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What are the differences between freeze-drying and conventional drying?
Release time:
Mar 12,2021
freeze-drying is one of the drying methods aimed at preserving items. The damage, decay, and deterioration of items are mainly caused by two factors: external and internal factors. External factors include the effects of air, water, temperature, and biological agents; internal factors are primarily the metabolic processes of the biological substances themselves. If the effects of both external and internal factors can be minimized to a lower level, it is possible to keep the items unchanged for a certain period. Freeze-dryers are now widely used in chemistry, pharmaceuticals, food industry, and scientific research, especially in the field of biopharmaceuticals containing bioactive substances.
Freeze-drying machines are one of the drying methods, aimed at preserving items. The damage, decay, and deterioration of items are mainly caused by two factors: external factors such as air, water, temperature, and biological influences; and internal factors, primarily the metabolism of the biological material itself. If the effects of external and internal factors can be minimized, it is possible to keep the items unchanged for a certain period. Freeze-drying machines are now widely used in chemistry, pharmaceuticals, food industry, and scientific research, especially in the field of biological drugs containing bioactive substances. What are the differences between freeze-drying and conventional drying?
Drying is a very ancient operation, but heating drying of powders and biological products often causes irreversible agglomeration of particles, especially in the preparation of ultrafine powders. In the liquid phase, nanoparticles tend to agglomerate into difficult-to-disperse clumps during drying, mainly because in the ordinary particle drying process, moisture evaporates from the pores between the particles, and surface tension creates extremely high additional pressure, compressing the particles together into clumps. However, using a freeze-drying machine can avoid this problem. Freeze-drying first freezes the gel or blood to a solid state, and then under reasonable conditions, the moisture is vaporized and removed through sublimation. Since the vaporization process of ice does not affect the agglomeration state of the solid particles, the original particles can be preserved without being compressed into clumps. Additionally, freeze-drying machines are very suitable for processing biological products, such as blood, because they do not involve high-temperature operations, preventing the deterioration of biological products.
The products obtained from drying generally have issues such as volume shrinkage and increased hardness, with most volatile components being lost. Some heat-sensitive substances undergo denaturation and inactivation, and some substances may even oxidize. Therefore, the properties of the dried products differ significantly from those before drying. Freeze-drying is basically conducted below 0°C, that is, in a frozen state, and only in the later stage, when reducing the residual moisture content of the product, is the temperature allowed to rise above 0°C, but generally not exceeding 40°C. Under vacuum conditions, when water vapor sublimates directly, the drug remains in the ice framework formed during freezing, creating a sponge-like loose porous structure, so the volume remains almost unchanged after drying with a freeze-drying machine. Before reuse, just adding sterile water will cause it to dissolve immediately.
There are various methods for drying with a freeze-drying machine, such as sun drying, boiling, drying, spray drying, and vacuum drying, but ordinary drying methods are usually conducted at temperatures above 0°C or higher. The products obtained from drying generally have issues such as volume shrinkage and increased hardness, with most volatile components being lost. Some heat-sensitive substances undergo denaturation and inactivation, and some substances may even oxidize. Therefore, the properties of the dried products differ significantly from those before drying. Freeze-drying is basically conducted below 0°C, that is, in a frozen state, and only in the later stage, when reducing the residual moisture content of the product, is the temperature allowed to rise above 0°C, but generally not exceeding 40°C. In a freeze-drying machine under vacuum conditions, when water vapor sublimates directly, the drug remains in the ice framework formed during freezing, creating a sponge-like loose porous structure, so its volume remains almost unchanged after drying. Before reuse, just adding sterile water will cause it to dissolve immediately. Compared to conventional methods, freeze-drying machines have the following advantages:
1. Many heat-sensitive substances do not undergo denaturation or inactivation.
2. When drying at low temperatures, the loss of some volatile components in the material is minimal.
3. During the freeze-drying process, the growth of microorganisms and the action of enzymes cannot occur, thus preserving the original properties.
4. Since drying is conducted in a frozen state, the volume remains almost unchanged, maintaining the original structure without concentration.
5. Because the moisture in the material exists in the form of ice crystals after pre-freezing, the originally dissolved inorganic salts are evenly distributed within the material.
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