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 Table of Contents  
REVIEW ARTICLE
Year : 2021  |  Volume : 7  |  Issue : 1  |  Page : 14-20

Detailed understanding of different extraction methods for the research on medicinal plants


1 Department of Public Health Dentistry, JSS Dental College and Hospital, JSS Academy of Higher Education and Research, Mysore, Karnataka, India
2 Department of Pediatric and Preventive Dentistry, JSS Dental College and Hospital, JSS Academy of Higher Education and Research, Mysore, Karnataka, India
3 Department of Oral Medicine and Radiology, JSS Dental College and Hospital, JSS Academy of Higher Education and Research, Mysore, Karnataka, India
4 Department of Pharmacognosy, JSS College of Pharmacy, JSS Academy of Higher Education and Research, Mysore, Karnataka, India
5 Department of Microbiology, JSS Medical College and Hospital, JSS Academy of Higher Education and Research, Mysore, Karnataka, India

Date of Submission04-Feb-2021
Date of Acceptance24-Feb-2021
Date of Web Publication12-Jul-2021

Correspondence Address:
Dr. Brinda Suhas Godhi
Pediatric and Preventive Dentistry, JSS Dental College and Hospital, JSS Academy of Higher Education and Research, Mysore - 570 015, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijohr.ijohr_3_21

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  Abstract 

Medicinal plants have to be prepared for experimental purposes and this is the first and foremost step toward attaining an excellent aftermath. The first crucial step in the preparation of plant formulations before proceeding with the planned biological testing is extraction. Research on medicinal plants begins with the preextraction and the extraction procedures, which are essential steps in the processing of the bioactive components from the plant materials. At the level of small manufacturing enterprises or in the small research settings, the conventionally applied methods of extraction are Soxhlet and Maceration. Considerable and remarkable progressions oriented to amplify the yield at an economical rate have been formed in the way medicinal plants are processed such as the modern extraction techniques and microwave-assisted, ultrasound-assisted extraction, and supercritical fluid extraction. In addition to this, modifications on the techniques are constantly evolving. The selection of an apt extraction method depends on numerous factors such as the type of the plant material, the nature of solvent, solvent pH, temperature, and the ratio of solvent to sample. With such a variety of methods available, the selection of correct and accurate extraction method requires systematic evaluation. The primary objective of this study is to describe the principle, strength, and limitation of the several methods employed in the process of medicinal plant extraction in our day-to-day research which would help in the selection of an appropriate method.

Keywords: Aqueous alcoholic extraction, maceration, medicinal plants, methods, microwave-assisted Soxhlet extraction, supercritical-fluid extraction, ultrasound-assisted extraction


How to cite this article:
Rudraswamy S, Godhi BS, Shankar HP, Kenganora M, Sumana M N. Detailed understanding of different extraction methods for the research on medicinal plants. Indian J Oral Health Res 2021;7:14-20

How to cite this URL:
Rudraswamy S, Godhi BS, Shankar HP, Kenganora M, Sumana M N. Detailed understanding of different extraction methods for the research on medicinal plants. Indian J Oral Health Res [serial online] 2021 [cited 2021 Sep 28];7:14-20. Available from: https://www.ijohr.org/text.asp?2021/7/1/14/321120


  Introduction Top


Plant as a medicinal source is gathering global fame. This is due to its natural origin, easy obtainability in aboriginal communities, affordability, easy administration, and perhaps less discomforting, decreased drug resistance, and reduced side and adverse effects. A plant comprising of ingredients that are active or metabolites that possesses biological activity, also called secondary metabolites, is referred to as a medicinal plant. A complete plant may be active medicinally or a part(s) of the plant may be medicinally active.[1],[2],[3] Herbal medicines are preparations consisting of active ingredients that are acquired from either the total plant or a part of it. Compounds made from by-products such as oils, gums, and other secretions of the plant are also deemed as herbal medicine.[1],[2],[3] Herbal medicine can be applied as an alternate choice in the treatment plans in case of several side effects and in the resistance of various drugs.[1],[4],[5],[6],[7] Common sugars, proteins, amino acids, and chlorophyll form the nutritional components and make up the primary plant constituents. These components have minimal or absolutely no medicinal properties. The secondary metabolites or secondary plant constituents include alkaloids, saponins, terpenoids, flavonoids, phenolic compounds, and tannins. These metabolites account for several of the biological and/or pharmacological properties.[2],[3]

