Saturday, July 25, 2020

Property of tannins

The name ‘tannin’ is derived from the French ‘tanin’ (tanning substance) and is used for a range of natural polyphenols. Tannins often are concentrated in epidermal tissues and in the bark of woody plants, but these phenolic compounds may be found in leaves, roots, stems, fruits, bark, wood, or other plant parts. Tannin content may vary widely during the growing season in a particular plant part.

Tannins are polyphenolic biomolecules, astringent with bitter taste. These are high molecular weight phenolic compounds. These are complex organic, non-nitrogenous and non-crystalline substances. The tannin compounds are widely distributed in many plant species, commonly found in both gymnosperms and angiosperms.

Tannins are water soluble polyphenols. Tea leaves are abundant natural sources of polyphenols which get oxidized during processing to prepare the final products. Of the three main types of tea, black tea is produced by complete oxidation (fermentation) while oolong tea is semi-oxidized.

Tannins are astringent, bitter plant polyphenols that either bind and precipitate or shrink proteins. The astringency from the tannins is that which causes the dry and puckery feeling in the mouth following the consumption of red wine, strong tea, or an unripened fruit.

On the basis of their structural characteristics it is therefore possible to divide the tannins into four major groups:
*Gallotannins are all those tannins in which galloyl units or their meta-depsidic derivatives are bound to diverse polyol-, catechin-, or triterpenoid units.

*Ellagitannins are those tannins in which at least two galloyl units are C–C coupled to each other, and do not contain a glycosidically linked catechin unit.

*Complex tannins are tannins in which a catechin unit is bound glycosidically to a gallotannin or an ellagitannin unit.

*Condensed tannins are all oligomeric and polymeric proanthocyanidins formed by linkage of C-4 of one catechin with C-8 or C-6 of the next monomeric catechin. Tannins are a diverse class of compounds and have various effects on health. The antioxidant and antimicrobial activities of tannin are well documented. They are also used as antiseptics and astringents. Antioxidant activities confer upon the anti-carcinogenic and anti-mutagenic properties of tannins. Antimicrobial properties of tannins are shown against diverse group of bacteria, fungi and viruses.

Tannic acid, Gallic acid, Catechins, Chlorogenic acid and Phloroglucino are belongs to tannins and plays an important role in the ripening of the fruit. Tannins are considered the sources of energy through their oxygen content. They serve as a protective to the plant.
Property of tannins

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