Extraction of Plant Material
Pharmacognosy I
Duhok University/ Faculty of Pharmacy
L.A. Dilbreen Barzanji
Extraction of plant material
• The commonly employed technique for
separation of active substance from crude drugs
is called ‘Extraction’ which involves the use of
different solvent.
• Whether samples are plants, microbes, marine
animals or insects they are referred to as
biomass.
• All plant material used should be properly
authenticated, as much time and money can be
wasted on the examination of material of
doubtful origin.
• Dried materials are usually powdered before
extraction, whereas fresh plants (e.g. leaves, etc) can
be homogenized or macerated with a solvent such as
alcohol. (Homogenizing is particularly useful for
stabilizing fresh leaves by dropping them into the
boiling solvent).
• Dried biomass is ground into small particles using
either a blender or a mill. Plant material is milled twice,
first using a course mill and then a fine mill to generate
a fine powder.
• The grinding process is important as effective
extraction depends on the size of the biomass
particles; large particles will be poorly extracted,
whereas small particles have a higher surface area and
will therefore be extracted more efficiently.
• Selection of the solvent extraction approach is
very important.
• If a plant is under investigation from an
ethnobotanical perspective, then extraction
should mimic the traditional use.
• For example; if indigenous people use a specific
extraction protocol such as a water extract, a
cold/heat tea, alcohol or alcohol-water mixtures,
then an identical or at least a very similar method
should be used in the laboratory so that the same
natural products are extracted.
• Failure to extract biomass properly may result in
loss of access to active compounds.
• Additionally, using an inappropriate extraction
method, such s strong heating of biomass with a
solvent, may result in degradation of natural
products and consequent loss of biological
activity.
• The choice of extraction procedure depends on the
nature of the plant material and the components to be
isolated.
• Alcohol is general solvent for many plant constituents
(most fixed oils are exception) and as such may give
problems in the subsequent elimination of pigments,
resins, etc.
• Water-immiscible solvents are widely used; Light
petroleum (essential and fixed oil, steroids),
• Ether and chloroform (alkaloids, quinines).
• The extraction of organic bases (e.g. alkaloids) usually
necessitates basification of plant material if a waterimmiscible solvent is to be used; for aromatic acids and
phenols acidification may be required.
• Special method for volatile oil , such as Clavenger
and sometimes Enfleurage process.( enflourage:
is the process of extracting fragrance from
flowers by using odorless fats or oils to capture
the essential oils. The perfumes of plants like
jasmine could only be extracted by enfleurage).
• Ultrasound may enhance the extraction
process of some plant materials.
• Ultrasound present several advantage several
advantages in term of:
1. shortening the time of process,
2. decrease the volume of the solvent,
3. increasing the yield of the extract in
comparison with conventional methods.
cold extraction
• Extraction itself may be performed by repeated
maceration with agitation, percolation or by
continuous extraction (e.g. in a Soxhlet extractor).
• Numerous extraction methods are available, the
simplest being cold extraction (in a large flask with
agitation of the biomass using a stirrer) in which the
ground dried material is extracted at room
temperature sequentially with solvents of increasing
polarity: first hexane (or petroleum ether), ethyl
acetate, acetone, methanol and finally water.
• The major advantage of this protocol is that it is a soft
extraction method as the extract is not heated and
there is little potential degradation of natural products.
• The use of sequential solvents of increasing polarity
enables division of natural products according to their
solubility (and polarity) in the extraction solvents. This
can greatly simplify an isolation process.
• Cold extraction allows most compounds to be
extracted, although some may have limited solubility in
the extracting solvent at room temperature.
hot percolation
• In hot percolation, the biomass is added to
round-bottomed flask containing solvent and the
mixture is heated gently under reflux.
• Typically, the plant material is ‘stewed’ using
solvents such as ethanol or aqueous ethanol
mixtures. The technique is sometimes referred to
as total extraction and has the advantage that,
with ethanol, the majority of lipophilic and polar
compounds is extracted.
• An equilibrium between compounds in solution
and in the biomass is established, resulting in
moderate extraction of natural products.
