Freezing method for improving meat quality of tuna sashimi

Abstract

The invention belongs to the technical field of fillet freezing, and particularly relates to a freezing method for improving the meat quality of tuna sashimi. The compound fresh-keeping liquid containing the mint extract and the citric acid is used for soaking the fillets, so that an anti-oxidation and antibacterial protection layer is formed on the surfaces of the fillets; through high-pressure freezing, first-time low-temperature freezing, green tea soaking and second-time low-temperature freezing, inhibition of microorganism and enzyme activity is facilitated, formation of ice crystals is reduced, the situation that in the freezing and unfreezing process of fish meat, due to the fact that cell walls are punctured by the ice crystals, the texture of the fish meat becomes poor is avoided, the elasticity and juiciness of the fish meat are kept, and the meat quality of the fish slices is improved. Therefore, according to the technical scheme, the quality guarantee period of the tuna sashimi can be prolonged, and the meat quality of the tuna sashimi can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fish fillet freezing, and particularly relates to a freezing method for improving the quality of tuna sashimi. Background Art

[0002] Tuna belongs to the Perciformes and Scombridae families and is a relatively large fish in the Scombridae family, widely distributed in the tropical and temperate waters of the world. Tuna not only has delicious meat but also is a high-protein, low-fat food ingredient, rich in various nutrients, and is mainly used for raw consumption.

[0003] However, tuna is generally caught in the open ocean and deep sea, and its fish meat is rich in myoglobin, which is easily combined with oxygen and deteriorated. Therefore, it should be quickly frozen in time after being caught to prevent the fish meat from browning and affecting the fish meat quality. However, conventional freezing methods cannot completely kill bacteria and parasites, and may cause the loss of nutrients (such as unsaturated fatty acids, proteins, etc.) in tuna during the freezing process, damage the fish meat cell structure, resulting in loose texture and juice loss of the fish meat after thawing, and the taste becomes worse, seriously affecting the market of tuna. Summary of the Invention

[0004] The purpose of the present invention is to provide a freezing method for improving the quality of tuna sashimi, which can not only extend the shelf life of tuna sashimi but also improve the quality of tuna sashimi.

[0005] The present invention provides a freezing method for improving the quality of tuna sashimi, including the following steps:

[0006] Washing and draining the fish fillets in sequence to obtain the drained fish fillets;

[0007] Soaking the drained fish fillets in a composite preservative solution to obtain the soaked fish fillets;

[0008] Performing high-pressure freezing treatment on the soaked fish fillets to obtain the pre-treated fish fillets;

[0009] Performing first low-temperature freezing, green tea soaking, and second low-temperature freezing on the pre-treated fish fillets in sequence;

[0010] The composite preservative solution uses water as a solvent and includes 2 - 3 g / L of citric acid and 1 - 3 mL / L of mint extract.

[0011] Preferably, the preparation method of the composite preservative solution includes:

[0012] Washing, drying, and pulverizing mint in sequence to obtain the pulverized material;

[0013] Mixing the pulverized material with water according to a mass-volume ratio of 1 g: 8 - 10 mL and decocting, and the obtained filtrate is the mint extract;

[0014] Mix the mint extract, citric acid and water evenly to obtain a composite preservation solution.

[0015] Preferably, the number of decoction times is 2 to 3 times; the decoction time is 15 to 20 min / time.

[0016] Preferably, when soaking the fish slices with the composite preservation solution, the soaking time is 3 to 5 min; the soaking temperature is 2 to 3 °C.

[0017] Preferably, the high-pressure freezing includes: a pressure of 80 to 90 Mpa, a temperature of -8 to -10 °C, and a time of 15 - 20 min.

[0018] Preferably, the first low-temperature freezing includes: a temperature of -20 to -25 °C and a time of 10 - 12 min.

[0019] Preferably, the second low-temperature freezing includes: a temperature of -35 to -40 °C.

[0020] Preferably, when soaking the fish slices with green tea, the soaking temperature is 1 to 2 °C, and the soaking time is 10 to 15 s;

[0021] The mass concentration of the green tea is 1% to 3%.

[0022] Preferably, the length and width of the fish slices are each < 8 cm;

[0023] The thickness of the fish slices is < 4 cm.

[0024] The present invention provides an application of the freezing method described in the above technical solution in extending the shelf life of tuna sashimi and / or improving the meat quality of tuna sashimi.

