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
*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