extraction and isolation of natural products Pharmacognosy •"Pharmacognosy" derives from two Greek words, "pharmakon" or drug, and "gnosis" or knowledge. ... •Natural products
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Pharmacognosy
• "Pharmacognosy" derives from two Greek words, "pharmakon" or drug, and "gnosis" or knowledge. While representing a classical field of science,
• Its scope includes the study of the physical, chemical, biochemical and biological properties of drugs, drug substances, or potential drugs or drug substances of natural origin as well as the search for new drugs from natural sources.
Herbal medicine
1 : the art or practice of using herbs and herbal preparations to maintain health and to prevent, alleviate, or cure disease.
2 : a plant or plant part or an extract or mixture of these used in herbal medicine.
• Natural products are important sources for drug
development. The amounts of bioactive natural
products in natural medicines are always fairly
low. Today, it is very crucial to develop effective
and selective methods for the extraction and
isolation of those bioactive natural products.
• In the USA, approximately 49% of the population has tried natural medicines for the prevention and treatment of diseases
• Natural products have provided the primary sources for new drug development. From the 1940s to the end of 2014, nearly half of the FDA approved chemical drugs for the treatment of human diseases were derived from or inspired by natural products
• Extraction is the first step to separate the desired natural products from the raw materials. The
• extraction of natural products stages
– (1) the solvent penetrates into the solid matrix;
– (2) the solute dissolves in the solvents;
– (3) the solute is diffused out of the solid matrix;
– (4) the extracted solutes are collected.
Any factor enhancing the diffusivity and solubility in the above steps will facilitate the extraction.
Factors affection Extraction
• Selection of the solvent: Selectivity, solubility, cost and safety should be considered.
• Polarity of the solvent and the solute: Based on the law like dissolves like, solvents with a polarity value near to the polarity of the solute are likely to perform better and vice versa. Alcohols (EtOH and MeOH) are universal solvents in solvent extraction for phytochemical investigation.
• Particle size: the finer the particle size is, the
better result the extraction achieves. The
extraction efficiency will be enhanced by the
small particle size due to the enhanced
penetration of solvents and diffusion of
solutes.
• Temperature: High temperatures increase the
solubility and diffusion. Temperatures that too
high, however, may cause solvents to be lost,
leading to extracts of undesirable impurities
and the decomposition of thermolabile
components.
• Duration: The extraction efficiency increases with the increase in extraction duration in a certain time range. Increasing time will not affect the extraction after the equilibrium of the solute is reached inside and outside the solid material.
• Amount of the solvent: The greater the solvent-to-solid ratio is, the higher the extraction yield is;
Extraction methods
• Traditional methods: maceration, percolation and reflux extraction, usually use organic solvents and require a large volume of solvents and long extraction time.
• Modern extraction methods: critical fluid extraction (SFC), pressurized liquid extraction (PLE) and microwave assisted extraction (MAE), have also been applied in natural products extraction – Advantages: lower organic solvent consumption,
shorter extraction time and higher selectivity.
Pre-extraction preparation of plant
samples • Pre-preparation of plant materials such as grinding and drying also
influences the preservation of phytochemicals in the final extracts.
• Fresh vs. dried samples
• Grinded vs. powdered samples
• Drying of plants samples
• Fresh vs. dried samples: Both fresh and dried sample is used in medicinal plants studies. In most cases, dried sample is preferred considering the time needed for experimental design.
• Grinded vs. powdered samples: Lowering particle size
increases surface contact between samples and
extraction solvents. Grinding resulted in coarse smaller
samples; meanwhile, powdered samples have a more
homogenized and smaller particle, leading to better
surface contact with extraction solvents. This particular
pre-preparation is important, as for efficient extraction
to occur, the solvent must make contact with the target
analytes and particle size smaller than 0.5 mm is ideal
for efficient extraction.
• Air-drying
usually takes from 3-7 days to months and up to a year
depending on the types of samples dried (e.g. leaves or seed).
Plant samples, usually plants leaves with stem were tied
together and hang to expose the plant to air at ambient
temperature. This drying method does not force dried plant
materials using high temperature; hence, heat-labile
compounds is preserved.
Drying of plants samples:
Microwave-drying
• Microwave-drying uses electromagnetic
radiation that possesses both electric and
magnetic fields. This method can shorten
drying time but sometimes causes
degradation of phytochemicals.
Oven-drying
• Oven-drying uses thermal energy to remove
moisture from the samples. This sample
preparation is considered as one of the easiest
and rapid thermal processing that can
preserved phytochemicals.
Freeze-drying
• Freeze-drying is a method base on the principle of sublimation.
