The structural change of (1) is mainly due to the mechanical damage of ice crystallization. During the freezing process, the moisture in the fiber moves outward, which causes the fiber to dehydrate and shrink, and promotes the protein particles in the fiber to approach and gather. After the water in muscle tissue is frozen, the volume increases by about 9%.
(2) Changes in Colloidal Properties Freezing will destroy the colloidal properties of muscle protein, thus reducing the quality of meat. The reason why the colloidal properties of protein were destroyed was that protein denatured during freezing.
(3) Other changes of meat during freezing and cold storage.
Drying shrinkage: the degree of drying shrinkage varies with air conditions (temperature, humidity, flow rate), meat grade and size, and packaging state. When the temperature is high, the humidity is low, the air velocity is fast, the cold storage time is long, the fat content is low, the shape is small and there is no packaging, the drying shrinkage rate increases significantly. When the above conditions are obviously unfavorable at the same time, the meat can be turned into a sponge, and the meat and fat are seriously oxidized. This is because the drying shrinkage during freezing and refrigeration is similar to the sublimation of ice. In this process, there is no movement of water. Therefore, a dehydrated sponge layer will be formed after the water on the surface of frozen meat evaporates. The ice crystals under the sponge layer continue to sublimate and penetrate the surface layer in the form of water vapor, and the sponge layer deepens.
Discoloration: the color of frozen meat gradually darkens during storage, mainly due to the oxidation of heme and the evaporation of surface water, which increases the concentration of pigment substances. The lower the freezing temperature, the smaller the color change. Almost no discoloration at -50 ~-80℃.
Juice loss: when frozen meat is thawed, the ice crystals inside melt into water, but the water at this time can not be completely absorbed by the tissue, so it is called juice loss when it flows out of the tissue. The loss of juice can be used as one of the indexes to judge the quality of frozen meat. The so-called juice loss generally refers to the juice that naturally flows out during and after thawing, which is called freedrip. The juice flowing out under the pressure of 98 ~ 1862 kPa is called squeezable dripping except for the loss of freedom. Both are always called juice loss.