Medicinal Plant Extraction

• Extraction is removing active constituents from a solid or liquid using a liquid solvent.
• It separates the medicinally active parts of plant or animal tissues from inactive parts using selective solvents.
• Natural product extraction progresses through these stages: solvent penetration, solute dissolution, solute diffusion, and collection.

Key Terms

• Menstruum is the solvent used for extraction.
• Marc is the inert, insoluble material remaining after extraction.
• Galenical is a medicine prepared by extracting one or more active constituents from a plant.

Steps for Medicinal Plant Extraction

• Size reduction
• Extraction
• Filtration
• Concentration
• Drying

Solvents in Extraction

Water

• Water is a polar solvent that extracts polar compounds and is valuable for extracting proteins, coloring matter, gums, glycosides, sugars, alkaloid salts, enzymes, organic acids, and salts.
• Waxes, fats, oils, and most alkyl halides do not dissolve in water.
• Water is cheap, nontoxic, nonflammable, and highly polar.
• Water may dissolve undesirable substances, promote mold/bacterial growth (requiring preservatives), cause drug hydrolysis, and lead to fermentation.

Alcohol

• Alcohol is polar, miscible with water, and can extract polar secondary metabolites like alkaloids, glycosides, volatile oils, and resins.
• Alcohol does not dissolve albuminous matter, gums, waxes, fats, fixed oils, and sugars.
• No mold or bacterial growth with 20%+ concentration (self-preservative)
• Selective active constraint of drug
• It is costly, flammable, and volatile.

Chloroform

• Chloroform is a nonpolar solvent useful for extracting terpenoids, flavonoids, fats, and oils.
• Colorless, sweet smell, soluble in alcohol. Absorbed/metabolized in the body.
• Chloroform is sedative and carcinogenic.

Ether

• Ether is useful for extracting alkaloids, terpenoids, coumarins, and fatty acids.
• Ether is miscible with water and has a low boiling point and is tasteless.
• Ether is highly volatile and flammable.

Ionic Liquids

• Ionic Liquids are polar, heat stable, and miscible with water + other solvents.
• Excellent at attracting/transmitting microwaves + Non-flammable

Extraction Types (Classification)

• Extraction separates an organic chemical compound with a chemical solvent (menstruum).

Liquid-Liquid Extraction

• Liquid-liquid extraction separates liquid mixture components by contact with a suitable insoluble solvent that preferentially dissolves one or more components.
• Separation depends on unequal distribution of components between immiscible liquids.
• Feed solution is phase 1, extraction solvent is phase 2.
• Feed and solvent form a homogeneous mixture and one of the two liquids are separated out.
• This method is widely used for separating active and aromatic compounds from plants.

Solid Phase Extraction (SPE)

• SPE isolates, enriches, and purifies components from aqueous solutions based on physical and chemical properties.
• Aqueous samples contact a solid phase or sorbent, where the component is adsorbed before elution.
• The extract amount is negligible compared to the analyte in the sample.
• This type of extraction is used widely in analytical laboratories.

Solid-Liquid Extraction (SLE)

• Solid-liquid extraction removes constituents from a solid mixture using a liquid solvent to dissolve them.
• Leaching produces a concentrated solution of an active principle or frees an insoluble constituent from a soluble material.
• Examples include maceration, percolation, and supercritical fluid extraction.

Extraction Methods

• Maceration
• Percolation
• Decoction
• Digestion
• Infusion
• Soxhlet extraction
• Microwave assisted extraction
• Sonication extraction
• Accelerated solvent extraction
• Supercritical fluid extraction

Maceration

• Maceration involves soaking plant materials (usually powdered/coarse) in a stoppered container with a defined solvent.
• Incubation: The setup stands at room temperature (+25°C) for ≥72 hours with shaking.
• The process softens and breaks up the plant's cell wall to release soluble bioactive metabolites.
• Filtration with Whatman no. 1 filter paper is performed after 3 days .
• Heat transfer is by convection and conduction, and solvent choice determines the phytochemicals extracted.
• Convenient and suitable for thermolabile plant material.

Simple Maceration

• Place the crude organized drug in a closed vessel and fill with the volume of menstruum.
• Shake occasionally for 7 days
• Strain the drug, press the marc
• Mix expressed liquid and strained liquid and filter to remove insoluble cell content.
• Example: tincture of orange, tincture of lemon.
• Marc is pressed because considerable liquid adheres to it and the volume is not adjusted, because variable amounts of soluble matter can be left in the marc.

