KERALA AGRICULTURAL UNIVERSITY
AROMATIC AND MEDICINAL PLANTS RESEARCH STATION, ODAKKALI
EXTRACTION AND UTILISATION OF MEDICNAL PLANTS
Medicinal principles are present in different parts of the plant like root, stem, bark, heartwood, leaf, flower, fruit or plant exudates. These medicinal principles are separated by different processes; the most common being extraction. Extraction is the separation of the required constituents from plant materials using a solvent. In the case of medicinal plants, the extraction procedure falls into two categories (Paroda, 1993).
a) Where it is sufficient to achieve within set limits equilibrium of concentration between drug components and the solution. Eg. Tinctures, decoction, teas, etc.
b) Where it is necessary to extract the drug to exhaustion, ie., until all solvent extractables are removed by the solvent.
Both the methods are employed depending on the requirement although in industry the latter method is mostly used. In all industrial procedures, the raw material is pre-treated with solvent outside the extractor before changing the latter. This prevents sudden bulk volume changes (which are the main cause of channelling during extraction) and facilitates the breaking up of the cell walls to release the extractables. To facilitate the extraction, the solvent should diffuse inside the cell and the substance must be sufficiently soluble in the solvent. The ideal solvent for complete extraction is one that is most selective, has the best capacity for extraction and is compatible with the properties of the material to be extracted. These parameters are predetermined experimentally. The cost and availability of the solvent are also taken into account. Alcohol, though widely used, because of its great extractive power it is often the least selective, in that it extracts all soluble constituents. Alcohol in various ratios is used to minimise selectivity. The ideal alcohol ratio for woody or bark material is 75%. For leafy material, it is often less than 50% thus avoiding extraction of the chlorophyll which makes purification difficult.
Some materials such as alkaloids being soluble in acids, their extraction is facilitated by adjusting the pH in the acidic range. A number of alkaloids can be extracted easily with hydrocarbons after they have been released from combination with organic acids by grinding with alkali. It is first ground with moist calcium oxide and extracted with chloroform. A large number of alkaloids can be extracted directly with aqueous acids, organic or inorganic acids, and the alkalised extracts counter extracted with hydrocarbons or other apolar solvents.
Experiment used for extraction with solvents usually comprise an extraction vessel with a heating jacket for steam heating or fitted with electrical devices, a condenser in reflux position, a solvent reservoir, a facility to convert to reboiler position or a separate reboiler and a short column for solvent recovery. Some times, sophisticated and costly equipment like the Carousel or the Inoxa extractor is employed.
Technology for the manufacture of standardised extracts and phytochemicals is available and there are many extracts already in the international market as drugs. A drug such as an extract of Centella asiatica can be manufactured as an extract containing a standard quantity of asiaticoside. Similarly for senna a standardised extract of which, containing a standard quantity of sennosides a and b could easily be produced with equipment that can be designed and constructed in most developing countries (Wijesekera, 1991).
The promotion and development of processing of medicinal and aromatic plants have gained momentum recently in many developing countries. Green consumerism and resurgence of interest for plant based products, liberalised and free market economy, increasing awareness about biodiversity conservation and sustainable use of natural resources coupled with poor socio-economic conditions of native populations are ground realities for planning and harnessing the low-cost and purpose oriented process technologies.
UNIDO has developed a Polyvalent Pilot Plant with a view to enabling developing countries to upgrade their technology for the processing of medicinal and aromatic plants. This plant incorporates all salient features of a low cost, efficient, small capacity factory which can carry out solvent extraction, solvent percolation, concentration of miscella, solvent recovery, steam distillation and oil separation (UNIDO, 1991; Silva, 1997). The design and fabrication of the process equipment need not be over emphasised, as even if a good design is available for adaptation, it must be done to fit the given situation.
The polyvalent plant is characterised by simplicity of design, installation, operation, maintenance and repair. Some of its features are
1. Modular construction so as to permit increase in capacity and function by duplicating or adding modules.
2. Simultaneous processing for more than one product, such as extraction at one end, production of solid extract or oleoresins at the other.
3. Standardised or optimised process control and measuring units, pumps and other ancillaries can be easily replaced.
4. All plumbing and electrical wiring are simple and easily accessible.
5. Multipurpose uses. Eg. Solvent/aqueous extraction, continuous extraction, preparation of solid extract and oleoresins, essential oil distillation, fractionation of essential oils and production of absolutes and concretes or even processing of other phytoproducts.
Formulation and Industrial Utilisation
Medicinal plants are used as raw materials for extraction of active constituents in pure form (eg. alkaloids like quinine and quinidine from cinchona bark, emetine from ipecacuanha root, glycosides from digitalis leaves, sennosides from senna leaves), as precursors for synthetic vitamins or steroids, and as preparations for herbal and indigenous medicines. Products such as ginseng, valerian and liquorice roots are part of the herbal and health food market, as well as the food flavours, fragrance and cosmetic industries. Certain plant products are industrially exploited like liquorice in confectionery and tobacco, papaine as meat tenderiser, quinine as soft drink tonic and cinchona as wine flavour. A large quantity of medicinal plant material is used in the preparation of herbal and medicinal teas, eg. chamomile. These herbal and food uses are of great importance, also to the exporters from developing countries. Hundreds of medicinal plants are items of commerce, however relatively small countries are used in formulated herbal remedies.
Several formulations like herbal teas, extracts, decoctions, infusions, tinctures, etc are prepared from medicinal plants (Kraisintu, 1997).