The segregation of the medicinally active parts of the plant or tissues of the animals from the inactive or inert elements through employing particular solvents in standard extraction procedures is termed as extraction. The derivatives so procured from the plants are mostly impure and unrefined powders, semisolids or liquids, meant solely for the external or oral use. These composed of compounds called as infusions, decoctions, fluid extracts, powdered extracts, semisolid extracts, and tinctures. These compounds are extensively known as galenicals, after Galen, a Greek physician.[8] Standardized extraction techniques for crude drugs are useful in achieving the curative desired elements and in eradication of the inert compounds by treating it with a particular and specific solvent called menstruum. Menstruum is a suitable liquid solvent selected for an effectual extraction procedure. The inert and insoluble drug substance that is remaining after the extraction procedure is termed as Marc.[5],[6]


  Parameters to be Considered before Extraction Top
[8]

  1. Verification and substantiation of the plant material is mandatory before performing the extraction and any foreign material such as soil, sand, stones, glass, dust, metal, and plastic. The absence of visible signs of contamination by molds, insects, animal, including excreta should be examined and be completely eliminated
  2. Record the geographic location, plant age, time of collection, season, locus of collection, and part of the plant for quality control purposes
  3. Use of the right plant part
  4. The composition of the chemical constituents of the plant material largely influences the drying process. Drying by cold or hot blowing air flow is usually preferred. In a situation wherein a high moisture containing crude drug is used, then the appropriate corrections in weight are to be employed
  5. Procedures that produce heat need to be prevented as practically as achievable for the grinding procedure and the method employed should be specified
  6. Appropriate sieves should be used to pass the powdered plant material through it to get the necessitated uniform-sized particles.


Schematic representation of the mechanism of extraction involving the penetration of the solvent into the plant cells and swelling of the cells and diffusion of the dissolved extractive substances out of the cell [Figure 1].
Figure 1: Schematic representation of the mechanism of extraction

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  Methods of Extraction of Medicinal Plants Top


There are numerous techniques that can be applied in the procedure of extraction of medicinal plants. Some recent, cutting edge approaches are still developing and the prevailing ones are undergoing variations and revisions.[5],[7] The selection of an appropriate method of extraction is crucial, thus the factors that influence this procedure need to be elaborated upon.[5],[8],[10]

  1. Nature of constituents


    1. Solvent nature. If water is the chosen solvent for the extraction, then the preferred method is maceration. Soxhlet method of extraction is used in the case of volatile solvent percolation. In case the therapeutic value resides in the nonpolar components, a solvent that is nonpolar in nature can be utilized
    2. For thermolabile constituents, extraction techniques such as cold maceration, percolation, and counter-current extraction are suitable. If the constituents are thermostable, the solvent used is nonaqueous, Soxhlet extraction is preferred, and in the case of water being the menstruum, decoction is used
    3. Appropriate preventive measures are required while using components that break down when kept in organic solvents, like phenyl propanoids and flavonoids
    4. When hot extraction is employed, higher than essential temperature is to be prevented. On the continuous exposure of high temperature, certain glycosides have the potential to degrade.


