In descending order of prices in the international market tuna is fresh, chilled , frozen products , dry goods and canned food , the most common way of living fish and canned food , as the rich tuna myoglobin , which flesh red, however, due to the individual , affecting muscle cooling rate and freezing speed , can easily cause muscle discoloration, so preservation is extremely important. In general, the appropriate shelf life of tuna to high-speed rail oxymyoglobin generation rate of 52% for the boundaries.
Four fresh technology in the preservation of tuna stored as follows:
A chilled Law
This is a common and simple method of preservation , in addition to ice , in general, also adding 3 % to 7% NaCl, sorbitol and the amount of phosphate in the composite food ice , the fish cut into 3 ~ 5cm thick fillets , put plastic film bag , and then the fish layer by layer in the form of ice into a plastic box stored in 2 ~ -4 ℃ cold storage for small slices of tuna or not directly covered by ice , with this method generally allows the preservation of tuna up to 40 days.
2 , micro-frozen preservation
The 3 ~ 5cm thick tuna fillets -1 ~ -3 ℃ under the conditions of partial freezing preservation, preservation generally 8 to 10 days , the same color and flavor the meat , raw fish available for use .
3 , freezing method
Because tuna myoglobin oxidation rate than mammals 1 to 3 times faster, and temperature influence is particularly evident , in order to maintain its flesh color of tuna in the long-term storage , the meat and taste the same, the general use of frozen storage.
With the advances in the improvement of people's quality requirements and technologies , frozen temperature getting lower and lower by -18 ℃ → -25 ℃ → -35 ℃ → -50 ℃ → -60 ℃, according to the study , 6 frozen -month period , generating a high rate of iron in the myoglobin -35 ℃ -18 ℃ frozen frozen lower than about 33 %, while higher than -78v frozen by only 2% , while energy consumption is so low many, therefore , according to the existing domestic situation , the proposed -35 ℃ frozen . If you want to further extend the storage period , you need to lower the temperature of frozen storage . In addition , it must be noted , frozen tuna must also quickly through temperature ranges -4 ℃ → -7 ℃, otherwise the muscles are easy to change. According to the freezing mechanism is divided into the following two methods :
1 ) the use of fresh frozen composite salt solution CaCl2 solution than the freezing point of sodium chloride (NaCl) solution mechanism of low freezing point and with increasing concentrations of CaCl2 decreased , freezing can be 10% NaCl ~ 20% CaCl2 complex salt solution freeze , the temperature can drop to below fish -30 ℃, such as using 15 ~ 30% CaCl2 ( calcium chloride ) was frozen , the temperature can fall to -35 ~ 50 ℃, characterized by fast freezing , the formation of small ice crystals , which less impact damage and muscle tissue color .
Its process: go head gutted tuna → Wash → CaCl2 brine ( salt compound ) Freeze average temperature treatment → → → secondary frozen ice pack clothing → frozen .
Because of the large fish , weighing dozens of kilograms to hundreds of kilograms from the freezing temperature of -18 ℃ to fish center takes two to three days time , thus affecting the quality of the fish , and quickly frozen, and could easily lead to rupture of the abdominal muscles , head this must be quickly frozen while using average temperature treatment process.
2 ) fresh liquid nitrogen freezer
Premenstrual processed fish will be placed in the tank of liquid nitrogen freezer , cis -speed cooling to -100 ℃ inside the cabinet , and then stored at -100 ℃ tens of minutes, when the center of the fish when the temperature dropped to -45 ℃ , so that the center close to the same temperature and the surface temperature , and then at -25 ℃ ~ -60 ℃ cold frozen . This method has frozen fast, small ice crystals , suitable for frozen tuna and other large fish .
4 , Atmosphere
Atmosphere is fresh tuna after cutting into the polyethylene bag , then filled with a certain percentage of the gas mixture (N215 ~ 20%, O215 ~ 21%, CO260%) sealed package , which can effectively prevent muscle color changes , such as combining 0 ℃ cold storage to extend shelf life to 20 to 25 days , will enable the preservation of micro- preserved frozen until 30 to 40 days . In addition, before MAP , with preservative before dipping sauce for fish muscle be processed, the better preservation .
[ The above information is for reference only and does not represent Keweijiani view]
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