Pharmacognosy: Conventional Extraction Techniques PDF

pharmacognosy Conventional extraction techniques Conventional extraction techniques Contents : Conventional extraction techniques 4 Maceration ( Cold Extraction ) 6 Hot Extraction Methods 11 Conventional extraction techniques Extraction efficiency of any conventional method mainly depends on the cho...

pharmacognosy Conventional extraction techniques Conventional extraction techniques Contents : Conventional extraction techniques 4 Maceration ( Cold Extraction ) 6 Hot Extraction Methods 11 Conventional extraction techniques Extraction efficiency of any conventional method mainly depends on the choice of solvents where the polarity of the targeted compound is the most important factor for solvent choice. Other factors that should be considered in the selection of solvent for extraction include molecular affinity between solvent and solute, mass transfer, use of co-solvent, environmental safety, human toxicity and financial feasibility. Conventional extraction techniques Conventional extraction techniques : Bioactive compounds from plant materials can be extracted by various classical extraction techniques. Most of these techniques are based on the extracting power of different solvents and the application of heat and/or mixing. The classical techniques include: 1. Soxhlet extraction. 2. Maceration. 3. Hydrodistillation. Conventional extraction techniques Extraction methods can be classified into cold and hot depending on whether the heat is applied ( if plant active constituents are heat stable) or not Conventional extraction techniques Maceration ( Cold Extraction ) : Maceration was used in homemade preparation of tonic from a long time. It became a popular and inexpensive way to get essential oils and bioactive compounds. For small scale extraction, maceration generally consists of several steps. Conventional extraction techniques Firstly, grinding of plant materials into small particle is used to increase the surface area for proper mixing with solvent. Secondly, in maceration process, appropriate solvent named as menstruum is added in a closed vessel. Thirdly, the liquid is strained off but the marc which is the solid residue of this extraction process is pressed to recover large amount of occluded solutions. Conventional extraction techniques The obtained strained and the press out liquid are mixed and separated from impurities by filtration. Occasional shaking in maceration facilitate extraction by two ways; A. increase diffusion. B. remove concentrated solution from the sample surface for bringing new solvent to the menstruum for more extraction yield. Conventional extraction techniques Conventional extraction techniques Advantages of Maceration : 1. Can be used for heat sensitive substances. 2. Easy and cheap. Disadvantages of Maceration 1. 1- Takes long time. 2. Large amount of solvent is required. 3. Non efficient. Conventional extraction techniques Hot Extraction Methods : 1. Infusion In this method the plant material is placed in a special container called infusion pot and a hot solvent is poured on it and cover the container with a lid containing sieves and left for a while then strained. 2. Decoction In this method the plant material is placed together with the solvent in a round bottom flask on a source of heat or direct flame. Conventional extraction techniques This method is usually used for hard plant materials like barks, stems and roots which contain a lot of fibers. 3. Digestion In this method the plant material is placed together with the solvent in a round bottom flask with the application of gentle heat which increases the solvent ability for extraction. Conventional extraction techniques 4. Soxhlet extractor : Soxhlet extractor was first proposed by German chemist Franz Ritter Von Soxhlet (1879). It was designed mainly for extraction of lipid but now it is not limited for this only. The Soxhlet extraction has widely been used for extracting valuable bioactive compounds from various natural sources. Conventional extraction techniques It is used as a model for the comparison of new extraction alternatives. Generally, a small amount of dry sample is placed in a thimble (which is made from cellulose). The thimble is then placed in the extractor which is placed on a round flask containing the solvent of particular interest and a cooling condenser is placed on the top of the extractor. Conventional extraction techniques Conventional extraction techniques The solvent is boiled and gets up to the condenser through a side tube, after condensation the solvent will drop on the thimble extracting the plant constituents. After reaching to an overflow level, the solvent in the thimble-holder (extractor) is aspirated by a siphon. Siphon unloads the solution back into the distillation flask. This solution carries extracted solutes into the bulk liquid. Solute is remained in the distillation flask and solvent passes back to the solid bed of plant. Conventional extraction techniques The process runs repeatedly until the extraction is completed. Soxhlet extractor or apparatus represents a closed system so it can be used for the extraction with dangerous organic solvents and in this method a small amount of solvent is required so it is economic; Another advantage of soxhlet extractor is that it can be used for the extraction of different active constituents by changing the solvent polarity and it is suitable method when the plant material is affected by direct heat Conventional extraction techniques 5. Reflex Extractor : In this method the plant material is placed together with the solvent in a round bottom flask which is attached to a condenser. The round bottom flask is placed on a source of heat; the heat is applied and when the solvent reaches its boiling points it will evaporate to the condenser where it condenses and returns back to the flask. Conventional extraction techniques This method has the same advantages as soxhlet extractor but the extract requires filtration and not suitable if plant material is affected by direct heat. Conventional extraction techniques Hydrodistillation: Hydrodistillation is a traditional method for extraction of bioactive compounds and essential oils from plants. Organic solvents are not involved and it can be performed before dehydration of plant materials. Conventional extraction techniques There are three types of hydrodistillation : 1. Water distillation. 2. Water and steam distillation. 3. Direct steam distillation. In hydrodistillation, first, the plant materials are packed in a still compartment; second, water is added in sufficient amount and then brought to boil. Alternatively, direct steam is injected into the plant sample. Conventional extraction techniques Hot water and steam act as the main influential factors to free bioactive compounds of plant tissue. Indirect cooling by water condenses the vapor mixture of water and oil. Condensed mixture flows from condenser to a separator, where oil and bioactive compounds separate automatically from the water. Conventional extraction techniques Hydrodistillation involves three main physicochemical processes; 1. Hydrodiffusion. 2. Hydrolysis. 3. Decomposition by heat. At a high extraction temperature some volatile components may be lost. This drawback limits its use for thermo labile compound extraction.