Lesson 5.1. Introduction to Tannins

phenoglycosides

Tannins are _____________________.

polyphenolic substances

Tannins are a.____________________ of higher molecular weight. They are found in many plants as products of b.__________________________.

a = ?

secondary metabolism

Tannins are a.____________________ of higher molecular weight. They are found in many plants as products of b.__________________________.

b = ?

water-soluble

Tannins are a.__________ nature allows easy extraction and is useful in various applications in the chemical and pharmaceutical industry.

It is also soluble in b._______________________________, but only sparingly soluble in other c.___________________.

a = ?

dilute alkali, alcohols, and acetone

Tannins are a.__________ nature allows easy extraction and is useful in various applications in the chemical and pharmaceutical industry.

It is also soluble in b._______________________________, but only sparingly soluble in other c.___________________.

b = ?

organic solvents

Tannins are a.__________ nature allows easy extraction and is useful in various applications in the chemical and pharmaceutical industry.

It is also soluble in b._______________________________, but only sparingly soluble in other c.___________________.

c = ?

complex, organic, non-nitrogenous, and cannot be crystallized

Characteristics of Tannins

pale yellow to light brown-red

PROPERTIES OF TANNINS:

1. ______________________ amorphous substances

2. solutions are acidic with a ____________________ taste

3. isolated from ________________________

4. causes precipitation of ____________________

1 = ?

sharp puckering

PROPERTIES OF TANNINS:

1. ______________________ amorphous substances

2. solutions are acidic with a ____________________ taste

3. isolated from ________________________

4. causes precipitation of ____________________

2 = ?

oak bark, sumac, and galls

PROPERTIES OF TANNINS:

1. ______________________ amorphous substances

2. solutions are acidic with a ____________________ taste

3. isolated from ________________________

4. causes precipitation of ____________________

3 = ?

proteins and alkaloids

PROPERTIES OF TANNINS:

1. ______________________ amorphous substances

2. solutions are acidic with a ____________________ taste

3. isolated from ________________________

4. causes precipitation of ____________________

4 = ?

astringent and antioxidant

medicinal use of tannins

leather manufacturing and dyeing

Industrial use of Tannins

styptics (stop hemorrhage)

MEDICAL AND BIOLOGICAL PROPERTIES

• Tannin-containing drugs precipitate proteins and have been traditionally used as a.______________________ and internally for the protection of b._______________ of mouth and throat.

a = ?

inflamed surfaces

MEDICAL AND BIOLOGICAL PROPERTIES

• Tannin-containing drugs precipitate proteins and have been traditionally used as a.______________________ and internally for the protection of b._______________ of mouth and throat.

b = ?

burns

MEDICAL AND BIOLOGICAL PROPERTIES

• They play an important role in treatment of a._____. They form a b.__________________________ on the surface of the injured skin below which c._________ of new tissue takes place

a = ?

mild aseptic protective layer

MEDICAL AND BIOLOGICAL PROPERTIES

• They play an important role in treatment of a._____. They form a b.__________________________ on the surface of the injured skin below which c._________ of new tissue takes place

b = ?

regeneration

MEDICAL AND BIOLOGICAL PROPERTIES

• They play an important role in treatment of a._____. They form a b.__________________________ on the surface of the injured skin below which c._________ of new tissue takes place

c = ?

anti-diarrheal

MEDICAL AND BIOLOGICAL PROPERTIES

• They act as ____________, although not recommended in this respect as they usually delay elimination of bacterial toxins from the body.

antidote in poisoning

MEDICAL AND BIOLOGICAL PROPERTIES

• Tannins have been employed as ___________________ by heavy metals, alkaloids and certain glycosides due to their precipitation as tannates

antioxidant

MEDICAL AND BIOLOGICAL PROPERTIES

• Recently, tannins as most polyphenols were proved to have a potent ____________ effect.

complexity of their chemical nature

The tannins are broadly classified into two groups based on the a.____________________ and according to their behavior on b.___________

a = ?

dry distillation

The tannins are broadly classified into two groups based on the a.____________________ and according to their behavior on b.___________

b = ?

Gallic Acid

EXAMPLES OF TANNINS:

1. Gallitannins

2. Ellagitannins

3. Catechols

1 = ?

Hexahydroxydiphenic acid

EXAMPLES OF TANNINS:

1. Gallitannins

2. Ellagitannins

3. Catechols

2 = ?

Flavan-3-ol

EXAMPLES OF TANNINS:

1. Gallitannins

2. Ellagitannins

3. Catechols

3 = ?

