Pharmacognosy- 1 PHG 222 - Psau · PDF fileProfessor of Pharmacognosy ... A. Drying of plant materials i-Natural drying ... changes in the appearance of the drug, especially loss of

Prof. Dr. Amani S. Awaad

Professor of PharmacognosyPharmacognosy Department,

College of Pharmacy Salman Bin Abdulaziz

University,

Al-Kharj. KSA.

Email: [email protected]

Pharmacognosy- 1

PHG 222

Preparation of crude drugs

*At the end of this lecture you should be

able to know :

How to prepare and collect plants

Extraction methods of crude drugs

Separation, purification and

identification of active materials

Preparation of crude drugs

To Prepare crude Drugs the following points must be fulfilled:

1- Selection& collection of promising plant materials.

a. Suitable time for collection

b. Methods of collection

c . Authentication of plant material

2- Preservation of plant materialA. Drying of plant materials

i-Natural drying

ii- Hot air drying

iii- Artificial drying ( freeze-drying).

B. Stabilization

C. Fermentation

3- Grinding of the dried plants

4- Storage &Packing of crude drugs

5- Extraction and fractionationi-What is a plant extract

ii-Types of the extracts

iii-Solvent choice

iv-Extraction parameters

v-Methods of extraction

6- Separation, purification and identification.

1. Selection &Collecting of medicinal plants

The choice of promising plant

depends upon the following:

1- A plant which have a biological

activity.

2- A plant used in folk medicine.

3- A plant which show a particular

toxicities

Before investing time, effort and money

in phytochemical

screening it is very important to select a

promising plant.

I. Selection

1. Collecting of medicinal plants

Drugs may be collected from:

1- Wild plants.

2- Cultivated plants.

Time of the day, time of the year and maturity

Wild plant Cultivated plant

Disadvantage Advantage

1- Scattered in large or

unlimited area

Present in limited area.

2- Difficult to reach Easy to reach

3- The collector must be

highly skilled botanists

The collector must not be

skillful person

4- Deficiency may occur due

to continuous collection

Continuous supply

II. Collecting

A. Suitable time for collection

*The proper time of the day, time of the year and maturity

stage of collection is particularly important because the

nature and quantity of constituents may vary greatly in

some species according to the season and time of

collection.

* The collected plant should be free from any

contamination.

* Collecting plants which are free from diseases (i.e.

which are not affected by viral, bacterial, fungal

infection).

B. Methods of collection

• Medicinal plants must be largely collected by hand. This is

especially true in the case of wild plants.

• With cultivation on a large scale, it may be possible to use

modern agricultural harvesters.

1. Selection &Collecting of medicinal plants

II. Collecting

C- Authentication of plant material.

This may be confirmed by:

1- Establishing the identity by a

taxonomy experts.

2- Collection of a common

species in their expected habitat

by a field botanist.

3- By comparing the collecting

plant with a voucher specimen

( herbarium sheet)

1. Selection &Collecting of medicinal plants

II. Collecting

2. Preservation of plant material

A. Drying of plant materials.

Drying is done in

i- Natural drying (Shade and in sunlight).

ii- Hot air drying

iii- Artificial drying ( freeze-drying).

Aim of drying:

1- Ease of transport.

2- Ease of grinding

3- Inhibit the growth of microorganisms.

4- Preservative of active constituents.

5- Enzymatic processes (in aqueous

solution).

6-decreases the risk of external attack

2. Preservation of plant material

A- Drying of plant materials.i-Natural drying:

Sun drying is most widely used method of drying

plant but some times sunlight destroys the active

constituents in the plants.

Shade drying requires full air circulation. It

should not be undertaken inside conventional

buildings but in an open-sided shed purposely

built for shade drying

(Shade & sunlight)

Changes may occur during the

drying:

Size and weight, Shape and

appearance, Color, Odor , Taste ,

Active constituent

ii- Hot air drying A- Drying of plant materials.

2. Preservation of plant material

The most efficient drying is achieved in

large driers of the tunnel type. The plant

material is spread out on shallow trays,

which are placed on mobile racks and

passed into a tunnel where they meet a

stream of warm air.

The air temperature is kept at 20-40 °C

for thin materials such as leaves, but is

often raised to 60-70 °C for plant parts

that are harder to dry, e.g. roots and

barks

A- Drying of plant materials.

