Extraction of plant materials by solvent extraction method

What is extraction of plant?

•Extraction can be defined as the treatment of the plant (or animal tissues) with solvent, where the medicinally active constituents are dissolved and most of the inert particles remain undissolved.
• The process of extraction developed into a distinct area and contributes mainly to the progress of phytochemistry.
• Extraction processes includes maceration, steam or hydro-distillation, pressing, decoction, infusion, percolation and Soxhlet extraction.
• It is difficult to find a production process in the perfume, cosmetic, pharmaceutical, food, bio fuel, or fine chemicals industries, which does not use extraction processes these days.

Why extraction process of plant materials important?

• To siphon the required chemical components from the plant materials for further separation and characterization.
• To isolate an unknown compound responsible for the particular activity.
• To discover bioactive constituents from plant materials.
• It has great impact on the reliability of a natural medicine.
• Significant for the standardization of herbal/ayurvedic products.

Solvent extraction method

• The efficient determination of biologically active compounds from plant material largely depends on the type of solvent used in the extraction process.
• The ruptured cells are integrated in the extracting solvent and the mixture is kept for some time (half an hour to 24 hr) to let the solvent prick all parts of the ruptured cells.

1. • Maceration:

   • The simplest mode of cold extraction process which is suitable mostly for the thermolabile drugs.
   • In a stoppered container, the powdered plant material is taken and soaked with the solvent for a specified period of time.
   • Agitation is performed until the soluble matter dissolves.

2. • Percolation:

   • It is the process in which movement of mass across a porous material takes place where a percolator is generally used.
   • Percolator is a narrow, cone-shaped vessel open at both ends.
   • The plant (Crude) material is taken in a percolation tube plugged with cotton or fitted with a filter and a stopcock and is moistened with an appropriate amount of solvent(esp. menstruum).
   • It is left to stand for approximately 4 hr in a well closed container.
   • Further menstruum is added to create a shallow layer above the mass, and the mixture is permitted to macerate in the closed percolator (for 24 hr)
   • The liquid contained is allowed to drip slowly by opening the outlet of the percolator.
   • Menstruum is added as desired, until the percolate measures about three-quarters of the desired volume of the final product.
   • The marc is then pressed and the obtained liquid is added to the percolate.
   • Marc is inert fibrous and other insoluble material remaining after extraction.

3. • Digestion:

   • It is a type of maceration in which mild heat (40-60oC) is applied.
   • It is used when moderately elevated temperature is acceptable.
   • It can be modified by mixing the material with the solvent using magnetic stirrer, mechanical stirrer or by shaking occasionally using hand.
   • The extract is filtered and fresh solvent is added after 8-12hrs.
   • The process is repeated until all the desired solutes are extracted.
   • It is used for the tougher plant parts or those that consist poorly soluble substances.

4. • Infusion:

   • The plant material is macerated in boiling water for a short period of time.
   • In this process, chemical compounds or flavours from plant material are siphoned in a solvent as water, oil or alcohol, by permitting the material to stay suspended in the solvent over a period of time.

5.  Decoction:

   • The crude plant material is boiled in a specified volume of water for a given time frame.
   • It is then cooled and strained or filtered.
   • Decoction time varies depending on the uniformity of the parts to extract.
   • It is suitable for extracting water soluble and heat stable constituents.
   • Decoctions are prepared for fresh purpose and shouldn’t be stored for more than 24 hours.
   • Decoction may be used to prepare herbal teas, leaf teas, coffees, tinctures and similar solutions.

Extraction with boiling solvents (Refluxion):

• The plant material is treated with boiling solvent and hence is a hot extraction process.
  The solvent vapor is recycled by a condenser fitted on top of the container, preferentially a round bottomed flask.

