this is a common and simple fresh-keeping method. in addition to crushed ice, 3-7% NaCl, proper sorbitol and compound food phosphate can be added during ice making, and the fish is washed and cut into 3-5 cm thick fillets, which are placed in plastic film bags, and then placed in plastic frames in the form of layers of fish ice for storage at 2-4℃.

2. Slightly frozen preservation

Tuna fillets with a thickness of 3 ~ 5 cm are slightly frozen at-1 ~-3℃, which can generally be preserved for 8 ~ 1 days, and the color and flavor of the meat remain unchanged, so they can be used as sashimi.

3. Freezing method

Because the oxidation speed of myoglobin in tuna is 1-3 times faster than that in mammals, and the temperature has a particularly obvious influence, in order to keep the color, meat taste and taste of tuna meat unchanged in long-term storage, frozen storage is generally adopted. With the improvement of people's quality requirements and the progress of technology, the temperature of frozen storage is getting lower and lower, from-18℃ to-25℃ → According to the research of Fujita, during the six-month frozen storage cycle, the production rate of methemoglobin is about 33% lower than that of -18℃ when frozen at -35℃, but only 2% higher than that of -78v, but the energy consumption is much lower. Therefore, according to the existing situation in China, it is recommended to freeze at -35℃. If the preservation period is to be further extended, a lower freezing temperature is needed. In addition, it must be noted that tuna must pass through the temperature range of -4℃→-7℃ quickly in frozen storage, otherwise the muscles will be easy to change color.