  2. Cost of drug - Maceration extraction method is preferred for low priced drugs, and percolation is used as an extraction method for costly drugs
  3. Duration of process of extraction - Plant material that demand longer exposure to menstruum is extracted using maceration, whereas for shorter period of exposure, methods like microwave or ultrasound-assisted extraction are preferred. The time of extraction has to be standardized, because partial extraction can occur if the time is insufficient, and if the duration of extraction time is longer then undesirable constituents may end up being extracted. The total aggregate of extractions needed for the completion is equally crucial as the length and duration of each extraction
  4. Final volume required - Soxhlet extraction is used in the preparation of concentrated products, whereas maceration is useful in the preparation of large volume compounds such as tinctures
  5. Intended use - Maceration is the method proposed for extracts that are to consumed by humans and product that are designed for testing in the experimental procedures are made by utilizing different techniques in augmentation to maceration.


Commonly used methods in the extraction of medicinal plants [Figure 2].[9]
Figure 2: Schematic representation of the various methods of extractions. (a) Percolation. (b) Soxhlet extraction. (c) Ultrasound-assisted extraction. (d) Supercritical fluid extraction (e) Microwave-assisted extraction. (f) Phytonics process

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Maceration

In this method, the whole or granular powdered crude drug along with the solvent is kept in a stoppered container. This is permitted to remain at the room temperature for approximately 3–7 days with repeated mixing till the soluble matter is dispersed. The mixture is filtered to obtain the marc (damp solid material), which is then pressed. After a period standing, the combined liquids obtained are refined through filtration or decantation. This technique is appropriate and convenient for the plant material that is thermolabile.[8],[10],[11]

Merits

  • Skilled operator not required
  • For substances that require only extended contact time with solvent and that are minimally soluble in solvent
  • For low priced drugs and less potent drugs.


Demerit

  • Time-consuming and incomplete extraction.


Infusion

This process is similar to that of maceration wherein the drug material is pounded and powdered to form a minute powder after which it is placed into a sterile holder. The drug compound is soaked in either hot or cold solvent for a small-time duration. This technique is useful in the extraction of readily soluble bioactive components. Fresh extract for immediate use can be prepared using this method. Depending on the planned purpose, the ratio of solvent to sample can either be 4:1 or 16:1.[4],[5],[6],[10]

Digestion

In this method, gentle heat is applied during the extraction. The preferred solvent and powdered drug compound is added into a sterile holder. This combination is then put into a water bath or into an oven that is heated to a temperature of nearly 50°C. The viscosity of extraction solvent is reduced by continuously heating it throughout the procedure of extraction, and this also helps increase the elimination of the secondary plant constituents. It is employed when moderately high heat is not unacceptable. The solvent effectiveness of menstruum is thus enhanced. This technique is preferred for plant materials that are readily soluble.[4],[6],[8],[10]

Decoction

The crude drug is boiled in a specific quantity of water for a set amount of time. This is later cooled and then strained or filtered. This method is appropriate in the extraction of water soluble and heat stable components. Ayurvedic extracts called “quash” or “kawath” are usually prepared using this method. The ratio of crude drug to water is kept constant in the start, for example, 1:4 or 1:16; after which the volume is reduced to one fourth the original by the process of boiling during this extraction technique. The obtained concentrated extract is filtered and can be used as it is or can be further processed. This method of extraction is apt for water soluble and heat stable plant material.[8],[10]

Percolation

This technique is most commonly used in the extraction of active constituents in the making of fluid extracts and tinctures. The extract is obtained by the continual displacement of the solvent downward through a crude drug material bed. This is achieved by the use of a percolator which is a narrow, cone-shaped vessel that is open at both the ends. Specified and suitable amount of menstruum is used to dampen the solid constituents, which is then permitted to remain in the same position for about 4 h in a tight container. The percolator top is closed after the mass is packed into it. Supplemental menstruum is introduced to form a shallow layer on top of the mass. This mixture is allowed to macerate in the closed percolator for at least 24 h. The liquid contained in the percolator is permitted to drip slowly from its outlet once it is opened. Extramenstruum is introduced as needed, till the percolate amounts to nearly three fourths of the mandatory quantity of the attained compound. The expressed liquid formed after pressing the marc is added to the percolate. Additional menstruum is used to produce the needed volume, and this mixture is refined by either the process of filtration or by standing that is followed by decanting.[5],[6],[8],[10]

Merits

  • Short time and more complete extraction
  • Thermolabial constituents can be extracted
  • Useful in the extraction of highly priced drugs and potent drugs.