• Sublimation is a process when a solid is changed into gas phase without entering the liquid phase.
• Lyophilization or freeze drying is a process in which water is removed from a product after it is frozen and placed under a vacuum, allowing the ice to change directly from solid to vapor without passing through a liquid phase.
• Sample is frozen at -80°C to -20°C prior to lyophilisation to solidify any liquid (eg. solvent, moisture) in the samples. After an overnight (12 h) freezing, sample is immediately lyophilized to avoid the frozen liquid in the sample from melting.
• However, freeze-drying is a complex and expensive methods of drying compared to regular air drying and microwave-drying. Thus, the use is restricted to delicate, heat-sensitive materials of high value.
Maceration
• Maceration This is a very simple extraction method with the disadvantage of long extraction time and low extraction efficiency. It could be used for the extraction of thermo-labile components.
• Maceration involved soaking plant materials (coarse or
powdered) in a stoppered container with a solvent and allowed to stand at room temperature for a period of minimum 3 days with frequent agitation. The processed intended to soften and break the plant’s cell wall to release the soluble phytochemicals. After 3 days, the mixture is pressed or strained by filtration.
• Digestion
This is a form of maceration in which gentle heat is used during the process of extraction.
Percolation
• Percolation is more efficient than maceration because it is a continuous process in which the saturated solvent is constantly being replaced by fresh solvent.
• This is the procedure used most frequently to extract active ingredients in the preparation of tinctures and fluid extracts. A percolator (a narrow, cone-shaped vessel open at both ends) is generally used.
Decoction
• In this process, the crude drug is boiled in a
specified volume of water for a defined time;
it is then cooled and strained or filtered. This
procedure is suitable for extracting water-
soluble, heat-stable constituents.
Reflux extraction
• Reflux extraction is more
efficient than percolation,
maceration and Decoction.
• It requires less extraction
time and solvent. It cannot
be used for the extraction of
thermo-labile natural
products.
Soxhlet extraction
• The Soxhlet extraction method integrates the advantages
of the reflux extraction and percolation, which utilizes the
principle of reflux and siphoning to continuously extract the
herb with fresh solvent. The Soxhlet extraction is an
automatic continuous extraction method with high
extraction efficiency that requires less time and solvent
consumption than maceration or percolation.
Hot Continuous Extraction (Soxhlet)
• In this method, the finely ground crude drug is
placed in a porous bag or “thimble” made of
strong filter paper, which is placed in a
chamber of the Soxhlet apparatus
Pressurized liquid extraction (PLE)
• It applies high pressure in extraction. High pressure
keeps solvents in a liquid state above their boiling point
resulting in a high solubility and high diffusion rate of
lipid solutes in the solvent, and a high penetration of
the solvent in the matrix.
• PLE dramatically decreased the consumption of
extraction time and solvent amount.
Supercritical fluid extraction (SFE)
• It uses supercritical fluid (SF) as the extraction solvent. SF has similar solubility to liquid and similar diffusivity to gas, and can dissolve a wide variety of natural products. Their solvating properties dramatically changed near their critical points due to small pressure and temperature changes.
• Supercritical carbon dioxide (S-CO2) was widely used in SFE because of its attractive merits such as low critical temperature (31 °C), selectivity, inertness, low cost, non-toxicity, and capability to extract thermally labile compounds.
Ultrasound assisted extraction
• also called ultrasonic extraction or sonication, uses ultrasonic wave energy in the extraction. Ultrasound in the solvent producing cavitation accelerates the dissolution and diffusion of the solute as well as the heat transfer, which improves the extraction efficiency.
• It is applicable for the extraction of thermo-labile and unstable compounds.
Microwave assisted extraction
• Microwaves generate heat by interacting with polar compounds such as water and some organic components in the plant matrix following the ionic conduction and dipole rotation mechanisms.
• Advantages: such as increasing the extract yield, decreasing the thermal degradation and selective heating of vegetal material.
Enzyme assisted extraction
• The structure of the cell membrane and cell wall,
micelles formed by macromolecules such
polysaccharides and protein, and the coagulation and
denaturation of proteins at high temperatures during
extraction are the main barriers to the extraction of
natural products. Cellulose, α-amylase and pectinase
are generally employed in EAE.
distillation
• Hydro and steam distillation Hydro distillation and
steam distillation are commonly used methods for the
extraction of volatile oil.
Separation methods
• The components in the extract from Previous methods are complex and contain a variety of natural products that require further separation and purification to obtain the active fraction or pure natural products. The separation depends on the physical or chemical difference of the individual natural product.
• Chromatography, especially column chromatography, is the main method used to obtain pure natural products from a complex mixture.
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