The drying methods are various, such as drying, boiling, drying, spray drying, and vacuum drying, but ordinary drying methods are usually performed at a temperature of 0° C. or higher. The dried products generally have the problem of shrinking the volume and hardening the texture. Most of the volatile components are lost. Some heat-sensitive substances are denatured and deactivated. Some of the substances even oxidize. Therefore, there is a large difference in the properties of the dried product compared to that before drying. The lyophilization method is basically carried out at a temperature below 0°C, that is, when the product is frozen, the product is allowed to rise above 0°C only when the residual moisture content of the product is later reduced, but generally does not exceed 40°C. Under vacuum conditions, when the water vapor sublimates directly, the drug remains in the frozen ice shelf, forming a spongy porous structure resembling a sponge, so that after drying it is almost constant in size. Before using it again, as soon as water for injection is added, it dissolves immediately.
Many heat-sensitive substances do not denature or deactivate.
When dried at low temperatures, some volatile components in the material lose little.
In the lyophilization process, the growth of microorganisms and the action of enzymes cannot be performed, and thus the original traits can be maintained.
Since the drying is performed in a frozen state, the volume is almost constant, the original structure is maintained, and no condensation occurs.
Since the moisture in the material exists in the form of ice crystals after pre-freeze, the dissolved inorganic salt dissolved in water is uniformly distributed in the material. During sublimation, dissolved substances dissolved in water are precipitated, which prevents surface hardening due to the precipitation of inorganic salts carried by the internal moisture of the material to the surface during general drying methods.
The dried material is loose and porous, and it is spongy. It dissolves quickly and completely after adding water, and it almost immediately restores its original properties.
Since the drying is carried out under vacuum, there is very little oxygen, so some easily oxidized substances are protected.
Drying can eliminate 95% to 99% of the water, so that the dried product can be stored for a long time without deterioration.
Because the material is in a frozen state, the temperature is very low, so the heat source's temperature is not required to be high, and a heater with a normal temperature or a low temperature can meet the requirements. If the freezer compartment and the desiccant compartment are separated, the desiccant compartment does not need to be insulated, and there will not be a lot of heat loss, so the utilization of thermal energy is very economical.
There is no perfect technology. The main disadvantage of vacuum freeze-drying technology is its high cost. Because it requires vacuum and cryogenic conditions, the vacuum freeze dryer is equipped with a vacuum system and a cryogenic system, which results in high investment and operating costs.