Method for producing frozen fish meat of yellowtail

Abstract

To provide a method capable of producing frozen fish meat of yellowtail resistant to browning of dark muscle during and after thawing.SOLUTION: A method for producing frozen fish meat of yellowtail comprises a freezing step of freezing the fish meat of yellowtail that has dark muscle with oxygen partial pressure of 150 mmHg or higher to obtain frozen fish meat.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing frozen yellowtail fish meat. [Background technology]

[0002] Yellowtail (fish belonging to the Carangidae family, Perciformes) are important farmed fish, accounting for approximately 60% of Japan's total marine aquaculture production. There is also a large demand for wild yellowtail. Demand for these fish is high not only within Japan, but also as an export product. In this situation, approximately 70% of yellowtail for export is frozen, with fresh yellowtail accounting for only about 30%. The reason for the low export volume of fresh yellowtail is that it is difficult to export fresh yellowtail, which has a short shelf life, due to factors such as inadequate cold chains in export destination countries and the time required for customs procedures in certain countries.

[0003] On the other hand, browning of the dark muscle (dark meat) during and after thawing is also an issue for frozen yellowtail. For this reason, products exported to some countries are treated with carbon monoxide to prevent browning of the dark muscle, but as the use of carbon monoxide is prohibited in many countries, this method cannot be relied upon alone.

[0004] As an example of a processing method that does not use carbon monoxide, Patent Document 1 discloses a method for supplying sashimi of yellowtail fish, in which landed fish are instantly slaughtered, bled, and cooled to below 10°C, the cooled fish are filleted into three or two pieces to form skin-on fillets, and within three hours of instant slaughter, the fillets are frozen at a temperature of below -30°C with the skin still on, packaged in film, and transported via a cold chain at -30 to -20°C.The fillets are thawed at a temperature of -1 to 5°C one to 24 hours before use, and at the time of use, the skin is removed from the fillets and the fillets are cut into sashimi pieces. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-153418 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method disclosed in Patent Document 1 requires detailed adjustment of temperature conditions (temperature control) in each process, and may not be effective enough in inhibiting browning of dark muscle after cold thawing. Furthermore, while feeds for improving the color of dark muscle have been reported, they are often ineffective in inhibiting browning of dark muscle after cold thawing. Therefore, the industry continues to demand the development of new technologies for inhibiting browning of dark muscle of yellowtail fish meat after cold thawing.

[0007] Therefore, an object of the present invention is to provide a method for producing frozen yellowtail fish meat in which the dark muscle is less likely to brown during and after thawing. [Means for solving the problem]

[0008] In order to solve the above problems, the present inventors conducted extensive research and found that the above problems can be solved by a production method including a freezing step in which yellowtail fish meat having an oxygen partial pressure of 150 mmHg or more in the dark muscle is frozen to obtain frozen fish meat, thereby completing the present invention.