Demerits

  • Requirement of skilled operator
  • Attention to material particle size is required throughout the whole process.


Soxhlet extraction

This technique is also referred to as the continuous hot extraction. The equipment used is called the Soxhlet extractor that is fabricated of glass. It comprises of a round bottomed flask, siphon tube, extraction chamber, and condenser at the top. A porous bag (thimble) fabricated of a clean cloth or strong filter paper containing dried, ground, and finely grinded plant material is positioned inside it and tightly closed. The solvent to be used in the extraction process is dispensed into the bottom of the flask, and the thimble is placed into the extraction chamber. The solvent is heated from the bottom flask, which then evaporates and goes through the condenser. Here, it condenses and streams to the extraction chamber and extraction of the drug occurs by the solvent coming in contact with it. Therefore, when the solvent level in the chamber reaches the top of the siphon, the solvent and the material that has been extracted, flow back into the flask. The entire process continues constantly till the drug is extracted completely. This occurs when the solvent flowing from extraction chamber does not leave any remnants. The benefit of this method, when equated to the methods described antecedently is that extraction of copious quantity of drug can be done with a much lower amount of solvent. This affects the economy incredibly in terms of time duration, energy, and subsequently financial intake. In small scales, it is used as a batch process. In medium large scale, it becomes more cost-effective and viable when it is converted to a continuous extraction process. This technique is apt for the plant compound that is partly soluble in the selected solvent and for plant compounds with insoluble contaminants. However, it is not an appropriate technique for thermolabile plant compounds since consistent shaking is not possible.[8],[10],[12],[13]


  Aqueous Alcoholic Extraction by Fermentation Top


This is a method of fermentation for the extraction of active principles is used in Ayurvedic preparation like asava and arista. The procedure includes soaking of the crude drug, either as a decoction; also called kasaya; or a powder, for definite time duration, throughout which it undergoes fermentation resulting in alcohol production in situ. This enables the active component extraction confined in the plant material. The alcohol produced functions as a preservative. A new earthen vessel should not be used for carrying out fermentation. Water should priorly be boiled in the vessel. Porcelain jars, wooden vats, or metal vessels can be used in the large-scale manufacture instead of earthen vessels. Karpurasava, kanakasava, and dasmularista are a few representatives of such preparations. This method is not standardized in Ayurveda yet, but with the exceptionally high improvement levels in fermentation technology, it should not be too hard in the standardization of this method for the development of herbal drug extracts.[8]

Counter-current Extraction

In this technique, wet raw substance is pulverized with toothed disc disintegrators to generate a fine slurry. The compound is shifted in one direction (usually in fine slurry form) inside the cylindrical extractor where it mixes with the extraction solvent. The concentration of the extract increases as the starting material moves further. Total extraction is hence achievable when the amounts of solvent, material, and their rate of flow are optimized. The method is incredibly efficacious, less time-consuming and offers no risk from high temperatures. Eventually, adequately concentrated extract is released at one end of the extractor while the marc (more or less devoid of visible solvent) is released from the opposite end.[8]

This method has substantial merits:

  1. Smaller volume of solvent is required for the extraction as compared to other extraction processes such as percolation, decoction, and maceration
  2. CCE is generally performed at room temperature, which preserves the thermolabile components against heat exposure that is applied in other methods
  3. The heat produced during disintegration is counteracted by water as the drug pulverization is performed under wet conditions. This additionally preserves the thermolabile components from heat exposure
  4. This procedure has been evaluated to be more efficacious and efficient than continuous hot extraction.