Hydrolyzable Tannins

hydrolyzed by acids or enzymes quickly and the products of hydrolysis are Gallic acid or ellagic acid

pyrogallol

Hydrolyzable Tannins

• On dry distillation, Gallic acid and other components get converted to _______________

blue

Hydrolyzable Tannins

• respond to ferric chloride solution, producing a ______ color

Gallotannin

The examples of hydrolysable tannins are:

1. found in nutgall, rhubarb, amla, clove, and chestnut

2. found in oak, myrobalans, and pomegranate bark

1 = ?

Ellagitannin

The examples of hydrolysable tannins are:

1. found in nutgall, rhubarb, amla, clove, and chestnut

2. found in oak, myrobalans, and pomegranate bark

2 = ?

Non-Hydrolyzable Tannins

also called condensed tannins, phlobatannins, or proanthocyanidins

flavonoids

Non-Hydrolyzable Tannins

• Hard to break down and come from a.___________

• when they are heated/treated, they form b._________ compounds

a = ?

red-brown

Non-Hydrolyzable Tannins

• Hard to break down and come from a.___________

• when they are heated/treated, they form b._________ compounds

b = ?

hydrolysis

Non-Hydrolyzable Tannins

• resistant to _________________

flavones

Non-Hydrolyzable Tannins

• Related to flavonoid pigments, formed via derivative of _____________, like catechin or flavan-3-ol or flavan-3,4-diols

phlobaphenes

Non-Hydrolyzable Tannins

• Unlike the hydrolysable tannins, on treatment with enzymes or mineral acids, they are polymerized or decomposed into red colored substances called __________________, which are insoluble in water and the typical brownish-red colour of many plants and drug color.

Cathecol

Non-Hydrolyzable Tannins

• On dry distillation they yield ______________

brownish-green

Non-Hydrolyzable Tannins

• treatment with ferric chloride produce

green tea and hamamelis leaves, cinchona, cinnamon and wild cherry bark, pale and black catechu

Non-Hydrolyzable Tannins

• found in:

Pseudotannins

A sub-group because they do not obey to gold-beaters skin test and are low molecular weight compounds

Chlorogenic acid

Examples of Pseudotannins

1. found in coffee and nix vomica

2. found in ipeacacuanha

3. found in cocoa

1 = ?

Ipecacuanha Acid

Examples of Pseudotannins

1. found in coffee and nix vomica

2. found in ipeacacuanha

3. found in cocoa

2 = ?

Catechins

Examples of Pseudotannins

1. found in coffee and nix vomica

2. found in ipeacacuanha

3. found in cocoa

3 = ?

water

Pseudotannins

• The detection test for chlorogenic acid is carried out by extracting the drug with __________

pure form

EXTRACTION OF TANNINS

1. As the tannins are high molecular weight compounds so it becomes difficult to isolate the tannins in ______________

2. Thus, the solvents used are the mixture of _______________________

3. Examples of Extracting Solvents

1 = ?

polar, non-polar and semi-polar solvent

EXTRACTION OF TANNINS

1. As the tannins are high molecular weight compounds so it becomes difficult to isolate the tannins in ______________

2. Thus, the solvents used are the mixture of _______________________

3. Examples of Extracting Solvents

2 = ?

alcohol, ether, water, acetone

EXTRACTION OF TANNINS

1. As the tannins are high molecular weight compounds so it becomes difficult to isolate the tannins in ______________

2. Thus, the solvents used are the mixture of _______________________

3. Examples of Extracting Solvents

3 = ?

hot water, ionic liquids, supercritical fluids, pressurized hot/subcritical water, microwave, ultrasound

Conventional tannins extraction with organic solvents

Solid-Liquid Extraction

• Most traditional method employed for tannins extraction

• Most common method with the use of organic solvents and Soxhlet apparatus

• Solvents: organic solvents, aq. sol’n, water, iconic liquids

Infusion and Maceration

Other Techniques for Extraction

Solvent Polarity

Parameters to observe high yield of tannin extractives:

• High extraction yields are generally obtained using water or methanol (ethanol)

• Poor extraction efficiency is achieved with hexane

pH

Parameters to observe high yield of tannin extractives:

• Slightly alkaline improves extraction

• Addition of NaOH, Na2CO3 , NaHSO3 improves extraction yields

• increments extraction efficiency and to lower the high viscosity of extracts derived from the tannin self-condensation reactions

Time

Parameters to observe high yield of tannin extractives:

• Longer contact time for solute and solvent results to increase yield.

• above 4.5 hrs yields a minimum amount of tannins because equilibrium was reached between the tannin concentration in the plant matrix and the solvent (Fick’s law of diffusion).

Temperature

Parameters to observe high yield of tannin extractives:

• increase in this improves the solubility and diffusion coefficient

• decreases solvent velocity which promotes extraction

• if it becomes too high, it can also lead to lower amounts of tannins due to denaturation owing to harsh conditions