Basic principle of vacuum freeze drying
1,The basic principle of freeze-drying is based on the three state change of water. Water (H2O) has three phase states, namely solid state, liquid state and gas state. The core technology of vacuum freeze-drying is to use the three-phase principle of water.
2,The use of vacuum freeze dryer to form a high vacuum environment, so that the water sublimates from the product, and then condenses on the surface of the condenser to achieve water transfer. With the continuous sublimation of moisture, the moisture content of the product is getting lower and lower, and finally the dry product is obtained.
3,OA, OB and OC curves represent the relationship between water vapor and temperature when water and steam, ice and water vapor, ice and water coexist, which are called vaporization curve, sublimation curve and melting curve respectively. The o-point is called the three-phase point, which corresponds to a temperature of 0.01 ℃ and a vapor pressure of 610.5pa (4.58mmhg). Under such a temperature and vapor pressure, water, ice and steam can coexist and balance with each other. Under the condition of high vacuum, using the sublimation principle, the moisture in the pre frozen material is directly sublimated into water vapor without ice melting, so as to achieve the purpose of freeze-drying. Vacuum freeze-drying products can ensure that the food protein, vitamins and other nutrients, especially those volatile heat sensitive ingredients are not lost. The freeze-dried products are spongy, no shrinkage, excellent rehydration, easy to eat, with little water content, and can be stored and transported at room temperature for a long time.
4,Because vacuum freeze drying has incomparable advantages over other drying methods, it has been more and more popular since it came out, and has been widely used in medicine, biological products and food. Serum, bacteria, Chinese and Western medicine and other biological products are mostly bioactive substances. Vacuum freeze-drying technology provides a good solution for the preservation of bioactivity. The vacuum freeze-dried products can well preserve the nutritional and health components of the raw materials, as well as the color, aroma, taste and shape. This excellent performance is particularly outstanding in convenient fast food, showing a strong momentum of development. For example, about 50% of convenient food in Japan is freeze-dried food.
