The content of tannins and their structure is a crucial factor for the quality of a wine. Part is mistakenly assumed that red wines are more or less long depending on the tannin durable. Although tannins prevents the oxidation of the wine, but this can be achieved by the addition of potassium ( potassium pyrosulfite ) nowadays. It gives the wine a characteristic rough touch of dryness, the so-called astringency. Tannin is also transferred from oak barrels for wine (barriques ), if they were not made wine in green. However, the supply of oxygen promotes the polymerization with anthocyanins, so that the tannin content of the wine after the Barrique is usually less than before. The tannin content of a wine decides less about the shelf life, but rather about its bearing means test: In the course of aging in the bottle the tannins polymerize with anthocyanins to not astringent, long-chain molecules. The astringency of the wine going back, constantly, making the wine leaves a pleasant drink. This requires the presence of a sufficient concentration of anthocyanins ( dyes).

The Enology knows about 30 different tannins today. Some are for the quality of the wine of meaning, others are classified as unfavorable. Basically play tannins in red wines a greater role than in white wines, as with the dyes always tannins are extracted from the grape skins. Late Vintage and high physiological maturity provide more mature and experienced as soft tannins. Unripe green tannins, however, taste, aggressive and furry.

Tea

Black and even more Green tea also contains tannins, which explains their bitter taste. The tannins are only after a certain brewing time released (more than two minutes).

Health effects

• Bloating and binding effect
• Obstructing the absorption of certain drugs ( such as digitalis ) through the intestinal mucosa
• Impeding the absorption of iron
• Obstructing the absorption of calcium

Use

The main technical use of the tannins is in the production of leather ( tanning ), where they are used as tanning agents for cross-linking of the collagen molecules and thus to increase the durability and protection against micro-organisms. Tannins are still used as a rust converter, wherein the water solubility and environmental compatibility to other drugs is advantageous. In the chemical industry tannins are used for the extraction of gallic acid and pyrogallol.

By condensation with suitable crosslinking agents (eg, formaldehyde) to high molecular weight condensation products, binders can be used for bonding wood materials produce. However, these binders could be technically and economically not prevail against the amino far.

As distinct antioxidants they find as a dietary supplement use, and are also used for food preservation. They also have anti -viral and anti-bacterial.

In medicine tannins used for its astringent effect as a hemostatic agent, as an antiseptic or treating excessive salivation ( drooling ). In folk medicine, also the expectorant effect is used by oak bark in Europe ( for baths) and the bark of the Gummiarabikumbaums in Africa.