Traditional Methods of Extraction of Traditional Chinese Medicines

Traditional methods of extraction for herbal medicine treatment include water decoction, maceration, percolation, modified gelatin, reflux, solvent extraction, water vapor distillation and sublimation. Among them, water decoction is the most commonly used method . Solvent extraction method is the most widely used method, it is based on the nature of the solubility of various active ingredients in Chinese herbal medicine, the choice of solvents for the need for the solubility of the ingredients and other components of the solubility of the solvents of the small, the desired active ingredients from the herbal tissue dissolved out of an extraction method .

The common extraction solvents can be divided into the following three categories:

1) Water: water is a strong polar solvent. Hydrophilic components in herbal medicine, such as inorganic salts, sugars, polysaccharides with not too large molecules, tannins, amino acids, proteins, organic acids, alkaloids and glycosides can be dissolved by water. In order to increase the solubility of certain components, acidic water and alkaline water are often used as extraction solvents. Acid extraction, alkaloids and acids can generate salts and dissolved, alkaline water extraction can make organic acids, flavonoids, anthraquinones, lactones, coumarins and phenolic components dissolved. However, water extraction is easy to enzymatically dissolve glycoside components, and easy to mold and deterioration. Certain herbs containing pectin, mucus-like components, the water extract is often difficult to filter. Boiling water extraction, the starch in the herbs can be pasteurized, and increase the difficulty of filtration. Therefore, herbs containing much starch should not be ground into fine powder and then added to water for decoction. Traditional Chinese medicine soup, mostly with Chinese medicine tablets straight fire decoction, heating can increase the solubility of Chinese medicine ingredients, but also may have with other ingredients to produce "aided solubility" phenomenon, increase the solubility of some of the small solubility in water, lipophilic components of the solubility of the strong. But most of the lipophilic ingredients in boiling water solubility is not large, even if the phenomenon of aided solubility exists, it is not easy to extract completely. If a large number of water decoction is applied, it will increase the difficulty of evaporation and concentration, and a large number of impurities will be dissolved, which will bring trouble to further separation and purification. Herbal water extract contains saponins and mucus components, in the decompression of concentration, but also produces a large number of foam, resulting in concentration difficulties. Usually can be installed in the distiller on a vapor-liquid separation splash ball to overcome, industry is commonly used film concentration device.

2) hydrophilic organic solvents: that is, generally speaking, and water can be miscible organic solvents, such as ethanol (alcohol), methanol (wood spirit), acetone, etc., ethanol is most commonly used. Ethanol has better solubility properties and stronger penetration ability to the cells of herbs. Most of the hydrophilic components can be dissolved in ethanol except proteins, mucilage, pectin, starch and some polysaccharides. Lipophilic components that are difficult to dissolve in water are also more soluble in ethanol. It is also possible to extract with different concentrations of ethanol according to the nature of the substance being extracted. Extraction with ethanol uses less water than the amount of water, the extraction time is shorter, and less water-soluble impurities are dissolved. Ethanol is an organic solvent, although flammable, but less toxic, cheap, convenient source, there is a certain equipment can be recycled for repeated use, and ethanol extract is not easy to mold and deterioration. For these reasons, the method of extraction with ethanol is historically one of the most commonly used methods. The properties of methanol and ethanol are similar, the boiling point is lower (64 ℃), but there is toxicity, the use of attention should be paid.

3) lipophilic organic solvents: that is, generally known as organic solvents that are not miscible with water, such as petroleum ether, benzene, chloroform, ethyl ether, ethyl acetate, ethylene dichloride and so on. These solvents have strong selective properties, can not or not easy to raise hydrophilic impurities. However, these solvents are volatile, mostly flammable (except chloroform), generally toxic, more expensive, more demanding equipment, and their ability to penetrate into plant tissues is weak, often requiring a long period of repeated extraction to extract completely. If the herbs contain more water, with this type of solvent is difficult to leach its active ingredients, therefore, a large number of extraction of herbal raw materials, the direct application of such solvents have certain limitations. Solid substances directly into the vapor state after heat, cold and solidified into the original solid substances, known as sublimation, (such as the extraction of danpi phenol) the principle of operation with the distillation method is almost the same.

Traditional methods of extraction of traditional Chinese medicine disadvantages:

Loss of active ingredients, especially water-insoluble components; extraction process of organic solvents may be with the role of the active ingredients, so that it loses its original utility; non-active ingredients can not be maximized to remove the rate of concentration is not high enough; extracts in addition to the active ingredients, often more impurities, there are still a small number of fat-soluble components to the refinery Adverse; high temperature operation will cause a large number of heat-sensitive active ingredients decomposition.