[0025] Beneficial effects:

[0026] The present invention provides a freezing method for improving the quality of tuna sashimi, comprising the following steps: successively washing and draining the fish slices to obtain drained fish slices; soaking the drained fish slices in a composite preservation solution to obtain soaked fish slices; subjecting the soaked fish slices to high-pressure freezing treatment to obtain pretreated fish slices; successively carrying out first low-temperature freezing, green tea soaking and second low-temperature freezing on the pretreated fish slices; the composite preservation solution uses water as a solvent and comprises 2-3 g / L of citric acid and 1-3 mL / L of mint extract. By soaking the fish slices in the composite preservation solution containing mint extract and citric acid, it is beneficial to form an antioxidant and antibacterial protective layer on the surface of the fish slices; through high-pressure freezing, first low-temperature freezing, green tea soaking and second low-temperature freezing, it is beneficial to inhibit the activities of microorganisms and enzymes, reduce the formation of ice crystals, avoid the deterioration of texture caused by ice crystals piercing the cell walls during the freezing and thawing of the fish meat, maintain the elasticity and juiciness of the fish meat, and improve the quality of the fish slices. Therefore, the technical solution of the present invention can not only extend the shelf life of tuna sashimi, but also improve the quality of tuna sashimi. Detailed implementation mode

[0027] In the present invention, unless otherwise specified, the raw materials, equipment and methods used are all conventional selections.

[0028] In the present invention, there are no special requirements for the type of tuna; the type of mint is preferably lemon mint (Mentha citrata).

[0029] In order to further illustrate the present invention, the solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they cannot be understood as limiting the protection scope of the present invention.

[0030] Example 1

[0031] A freezing method for improving the quality of tuna sashimi, the steps are as follows:

[0032] (1) After slaughtering the tuna, make fish slices (the thickness of the fish slices is 4 cm, and the length and width are 8 cm respectively), wash them clean and drain the water until there is no dripping water on the surface of the fish slices;

[0033] (2) Crush the washed and dried mint to obtain a crushed product (the crushed product is the material passing through a 100-mesh sieve);

[0034] Mix the crushed product and water according to the mass-volume ratio of 1 g:10 mL and decoct for 20 min for the first time, filter to obtain the first filter residue and the first filtrate; mix the first filter residue and water according to the mass-volume ratio of 1 g:10 mL and decoct for 20 min for the second time, filter to obtain the second filtrate; mix the first filtrate and the second filtrate to obtain mint extract;

[0035] Dissolve the above substances in water according to the dosages of 2 g / L citric acid and 3 mL / L mint extract to obtain a composite preservation solution;

[0036] Cool the composite preservation solution to 2 - 3 °C, and soak the drained fish slices in the composite preservation solution for 5 min. There are no special requirements for the dosage of the composite preservation solution during soaking, as long as the fish slices are completely submerged, to obtain soaked fish slices;

[0037] (3) At 90 Mpa and -10 °C, subject the soaked fish slices to high-pressure freezing for 20 min to obtain pretreated fish slices; at -25 °C, freeze the pretreated fish slices for 10 min to obtain frozen fish slices;

[0038] (4) Prepare a green tea solution with a mass concentration of 2% (there are no requirements for the preparation method of the green tea solution, and it can be brewed conventionally). After cooling the green tea solution to 1 - 2 °C, soak the frozen fish slices in the green tea solution for 10 s, and then freeze and store the fish slices at -40 °C.

[0039] Example 2

[0040] A freezing method for improving the meat quality of tuna sashimi, the steps are as follows:

[0041] (1) Slaughter the tuna and make it into fish slices (the thickness of the fish slices is 4 cm, and the length and width are 7 cm respectively), wash them clean and drain the water until no water drips from the surface of the fish slices;

[0042] (2) Crush the washed and dried mint to obtain a crushed product (the crushed product is the material passing through a 100-mesh sieve);

[0043] Mix the crushed product with water at a mass-to-volume ratio of 1 g:10 mL and decoct for the first time for 20 min, filter to obtain the first filter residue and the first filtrate; mix the first filter residue with water at a mass-to-volume ratio of 1 g:10 mL and decoct for the second time for 20 min, filter to obtain the second filtrate; mix the first filtrate and the second filtrate to obtain mint extract;

[0044] Dissolve the above substances in water according to the dosages of 3 g / L citric acid and 1 mL / L mint extract to obtain a composite preservation solution;