Microwave-assisted extraction

This is regarded as one of the ingenious extraction procedures in medicinal plant preparation. This method is based on the mechanism of dipole rotation and ionic transfer by displacement of charged ions that are found in the solvent and drug material. This technique is apt for flavonoid extraction. It comprises of the application of electromagnetic radiation in between frequencies of 300 MHz and 300 GHz and wavelength of 1 cm and 1 m. When the microwaves were applied at a frequency of 2450 Hz, they yielded energy between 600 and 700 W. The method uses microwave radiation to bombard and strike an object, which then absorbs the electromagnetic energy and transforms it into heat. Thereafter, the heat generated promotes the solvent movement into the matrix of the drug. When polar solvent is used, there is occurrence of dipole rotation and migration of ions, increasing the penetration of solvent and assisting in the process of extraction. However, when nonpolar solvent is employed, a small amount of heat is generated from the released microwave radiation; thus this technique does not favor the use of nonpolar solvents. Microwave-assisted extraction has superior benefits like reducing the quantity of solvent and duration of extraction and increasing the final yield. This technique is appropriate only for flavonoids and phenolic compounds. Compounds like tannins and anthocyanins may degenerate because of the involvement of high temperature.[1],[4],[14],[15]

Ultrasound-assisted extraction

The extraction process applies the mechanism of ultrasound waves, that have frequencies >20 kHz, that influence a greatly on the yield of extraction and kinetics. In this process there is disintegration of the plant cell which increases the surface area of the drug for solvent penetration. As a result, there is a release of secondary metabolites. In this technique, plant material is dried, ground and properly sieved. This preparation is mixed with suitable solvent and packed into an ultrasonic extractor. The high sound energy applied hastens the process of extraction by decreasing the requirement of heat. Ultrasound-assisted extraction is applicative to small samples. It decreases the time required for extraction, the solvent volume used, and increases the yield. This technique is challenging to reproduce. Also, the high energy amount used may degrade the phytochemicals by generating free radicals.[5],[6],[14]


  Supercritical Fluid Extraction Top


Each substance has a critical temperature (Tc) and pressure (Pc) beyond which no applied pressure can force the substance into its liquid phase. If both the temperature and pressure of a substance are greater than the Tc and Pc for that particular substance, it is referred to as a supercritical fluid.

Supercritical fluid extraction (SFE) is another sample preparation method with over-all goals of decreased use of organic solvents and improved output of sample. The factors that influence this method include pressure, temperature, sample volume, modifier (co-solvent) addition analyte collection, restrictors, and flow and pressure control. Usually, cylindrical extraction vessels are used for SFE and its performance is satisfactory without any doubt (Handa et al. 2008).

Collecting of the extracted analyte following SFE is a significant step: substantial analyte loss can happen during this step, guiding the predictor to assume that the actual efficacy was unsatisfactory.

Numerous benefits of using CO2 as the extracting fluid have been observed. In addition to the favorable physical properties of carbon dioxide, it is also economical, harmless and in abundance. Although carbon dioxide is the chosen fluid for SFE, it commands a number of polarity constraints. Solvent polarity is crucial during extraction of polar solutes and when there is presence of strong analyte-matrix interactions. Organic solvents are often introduced to the carbon dioxide extracting fluid to mitigate the constraints of the polarity. In recent times, carbon dioxide is substituted by argon due to argon being economical and inert. The constituent recovery rates normally amplify with increasing pressure or temperature. The highest rates of recovery are obtained at 500 atm and 150°C in case of argon.

This method has significant advantages:

  1. Damage to the organic solvents from heat is avoided as extraction is done at low temperatures
  2. Negligent residues from solvent
  3. Eco friendly process.


