◆ The drying of the extract of the traditional Chinese medicine is usually carried out by vacuum drying, spray drying, and microwave vacuum drying which has recently arisen. The three drying methods are dried by heat conduction, heat convection, and dielectric heating, respectively. When vacuum drying, moisture begins to evaporate from the surface, and the internal moisture slowly diffuses to the surface, and the energy is transmitted inward from the outside of the material, resulting in the opposite direction of heat transfer and mass transfer, which is prone to surface dry drying. Microwave vacuum drying is heated by microwave radiation, which is heated internally and externally, and the heat transfer is consistent with the mass transfer direction. Therefore, microwave vacuum drying is less prone to surface pseudo-drying and encrustation. When the spray is dried, the extract is ejected from the atomizer, and heat exchange is performed with the hot gas stream to rapidly evaporate the solvent in the mist droplets to obtain a dry extract powder.
◆ Different pharmaceutical processes cause differences in the physical properties of the extract, and differences in physical properties can affect the subsequent formulation process and the quality of the final formulation. Different drying methods will inevitably lead to differences in the powder properties of the dried products due to the different heating methods and principles. The powder properties of Chinese herbal extracts are closely related to the subsequent formulation process and the quality of the final formulation. If the particle size of the powder affects the dissolution rate and absorption of the drug, the fluidity affects the molding process and product quality. The specific surface area and porosity affect the hygroscopicity of the drug and its dissolution rate and absorption. The hygroscopicity affects the fluidity of the drug powder and Its stability and formability directly affect the molding process of the tablet. The powdery properties of traditional Chinese medicine extracts can affect the efficacy of the entire preparation process and even the preparation.
◆ Microwave vacuum drying and vacuum-dried extract powder have irregular shapes and large differences in size. There was no significant difference between the obtained vacuum powder obtained by microwave vacuum drying and the powder obtained by vacuum drying. The powder obtained by spray drying is rounder, more uniform in size and finer than vacuum drying and microwave vacuum drying.
◆ The drying method has a great influence on the powder properties of traditional Chinese medicine extracts, and there are certain differences in the powder properties. The specific surface area and porosity of the powder can affect the hygroscopicity, and the powder obtained by spray drying has the largest specific surface area and porosity, and the most hygroscopicity. The specific surface area of the powder is determined by its particle size and porosity. The smaller the particle size, the larger the porosity and the larger the specific surface area. The particle size and porosity of the powder are related to the formability of the tablet. The smaller the powder particles and the larger the specific surface area, the more easily the powder particles coalesce and the better the moldability. The powder with high porosity has a greater deformation potential when the powder is compressed. When the pressure is the same, the powder with a large porosity is harder. The powder obtained by spray drying has the smallest particle size and the largest porosity, and the formability is also the best.
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