Extraction of Active Medicinal Principles from Natural Sources
Session 14: Extraction of Active Medicinal Principles from Natural Sources
Total Session Time: 120 minutes
Prerequisites
Learning Tasks
By the end of this session students are expected to be able to:
Resources Needed:
SESSION OVERVIEW
|Step |Time |Activity/ |Content |
| | |Method | |
|1 |05 minutes |Presentation |Introduction, Learning |
| | | |Tasks |
|2 |10 minutes |presentation |Definition of terms |
|3 |05 minutes |Presentation |Types of extracts |
|4 |30 minutes |Presentation |Properties and types of |
| | |buzzing |solvents |
|5 |15 minutes |Presentation |Mechanism of Solvent |
| | | |Extraction |
|6 |05 minutes |Presentation |Factors affecting |
| | | |extraction |
|7 |40 minutes |Presentation |Methods of extraction |
| | |Small group Discussion| |
|8 |05 minutes |Presentation |Key Points |
|9 |05 minutes |Presentation |Evaluation |
SESSION CONTENTS
STEP 1: Presentation of Session Title and Learning Objectives (05 minutes)
READ or ASK students to read the learning objectives and clarify
ASK students if they have any questions before continuing.
STEP 2: Definition of terms (10 Minutes)
liquid by means of liquid solvent.
o The separation of medicinally active portions of plant or animal
tissues from the inactive or inert components by using selective
solvents.
o In this method the wanted components are dissolved by the use of
selective solvents known as menstrum & undissolved part is a marc,
after the extraction unwanted matter is removed.
contain all the constituents which are soluble in the solvent.
(solutes) without chemical changes.
o (The term “Solvents” refers to a class of chemical compounds described
by function – the term derives from Latin, meaning roughly to “loosen.”
In chemistry, solvents – which are generally in liquid form – are used
to dissolve, suspend or extract other materials, usually without
chemically changing either the solvents or the other materials
Step 3: Types of Extracts (05 minutes)
o Dry extract (Tab, cap.) E.g. belladonna extract
o Soft (Ointment, suppository) E.g. glycerrhiza extract.
o Liquid: As tincture.
STEP 4: Properties and Types of Solvents (30 minutes)
|Activity: Buzzing (10 minutes) |
| |
|DIVIDE students into small manageable groups |
| |
|ASK students to discuss on the following question |
| |
|What are types of solvents? |
| |
|ALLOW students to discuss for 15 minutes |
| |
|ALLOW few groups to present and the rest to add points not |
|mentioned |
| |
|CLARIFY and SUMMARIZE by using the contents below |
o Molecular structure of solvents
o Inorganic solvents
o Organic solvents
o Molecular structure of solvents, Ability of a substance to dissolve
another substance is determined by compatibility of their molecular
structures (like dissolves like).
o A polar protic molecule consists of a polar group OH and a non-
polar tail. The structure may be represented by a formula R-OH.
Polar protic solvents dissolve other substances with polar protic
molecular structure. Polar protic solvents are miscible with water
(hydrophilic).
Examples of polar protic solvents:
o Dipolar aprotic molecules possess a large bond dipole moment (a
measure of polarity of a molecule chemical bond). They do not
contain OH group.
Examples of dipolar aprotic solvents:\
o Electric charge in the molecules of non-polar solvents is evenly
distributed, therefore the molecules have low dielectric
constant. Non-polar solvents are hydrophobic (immiscible with
water). Non-polar solvents are liphophilic as they dissolve non-
polar substances such as oils, fats, greases.
Examples of non-polar solvents:
o The most popular inorganic (not containing carbon) solvents are
o water (H2O) and aqueous solutions containing special additives
(surfacants, detergents, PH buffers, inhibitors).
o Other inorganic solvents are liquid anhydrous
o Oxygenated solvent is an organic solvent, molecules of which contain
oxygen. Oxygenated solvents are widely used in the paints, inks,
pharmaceuticals, fragrance sectors, adhesives, cosmetics, detergents,
food industries.
Examples of oxygenated solvents:
STEP 5: Mechanism of Solvent Extraction (15 minutes)
o Dissolution of extractive substances out of disintegrated cells.
o Dissolution of extractive substances out of intact plant cell by
diffusion (requires steeping and swelling)
o Penetration of the solvent into the plant cells and swelling of the
cells.
o Diffusion of the dissolved extractive substances out of the cell.
o Plant constituents are usually contained inside the cells.
o Therefore, the solvent used for extraction must diffuse into the cell
to dissolve the desired compounds whereupon the solution must pass the
cell wall in the opposite direction and mix with the surrounding
liquid.
o An equilibrium is established between the solute inside the cells and
the solvent surrounding the fragmented plant tissues
STEP 6: Factors Affecting Extraction Process (05 Minutes)
STEP 7: Methods of extraction (45 minutes)
Percolation, Continues hot extraction, Supercritical fluid extraction,
counter current extraction, Microwave assisted extraction, Ultra
sonication-Assisted Extraction:
o Infusion
drug for a short period of time with cold or boiling water. These
are dilute solutions of the readily soluble constituents of crude
drugs.
o Fresh Infusion: e.g. Infusion of orange (
o Concentrated Infusion: e.g. concentrated infusion of Quassia
o Decoction
volume of water for a defined time; it is then cooled and strained or
filtered. This procedure is suitable for extracting water-soluble,
heat stable constituents. e.g. Tea , Coffee
o Digestion
the process of extraction. It is used when moderately elevated
temperature is not objectionable. The solvent efficiency of the
menstruum is thereby increased. e.g. Extraction of Morphine
o Maceration
stoppered container with the whole of the solvent and allowed to
stand for a period of at least 3 days (3 – 7 days) with frequent
agitation, until soluble matter is dissolved. The mixture is then
strained (through sieves / nets), the marc pressed and the combined
liquids clarified (cleaned by filtration) or by decantation, after
standing.
o Simple maceration: for organized and unorganized Crude drug e.g.
Squill
o Double maceration: Concentrated infusion of orange
o Triple maceration: The maceration process may be carried out with
help of heat or stirring e.g. i) Concentrated infusion of Quassia
STEP 8: Key Points (5 minutes)
from crude drug material.
STEP 9: Evaluation (5 minutes)
References
Trease, G. E., Evans, W. C., & Evans, D. (2009). Trease and Evans
pharmacognosy. London: Saunders.
Joanne Barnes et al (2002), Herbal medicines 3rd Edition: Pharmaceutical
Press
Wallis, T. E. (2005). Textbook of pharmacognosy. New Delhi: CBS.
Robbers, J. E., Speedie, M. K., Tyler, V. E., & Tyler, V. E. (1996).
Pharmacognosy and pharmacobiotechnology. Baltimore: Williams &
Wilkins.
Heinrich, M., Kinghorn, A. D., Maizels, D., Gibbons, S., & Phillipson, J.
Churchill Livingstone/Elsevier.
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