It is mainly determined by the initial quality the final quality. The initial quality is determined by P.P.P., that is, the processing packing of raw materials before freezing. The final quality is determined by t.t.t., which reflects the relationship between the time temperature that the frozen food can endure. The initial quality of quick-frozen vegetables is good, but the final quality will change through each circulation procedure. The quality of the product will also change when it is frozen. The extent of the change mainly comes the temperature the length of the freezing time. The lower the temperature is, the smaller the change of mass is, the longer the freezing time is; at the same temperature, the longer the refrigeration time is, the greater the change of quality will be, the final quality will become worse.

Through cleaning raw materials, dust, broken leaves, foreign bodies pesticides attached to the surface of fruits vegetables can be removed. Secondly, the raw materials should be sorted out, that is to say, the inedible parts should be cut off, the edible parts should be peeled, seeded cut into strips, segments, slices, blocks silk according to different cooking habits. Thirdly, brittleness preservation treatment is carried out, that is, soaking in calcium salt before quick freezing, washing with water after soaking. Finally, blanching, cooling preventing discoloration are carried out. Some vegetables should be blanched before quick freezing in order to destroy enzyme activity prevent browning, then immediately put them into cold water for cooling. The fruits are easy to be oxidized discolored in peeling, slicing quick-frozen preservation thawing. They can be immersed in 0.4% sulfur dioxide solution for 2-5 minutes immediately after peeling slicing, then sent to quick freezing.

Blanching has four functions: one is to inactivate the enzyme in the tender stick prevent the nutrition being destroyed. The second is to kill the microorganisms eggs attached to the surface of the ear to ensure food safety. The third is to eliminate the air in the tender corn, reduce the pressure of ice crystal formation during freezing, reduce the oxidation degree of raw materials, so as to maintain the color nutrition of the product. The fourth is to prevent the products aging, scalding changing the taste. Using hot steam blanching process, the control temperature is 95-105 ℃, the time is 10-15 minutes. Blanched tender sticks should be cooled immediately to ensure the color of the product. In order to save water, sectional cooling method can be adopted, but the central temperature of tender rod in the terminal cooling pool should be controlled at 10 ℃.