[0009] That is, the present invention provides the following: <1> ~ <6> This includes embodiments of the present invention. <1> A method for producing frozen yellowtail fish meat, comprising a freezing step of freezing yellowtail fish meat having an oxygen partial pressure of 150 mmHg or more in the dark muscle to obtain the frozen fish meat. <2> The method comprises a cutting step of cutting the tail vein or tail artery of yellowtail fish bodies, a cooling step of cooling the fish bodies whose tail vein or tail artery has been cut in the cutting step, and an oxygen gas injection step of inserting a thin tube into the tail vein or tail artery of the fish bodies cooled in the cooling step and injecting oxygen gas with an oxygen concentration of 50% or more from the thin tube into the fish bodies to obtain fish bodies containing fish meat having an oxygen partial pressure of 150 mmHg or more in the dark muscle. <1> The method for producing frozen yellowtail fish meat according to claim 1. <3> The cutting step is a step of cutting the tail vein or tail artery in the immobilized body of a yellowtail fish. <2> The method for producing frozen yellowtail fish meat according to claim 1. <4> the thin tube used in the oxygen gas injection step is a cannula having an outer diameter of 2 to 5 mm, an inner diameter of 1 to 4 mm, and a length of 3 to 30 cm, and the oxygen gas is injected under conditions in which the pressure of the oxygen gas injection cylinder is 0.1 MPa or more and 0.3 MPa or less, and the injection is carried out for 10 minutes or more; <2> or <3> The method for producing frozen yellowtail fish meat according to claim 1. <5> In the cooling step, the fish is cooled statically for 24 hours or more and 48 hours or less. <2> ~ <4> 1. A method for producing frozen yellowtail fish meat according to any one of the above. <6> After obtaining the fish meat in which the oxygen partial pressure in the dark muscle has been increased to 150 mmHg or more, the fish meat is frozen in the freezing step within 6 hours while being maintained at 5°C or less to obtain the frozen fish meat. <1> ~ <5> 1. A method for producing frozen yellowtail fish meat according to any one of the above. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for producing frozen yellowtail fish meat in which the dark muscle is less likely to brown during and after thawing. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1A is a schematic diagram of an example of an oxygen gas injection device equipped with a thin tube used in an embodiment of the present invention, and FIG. 1B is a schematic diagram of an example of an embodiment in which the thin tube of this oxygen gas injection device is inserted into the tail vein to inject oxygen gas into the yellowtail fish body. [Figure 2] 1 is a graph showing the intensity of redness (a*) and oxygen partial pressure (mmHg) (upper row) in the dark muscle of yellowtail fillets before freezing, and the intensity of redness (a*) and the proportion of metmyoglobin (metMb, %) (lower row) in the dark muscle of yellowtail fillets after freezing and thawing, measured and calculated in Example 1. [Figure 3] 1 is a graph showing the percentage of the area of ​​oxygenated parts (oxygenation percentage, %), oxygen partial pressure (mmHg), and redness intensity (a*) in the dark muscles of pre-frozen fillets of yellowtail head, middle, and tail, measured and calculated in Example 2. [Figure 4] 1 is a graph showing the intensity of redness (a*) in the dark muscle of yellowtail head, middle, and tail fillets after freezing and thawing, measured in Example 2. [Figure 5] 1 is a graph showing the percentage of the area of ​​oxygenated parts (oxygenation percentage, %), oxygen partial pressure (mmHg), and redness intensity (a*) in the dark muscles of pre-frozen fillets of yellowtail head, middle, and tail, measured and calculated in Example 3. [Figure 6] 1 is a graph showing the intensity of redness (a*) in the dark muscle of yellowtail head, middle, and tail fillets after freezing and thawing, measured in Example 3. [Figure 7] 1 is a graph showing the percentage of the area of ​​oxygenated parts (oxygenation percentage, %), oxygen partial pressure (mmHg), and redness intensity (a*) in the dark muscles of pre-frozen fillets of yellowtail head, middle, and tail, measured and calculated in Example 4. [Figure 8] 1 is a graph showing the intensity of redness (a*) in the dark muscle of yellowtail head, middle, and tail fillets after freezing and thawing, measured in Example 4. [Figure 9] FIG. 1 is a scatter diagram graph summarizing the relationship between the intensity of redness (a*) of the dark muscle of yellowtail fillets before freezing or after freezing and thawing and the oxygen partial pressure (mmHg) before freezing in Examples 1 to 4. [Figure 10] 1 is a graph showing the oxygen partial pressure (mmHg) and redness intensity (a*) in the dark muscle of yellowtail head fillets before freezing or after freezing and thawing, measured in Example 5. [Figure 11] 1 is a graph showing the change over time in oxygen partial pressure (mmHg) after oxygen gas injection in the dark muscle of a yellowtail head fillet before freezing, as measured in Example 6. [Figure 12] 10 is a graph showing the intensity of redness (a*) in the dark muscle of amberjack head fillets before freezing or after freezing and thawing, measured in Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will now be described. The present invention relates to a method for producing frozen yellowtail fish meat, which includes a freezing step of freezing yellowtail fish meat having an oxygen partial pressure of 150 mmHg or more in the dark muscle to obtain the frozen fish meat. Hereinafter, this method may also be referred to as the "method for producing frozen yellowtail fish meat according to the present invention."