2. Preservation of plant material

Freeze-drying (lyophilization).

Frozen material is placed in an

evacuated apparatus which has

a cold surface maintained at -

60 to -80 °C. Water vapor from

the frozen material then passes

rapidly to the cold surface.

The method requires

(1) a relatively complicated

apparatus and

(2) is much more expensive

than hot-air drying. ( not used

as a routine method, heat-

sensitive substances)

iii- Artificial drying ( freeze-drying).

B- Stabilization

A- Drying of plant materials.

2. Preservation of plant material

Its value for the isolation of compounds that

are very susceptible to enzymatic

degradation e.g. aloe.

long storage, enzymatic reactions will

slowly destroy the constituents (Bec. traces

of water can never be removed).

Stabilization is a process to destroy enzyme

This process eliminates both bacteria and

anthraquinones (laxatives) via a super chilled

ethanol bath. In this cold bath, the stabilized

aloe solids separate from water and ethanol

C- FermentationA- Drying of plant materials.

2. Preservation of plant material

Enzymatic transformation of the original

plant constituents is sometimes desirable.

The fresh material is then placed in thick

layers, sometimes covered and often

exposed to raised temperatures (30-40 °C)

and humidity, so as to accelerate the

enzymatic processes.

(This treatment is usually called

fermentation).

The fermented product must, of course, be

dried afterwards to prevent attack by.

C- FermentationA- Drying of plant materials.

2. Preservation of plant material

Fermentation is mostly used to

remove bitter or unpleasant-tasting

substances or to promote the

formation of aromatic compounds

with a pleasant smell or taste.

It is mainly applied to drugs used

as spices or stimulants, e.g. vanilla,

tea and cacao.

CH3O

Glu-O

CH2OH CH2OHCH3O

HO

CHOCH3O

HO

Enz

H2OEnz

[O]

VanillinGlucovanillic alcohol (glucoside)

3- Grinding of the dried plants.

The first operation that must be performed is grinding of the

plant material to a powder of suitable particle size.

It is important that the particles are of as uniform in size as

possible.

Excessive dust can clog percolators and result in a turbid extract

which is hard to clarify.

Large particles take a longer time for complete extraction than

small ones and large differences in particle size thus slow down

the extraction process.

Types of machines grinding crude drugs:Hammer mill; a common type for grinding crude drugs.

Knife mill; is useful for production of low-dust powders

of leaves, barks and roots for subsequent percolation or

maceration.

Tooth mill; is used for production of very fine powders.

3- Grinding of the dried plants.

Following grinding, the material must be sifted to ensure the

proper particle size.

Sifting can be performed according to two different principles:

sieving and blast sifting.

Sieving

In sieving the material is passed through

a sieve of suitable mesh size giving two fractions.

The fraction passing the sieve consists of particles

with a size smaller than or corresponding to the

mesh size. The remaining fraction consists of

coarser particles which are returned to the mill for

continued grinding.

Blast sifting

In blast sifting the material to be

classified is blown with compressed air into an

apparatus which allows the particles to sediment

according to their weight. Coarse, heavy particles

settle fast whereas small, light particles stay for a

long time in the air stream.

4- Storage &Packing of crude drugs

Drugs containing glycosides and esters are usually less

stable than those containing alkaloids.

Drugs with essential oils deteriorate rather quickly

through evaporation, oxidation and polymerization of

the substances constituting the essential oil.

Tannins on the other hand, have an almost unlimited

durability.

• In order to keep crude drugs as long as possible:

It is essential to store them in a dry condition in carefully closed

containers at low temperature.

1. It is also advisable to exclude light, because - even if it does

not affect the active constituents - it almost always causes

changes in the appearance of the drug, especially loss of

color.

2. It is also necessary to protect the drug against insect attack.

5- Extraction and fractionation

A plant extract must be obtained from a solid-

liquid extraction.

Solid-liquid extraction is defined as an

operation to separate elements contained in a

solid body by solubilization with a solvent, and

it may be followed by purification.

The extract is contained in the solvent.

If the solvent is an edible solvent, it is not

necessary to dissociate it from the extract.

If the solvent is not an edible solvent,

separation allows obtaining a dry extract.

i-What is a plant extract?

5- Extraction and fractionation

ii-Types of the extracts

1-Dry extracts: all solvent has been

removed.

