The general principles and mechanisms involved in maceration, percolation and infusion for the extraction of the crude drugs are same as to those for the extraction of soluble constituents from solid materials using solvent, which is generally referred to as leaching. The processes of leaching may involve simple physical solution or dissolution.
The extraction procedures are affected by various factors, namely the rate of transport of solvent into the mass, the rate of solubilization of the soluble constituents by the solvent, the rate of transport of solution out of the insoluble material.
The extraction of crude drugs is mostly favored by increasing the surface area of the material to be extracted and decreasing the radial distances traversed between the solids (crude drug particle).
Mass transfer theory states that the maximum surface area is obtained by size reductions which entail reduction of material into individual cells. However, this is not possible or desirable in many cases of vegetable material. It has been demonstrated that even 200 mesh particles contain hundred of unbroken cells with intact cell wall. Therefore, it is pertinent to carry out extraction with unbroken cells to obtain an extract with a high degree of purity and to allow enough time for the diffusion of solvent through the cell wall for dissolution of the desired solute (groups of constituents) and for diffusion of the solution (extract) to the surface of the cell wall.
MCQ Quiz
1. The general principle of maceration, percolation, and infusion in crude drug extraction is similar to which process?
a) Distillation
b) Filtration
c) Leaching
d) Crystallization
Answer: c) Leaching
2. Which factor does NOT directly affect the extraction procedure of crude drugs?
a) Rate of solvent transport into the drug mass
b) Rate of solubilization of constituents by solvent
c) Rate of solution transport out of the insoluble material
d) Color of the crude drug powder
Answer: d) Color of the crude drug powder
3. Increasing the surface area of the crude drug material to be extracted mainly favors extraction by:
a) Increasing solvent polarity
b) Reducing radial distance for solvent diffusion
c) Heating the solvent to boiling point
d) Changing the solvent type
Answer: b) Reducing radial distance for solvent diffusion
4. According to mass transfer theory, the maximum surface area for extraction is obtained by:
a) Size reduction to individual cells
b) Increasing solvent temperature
c) Using stronger solvents
d) Prolonged extraction time
Answer: a) Size reduction to individual cells
5. Why is it sometimes undesirable to break all cells of plant material during extraction?
a) It decreases extraction efficiency
b) It produces extracts with lower purity
c) It increases solvent consumption
d) It causes cell wall thickening
Answer: b) It produces extracts with lower purity
6. In crude drug extraction, diffusion through the cell wall allows:
a) Evaporation of solvents
b) Dissolution of desired solutes and transport of extract to surface
c) Immediate precipitation of solutes
d) Disintegration of the insoluble material
Answer: b) Dissolution of desired solutes and transport of extract to surface