[0045] Cool the composite preservation solution to 2 - 3 °C, and soak the drained fish slices in the composite preservation solution for 5 min. There are no special requirements for the dosage of the composite preservation solution during soaking, as long as the fish slices are completely submerged, to obtain soaked fish slices;

[0046] (3) At 90 Mpa and -10 °C, the soaked fish slices were frozen under high pressure for 20 min to obtain pre-treated fish slices; at -25 °C, the pre-treated fish slices were frozen for 10 min to obtain frozen fish slices;

[0047] (4) Prepare a green tea solution with a mass concentration of 2% (there is no requirement for the preparation method of the green tea solution, and conventional brewing is fine). After cooling the green tea solution to 1 - 2 °C, soak the frozen fish slices in the green tea solution for 10 s, and then freeze and store the fish slices at -40 °C.

[0048] Example 3

[0049] A freezing method for improving the quality of tuna sashimi, the steps are as follows:

[0050] (1) After slaughtering the tuna, make it into fish slices (the thickness of the fish slices is 4 cm, and the length and width are 7 cm respectively), wash them clean and drain the water until no water drips from the surface of the fish slices;

[0051] (2) Crush the cleaned and dried mint to obtain a crushed product (the crushed product is the material passing through a 100-mesh sieve);

[0052] Mix the crushed product with water at a mass-to-volume ratio of 1 g:10 mL and decoct for the first time for 20 min, filter to obtain the first filter residue and the first filtrate; mix the first filter residue with water at a mass-to-volume ratio of 1 g:10 mL and decoct for the second time for 20 min, filter to obtain the second filtrate; mix the first filtrate and the second filtrate to obtain the mint extract;

[0053] Dissolve the above substances in water according to the dosages of 2 g / L citric acid and 3 mL / L mint extract to obtain a composite preservation solution;

[0054] Cool the composite preservation solution to 2 - 3 °C, soak the drained fish slices in the composite preservation solution for 4 min. There is no special requirement for the dosage of the composite preservation solution during soaking, as long as the fish slices are completely submerged, to obtain the soaked fish slices;

[0055] (3) At 85 Mpa and -10 °C, freeze the soaked fish slices under high pressure for 15 min to obtain pre-treated fish slices; at -25 °C, freeze the pre-treated fish slices for 10 min to obtain frozen fish slices;

[0056] (4) Prepare a green tea solution with a mass concentration of 1% (there is no requirement for the preparation method of the green tea solution, and conventional brewing is fine). After cooling the green tea solution to 1 - 2 °C, soak the frozen fish slices in the green tea solution for 10 s, and then freeze and store the fish slices at -38 °C.

[0057] Comparative Example 1

[0058] A freezing method for improving the meat quality of tuna sashimi, the steps are as follows:

[0059] (1) After slaughtering the tuna, make it into fish slices (the thickness of the fish slices is 6 cm, and the length and width are 8 cm respectively), wash them clean and drain the water until there is no dripping on the surface of the fish slices;

[0060] (2) Crush the washed and dried mint to obtain a crushed product (the crushed product is the material passing through a 100-mesh sieve);

[0061] Mix the crushed product with water at a mass-to-volume ratio of 1 g:10 mL and decoct for 20 min for the first time. After filtration, obtain the first filter residue and the first filtrate; mix the first filter residue with water at a mass-to-volume ratio of 1 g:10 mL and decoct for 20 min for the second time. After filtration, obtain the second filtrate; mix the first filtrate and the second filtrate to obtain a mint extract;

[0062] Add the above substances to water for dissolution according to the dosages of 5 g / L citric acid and 5 mL / L mint extract to obtain a composite preservative solution;

[0063] Cool the composite preservative solution to 2 - 3 °C, soak the drained fish slices in the composite preservative solution for 5 min. There is no special requirement for the dosage of the composite preservative solution during soaking, as long as the fish slices are completely submerged, to obtain the soaked fish slices;

[0064] (3) At 90 Mpa and -10 °C, subject the soaked fish slices to high-pressure freezing for 20 min to obtain pre-treated fish slices; at -25 °C, freeze the pre-treated fish slices for 10 min to obtain frozen fish slices;

[0065] (4) Prepare a green tea solution with a mass concentration of 2% (there is no requirement for the preparation method of the green tea solution, and it can be brewed conventionally). After cooling the green tea solution to 1 - 2 °C, soak the frozen fish slices in the green tea solution for 10 s, and then freeze and store the fish slices at -40 °C.

