Analytical drying is also referred to as the second stage of drying. After the first stage of drying, about 10% of the moisture in the product is adsorbed on the capillary wall and the polar group of the dry substance, and this part of the water is not frozen. When they reach a certain level, they provide conditions for the growth and reproduction of microorganisms and certain chemical reactions. Experiments have shown that even a single molecule layer adsorbs the following low water content, and can be a solution of certain compounds, producing the same mobility and reactivity as the aqueous solution. Therefore, in order to improve the storage stability of the product and prolong its shelf life, it is necessary to remove the moisture. This is the purpose of analytical drying.
Since this part of the water is bound water adsorbed on the medicine by weak molecular forces such as van der Waals force and hydrogen bonding, it is necessary to overcome the intermolecular force and require more energy to remove this part of the water. At this time, the temperature of the product can be heated to the maximum temperature allowed (the allowable temperature of the product depends on the product variety, generally about 25 ° C -40 ° C. The viral product is 25 ° C, the bacterial product is 30 ° C, serum , antibiotics can be as high as 40 ° C), maintain a certain time (depending on the characteristics of the product), so that the residual moisture content reaches a predetermined value, the entire freeze-drying process is over.
If the eutectic point of the product is high, the vacuum degree of the system can be maintained well, and the condenser has sufficient cooling capacity, and the temperature of the shelf can be raised to the maximum allowable temperature until the end of lyophilization. However, it is also necessary to ensure that the temperature of the product does not exceed the eutectic point when it is sublimated.
In the analytical drying stage, due to the decrease of the moisture in the product, the decrease in the temperature of the condenser causes the pressure of the water vapor in the system to decrease, which tends to lower the total pressure of the freeze-drying box to less than 10 Pa, which makes the freeze-drying box The heat transfer within the convection almost disappears. In order to improve the heat transfer of the freeze-drying box and make the temperature of the product reach the maximum allowable temperature faster, in order to shorten the time of the analytical drying stage, the pressure in the freeze-drying box is controlled, and the controlled pressure range is between 15 and 30 Pa.
After the product temperature reaches the permissible temperature, in order to further reduce the residual moisture content in the product, it is necessary to restore the high vacuum. At the same time, the condenser reaches the limit low temperature due to the load reduction, so that the water vapor pressure difference between the freeze-drying tank and the condenser The maximum value has been reached. This condition is very beneficial for the escape of residual moisture in the product.
Since the residual moisture in the freeze-dried medicine has a great influence on the freeze-dried biochemical drugs, the residual moisture is excessive, and the biochemical active material is easily deactivated, thereby greatly reducing the stability. The key to controlling residual moisture in lyophilized drugs is the control of re-drying in the second stage. In this stage, the temperature should be selected to the highest temperature allowed; the control of the vacuum is as high as possible, which is beneficial to the escape of residual moisture; the longer the duration, the better, the general process takes 4-6 hours; Higher lyophilizers can be controlled by a pressure rise test to ensure that the moisture content of the lyophilized drug is less than 3%.
Squid Rings Raw,Frozen squid rings,This year's Squid Rings
ZHOUSHAN GENHO FOOD CO.,LTD , https://www.genho-food.com