Tannins

Question 1

What are plant phenols , where are they derived from and BIOSYNTHESIZED

Answer 1

Aromatic ring bearing a hydroxyl group.
Derived from aromatic amino acids, such as tyrosin
biosynthesized via Shikimic acid pathway/ Phenylpropanoid pathway

Question 2

Egs of phenols

Answer 2

Simple phenolics( phenolic and coumarins) ,flavonoids ,quinones, lignins and tannins

Question 3

What are the two polyphenols

Answer 3

tannins and flavonoids

Question 4

The two definitions or tannins

Answer 4

1. Tannins are high molecular weight, poly-hydroxy phenolic compounds capable of forming strong complexes with proteins and other macromolecules.
2. They are condensation products of Gallic acid or Flavan-3-ol as well as their glycosides.

Question 5

Are tannins non nitrogenous

Answer 5

Yes

Question 6

Where are tannins distributed

Answer 6

distributed in many angiosperms and gymnosperms usually located in the leaf, seed, root, bud, wood and stem

Question 7

What tissues do tannins help grow

Answer 7

secondary phloem and xylem and in between the cortex and epidermis.

Question 8

What are the four physiological roles of tannins to plants

Answer 8

• 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

Question 9

What are the dietary sources of tannins

Answer 9

Wine

Fruits: strawberries, blue berries, nuts e.g. almond, walnuts; herbs and spices e.g. Clove, vanilla, cinnamon cumin

Tea

Question 10

What causes dry puckery aftertaste after taking unripe fruit wine or tea

Answer 10

The astringency from the tannins (drawing of residual proteins from tongue and mouth).

Question 11

What are the four PHYSICAL properties of tannins

Answer 11

–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

Question 12

What compounds do tannins precipitate with

Answer 12

• Heavy metals- e.g. Lead
• Alkaloidal salts
• Proteins e.g. gelatin( 1% solution)
• Glycosides

Question 13

What substance does tannin form colored reactions with

Answer 13

Iron Salts

Eg; FeCl3

Question 14

Reaction of tannins with ammonia/potassium ferricyanide produces ?

Answer 14

Deep red color

Question 15

What propety does accumulation give tannins

Answer 15

Anti oxidizing properties

Question 16

How are tannins detected quantitavely and qualitatively

Answer 16

Gold beaters test

Standard hide powder

Question 17

What are true tannins

Answer 17

High molecular weight ploy-phenolic compounds which test positive for gold beaters test

Question 18

What are pseudorannins

Answer 18

Low molecular weight which don’t respond to goldbeater’s test

Question 19

What is the molecular weight range of true tannins

Answer 19

1000-5000 DA

Question 20

When do pseudotannis precipitate gelatin and retain hide powder

Answer 20

In high concentrations

Question 21

Examples of pseudtannins

Answer 21

Gallic acid- rhubarb

Salicylic acid

Catechin- acacia cutch, cocoa, many Australian kinos, guarana, catechu

Phloroglucinol

Chlorogenic acid- mate, coffee(unroasted) Num vomica ( small quantities)

Question 22

On what bases are true tannins described

Answer 22

Based on type of phenolic nuclei, linkages present and dry distillation products

Question 23

true tannins are classified as:

Answer 23

Hydrolysable tannins

2. Condensed tannins
   * **Complex tannins

Question 24

What hydrolyses hydrolysable tannins

Answer 24

Enzyme tannase

Acids

Question 25

What are the precursors if hydrolysabke tannins

Answer 25

Phenolic acid
Gallic , ellagic acid and hexahydroxydiphenic acid

Glucose residue

Question 26

Compound with monicyclic units linked by esters

Answer 26

Depside

Question 27

the depside of Hexahydroxydiphenic acid) which arises by lactonization during chemical hydrolysis of the tannin.

Answer 27

Ellagic acid

Question 28

What are the two types of hydrolysable tannins and their differences

Answer 28

gallotannins (composed of gallic acid units) and ellagitannins (composed of hexahydroxydiphenic acid units)

Question 29

Differences btn gallotannins (and ellagitannins

Answer 29

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

Question 30

Hydrolysable tannin + iron salts will give?

Answer 30

Blue fluorescence

Question 31

derivatives of the flavonols: catechin and flavonol-3-4-diol

Answer 31

Condensed tannins

Question 32

What are the other names for condensed tannins

Answer 32

non-hydrolysable tannins, pro-anthocyanidins, catechol type tannins.

Question 33

Do condensed tannins have sugar residue

Are they susceptible to enzymes or acids cleavage

Answer 33

No

No

Question 34

What happens when condensed tannins are treated with enzymes

What do they yield on dry distillation

Answer 34

converted to red insoluble compounds known as phlobaphenes.

On dry distillation they yield catechol and are sometimes called catechol tannins.

Question 35

What is is responsible for the colours observed in many flowers, leaves, fruits juices and wines.

Answer 35

Anthocyanide pigments

Question 36

What are proanthocyanides

Answer 36

derived from the acid-catalyzed oxidation reaction of CTs (heating PAs in acidic alcohol solutions) to produce red anthocyanidins.

Question 37

Sources of condensed tannins

Answer 37

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.

Question 38

group of tannins that are biosynthesized from both hydrolysable tannin (mostly a C-glucoside ellagitannin) and condensed tannin.

Answer 38

Complex tannins

Eg. Flavano-ellagitannin