[0066] Comparative Example 2

[0067] A freezing method for improving the meat quality of tuna sashimi, the steps are as follows:

[0068] (1) After slaughtering the tuna, make it into fish slices (the thickness of the fish slices is 4 cm, and the length and width are 8 cm respectively), wash them clean and drain the water until there is no dripping on the surface of the fish slices;

[0069] (2) Add the above substances to water for dissolution according to the dosage of 2 g / L citric acid to obtain a preservative solution;

[0070] Cool the fresh-keeping liquid to 2 - 3°C, soak the drained fish slices in the fresh-keeping liquid for 5 min. There are no special requirements for the amount of the fresh-keeping liquid during soaking, as long as the fish slices are completely submerged, and the soaked fish slices are obtained.

[0071] (3) At 90 Mpa and -10°C, high-pressure freeze the soaked fish slices for 20 min to obtain pre-treated fish slices; at -25°C, freeze the pre-treated fish slices for 10 min to obtain frozen fish slices.

[0072] (4) Prepare a green tea solution with a mass concentration of 2% (there are no requirements for the preparation method of the green tea solution, and conventional brewing is fine). After cooling the green tea solution to 1 - 2°C, soak the frozen fish slices in the green tea solution for 10 s, and then freeze and store the fish slices at -40°C.

[0073] Comparative Example 3

[0074] A freezing method for improving the quality of tuna sashimi, the steps are as follows:

[0075] (1) After slaughtering the tuna, make it into fish slices (the thickness of the fish slices is 4 cm, and the length and width are 8 cm respectively), wash them clean and drain the water until no water drips from the surface of the fish slices.

[0076] (2) Crush the washed and dried mint to obtain a crushed product (the crushed product is the material passing through a 100-mesh sieve).

[0077] Mix the crushed product and water according to the mass-to-volume ratio of 1 g:10 mL and decoct for the first time for 20 min, then filter to obtain the first filter residue and the first filtrate; mix the first filter residue and water according to the mass-to-volume ratio of 1 g:10 mL and decoct for the second time for 20 min, then filter to obtain the second filtrate; mix the first filtrate and the second filtrate to obtain the mint extract.

[0078] Dissolve the above substances in water according to the dosages of 2 g / L citric acid and 3 mL / L mint extract to obtain a composite fresh-keeping liquid.

[0079] Cool the composite fresh-keeping liquid to 8 - 9°C, soak the drained fish slices in the composite fresh-keeping liquid for 8 min. There are no special requirements for the amount of the composite fresh-keeping liquid during soaking, as long as the fish slices are completely submerged, and the soaked fish slices are obtained.

[0080] (3) At 90 Mpa and -10°C, high-pressure freeze the soaked fish slices for 20 min to obtain pre-treated fish slices; at -25°C, freeze the pre-treated fish slices for 10 min to obtain frozen fish slices.

[0081] (4) Prepare a green tea solution with a mass concentration of 2% (there are no requirements for the preparation method of the green tea solution, regular brewing is fine). After cooling the green tea solution to 1 - 2 °C, soak the frozen fish slices in the green tea solution for 10 s, and then freeze and store the fish slices at -40 °C.

[0082] Comparative Example 4

[0083] A freezing method for improving the quality of tuna sashimi, the steps are as follows:

[0084] (1) Slaughter the tuna and make it into fish slices (the thickness of the fish slices is 4 cm, and the length and width are 8 cm respectively). Wash them clean and drain the water until there is no dripping on the surface of the fish slices.

[0085] (2) Crush the washed and dried mint to obtain a crushed product (the crushed product is the material passing through a 100-mesh sieve).

[0086] Mix the crushed product and water according to the mass-volume ratio of 1 g:10 mL and decoct for the first time for 20 min. After filtration, obtain the first filter residue and the first filtrate; mix the first filter residue and water according to the mass-volume ratio of 1 g:10 mL and decoct for the second time for 20 min. After filtration, obtain the second filtrate; mix the first filtrate and the second filtrate to obtain the mint extract.

[0087] Dissolve the above substances in water according to the dosages of 2 g / L citric acid and 3 mL / L mint extract to obtain a composite preservative solution.

