Factors affecting selection of an extraction process
Character of Herb:- The knowledge of pharmacognosy of the herb is essential to select the right method of extraction process. The maceration process is used when the herb is soft, unorganized unpowerderable and to avoid powdering of it. The percolation process is used when the herb is hard and tough.
Therapeutic value of the herb:- When the herb has considerable therapeutic value, the maximum extraction is required, so the percolation process is used e.g. Belladonna. In case the herb has little therapeutic value, the efficiency of extraction is unimportant, and maceration process can be used to extract the herb.
Stability of herb:- Continuous hot extraction process should be avoided when the constituents of the herb are thermo labile in nature; in that case maceration or percolation process may be used to extract the active constituents of the herb.
If water is used as a solvent the maceration process should be recommended. The percolation process should be preferred if non-aqueous solvents are used for extraction.
Concentration of product:-
The dilute products such as tinctures can be made by using maceration or percolation process, depending on the other factors. For semi-concentrated preparations, such as concentrated infusions, double or triple maceration process can be used. The liquid extracts or dry extracts which are concentrated preparations are prepared by using percolation process.