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Classification of Tannins

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 1). True tannins: 

(a) Hydrolysable group: 

Hydrolyzed by acids or enzymes (Tannase). 

• They are esters of a sugar (β-D-glucose), with one or more trihydroxy-benzene carboxylic acid. 

• The tannins which is derived from Gallic acid called Gallo-tannin or gluco-gallin like in Rhubarb rhizomes, Clove buds etc.

• Tannis which is derived from ellagic acid called ellagotannin or glucoellagin like in Pomegranate roots bark and Eucalyptus leaves (which also contain Tannic acid which is Gallotannin). 

• They form dark blue color with FeClз

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(b) Non hydrolysable group of tannin: 
• They are known as condensed tannins or proanthocyanidins. 
• They have resistance to acid or enzymatic hydrolysis. 
• They are Flavanol derivatives: 
         1). Flavan-3-ol like catechin. 
         2). Flavan-4-ol like leucocyanidin. 
• They are founded: 
          ✓ In barks like: Cinnamon (Phlobatannins), Cinchona (Cinchotannin), Wild cherry. 
         ✓ In seeds: Cacao, Cola (Colacatechin). 
         ✓ In leaves: Tea. 
• They produce dark green color with FeClз
• They produce Catechol with conc. HCl and vanillin. 

2. Pseudo tannins: 

• They have low molecular weight. 
• They occur: 
        ✓ As Gallic acid like in Rhubarb rhizomes. 
        ✓ As catechin like in Cacao, Acacia. 
        ✓ As chlorogenic acid like in coffee.
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