The vacuum freeze-drying process can generally be divided into four main stages: pre-treatment, pre-freezing, drying and post-treatment.
First, vacuum freeze drying pretreatment
The pretreatment method is different for different materials to be dried. Some processes are more complicated, and some processes are relatively simple. However, in order to obtain safe and hygienic products, it is an indispensable process to sterilize freeze-drying equipment. Commonly used disinfection methods are:
(1) Gas Sterilization Method This disinfection method utilizes gaseous or vaporized chemicals to treat equipment or materials. Commonly used disinfectants are: ethylene oxide, formaldehyde, propylene oxide, methyl bromide and ? propanol. fat.
(2) Heat sterilization: dry heating: killing bacteria by oxidation, in fact, most of them are incinerated; direct steam heating: using a special low-pressure steam sterilization steamer, the steam temperature is required to be maintained at about 120 ° C, duration of at least 30 minute. In order to prevent steam from heating up to a dead angle, the entire system should be evacuated to 100 Pa before steaming. Spray with 70% alcohol in the box, dry with a sterilizing cloth after 24 hours; heat the sterilizing agent with negative pressure steam: vacuum the lyophilization box and the whole system to below 10Pa, and pass steam at 70-90 °C. Marlin solvent, keeping the container in a hot state for 2 hours.
(3) Radiation sterilization UV radiation: low-pressure mercury discharge lamp is used as the radiation source to generate ultraviolet radiation with a wavelength of 2.537×10-3m. These ultraviolet rays are harmful to the skin and eyes of the human body. Pay special attention when using it. Protection; X-ray: X-rays generated under high pressure have strong penetrating power and can be used to disinfect foods and medicines. It has a killing effect on various microorganisms, but it takes a long time to kill all the bacteria; Cathode ray: Cathode ray has a rapid bactericidal effect.
Second, vacuum freeze-drying pre-freezing
Pre-freezing is to solidify the free water in the material to ensure that the dried product has the same shape as before drying, preventing irreversible changes such as foaming, shrinkage, concentration and solute movement during vacuum drying, and reducing the temperature after vacuum drying. The decrease causes a decrease in the solubility of the substance and a change in the life characteristics of the substance. Pre-freezing plays a crucial role in the quality of the lyophilized product, so two basic requirements must be met: an appropriate cooling rate.
vacuum freeze-drying.
