Tannins Flashcards
(38 cards)
What are plant phenols , where are they derived from and BIOSYNTHESIZED
Aromatic ring bearing a hydroxyl group.
Derived from aromatic amino acids, such as tyrosin
biosynthesized via Shikimic acid pathway/ Phenylpropanoid pathway
Egs of phenols
Simple phenolics( phenolic and coumarins) ,flavonoids ,quinones, lignins and tannins
What are the two polyphenols
tannins and flavonoids
The two definitions or tannins
- Tannins are high molecular weight, poly-hydroxy phenolic compounds capable of forming strong complexes with proteins and other macromolecules.
- They are condensation products of Gallic acid or Flavan-3-ol as well as their glycosides.
Are tannins non nitrogenous
Yes
Where are tannins distributed
distributed in many angiosperms and gymnosperms usually located in the leaf, seed, root, bud, wood and stem
What tissues do tannins help grow
secondary phloem and xylem and in between the cortex and epidermis.
What are the four physiological roles of tannins to plants
- They exert inhibitory effect on many enzymes due to protein precipitation and hence may contribute a protective function in barks and heartwoods.
- They play an important role in the mechanism of hydrogen transfer in plant cells due to their high affinity for oxygen.
- Act as deterring agents active against predators
- Barrier to microorganisms
What are the dietary sources of tannins
Wine
Fruits: strawberries, blue berries, nuts e.g. almond, walnuts; herbs and spices e.g. Clove, vanilla, cinnamon cumin
Tea
What causes dry puckery aftertaste after taking unripe fruit wine or tea
The astringency from the tannins (drawing of residual proteins from tongue and mouth).
What are the four PHYSICAL properties of tannins
–Astringent- react with protein of mucous membrane and cause precipitation
–Non-crystalline/ powdery
–Solubility- water, alcohol, dilute alkalis, glycerols and acetone, sparingly soluble in other organic solvents
–Generally dark yellow to reddish brown in colour
What compounds do tannins precipitate with
- Heavy metals- e.g. Lead
- Alkaloidal salts
- Proteins e.g. gelatin( 1% solution)
- Glycosides
What substance does tannin form colored reactions with
Iron Salts
Eg; FeCl3
Reaction of tannins with ammonia/potassium ferricyanide produces ?
Deep red color
What propety does accumulation give tannins
Anti oxidizing properties
How are tannins detected quantitavely and qualitatively
Gold beaters test
Standard hide powder
What are true tannins
High molecular weight ploy-phenolic compounds which test positive for gold beaters test
What are pseudorannins
Low molecular weight which don’t respond to goldbeater’s test
What is the molecular weight range of true tannins
1000-5000 DA
When do pseudotannis precipitate gelatin and retain hide powder
In high concentrations
Examples of pseudtannins
Gallic acid- rhubarb
Salicylic acid
Catechin- acacia cutch, cocoa, many Australian kinos, guarana, catechu
Phloroglucinol
Chlorogenic acid- mate, coffee(unroasted) Num vomica ( small quantities)
On what bases are true tannins described
Based on type of phenolic nuclei, linkages present and dry distillation products
true tannins are classified as:
Hydrolysable tannins
- Condensed tannins
* **Complex tannins
What hydrolyses hydrolysable tannins
Enzyme tannase
Acids
