Medicinal Plant Extraction for Scientific Research
Medicinal Plant Extraction is the important process for both research work and manufacturing. It is the first step to discovered natural bioactive substances and their pharmacological activities. In the extraction process, proper solvent should be selected based on the groups of natural compound needed together with the process recommended in the traditional recipe. The natural compounds are divided into three main groups, polar or water soluble compounds, semi-polar or alcoholic compounds and non-polar or organic solvent soluble compounds. The organic solvents are the by-product of oil refineries and are proved to be highly toxic to human and environment. In addition, extraction does not only result in concentrated extracts, but also helps to eliminate contaminated microorganisms found in raw materials. Relevant procedures include raw material preparations and drying procedures.
Preparation of crude Materials
Raw materials play important role for the quality of extracts. In raw materials markets, most of them are collected from the wild, and usually cut into pieces or ground into powders. Therefore, identification should be strictly managed. The monographs of commonly used medicinal plants are stated in Thai Herbal Pharmacopoeia, including botanical nomenclatures, plant parts used, physical and chemical properties. The adulterant plants, microbes, inorganic matters, heavy metals and pesticides should also be controlled. The cultivated raw materials need qualified variety, proper growing area, proper planting and harvesting methods
Cleaning Process
After the plants are harvested, they are more or less contaminated with dirt and microbes. Cleaning with water before drying is necessary. The dried crude materials bought from retailers, also need to be washed again. For delicate parts like flowers or leaves, screening is more suitable.
Drying Process
After cleaning, the medicinal plant must be reduced into smaller sizes and absolutely dried to avoid fungi. The plants can be naturally dried in direct sunlight or under shading, depending on the plant nature. This slow-drying method is likely to cause fungi, especially succulent tubers or rhizomes. Presently, the continued drying at 40-60°C in the oven until it thoroughly dried is more preferable. If absolutely dried crude drugs are well kept in good packing and carefully stored, their good quality can be maintained for a longer period of time.
Grinding process
Grinding plant material to the appropriate size, in order to increase the surface area, will facilitates the effective permeability of chemical compounds from the plant cells, results in effective extraction. Coarse powder is suitable for boiling, maceration and soaking. Other extraction methods require different particle sizes. Too fine particles may obstruct the instrument and is difficult to filter.
