Extraction from Plant Samples

In this extraction from plant samples post we have briefly explained about different methods employed in extraction of plant material.

Extraction from Plant Samples

Quite numbers of procedures were technically used in the extraction of plant material. Some newer techniques are still evolving, whereas the existing ones are undergoing modifications. The choice of an appropriate way of extraction of plant material is very vital, which in some cases depends on the intended use of an extract.

Heat-stable plant material is extracted using Soxhlet extraction of plant material or microwave-assisted extraction of plant material, whereas plant materials that are not heat stable are extracted using maceration or percolation.

If the solvent of extraction of plant material is water, maceration is a suitable method but for volatile solvent percolation and Soxhlet extraction of plant material are more appropriate. Cheap drugs are extracted using maceration, whereas costly drugs are preferably extracted using percolation.

Maceration is suitable for plant material requiring long exposure to the menstruum, whereas techniques such as microwave- or ultrasound-assisted extraction are used for a shorter duration.

Large volume products such as tinctures are prepared by maceration, whereas concentrated products are produced by percolation or Soxhlet extraction. Extracts intended for consumption by human are usually prepared by maceration, whereas products intended for experimental testing are prepared using other methods in addition to maceration. 

Extraction of Plant Material

1. Maceration

In this process, the whole or coarsely 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 with frequent agitation until the soluble matter has dissolved. The mixture then is strained, the marc (the damp solid material) is pressed, and the combined liquids are clarified by filtration or decantation after standing.

2. Infusion

This is an extraction of plant material process such as maceration. The drug material is grinded into fine powder, and then placed inside a clean container. The extraction of plant material solvent hot or cold is then poured on top of the drug material, soaked, and kept for a short period of time. This method is suitable for extraction bioactive constituents that are readily soluble. In addition, it is an appropriate method for preparation of fresh extract before use. The solvent to sample ratio is usually 4:1 or 16:1 depending on the intended use.

3. Digestion

This is an extraction of plant material method that involves the use of moderate heat during extraction of plant material process. The solvent of extraction is poured into a clean container followed by powdered drug material. The mixture is placed over water bath or in an oven at a temperature about 50C. Heat was applied throughout the extraction of plant material process to decrease the viscosity of extraction of plant material solvent and enhance the removal of secondary metabolites. This method is suitable for plant materials that are readily soluble.

4. Decoctiona

This is a process that involves continuous hot extraction of plant material of plant material using specified volume of water as a solvent. A dried, grinded, and powdered plant material is placed into a clean container. Water is then poured and stirred. Heat is then applied throughout the process to hasten the extraction of plant material of plant material. The process is lasted for a short duration usually about 15min. The ratio of solvent to crude drug is usually 4:1 or 16:1. It is used for extraction of plant material of water soluble and heat stable plant material.

5. Percolation

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. The solid ingredients are moistened with an appropriate amount of the specified menstruum and allowed to stand for approximately 4 h in a well closed container, after which the mass is packed and the top of the percolator is closed.

Additional menstruum is added to form a shallow layer above the mass, and the mixture is allowed to macerate in the closed percolator for 24 h. The outlet of the percolator then is opened and the liquid contained therein is allowed to drip slowly. Additional menstruum is added as required, until the percolate measures about three-quarters of the required volume of the finished product. The marc is then pressed and the expressed liquid is added to the percolate. Sufficient menstruum is added to produce the required volume, and the mixed liquid is clarified by filtration or by standing followed by decanting.

6. Soxhlet extraction

This process is otherwise known as continuous hot extraction of plant material. The apparatus is called Soxhlet extractor made up of glass. It consists of a round bottom flask, extraction of plant material chamber, siphon tube, and condenser at the top. A dried, grinded, and finely powdered plant material is placed inside porous bag (thimble) made up of a clean cloth or strong filter paper and tightly closed.

The extraction of plant material solvent is poured into the bottom flask, followed by the thimble into the extraction chamber. The solvent is then heated from the bottom flask, evaporates, and passes through the condenser where it condenses and flow down to the extraction chamber and extracts the drug by coming in contact.

7. Microwave extraction

This is one of the advanced extraction of plant material procedures in preparation of medicinal plants. The technique uses mechanism of dipole rotation and ionic transfer by displacement of charged ions present in the solvent and drug material. This method is suitable for extraction of plant material of flavonoids. It involves the application of electromagnetic radiation in frequencies between 300 MHz and 300 GHz and wavelength between 1cm and 1 m.

The microwaves applied at frequency of 2450 Hz yielded energy between 600 and 700 W. The technique uses microwave radiation to bombard an object, which can absorb electromagnetic energy and convert it into heat. Subsequently, the heat produced facilitates movement of solvent into the drug matrix.

8. Ultrasound extraction

This process involves application of sound energy at a very high frequency greater than 20 KHz to disrupt plant cell all and increase the drug surface area for solvent penetration. Consequently, secondary metabolites will be released. In this method, plant material should dry first, grinded into fine power, and sieved properly. The prepared sample is then mixed with and appropriate solvent of extraction of plant material and packed into the ultrasonic extractor. The high sound energy applies hasten the extraction of plant material process by reducing the heat requirements.

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