Extraction principle of plant medicinal materials

Whether the solvent can make the surface of the drug wetted in the infiltration and infiltration stage is related to the nature of the solvent and the nature of the drug, and depends on the characteristics of the attachment layer (the layer where the liquid contacts the solid) If the adhesion between the drug and the solvent is greater than the cohesion between the solvent molecules, the drug is easy to be wetted; otherwise, if the cohesion of the solvent is greater than the adhesion between the drug and the solvent, the drug is not easy to be wetted In most cases, medicinal materials can be wetted by solvents Because there are substances with polar groups in medicinal materials, such as protein, pectin, sugars, cellulose, etc., they can be wetted by polar solvents such as water and alcohol After wetting, due to the effect of hydrostatic pressure and capillary, the solvent enters into the gap and crack of the medicine, penetrates into the cell tissue, makes the stem wrinkle cell expand, restores the permeability, and the solvent further penetrates into the cell interior However, if the solvent is not properly selected, or if there are special components in the herbal medicine that hinder the extraction, it will be difficult to wet and the solvent will be difficult to penetrate into the cells For example, in order to extract water-soluble components from Chinese herbal medicines with more fat oil, degreasing treatment should be carried out first; when extracting fat soluble components with non-polar solvents such as ether and chloroform, the herbal medicines should be dried first In order to help the solvent to wet the medicinal materials, an appropriate amount of surfactant can sometimes be added to the solvent Whether the solvent can penetrate into the cell smoothly is also related to whether there is gas embolism in the capillary Therefore, after adding the solvent, the air in the capillary can be discharged by extrusion or decompression in a closed container, which is beneficial to the penetration of the solvent into the cell tissue During the desorption and dissolution stage, the soluble components gradually dissolve when the solvent enters the cell, and the colloidal substances are transferred into the solution or expanded to form gels due to gelation With the solubilization and gelling of the components, the concentration of the extract gradually increased, the osmotic pressure increased, the solvent continued to penetrate into the cells, and some cell walls expanded and cracked, which created favorable conditions for the outward diffusion of the dissolved components Because some components in the medicinal materials have strong adsorption (affinity) on other components, so that these components cannot be directly dissolved in the solvent, it is necessary to remove this adsorption, so that they can be dissolved Therefore, when extracting the medicinal materials, it is necessary to select the solvent with desorption effect, such as water, ethanol, etc If necessary, add appropriate amount of acid, alkali, glycerin and surfactant to the solvent to help desorption and increase the dissolution of effective components After the extraction solvent enters the cell tissue through the capillary and the cell gap, all the components that have been desorbed are transferred into the solvent, which is the dissolution stage Whether the components can be dissolved or not depends on the structure of the components and the nature of the solvent, and follows the law of "similar dissolving" Water can dissolve crystal and colloid, so there are more colloidal substances in the leach solution, less colloidal substances in the ethanol leach solution, and no colloid in the non-polar solvent leach solution In the phase of component dissolution, when a large number of drug components are dissolved by the leaching solvent, the concentration of the liquid in the cell increases significantly, resulting in the difference of concentration and osmotic pressure inside and outside the cell Therefore, the pure solvent or dilute solution outside the cell infiltrates into the cell, and the high concentration liquid inside the cell can continuously diffuse to the surrounding low concentration direction until the internal and external concentrations are equal When the osmotic pressure is balanced, the diffusion stops Therefore, the concentration difference is the driving force of infiltration or diffusion The diffusion rate of substance can be explained by Fick's first diffusion formula: in the above formula, DT is the diffusion time; DS is the diffusion amount of substance (solute) in DT time; F is the diffusion area, which represents the particle size and surface state of medicinal materials; DC / DX is the concentration gradient; D is the diffusion coefficient; negative sign indicates that the concentration decreases when the diffusion tends to balance The diffusion coefficient D varies with the medicinal materials, and it is also related to the nature of the extraction solvent It is not a constant It can be obtained from the following formula: in the above formula, R is the molar gas constant, t is the absolute temperature, n is the Avogadro constant, R is the molecular radius of the diffusion substance (solute), and η is the viscosity It can be seen from the above two formulas that the diffusion rate (DS / DT) is directly proportional to the diffusion area (f), concentration difference (DC / DX), temperature (T), and inversely proportional to the molecular radius (R) of the diffusion substance (solute) and viscosity (η) of the liquid The most important thing in production is to maintain the maximum concentration gradient (DC / DX) If there is no concentration gradient, other factors such as D value, F value and t value (time) will lose their effect Therefore, the key to the design of extraction method and equipment is to "replace" the concentrated extract around the medicinal materials at any time with extraction solvent or dilute extract to create the maximum concentration gradient.