Tannins in tea

Tea is known to have benefits such as anti-antioxidants and artificial coloring. It may because tea leaves contain active chemicals such as tannins. As a natural part of every tea plant, tannins contribute to the growth process and health benefits of all teas, as well as the color and flavor.

Tannins (commonly referred to as tannic acid) are water-soluble polyphenols, molecular weight between 500 and 3 000, which, in addition to displaying the classic reactions of phenols, can precipitate alkaloids, gelatine, and other proteins.” Tannins are a diverse class of compounds and have various effects on health.

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.

Tannin with chemical formula C76H52O46 is a polyphenol compound that is colorless to yellowish, which can affect the tea itself taste, color and aroma. Tannins give tea astringency, color, and flavor. Tannins also cause darker colors in tea, which can be perceived as a sign of flavor strength. In fact, the development of tannins is unrelated to that of the aromatic compounds that create variety in tea flavor.

Tannins are mainly found in the cell vacuoles or in the cuticle (here cells don’t interfere with plant processes: only after death and cell breakdown do they become active in metabolic processes)
Tannins in tea

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

What are tannins?

Tea is a popular beverage throughout the world. It is pleasant and mildly stimulating. Tannins are a family of astringent compounds called polyphenols.

Polyphenols constitute over 48.5% of the total solids in a cup of tea. They’re found in several kinds of plants, including dark sorghum, some apples and yerba mate, a popular South American drink made from the leaves and branches of an evergreen tree.

Tea is often included in the list of tannins-containing foods.   The tea leaves contain varying amounts of tannins: Green teas, which have unfermented leaves, contain the most tannins; black teas including pekoe, which are fermented, contain the fewest.

By definition, tannins are biologically active, that is tannins bond protein, a process that is pH dependent. Most of the phenolic groups in tannins are free. Tannins have a molecular weight between 500 and 3000, and generally are soluble in water.

Tannins are usually divided into two classes: those can be hydrolyzed (react with water) and those that cannot.  The nonhydrolysable tannins found in tea are condensation polymers of catechin.

The occurrence of tannins is reported in unripe fruits such as mango, dates and persimmons. The tannins diminish in amounts as the fruits ripen.

Other food sources of tannins are grapes (condensed tannins, on average 5000 mg/kg of grapes). Grape juice, wines (red wine: 1.2 – 4l4 g/L of wine) and some sorghum grain varieties.
What are tannins? 

Processing of Black and Green tea

Processing of Black and Green tea
Black and green teas result from different postharvest treatment. In the case of black teas, the freshly picked green leaves are spread out on mats and allowed to dry out slowly and wither after which they mechanically rolled to break up the cells and liberate any enzymes which may present.

The rolled leaves are then fermented for several hours, either in baskets or spread out under damp cloths. During this stage the colorless tea tannins are partially oxidized changing to a reddish-brown color and some essential oil is developed.

This process is stopped by subsequent hot-air drying (frying). The whole process determines the flavor, strength, smoothness and color of the resulting infusion and calls for skill and experience to achieve consistent result.

Green teas are not fermented. The freshly picked leaves are steamed which prevent fermentation and blackening during the final drying process. The tea tannins are in consequence, largely in their original state as no essential oil is developed unfermented teas lack the aromatic character of the fermented varieties.

Oolong teas have a half way character; the leaves are allowed to wither and partially ferment before being rapidly dried at a high temperature. This results in a tea having a fine fragrant character.
Processing of Black and Green tea