Tannins

Defination of Tannins, properties,Classification,Pharmacological action,Side effect

1. Tannins

2. Defination of tannin Tannins are complex organic, non-nitrogenous and non-crystalline substances, occurs as a mixture of polyphenols and from colloidal solutions with water that are widely distributed in plant (vegetable) kingdom.

3. Properties of tannins 1.Tannins are non- crystalysable compound. 2. They are soluble in water and from colloidal solution. 3. They are aquous solution are acidic in nature and posseses a sharp pungent taste, seen this solution is acidic weak and identify them litmus paper. 4. They are soluble in dilute alkali, alcohol, glycerol and acetone but sparingly soluble in other organic solvents. 5. They cause the precipitation of solution of the gelatin, alkaloids, heavy metal and glycosides.

4. Properties of tannins 6. They formed dark blue and greenish black soluble compound with ferric salt. 7. They produce a deep red color with potassium ferricyanide at ammonia. 8. Tannins are precipitate by salt of copper(Cu), lead( Pb ), tin(Sn), and by strong aquous potassium dichromate solution or 1% chromic acid solution. 9. In alkaloin solution many of their derivatives readily absorb oxygen from the atmosphere. 10. Tannin precipitate and combine with protein renderning them resistance to proteolytic enzymes.

5. Classification of tannins Hydrolysable tannins. Condensed tannins. Pseudotannins .

6. Hydrolysable tannins These tannins are the esters of a sugar usually glucose with one or more trihydroxy benzo carboxylic acid.They are hydrolyzed by acids, or enzyme and produce gallic acid and ellagic acid.

7. Condensed tannins These tannins are resistant to hydrolysis and they derived from the flavonols , catechins and flavan-3, 4-diols. On treatment with acids or enzymes they are decomposed into phlobaphenes . On dry distillation condensed tannin produce catechol. These tannins are called as catechol tannins. 

8. Pseudotannins They are phenolic compounds of lower molecular weight and do not show the goldbeater’s skin test. They occurs as gallic acid, catechins , chlorogenic acid etc.

9. Pharmacological activity of tannins Pharmaceutically — Tannins are used as an astringent in the GIT and skin abrasions. It is used in the treatment of burns. It also act as preservative because of its antiseptic properties. Tannins are widely used as an application to sprains, bruises and superficial wounds. ( Hamamelis ) It is used as an ingredient of eye lotions. ( Hamamelis ) It is used as styptic. (Nutgalls)

10. Pharmacological activity of tannins Industrially— It is used in the manufacture of inks. Tannins are utilized in the laboratory as astringents for the detection of gelatin, proteins and alkaloids. Tannins are used in the tanning process of animal hides to convert them into leather.

11. Side effects of tannins Absorb tannic acid can cause severe necrosis of the liver. Prolonged utilization of certain tannin rich plant materials may be dangerous owing to their carcinogenic potential. Eg . The habitual chewing betel nut rich in condensed catechin tannin has been link to high rate of oral and esophageal cancer in India and South Africa.

12. Tests for tannins 1. Solution of tannin precipitated heavy metal, alkaloids, glycosides and gelatin with ferric salt, galli tannins, ellagi tannins, give blue black precipitate and condensed tannin give brownish green precipitate. 2. Gold beater’s skin test: A membrane prepared or isolated from the intestine of oxe can be used as gold beater’s skin. Small piece of gold beater’s skin is soaked in 2% HCL acid, then it is taken out rinsed with distilled water and placed in the experimental solution of tannin for 5 minutes. Then it is washed with distilled water and transferred to 1% of ferrus sulphate (FeSO 4 ) solution. A brown or black color on the skin denotes the presence of tannin. 3. Gelatin test: About 0.5 to 1% solution of tannin is kept in 1% solution of gelatin containing 10% NaCl . The formation precipitation denotes the presence of tannin.

13. Tests for tannins 4. Phenozone test : 0.5 gm NaH 2 PO 4 is added to about 5ml of an aquous extract of the drug. Then it is warned , cooled and filter. 2% solution of phenozone added to the filtrate. If precipitate occurs it indicate the presence of tannin. 5. Test for catechin : A match stick is dipped in aqueous plant extract, dried near burner and moistened with concentrated hydrochloric acid. On warming near flame, the matchstick wood turns pink or red due to formation of phloroglucinol . 6. Test for chlorogenic acid: When the extract is treated with aquous NH 3 and exposed to air, it gradually develops green color. The development of the green color denotes the presence of tannin containing chlorogenic acid.  

14. Nut gall Biological source: Quercus infectoria . Chemical constituents: Gallo tannic acid, gallic acid, ellagic acid, β- sitosterol , methyl betulate , methyl oleonolate , Ca-oxalate, resin. Uses: 1. Source of tannic acid. 2. In the tanning and dyeing industry. 3. As astringent and styptic. 4. In the production of ink.

15. Black catechu Biological source: Acacia catechu Chemical constituents: Catechin , phlobatannin , gummymaterial , quercetin, quercitrin . Uses : 1. Possess cooling and digestive properties. 2. Used in relaxed condition of throat and mouth. 3. As astringent in skin eruptions.

16. Hamamelis leaf Biological source: Hamamelis virginiana . Chemical constituents: Galli tannin, ellagi tannin, gallic acid, proanthocyanidin , Ca-oxalate. Uses : 1. Astringent . 2. Used in the preparation of trating insect bite, sting bite etc. 3. Used in tooth prepation , eye lotion. 4. As flavoring agents.

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