The maximum region of growth in the advancement of SFE has been the speedy expansion of its operations. SFE finds widespread use in the extraction of environmental samples, fragrances, pesticides essential oils, foods, polymers, and natural products. The predominant obstacle in the application of the extraction technique in the mass market is its high-priced capital investment.[8]


  Phytonics Process Top


This technique utilizes a hydrofluorocarbon-134a based new solvent, and a novel technology to optimize its astounding properties in the extraction process of plant materials. This offers considerable environmental benefits and health and safety advantages done traditional processes for the production of high-quality natural fragrant oils, flavors, and biological extracts. This patented technology termed “phytonics process” has been established by Advanced Phytonics Limited (Machester, UK). The products extracted by this process are fragrant constituents of essential oils and biological or phytopharmacological extracts which can be used forthrightly without any further physical or chemical treatment.[8]

The attributes of the new generation of fluorocarbon solvents have been applicative in the extraction of plant materials. 1, 1, 2, 2-tetrafluroethane, also called as Hydrofluorocarbon-134a, makes up the solvent core. This product was developed as a replacement product for chlorofluorocarbons. The boiling point of this is −25° C. It is noninflammable and is nontoxic. It does not deplete the ozone layer when compared with chlorofluorocarbons and has a vapor pressure of 5.6 bar at ambient temperature. This is a poor solvent, it does not mix with mineral oils or triglycerides, and it does not dissolve plant wastes.

This technique is beneficial because the solvents can be adjusted and customized. The process can be made highly selective by using modified solvents with HFC-134a to extract a certain class of phytoconstituents. Correspondingly, other solvents can be used to extract a broader extent of constituents. The biological products made by this process have substantially low residual solvent. The residuals are perpetually <20 parts/billion and are usually below the detection levels. These solvents are neither acidic nor alkaline, and hence, have minimum potential reaction effects on the botanical materials. The processing plant is completely sealed. This facilitates continual recycling of solvent and recovery of the same at the end of each cycle of production. Electricity is the only utility needed to operate these systems. Even then, these systems do not require a lot of energy. There is no chance for the solvents escaping, and even if they do, they do not contain any chlorine which prevents ozone layer damage making them ecofriendly. The waste biomass from these plants is dry.[8]

Merits of the process

  • The phytonics process is casual and mild, and the products are not destructed by high temperature or temperature higher than the ambient. This advantage differentiates it from the other processes
  • No vacuum stripping is required which prevents the loss of precious volatiles.
  • The products do not undergo acid hydrolysis or oxidation as the procedure is performed at neutral pH and in the absence of oxygen
  • The technique is highly selective, extending a choice of operating conditions and thus giving a choice of end products
  • It is an environmental friendly procedure
  • Minimal electrical energy required
  • No deleterious emissions are released into the surrounding environment and the resultant waste products (spent biomass) are harmless and have no effluent disposition problems
  • The solvents employed in this process are noninflammable, nontoxic, and nonozone depleting
  • Complete recycling of solvents in each production cycle.


Applications

The phytonics process can be used as a method of extraction in the biotechnological industry (e.g., antibiotic production and manufacturing), in the herbal drug industry, in the food and flavor industry, essential oils industries, and in manufacturing of other pharmacologically active products. In general, this process finds its application in the production of top-class pharmaceutical-grade extracts, pharmacologically active intermediate compounds, antibiotic extracts, and phytopharmaceuticals. Nevertheless, this process can be used in other areas also apart from the aforementioned. The technique is also being employed in the extraction of high-quality essential oils, oleoresins, natural food coloring, flavoring, and aromatic oils from numerous types of plant materials. In addition to these areas of application, this processes also used in the refinement of crude products acquired from other extraction sources. Extraction is completed without waxes or any other contaminants. It helps in the removal of many biocides from the contaminated biomass.


  Conclusion Top


Extensive research has been performed on medicinal plants to either investigate and explore and validate a reported claim of biological activity or to imitate its traditional medicinal properties based on ethnomedicinal survey. A number of medicinal plants have been extracted successfully. In addition to this, the compounds that were acquired were tested for biological or pharmacological activity. In most of the cases, they were found to be active. Nevertheless, the exactitude in the selection and proper execution of extraction methods determines the success rate and authenticity of the findings. Hence, correct and thorough knowledge and implementation of the procedures are integral and crucial. Advancement and upgradation of these techniques consistently will facilitate research and enhance the final end result.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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