[0088] Cool the composite preservative solution to 2 - 3 °C, soak the drained fish slices in the composite preservative solution for 5 min. There are no special requirements for the dosage of the composite preservative solution during soaking, as long as the fish slices are completely immersed, and obtain the soaked fish slices.

[0089] (3) At 100 Mpa and -10 °C, subject the soaked fish slices to high-pressure freezing for 25 min to obtain pre-treated fish slices; at -25 °C, freeze the pre-treated fish slices for 10 min to obtain frozen fish slices.

[0090] (4) Prepare a green tea solution with a mass concentration of 2% (there are no requirements for the preparation method of the green tea solution, regular brewing is fine). After cooling the green tea solution to 1 - 2 °C, soak the frozen fish slices in the green tea solution for 10 s, and then freeze and store the fish slices at -40 °C.

[0091] Comparative Example 5

[0092] A freezing method for improving the quality of tuna sashimi, the steps are as follows:

[0093] (1) Slaughter the tuna and make it into fish slices (the thickness of the fish slices is 4 cm, and the length and width are 8 cm respectively). Wash them clean and drain the water until no water drips from the surface of the fish slices;

[0094] (2) Crush the washed and dried mint to obtain a crushed product (the crushed product is the material passing through a 100-mesh sieve);

[0095] Mix the crushed product with water at a mass-to-volume ratio of 1 g:10 mL and decoct for 20 min for the first time. After filtration, obtain the first filter residue and the first filtrate; mix the first filter residue with water at a mass-to-volume ratio of 1 g:10 mL and decoct for 20 min for the second time. After filtration, obtain the second filtrate; mix the first filtrate and the second filtrate to obtain the mint extract;

[0096] Dissolve the above substances in water according to the dosages of 2 g / L citric acid and 3 mL / L mint extract to obtain a composite preservative solution;

[0097] Cool the composite preservative solution to 2 - 3 °C, soak the drained fish slices in the composite preservative solution for 5 min. There is no special requirement for the dosage of the composite preservative solution during soaking, as long as the fish slices are completely immersed, to obtain the soaked fish slices;

[0098] (3) At 90 Mpa and -10 °C, subject the soaked fish slices to high-pressure freezing for 20 min to obtain pre-treated fish slices; at -30 °C, freeze the pre-treated fish slices for 10 min to obtain frozen fish slices;

[0099] (4) Prepare a green tea solution with a mass concentration of 2% (there is no requirement for the preparation method of the green tea solution, and it can be brewed conventionally). After cooling the green tea solution to 1 - 2 °C, soak the frozen fish slices in the green tea solution for 10 s, and then freeze and store the fish slices at -45 °C.

[0100] Comparative Example 6

[0101] A freezing method for improving the quality of tuna sashimi, the steps are as follows:

[0102] (1) Slaughter the tuna and make it into fish slices (the thickness of the fish slices is 4 cm, and the length and width are 8 cm respectively). Wash them clean and drain the water until no water drips from the surface of the fish slices;

[0103] (2) At 90 Mpa and -10 °C, subject the drained fish slices to high-pressure freezing for 20 min to obtain pre-treated fish slices; at -25 °C, freeze the pre-treated fish slices for 10 min to obtain frozen fish slices; then freeze and store the fish slices at -40 °C.

[0104] Application Example 1

[0105] Taking the fish slices stored for 30 days in Examples 1-3 and Comparative Examples 1-6 as experimental objects, the gradient plate dilution method was used to determine the total number of colonies. Each treatment was repeated three times in parallel. The specific method refers to GB / T 4789.2-2022 "Microbiological examination of food hygiene: Determination of total number of colonies". Finally, the average value was statistically analyzed, and the results are shown in Table 1.

[0106] Table 1 Total number of colonies in different treatments

[0107] Treatment 30d(log CFU / g) Example 1 4.1 Example 2 4.4 Example 3 4.5 Comparative Example 1 5.7 Comparative Example 2 5.5 Comparative Example 3 5.8 Comparative Example 4 5.7 Comparative Example 5 6.3 Comparative Example 6 6.5

[0108] It can be seen from the data in Table 1 that after freezing and storing the tuna sashimi for 30 days using the methods provided in Examples 1-3, the number of colonies in the fish meat was 4.1-4.5 log CFU / g; while after using the methods provided in the comparative examples, the number of colonies in the fish meat reached up to 6.5 log CFU / g. Thus, it can be seen that the technical solution provided by the present invention is beneficial to inhibiting the reproduction of microorganisms during storage, and thus extending the storage period of tuna.