[0013] In the present invention, "yellowtail" refers to nine species of fish belonging to the family Carangidae of the order Perciformes, genus Yellowtail. Specifically, it refers to any of the following: yellowtail, amberjack, longfin amberjack, yellowtail kingfish, Samsonfish, Guinean amberjack, lesser amberjack, fortune jack, or banded ladderfish. Yellowtail are classified by their total length (length from head to tail), with those over 80 cm in length being called yellowtail, and those under 80 cm being called yellowtail, Japanese amberjack, Spanish mackerel, Japanese Spanish mackerel, or Japanese mejiro, but they are all the same species. The yellowtails in the present invention may be either farmed or wild fish, but the method for producing frozen yellowtail fish meat according to the present invention is particularly suitable for use in producing frozen fish meat of farmed yellowtail fish (e.g., sea-farmed fish).

[0014] Hereinafter, the steps included in the method for producing frozen yellowtail fish meat according to the present invention will be described in detail with reference to the drawings. In the drawings, like components are given the same reference numerals, and redundant explanations are omitted where appropriate. For convenience, some parts are not given reference numerals (omitted). The shapes, dimensions, arrangements, materials, etc. of the components described below may be changed or improved without departing from the spirit of the present invention, and the present invention naturally includes equivalents thereof.

[0015] <Freezing process> The method for producing frozen yellowtail fish meat according to the present invention includes at least a freezing step of freezing yellowtail fish meat in which the dark muscle has an oxygen partial pressure of 150 mmHg or more to obtain the frozen fish meat (frozen yellowtail fish meat containing dark muscle). By freezing such yellowtail fish meat in which the dark muscle has an oxygen partial pressure of 150 mmHg or more, the dark muscle is frozen in a sufficiently oxygenated state, and browning of the dark muscle during and after thawing of the obtained frozen yellowtail fish meat can be suppressed. The oxygen partial pressure of the dark muscle is more preferably 160 mmHg or more (defined as 160 mmHg or more), more preferably 200 mmHg or more (defined as 200 mmHg or more), even more preferably 230 mmHg or more (defined as 230 mmHg or more), still more preferably 250 mmHg or more (defined as 250 mmHg or more), and even more preferably 300 mmHg or more (defined as 300 mmHg or more), because this makes it easier to achieve uniform and sufficient oxygenation of the entire dark muscle and makes it easier to achieve the effects of the present invention. ), more preferably 350mmHg or more (defined as 350mmHg or more), even more preferably 400mmHg or more (defined as 400mmHg or more), even more preferably 440mmHg or more (defined as 440mmHg or more), even more preferably 500mmHg or more (defined as 500mmHg or more), even more preferably 550mmHg or more (defined as 550mmHg or more), and even more preferably 600mmHg or more (defined as 600mmHg or more).

[0016] Here, the "oxygen partial pressure in dark muscle" refers to the oxygen partial pressure (average of the three measurements) measured using an oxygen monitor (e.g., a FireSting manufactured by BAS) and a sensor (e.g., an OXF1100 fixed-needle O2 mini sensor manufactured by BAS) by inserting the sensor's detection part into three arbitrary locations on the inner side of the dark muscle of yellowtail. Furthermore, the "inner side of the dark muscle" refers to the inner side that does not include the outer edge when the volume of the area that constitutes the dark muscle is divided into two equal parts: an outer region that includes its outer edge (the edge or cut surface that forms the boundary with other areas such as ordinary muscle) and an inner region that does not include the outer edge. Therefore, this "oxygen partial pressure in dark muscle" essentially means the oxygen partial pressure on the inner side of the dark muscle. The same applies hereinafter.

[0017] This freezing process must involve adjusting the oxygen partial pressure in the dark muscle of fresh yellowtail fish meat to a predetermined level or higher, and then freezing the meat to obtain frozen fish meat. For example, even if frozen yellowtail fish meat (frozen fish meat) is maintained or stored in an oxygen gas atmosphere using oxygen-gas replacement packaging or the like, oxygen gas is difficult to penetrate into the frozen dark muscle, and areas where oxygen gas does not penetrate are likely to occur, such as on the interior side, so browning of the dark muscle during and after thawing may not be sufficiently suppressed. Therefore, in this freezing process, to fully demonstrate the effects of the present invention, it is necessary to process fresh yellowtail fish meat (unfrozen yellowtail fish meat) to adjust the oxygen partial pressure in the dark muscle to a predetermined level or higher, and then freeze this yellowtail fish meat (unfrozen fish meat) with an oxygen partial pressure in the dark muscle that is above the predetermined level. This enables the suppression of browning as described above, including the interior side of the dark muscle.

