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
(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.