• Heating the extracts for long periods may also
degrade labile compounds; therefore a pilot
experiment should first be attempted and
extracts assessed for biological activity to
ascertain whether this extraction method
degrades the bioactive natural products.
• Care should be taken, as extraction is never truly
total; for example, some highly lipophilic natural
products are insoluble .
decoction
• The decoction is used for active ingredients
that doesn´t modify with temperature. In this
process the drug is boiled in water for 15 to 60
minutes depending on the plant or the active
ingredient to extract.
Supercritical fluid extraction
• Supercritical fluid extraction utilizes the fact that some
gases behave as liquids when under pressure and have
solvating properties. The most important example is
carbon dioxide which can be used to extract biomass
and has the advantage that, once the pressure has
been removed, the gas boils off leaving a clean extract.
• Carbon dioxide is a non-polar solvent but the polarity
of the supercritical fluid extraction solvent may be
increased by addition of modifying agent, which is
usually another solvent (e.g. methanol or
dichloromethane).
Soxhlet extraction
• The most widely used method for extraction of
plant natural products is Soxhlet extraction. This
technique uses continuous extraction by solvents
of increasing polarity.
• The biomass is placed in a Soxhlet thimble
constructed of filter paper, through which solvent
is continuously refluxed.
• The Soxhlet apparatus will empty its contents into
the round-bottomed flask once the solvent
reaches a certain level.
• As fresh solvents enters the apparatus by a reflux
condenser, extraction is very efficient and
compounds are effectively drawn into the solvent
from biomass due to their low initial
concentration in the solvent.
• The method suffers from the same drawbacks as
other hot extraction methods (possible
degradation of products), but it is the best
extraction method for the recovery of a big yields
of extract. Moreover, providing biological activity
is not lost on heating, the technique can be used
in drug lead discovery.
• In general terms, regardless of the extraction method
used, extracts are of two types: lipophilic (‘fat-loving’),
resulting from extraction by non-polar solvents ( e.g.
petroleum, ethyl acetate, chloroform,
dichloromethane) and hydrophilic (‘water-loving’),
produced by extracting biomass with polar solvents
(e.g. acetone, methanol, water).
• The value of using solvents of different polarities is that
the chemical complexity of the biomass is simplified
when taken into the extract, according to the solubility
of the components. This can greatly simplify the
isolation of an active compound from the extract.
• Additionally, certain classes of compounds may
have high solubilities in a particular solvent (e.g.
monoterpens in hexane), which again can
simplify the chemical complexity of an extract
and help with isolation process.
• Regardless of the extraction technique used,
extracts are concentrated under vacuum using
rotary evaporators for large volumes of solvent
(> 5 ml) or ‘blown down’ under nitrogen for small
volumes (1-5 ml), ensuring that volatile
components are not lost.
• Removal of solvent should be carried out
immediately after extraction, as natural
products may be unstable in the solvent.
• Aqueous extracts are generally freeze-dried
using a lyophilizer.
• Dried extracts should be stored at -20 0C prior
to screening for biological activity as this will
decrease the possibility of degradation of
bioactive natural product.
Sublimation
• Sublimation may sometimes be possible on whole drug, as
in the isolation of caffeine from tea or for the purification
of materials present in a crude extract. Modern equipment
employs low pressures with a strict control of temperature.
• Freeze-drying or lyophilization requires a first step where
the temperature of the extract (solutes and solvents) is
reduced until they are frozen, followed by a sublimation
step carried out via a very high vacuum which sometimes
accompanied by heating.
• Freeze drying is widely applied whenever a thermolabile
substance is of interest. It forms part of extraction process
of several products, for example; antibiotics, antioxidants,
hormones, etc.
Distillation
• Fractional distillation has been traditionally used for
separation of the components of volatile mixtures; in
phytochemistry it has been widely used for isolation of
components of volatile oils.
• On a laboratory scale it is not easy by this method to
separate minor components of a mixture in a pure
state and gas chromatography is now routinely used.
• Steam distillation is much used to isolate volatile oils
and hydrocyanic acid from plant material.