1.  Hot Continuous Extraction (Soxhlet):
   • It is named after ‘Franz Ritter von Soxhlet’, a German agricultural chemist.
   • It is the convenient method for the continuous extraction of a solid by a hot solvent.
   • In this process, the transfer of partially soluble components of a solid to the liquid phase takes place using a Soxhlet extractor.
   • The finely ground crude plant material is placed in a thimble, which is made of strong filter paper that allows liquid to pass through and is placed inside the Soxhlet apparatus.
   • The apparatus is then fitted to a round bottomed (RB) flask containing the solvent and to a reflex condenser.
   • The solvent in the RB flask is boiled mildly.
   • The vapor passes up through the side tube, gets condensed by the condenser and falls into the thimble containing the material and slowly fills the Soxhlet.
   • When the solvent reaches the top, it extracts over into the flask, removing portion of the substance which it has siphoned and the process repeats.
   • After extraction, solvent is eliminated by means of a rotary evaporator, resulting extracted compound.
   • The non-soluble portion of the extracted solid stays in thimble and is usually relinquished.
   • Advantages:
   • Large amount of drugs can be extracted with much smaller quantity of solvent.
   • More economical and feasible on medium or large scale.
2. • Steam Distillation:
   • It is used for the separation of essential oil from crude plant material.
   • Simple vaporization is gained by passing steam directly through the material.
   • The steam vaporizes the plant material’s volatile compounds which finally pass through a condensation and collection process.
   • Since water and oil do not mix in collection process, the essential oil floats on top of the water and it is extracted off.
3. • Hydro Distillation:
   • It is used instead of steam distillation.
   • The plant material is soaked in water and boiled by use of heating mantle.
   • Due to the impact of hot water, the essential oil is freed from the oil glands in the plant tissues and passed along with the steam.
   • In a typical glass apparatus known as Clevenger apparatus, the steam oil mixture is condensed and oil is separated from water and the condensed water is recycled.
4. • Enfluerage:
   • It is used for the extraction of delicate fragrances as that of some flowers.
   • The flower petals are spread over a layer of refined fat which picks up the odour of the flowers.
   • The saturated fat is handled with a solvent, usually alcohol in which the fragrant components are soluble.
   • The residual fat dissolved in alcohol may be eliminated by cooling the alcohol extract to 20oC, when fat separates out.
   • The volatile components are then retrieved from alcohol by concentrating the solution at reduced pressure in a rotavapor.

• Supercritical Fluid Extraction (SFE):

• Critical point represents the conditions above which distinct liquid and gas phases do not exist, but a homogenous supercritical fluid state exists.
• Supercritical fluid is obtained by heating above the critical temperature and compressing above the critical pressure and has the properties of a liquid as well as that of a gas.
• Alternative method with reduced use of organic solvents and increased sample throughput.
• Most commonly used supercritical fluid is CO2 .
• The lower viscosities and higher diffusion rates of supercritical fluids compared to liquids amplifies the extraction process.
• It is non inflammable, chemically inert, odour free, easy for disposal and economical with high purity and also can be recycled.
• Other gases such as ethylene, ethane, propylene, propane and nitrous oxide can also be used.
• High pressure carbon dioxide can be applied in place of various traditional organic solvents and steam distillation.
• Above 1100 psi and 31.70C, carbon dioxide reaches in “supercritical region.”
• Under these conditions, it has the solvating power of a liquid and the diffusion property of a gas.
• Carbon dioxide, being a supercritical fluid is a superior solvent for the extraction of a wide variety of natural products.
• This technique has been in use in industry for decaffeination of coffee and the removal of nicotine from tobacco.
• It is a more efficient method for the extraction of taxol and baccatin from the Yew tree.
• The major advantage is the implementation of mild conditions, which avoid the risk of thermal degradation compared to distillation and solvent extraction.

• Ultrasonic Extraction:

• It involves the use of ultrasound with frequencies ranging from 20 kHz to 2000 kHz.
• It increases the porosity of cell walls and produces cavitation.
• Ultrasound aided extraction can be used with mixtures of immiscible solvents such as hexane with methanol/water.
• In cases where the process creates heat, the extraction container is placed in ice bath to prevent heat labile compounds from decomposition.

• Microwave Assisted Extraction:

• Microwaves are electromagnetic radiations with the frequency range 0.3 to 300 GHz.
• It is made up of two oscillating perpendicular fields: electrical field and magnetic field.
• They can be used as information carriers or as energy vectors.
• Ionic conduction and dipole rotation in both the solvent and the sample which efficiently changes microwave energy to thermal energy.
• If the solvent selected has a high dielectric constant it strongly absorbs the microwave energy.
• However, in some cases, only the sample matrix may be heated, so that the solutes are freed in a cold solvent to avoid the degradation of thermolabile compounds.
• Microwave energy is applied to the sample suspended in solvent, with short intervals of cooling time.
• It’s merits include e.g., shorter extraction time, less solvent, higher extraction rate and lower cost.