Tannins Flashcards
What class of secondary metabolites do tannins fall under?
Phenolic compounds
Why is their phenolic nature important?
Allows them to effectively complex alkaloids and proteins
Where are tannins found?
Skins of fruits and veggies, found in vacuoles of cells
What are the properties of tannins?
State - NON-crystalline/amorphous solid
Colour - Yellow to light brown
Taste - Drying, puckering, astringent
Solubility - water soluble, plus alcohol, acetone, glycerol, and dilute alkali
Precipitate - Cellulose, pectins, proteins, gelatin. alkaloids, glycosides, heavy metals
Why are the precipitation properties important?
Identification tests, Chealating, Formulation diagnosis
How do tannins react with ferric salts?
Hydrolysable = Blue/Black precipite Condensed = Brown/Green precipitate
How do tannins react with Potassium Ferricyanide
turns a deep red
What are the effects of tannins
Leathery skin/mucous membranes
Astringent - Antimicrobial, Vasoconstrictor, Antioxidant
Negative - Prevent absobtion of nutrients, Irritant, Damaged organs
What are the therapeutic effects of tannins?
- Herbs will precipitate proteins
- Waterproof skin
- Vasoconstrictor effect
- Limits fluid loss and enhances tissue regeneration
- Antidiarrhoeal
- Antiseptic effects
What are the three types of tannins?
Hydrolysable - Phenolic acid ester-linked to central glucose, gallic and ellagic acids are the two types of hydrolysable tannins
Condensed - No sugar residue, found in many fruits
Complex - Mix of the other two, found in tea
What are the identification tests? (4)
1) Colour reaction (iron salts) - Condensed = green fluorescence, Hydrolysable = Blue fluorescence
2) Matchstick test - HCl + heat = pink/red
3) Gelatin test - tannin precipitates gelatin
4) Gold Beaters skin test - soak ox intestine skin in HCl, then the solution and then in ferrous sulphate