Modified Maceration

• Place the drug in a vessel and add 4/5 of the menstruum.
• Shake occasionally on days 2-7
• Decant the liquid, the marc is not pressed.
• Filter the liquid and add the remaining menstruum(1/5 part) to adjust the final volume
• Example: Tincture of tolu, compound tincture of benzoin, etc.
• The marc is not pressed because the desirable material is mostly dissolved and the remaining marc is gummy and slimy.

Percolation

• A narrow cone-shaped percolator vessel which is open at both ends is generally used.
• The solid ingredients get moistened with the set amount of menstruum and set aside for 4 hours in a closed container.
• The wet mass is packed and the top of the percolator is closed and extra menstruum is added to form a shallow layer above the mass.
• The mixture is allowed to macerate in the closed percolator for 24 hours.
• The outlet of the percolator is then opened and liquid contained is allowed to drip slowly.
• The percolate is mixed till it measures about three-quarters of the required volume.
• Properly prepared menstruum is added to produce the required volume, and any excess liquid is eliminated by filtration or by standing followed by decanting.

Decoction

• The harvested crude product is boiled in a specified volume of water for a defined period, cooled, then strained/filtered.
• Applicable for the extraction of water-soluble, heat-stable metabolites.
• The extract is concentrated to one-fourth of its original volume by boiling, filtered, and processed further.
• The decoction is suitable for extracting heat-stable compounds in hard plant parts such as roots and barks.
• Decoction gives more oil-soluble phytochemicals compared to maceration and infusion.

Digestion

• Digestion is a maceration method that includes the application of gentle heat during extraction when more of a raised temperature is needed to increase the efficiency of menstruum.
• In the process, the drug is extracted by heating at a particular pressure to increase the penetration power of the menstruum and there is complete extraction of the drug.
• The apparatus used is known as ‘Digestor' which is a vessel made of metal.
• The whole of the drug is placed in the covered digestor and bolted with the help of nuts.
• The drug is treated with menstruum for a definite period under specified condition of temperature and pressure.

Infusion

• Fresh infusions are prepared by macerating the crude drug for a short period with cold or boiling water.
• The drug is placed at the bottom of the pot, then add water/hot water and stirred three to four times, stand it for 15 min, filtering off the liquid without pressing the marc.
• Fresh infusion should be used within 12 hours after its preparation to avoid fungal and bacterial growth.
• Concentrated infusion is prepared by double/triple maceration processes and is 8 times stronger than fresh infusion.
• Alcohol(20-25% concentration) is used as a solvent and can be stored for a longer period of time.

Soxhlet Extraction

• The Soxhlet extraction is an automatic continuous extraction method with high extraction efficiency with requires less time and solvent consumption than maceration or percolation
• Utilizes the principle of reflux and syphoning to continuously extract the herb with fresh solvent; the method works when the menstruum has less penetration into the cellular tissue and active constituents are not readily extracted with a solvent.
• Fixed oil from seeds and alkaloids from drugs are extracted by soxhlet extraction process using benzene, chloroform and petroleum, ether, etc.
• The high temperature and long extraction time can increase the possibilities of thermal degradation
• Consists of: a flask (round bottom) containing the boiling solvent; a Soxhlet extractor for containing the drug; a condenser to condense the vapors of the solvent.

Soxhlet Procedure

• Finely ground crude drug is packed in a filter paper thimble in a Soxhlet extractor.
• The solvent is placed in the flask and boiled.
• Solvent vapors rise, condense, and drip into the extractor, dissolving the drug.
• When full, the extractor siphons the solvent back into the flask. It repeats until the drug is exhausted.
• Normally the process is repeated about 15 times for complete exhaustion of the drug.

Extraction Applications

• Antibiotic and protein recovery
• Recovering high-boiling components (phosphoric/boric acid, sodium hydroxide)
• Obtaining therapeutically active constituents from plant parts and to eliminate the inert material.
• Isolating enzymes (renin) and hormones (insulin) from animal sources.
• Gelatin production from skin/bone collagen treated with lime/diluted acid and warm water.
• Extraction of fixed oils from seeds.