Tannins PDF

Tannins Complex organic natural compounds. Widely distributed in the nature & in all plant parts, specially in the new leaves & immature fruits to protect them from animals, bacteria & insects. Most of them poly-phenolics. Most of them have very large molecular weight except pseudo-t...

Tannins Complex organic natural compounds. Widely distributed in the nature & in all plant parts, specially in the new leaves & immature fruits to protect them from animals, bacteria & insects. Most of them poly-phenolics. Most of them have very large molecular weight except pseudo-tannin. Derived from: - Flavan-ol -poly hydroxy benzoic acid. Properties of Tannins: -most of them form colloidal solution with H2O. -Aqueous tannin solution is acidic. -They have sharp puckering taste. -Astringent character. -React with FeCl3 (bluish or greenish color) as they are Phenolic. -Precipitate proteins and Gelatin. -Form complex with alkaloids, heavy metals ( 5% tannic acid solution in case of poisoning).  Classification of Tannins: True Tannins Pseudotannins (High molecular weight compounds) Low molecular weight compounds e.g. Gallic acid, Flavan-3,4-diol Hydrolysable Tannins Condensed Tannins (Pyrogallol) (Catechol) Not hydrolysable, no sugar in mol.  1) Pyrogallol(hydrolysable) Tannins Most of them are esters of B-D- glucose withthri hydroxy benzen carboxylic acid (gallic or ellagic acid). They can be hydrolyzed by acids or enzymes. They produce sugars and: – Gallic acid……Gallotannins. (Rubarb rhyzomes, Clove buds , Hammamelis) – Ellagic acid…….Ellagitannins. (Eucalypus leaves, pomegranate roots) - Produce pyrogallol on dry distillation. OH COOH HO O O HO OH HO OH OH O OH O OH pyrogallol OH Ellagic acid Gallic acid hydrolysableTannins ester suger gallic acid gallic acid ellagic acid Hydrolysable tannin (1,3,6Trigalloyl glucose) Corilagin Tannic acid (2) Condensed- non hydrolysableTannins Condensation product of Flavan-3,4-diol. They resist hydrolysis. - Produce catechol on dry distillation. - Present in Cinchona, Cinnamon, Green tea. HO OH HO O OH OH OH OH OH catechol Flavan-3,4-diol Condensed Tannins  Pseudo tannins: 1- they have low molecular weight. 2- they occur: as Gallic acid like in Rhubarb rhizomes. as catechin like in Cacao, Acacia. as chlorogenic acid like in coffee. Chemical test for Identification: FeCl3: Hydrolysable tannins Bluish colour. Condensed tannins Greenish colour. Goldbeater’s Skin test (Ox- Intestine): Soak piece of Goldbeater’s skin in 2% HCl, wash with water, soak in test solution, wash with water, finally soak with FeSO4 Brown or Black colour. Gelatin test: Tannins + 1% Gelatin solution in NaCl white precipitate  Uses of Tannins: 1) Antioxidant. 2) Antidiarrheal. 3) Antidote for heavy metals poisoning. 4)Treatment of burns, ulcers, inflammations 4) Astringent to stop bleeding (hemorrhage). 5)Treatment of Hemorrhoids. 6) Tanning industry oak gall.  Green and Black Tea Green Tea: OH -Prepared by rapid drying at HO O OH elevated temperature to deactivate the enzymes. OH (+) catechin -Contain Catechins with high OH antioxidant properties. Black Tea: -Undergo slow drying (Fermentation). -Enzyme action results in Hydrolysis and Oxidation (theaflavin). -Antioxidant properties is greatly decreased. theaflavin