[0109] Application Example 2

[0110] According to the results of Application Example 1, taking the fish slices stored for 35 days in Examples 1-3, Comparative Example 1, 2 and Comparative Example 4 as experimental objects, after thawing them, sensory evaluation was carried out. The evaluation criteria are shown in Table 2.

[0111] Table 2 Sensory evaluation criteria

[0112]

[0113]

[0114] Eighteen tasters were randomly divided into 6 groups, with 3 people in each group. They randomly evaluated and scored the fish slices in Examples 1-3, Comparative Example 1, 2 and Comparative Example 4. The results are shown in Table 3.

[0115] Table 3 Sensory scores of fish slices in different treatments

[0116]

[0117] It can be seen from the data in Table 3 that after freezing and storing the tuna sashimi using the methods provided in Examples 1-3, the color, appearance and smell of the sashimi can be well maintained; while after using the methods provided in Comparative Example 1, 2 or 4, the color of the fish meat becomes dull, its appearance is poor, and there is a fishy smell, which is not conducive to improving the quality of the sashimi.

[0118] Application Example 3

[0119] Take the fish meat refrigerated for 35 days in Examples 1-3 and Comparative Example 4, and use a texture analyzer to measure the shear force. Each treatment is repeated three times in parallel, and the average results are statistically analyzed. The results are shown in Table 4.

[0120] Table 4 Shear force of fish meat in different treatments

[0121] Treatment Shearing force (N) Example 1 3.15 Example 2 3.27 Example 3 3.20 Comparative Example 4 1.50

[0122] As can be seen from the data in Table 4, after the sashimi of tuna is frozen for 35 days by the methods in Examples 1-3, the shear force of the fish meat remains at 3.15-3.27 N, while the shear force of the fish meat in Comparative Example 4 is only 1.50 N. This shows that the technical solution provided by the present invention is beneficial to improving the elasticity of tuna meat.

[0123] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all of them. People can also obtain other embodiments based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A freezing method for improving the quality of tuna sashimi, characterized in that: The steps include: Washing and draining the fish fillets in sequence to obtain drained fish fillets; soaking the drained fish fillets in a composite fresh-keeping liquid to obtain soaked fish fillets; The soaked fish fillets are subjected to high pressure freezing treatment to obtain pretreated fish fillets; The pretreated fish fillet is sequentially subjected to a first low-temperature freezing, a green tea soaking and a second low-temperature freezing; The composite fresh-keeping liquid uses water as a solvent and comprises 2-3 g / L of citric acid and 1-3 mL / L of mint extract.

2. The freezing method according to claim 1, characterized in that The preparation method of the composite fresh-keeping liquid comprises: Washing, drying and crushing the mint in sequence to obtain a crushed product; The crushed material is mixed with water in a mass volume ratio of 1 g: 8-10 mL and boiled, and the obtained filtrate is a peppermint extract; The mint extract, citric acid and water are evenly mixed to obtain a composite fresh-keeping liquid.

3. The freezing method according to claim 2, characterized in that: The decoction is performed 2 to 3 times, and the decoction time is 15 to 20 minutes per time.

4. The freezing method according to claim 1 or 2, characterized in that: When the fish fillet is soaked in the composite fresh-keeping liquid, the soaking time is 3 to 5 minutes; and the soaking temperature is 2 to 3°C.

5. The freezing method according to claim 1, characterized in that: The high-pressure freezing includes: a pressure of 80 to 90 MPa, a temperature of -8 to -10°C, and a time of 15 to 20 minutes.

6. The freezing method according to claim 1, characterized in that: The first low-temperature freezing includes: a temperature of -20 to -25°C and a time of 10 to 12 minutes.

7. The freezing method according to claim 1, characterized in that: The second low-temperature freezing includes: a temperature of -35 to -40°C.

8. The freezing method according to claim 1, characterized in that: When the fish fillet is soaked in green tea, the soaking temperature is 1-2° C. and the soaking time is 10-15 seconds; The mass concentration of the green tea is 1% to 3%.

9. The freezing method according to any one of claims 1 to 6, characterized in that: The length and width of the fish fillet are respectively less than 8 cm; The thickness of the fish fillet is <4 cm.

10. Use of the freezing method according to any one of claims 1 to 9 in extending the shelf life of tuna sashimi and / or improving the quality of tuna sashimi.

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