2-Soft extracts & fluid extracts are

prepared with mixtures of water and

ethanol as solvent.

3-Tinctures are prepared by extraction of

the crude drug (or plant) with 5 to 10 parts

of ethanol of varying concentration,

without concentration of the final product.

iii-Solvent choice

The ideal solvent for a certain pharmacologically active constituent should be:

1. Highly selective for the compound to be extracted.

2. Have a high capacity for extraction in terms of coefficient of saturation of the compound in the medium.

3. Not react with the extracted compound or with other compounds in the plant material.

4. Have a low price, volatile and harmless to man and environment.

According to the pharmacopoeias, ethyl alcohol is the solvent of

choice for obtaining all types of extracts.

The ethanol is usually mixed with water to induce swelling of the

plant particles and to increase the porosity of the cell walls which

facilitates the diffusion of extracted substances from inside the

cells to the surrounding solvent.

5- Extraction and fractionation

Extraction of plant materials is varied.

It depends on different parameter

such as

1- The texture of the plant material.

2- The water content of the plant

material.

3- The type of substances to be

extracted or nature of active

constituents.

5- Extraction and fractionation

iv-Extraction parameters

v-Methods of extraction

1- Maceration

2- Percolation

3- Infusion

Percolation, on the other hand, is the

method of filtration in which plant passed

through solvent to take out their substance.

powdered crude drug is placed in a stoppered

container with the solvent and allowed to stand

at room temperature for a period of at least 3

days. The mixture clarified by filtration

Fresh infusions are prepared by macerating

the crude drug for a short period of time

with cold or boiling solvent.

5- Extraction and fractionation

Methods of extraction cont..

4- Digestion

6- Continuos hot extraction

5- Decoction

This is a form of maceration in which gentle heat is used

during the process of extraction.

It is considered as maceration but with relatively elevated

temperature(35-45)

In this process, the crude drug is boiled in a specified

volume of solvent

- cooled & -filtered. (heat stable & continues)

The powdered material is continuously

extracted in a Soxhlet apparatus with

suitable solvents. Avoid with heat sensitive

materials

5- Extraction and fractionation

Methods of extraction cont..

7-Counter-current Extraction

5- Extraction and fractionation

In counter-current extraction (CCE), wet

raw material is pulverized and produce a

fine slurry. Here the material to be

extracted is moved in one direction within

a cylindrical extractor where it comes in

contact with extraction solvent. The

further the starting material moves, the

more concentrated the extract becomes.

Complete extraction is thus possible when

the quantities of solvent and material and

their flow rates are optimized. Finally,

sufficiently concentrated extract comes

out at one end of the extractor while the

marc falls out from the other end.

Methods of extraction cont..

8-Ultrasound Extraction (Sonication)

5- Extraction and fractionation

the acoustic characteristics of any use to

transmit information or to the related material,

all known as ultrasound.

Ultrasound is often used by the current

frequency range of KHz ~ MHz, can enjoy the

use of function and to determine the frequency

of use.

When the ultrasonic is propagating in the

extracted liquid, the ordered and high-speed

ultrasonic vibration will result in cavitations

bubbles in a solvent material. When these

bubbles collapse near the cell walls, the

resulting shock waves and liquid jets cause

those cells walls to break and release their

contents into a solvent

Methods of extraction cont..

9-Supercritical Fluid

5- Extraction and fractionation

A supercritical fluid is any

substance at a temperature

and pressure above its

critical point, where distinct

liquid and gas phases do not

exist. It can effuse through

solids like a gas, and

dissolve materials like a

liquid. In addition, close to

the critical point, small

changes in pressure or

temperature result in large

changes in density, allowing

many properties of a

supercritical fluid to be

"fine-tuned".

Methods of extraction cont..

10- Distillation

5- Extraction and fractionation

is a process of separating the

component substances from a

liquid mixture by selective

evaporation and condensation.

Distillation may result in

essentially complete separation

(nearly pure components), or it

may be a partial separation that

increases the concentration of

selected components of the

mixture.

6- Separation, purification, and identification.

The

separation,

purification and

identification of the

components of a

mixture are among the

everyday problems

faced by both

industrial and research

chemists. This can be

carried out using

different method of

chromatography

Biological screening

Extraction

Solvent removal

In-vitroIn-vivo

Isolation &identification