Vacuum freeze-drying which is freeze-drying, is one of the drying methods. The purpose is of long-term storage of food, articles or drugs. Food, goods can be damaged, rotten, deteriorated, mainly due to external and internal causes. External causes include air, water, temperature, biological and other effects. Internal causes are mainly the metabolism of biological matter itself. If the effect of external cause and internal cause can be reduced to the lowest degree, it can make goods remain unchanged in a certain period of time. Organic freeze dried food drying is one of the ways to keep materials from spoiling.
There are many drying methods, such as sun drying, boiling, drying, spray drying and vacuum drying. But these drying methods are carried out at temperatures above 0℃ or higher. The products obtained by drying are generally reduced in size and hardened in texture. Some substances have been oxidized, and most of the volatile components will be lost. Some heat-sensitive substances, such as proteins and vitamins, will be denaturated. Microorganisms will lose biological vitality, and dry material is not easy to dissolve in water, let alone the appearance or performance of the recovery, so in character the product after drying compared with before drying has a lot of difference. Among these drying methods, only vacuum freeze-drying of freeze dried products is the most ideal method to preserve living biological matter.
Lyophilization has the following outstanding advantages compared with the usual sun drying, drying, boiling, spray drying and vacuum drying:
(1) Organic freeze dried food are dried at low temperature, which will not denaturate proteins, but can make microorganisms and other biological activities lose. This is especially suitable for the dry preservation of bioactive products, biochemical products, genetic engineering products and blood products with poor thermal stability.
(2) Due to low temperature drying, the loss of volatile components and heat denatured nutrients and aromatic components in the material is very small, so it is a high-quality drying method for chemical products, drugs and food.
(3) In the low-temperature drying process, the growth of microorganisms and the action of enzymes are almost impossible, so that the original properties of the material can be best preserved.
(4) After drying, the volume and shape are basically unchanged and the substance is spongy, without drying shrinkage. The contact surface with water is large, which can be rapidly reduced to the original shape.
(5) Organic freeze dried food is generally dried under vacuum, so oxygen is very little, so that the easily oxidized substances are protected.
(6) It can remove 95% ~ 99.5% of the water in the material and the storage period of products is long.