The test of freezing drying cooked food
Brief introduction of freeze-drying
Drying is one of the ways to keep substances from spoilage. Freeze-drying is a new type of drying technology, that is, freezing wet materials at low temperature and heating them under higher test conditions to sublimate solid ice and remove moisture from materials. It is called vacuum freeze-drying technology, or freeze-drying technology for short. The food obtained by freeze-drying technology is called freeze-dried food.
Different materials need to be pretreated before freezing and freeze-drying in order to facilitate processing. Fruits and vegetables need to be sorted, tested, cleaned, cut, blanched and cooled. Meat and aquatic products need to be screened, cooled and acidified, sliced (after the pre-freezing step). Cooked food products (such as fish-flavored meat shredded and other Chinese dishes) need to be selected and mixed according to the standard after cooking. Water content is measured by sampling in order to determine the technical parameters of freeze-drying. Proteins and dairy products need to be protected by proteins such as glycerol, sorbitol, disaccharides, amino acids, polyethylene glycol and recombinant proteins to avoid protein instability caused by freeze-drying stress, drying stress and low temperature stress.
2, pre-freezing process
The pre-freezing process is not only to protect the main properties of the substance, but also to have a reasonable structure of the frozen drug, which is conducive to the sublimation of water, as well as an appropriate volume. The effect of pre-freezing mainly depends on three aspects: pre-freezing quick test, pre-freezing minimum temperature and pre-freezing time.
3. The first stage drying of products
The sublimation process before freezing ice disappears is the first stage of drying, namely sublimation drying. Sublimation is an endothermic process, so the product must be heated at a low temperature, but it must never exceed the eutectic temperature. If the heating temperature is too high below the eutectic point, the sublimation rate decreases and the time of the sublimation stage is prolonged.
4. Second stage drying of products
The product without freezing ice still contains 10% water. In order to achieve the expected residual water content, it must be further dried, which is called analytical drying. At this stage, the temperature of the product can be increased to the maximum temperature allowed for the product test, which is beneficial to reducing the residual water and reducing the time of analytic drying.
5. Post-treatment of freeze-dried food
After drying, the food is regulated: before the vacuum environment is removed, it needs to be stabilized for a period of time, so that the residual moisture and temperature in the food are completely uniform. In order to inhibit microbial growth after eliminating the vacuum environment, dry and clean sterile nitrogen should be used to eliminate the vacuum, and sterile dry air should be put into the box when it comes out. The dried products should be quickly packed and stored or temporarily stored in the drying cabinet, packed and labeled as soon as possible, and become official products after passing the test.
The cooked food are in the process of freeze-drying
Freeze-dried cooked food is OK now.