1. Herbal teas, Herbal remedies: herbal tea or infusion mixtures are mixture of unground or suitably ground medicinal plants to which drug plant extracts, ethereal oils or medicinal substances can be added. Infusion mixtures should be as homogenous as possible.
2. Drug extracts: They are preparations obtained by extracting drugs of a certain particle size with suitable extraction agents (menstrua). The extract obtained after separation of the liquid from the drug residue is called miscella. It may already represent the final liquid dose form eg. as a so called fluid extract, or be used as an intermediary product which is to be further processed as quickly as possible.
3. Aqueous drug extracts: The following degrees of comminution are used for the extract depending on the type of plant parts. Leaves, flowers and herbs shredded (4000mm); woods, barks and roots shredded (2800mm); fruits and seeds (2000mm). Alkaloid containing drugs powdered (700mm).
3.1. Decoctions: The drug in the prescribed comminution is put in to water at a temperature above 90°C. The container is suspended in a water bath and maintained at this temperature for 30 minutes, with repeated stirring. The mixture is then strained while still hot.
3.2. Infusions: One part of the comminuted drug is kneaded several times in a mortar with 3-5 parts of water and left to stand for 15 minutes. The rest of the boiling water is then poured on to the mixture, which is suspended in a container in a water bath and kept for 5 minutes, with repeated stirring at a temperature above 90°C. The mixture is covered and left to stand until cool.
3.3. Macerates: The comminuted drug is left to stand, with occasional stirring, for 30 minutes after the required quantity of water has been poured on to it at room temperature. The extract is then strained and made up to the prescribed weight with rinsings.
3.4. Tinctures: Tinctures are extracts from drug plants prepared with ethanol of varying concentration, ether or mixtures of these, perhaps with certain additives, in such a way that one part of drug is extracted with more than two parts, but at most ten parts, of extraction liquid.
3.5. Fluid extracts: Like tinctures, they are liquid preparations, the difference being that they are more concentrated.
3.6. Dry extracts: They are usually very hygroscopic and should therefore be ground and mixed under conditions which exclude moisture as much as possible. Intermediate and end product must also be stored under dry conditions.
There are also liquid, semisolid, solid and controlled release formulations or preparations. The other dose forms are injections, implants, ocular preparations, inhalations and transdermal systems. Liquid formulations may be solutions, emulsions, colloids or suspensions in the increasing order of particle size. They may be intended for administration parenterally, orally or topically including administration into body cavities. Homogeneity for the formulations is very important, particularly where the active ingredient is present in lower concentration.
A generalised production scheme include the following (Kraisintu, 1997):
1. Pre-processing: Washing, particle size optimisation, moisture reduction, refinement or concentration.
2. Solublisation: Insolubles removal, product stabilisation.
3. Primary extraction: Primary contaminations removal.
4. Purification: Secondary contaminations removal, decolourisation, concentration, recemization
5. Derivatization (optional): Chemical modification.
6. Drying(optional): Lyophilization or spray drying
Compounding of drugs
According to the guidelines of formulations, a prescription is composed of four different component parts of ingredients as given below (Jiaxiang, 1997).
1. The principal ingredient which provides the principal curative action
2. The adjuvent which strengthen the principal action
3. The auxillary ingredient which relieves secondary symptoms or tempers the action of principle ingredient
4. The conductant which directs action to the affected conduit or site. It may also be a less significant auxillary ingredient.
The introduction of a polyvalent pilot plant has been the most significant contribution of UNIDO to the development of the industrial utilisation of medicinal and aromatic plants in developing countries. The gap that prevented the transfer of processes and products developed on a laboratory to industry can be bridged by introducing pilot plant processing facility and multidisciplinary teamwork. Many research and development institutions in developing countries lacked the support of their engineering counter parts and most research therefore was confined to academic pursuits. If one is to undertake commercial production of herbal medicines, the vital role played by chemical engineers in translating laboratory findings to industrial scale outputs through pilot scale process parameter development has to be recognised.
Developing countries need to build up technological and scientific capabilities to develop and improve the production of medicinal principles for use in their countries and to conduct R&D to develop products for export thereby, enabling countries to supply new markets which are being created as a result of consumer orientation of societies, increasing affluence and demand for green products. Sustainable use of this renewable natural resource will not only contribute to rural industrial development and poverty alleviation but also to biodiversity and forest conservation.
Requirement for plant based industries
Major requirements for establishing medicinal and aromatic plant based industries in developing countries are the following (Silva, 1997):
- Availability of natural forest resources capable of being sustainably harvested.
- Initiation of systematic cultivation programmes
- Selection of plants for processing based on facilities available and marketability
- Fabrication or procurement of equipment, provision of required services (water, energy, chemical)
- Transfer of expertise on agronomical practices, harvesting and post-harvest treatment.
- Training in methods of processing and quality control
- Actual processing with assistance from experts and NGO’s and international agencies
- Packaging and storage of finished products
- Marketing outlets
In some cases the primary processed product could be used as a raw material for downstream processing such as production of medicinal principles, aroma chemicals, isolates, flavours, perfumes, extraction of pure chemicals and other consumer products. The following aspects have to be taken into consideration in designing country specific programmes for implementation.
- Suitability of climate and soil conditions
- Availability of raw materials
- Economic benefit, if any from export as well as import substitution
- Factors that hinder systematic cultivation and industrial production.
- Appropriate technologies that could be absorbed
- Prospects for regional, inter regional and global co-operation
- Inter agency co-operation and collaboration
- Other issues such as conservation, energy, employment generation and involvement of women.
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