Tannins.pptx

Phytochemicals

1. TANNI N S

2. Introduction T h e term Tannin was coin ed by Segu in in 17 9 6. Tannins are naturally occurring complex organic compounds. These are the secondary metabolites of the plants which possess the high medicinal property. It possess nitrogen free polyphenols of high molecular weight. 3

3. “The complex organic non nitrogenous, poly phenolic s u bst a nces of h i gh molecul a r we i ght.” 4 Tannins are complex phenolic compounds, found in many plant species, with a molecular weight ranging from 500–3000 Da. They are found in  fruits, berries, chocolates, and other dietary components .

4. P r o p e r t i e s Dark brown or reddish brown in color Astringent taste. Non crystalline in nature. They are so l uble in wate r . They are soluble in dilute alkalis, alcohols, glycerol, and acetone. They are sparingly soluble in organic solvents. Their solutions precipitate all heavy metals

5. Medicinal & Biological Properties 6 Tannins can stop hemorrhage. They precip itate proteins. They are u sed as an astr in g ent. They are u sed in the t r eatment of bu r ns. They a c t as a n ti diarrheal. They are employed as an antidote for heavy metal poisoning. They are m ost p o tent a n tioxidant.

6. “ C l a s s i f i c a t i o n o f T a nn i n s T annins True Tannins Hydrolysable tannins Condensed tannins Complex tannins Pseudo T annins 7

7. H y d r o l y s a b l e T a n n i n s 8 The tan n ins w h i c h c a n be h ydro l y z ed by a c ids or en z y mes a n d produ c e G a l lic or el l a g ic a c id. On dry distillation, Gallic acid and other components get converted to pyrogallol. They respond to ferric chloride solution, producing blue colour. The tannins derived from the Gallic acids are called gallitannins . The tannins derived from the ellagic acid are called ellagictannins . E.g.: Gallo tannin in nutgall, rhubarb, amla, clove and chestnut; ellagitannin from oak, myrobalans and pomegranate bark Gal l ic ac i d are prese nt in c l o v e, rhubarb, et c , . Ellagic acid is present in eucalyptus leaf, pomegranate bark,etc .

8. Condensed tannins : They are also called as non- hydrolysable tannins, ph l obatannins or proanthocyanidins. They are much resistant to hydrolysis . They are related to flavonoid pigments, because they are formed via derivatives of flavones, like catechin or flavan-3-ol or flavan-3,4-diols. Unlike the hydrolysable tannins, on treatment with enzymes or mineral acids, they are polymerized or decomposed into red colored substances called phlobaphenes. which are insoluble in water and indicate the typical brownish-red colour of many plants . On dry distillation they yield catechol . Wit h ferric chloride , produce brownish-green colour . They are distributed in different parts of plants. The green tea and hamamelis leaves, cinchona, cinnamon and wild cherry bark, pale and black catechu contain these types of tannins.

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10. P s e u d o t a nn i n s They are phenolic compounds of lower molecular weight. They do not show positive results in G oldbeater ’s te st. Chlorogenic acid in coffee and nuxvomica , ipecacuanhic acid in ipecacuanha and catechins in cocoa are examples of pseudotannins . The detection test for chlorogenic acid is carried out by extracting the drug with water. .

11. I d e n t i f i c a t i on T e s t s G e l a t i n te s t : To a solution of tannin, aqueous solution of gelatin and sodium chloride are added. A white buff colored precipitate is formed. G ol d b e a t e r ’ s s k i n te s t : A small piece of skin (membrane prepared from the intestine of an ox) is soaked in 20% hydrochloric acid, rin s ed with distilled water and placed in a solution of tannin for 5 minutes. The skin piece is washed with distilled water and kept in a solution of ferrous sulphate. A brown or black colour is produced on the skin due presence of tannins. Phenazone test: A mixture of aqueous extract of a drug and sodium acid phosphate is heated and cooled and filtered. A solution of phenazone is added to the filtrate. A b lue coloured precipitate is formed.

12. 4 . M a t c h s t i c k t e s t ( C a t e c h i n t e st ) : A match stick is dipped in aqueous plant extract, dried and moistened with concentrated hydrochloric acid. On warming near flame, the matchstick wood turns pink or red due to formation of phloroglucinol. 5. Test with ferric chloride -To the solution of tannins add ferric chloride solution. A blue, black, violet or green precipitate or colour confirms the presence of tannins. 6. Test with Vanillin HCl – The sample solution is treated with Vanillin HCl solution. Red colour change indicates the presence of true and pseudo tannins.