Tannins Flashcards
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
What are the precursors if hydrolysabke tannins
Phenolic acid
Gallic , ellagic acid and hexahydroxydiphenic acid
Glucose residue
Compound with monicyclic units linked by esters
Depside
the depside of Hexahydroxydiphenic acid) which arises by lactonization during chemical hydrolysis of the tannin.
Ellagic acid
What are the two types of hydrolysable tannins and their differences
gallotannins (composed of gallic acid units) and ellagitannins (composed of hexahydroxydiphenic acid units)
Differences btn gallotannins (and ellagitannins
Gallitannins
Upon acid hydrolysis of Gallitannins, Gallic acid is produced
•Rapidly soluble in water
•Free Gallic acid in plant is converted to gluco-gallitannins
•the galloyl groups in gallotannins are linked by depside bonds.
Ellagic
•the galloyl groups are linked through C-C bonds
Upon acid hydrolysis of Ellagitannins yields ellagic acid.
- Slowly soluble in water
- Present in plants in open and ring forms as Hexa hydroxyl diphenic acid
Hydrolysable tannin + iron salts will give?
Blue fluorescence
derivatives of the flavonols: catechin and flavonol-3-4-diol
Condensed tannins
What are the other names for condensed tannins
non-hydrolysable tannins, pro-anthocyanidins, catechol type tannins.
Do condensed tannins have sugar residue
Are they susceptible to enzymes or acids cleavage
No
No
What happens when condensed tannins are treated with enzymes
What do they yield on dry distillation
converted to red insoluble compounds known as phlobaphenes.
On dry distillation they yield catechol and are sometimes called catechol tannins.
What is is responsible for the colours observed in many flowers, leaves, fruits juices and wines.
Anthocyanide pigments
What are proanthocyanides
derived from the acid-catalyzed oxidation reaction of CTs (heating PAs in acidic alcohol solutions) to produce red anthocyanidins.
Sources of condensed tannins
Barks: cinnamon, wild cherry, cinchona, willow, acacia, hamamelis
(2) Roots and rhizomes: krameria (rhatany) and male fern
(3) Flowers: lime and hawthorn
(4) Seeds: cocoa, kola and areca
(5) Fruits: cranberries, grapes (red wines)
(6) Leaves: hamamelis, tea,
(7) Extracts and dried juices: catechu, acacia and mangrove, eucalyptus.
group of tannins that are biosynthesized from both hydrolysable tannin (mostly a C-glucoside ellagitannin) and condensed tannin.
Complex tannins
Eg. Flavano-ellagitannin
