Generally speaking,the freshness glided down when the tuna were caught.In order to let consumer to enjoy the fresh quality just like the tuna were caught.Japanese invents the tuna freezing technology in ultra-low temperature.

Freezing fish is mainly for anti-corruption for fish body.Freezing the central fish body under 5 Celsius degrees below zero may cause the bacterium death,the biochemistry stop,achieve the purpose of anti-corruption.But only anti-corruption,it can't reserve the original fresh,delicacy,taste and color.

In Japan,we can say,tuna's Sashimi is the basic material of Japanese Sashimi.In order to maintain the tuna's quality,when tuna were caught,they must be preprocessed with blood letting,fin cutting,gill cutting,and viscus cleaning.And then freeze the fish body in 55 to 60 Celsius degrees below zero in the rapidly freezing house.

By experiment,the so-called complete freeze is,when the central temperature of fresh body drops gradually to 50 to 60 Celsius degrees below zero,the moisture in tuna's 70% of body completely solid,the nutrients reserved and the retention may reach for 3 years.So it prevents the quality change caused by the fluidity and further guarantees the fish fresh.

On the other hand, in order to maintain the color and the taste feeling in the mouth,the fish must be preserved in the ultra-low temperature environment to avoid tuna's turning brown and the acidfication.