[0018] The freezing method is not particularly limited, as long as it is a process for freezing yellowtail fish meat whose dark muscle has an oxygen partial pressure equal to or higher than a predetermined level. For example, it may be a method in which the fish meat is left to freeze at an ambient temperature of −20°C or below, or a method in which the fish meat is immersed in a brine solution at −20°C or below and frozen. Furthermore, the fish meat to be frozen may contain other muscle tissues, such as ordinary muscle, in addition to the dark muscle, and may be integrated with other parts (skin, bones, etc.). From the standpoint of ease of freezing and subsequent thawing, the fish meat to be frozen is preferably a processed product containing the dark muscle, such as semi-dressed, dressed, fillet, loin, or fillet (slices), with fillet (slices) being particularly preferred, although round fish (whole fish) may also be used. After freezing (before and after thawing), the fish meat may be processed into the above-mentioned processed products. Since freezing is easier when the oxygen partial pressure in the dark muscle is above a predetermined level, it is more preferable to obtain yellowtail fish meat with an oxygen partial pressure in the dark muscle above a predetermined level, and then freeze (rapidly freeze) this fish meat (including fish and processed fish products containing it) using the freezing step described above within 6 hours, and more preferably within 3 hours, while maintaining it at 5°C or below, more preferably 4°C or below, to obtain frozen fish meat. In other words, it is more preferable to obtain yellowtail fish meat with an oxygen partial pressure in the dark muscle above a predetermined level, and then rapidly freeze this using the freezing step described above within 6 hours, and even more preferably within 3 hours, while maintaining it at 5°C or below, to obtain frozen fish meat (it is more preferable to complete freezing of the entire fish meat within 6 hours, and even more preferably within 3 hours, from the time the oxygen partial pressure in the dark muscle reaches a predetermined level, within 6 hours, and even more preferably within 3 hours, from the time the oxygen partial pressure in the dark muscle reaches a predetermined level). Before freezing, the fish meat is preferably kept at 5°C or below, more preferably 4°C or below, using cold air or ice water (preferably, the temperature of the yellowtail meat, with the oxygen partial pressure in the dark muscle set to a predetermined level, is set to 0°C or above and 5°C or below, more preferably 0°C or above and 4°C or below).

[0019] The method for producing frozen yellowtail fish meat according to the present invention preferably further comprises, prior to the freezing step, a cutting step of severing the tail vein or tail artery in the yellowtail body, a cooling step of cooling the yellowtail body whose tail vein or tail artery has been cut in the cutting step, and an oxygen gas injection step of inserting a thin tube into the tail vein or tail artery of the yellowtail body cooled in the cooling step and injecting oxygen gas with an oxygen concentration of 50% or more through the thin tube into the body to obtain yellowtail body containing fish meat with an oxygen partial pressure of 150 mmHg or more in the dark muscle. This facilitates uniform penetration of oxygen gas into the dark muscle (entire muscle tissue) of the entire fish, making it easier to maintain a uniform oxygen partial pressure of 150 mmHg or more in the dark muscle of the entire fish. These steps will be described in detail below. Note that these steps are steps that are carried out in the above order before the freezing step, as described above.

[0020] <Cutting process> This cutting step is a step of cutting the vein (tail vein) or artery (tail artery) located along the caudal vertebrae in the tail of a yellowtail fish body (fresh fish body). In addition, the yellowtail fish bodies whose tail vein or tail artery is cut in this cutting process are preferably immobilized yellowtail fish bodies, because this makes it easier to improve the quality of the resulting frozen yellowtail meat when thawed and also improves workability. Methods for obtaining immobilized yellowtail fish bodies include, for example, inserting a pick or knife into the area behind the eye (near the caudal direction) of a live fish to destroy the medulla oblongata, applying electrical stimulation to the fish using an electric mat or the like to sedate it (with ice cooling, if necessary), immersing the fish in ice water, bubbling carbon dioxide (and oxygen, if necessary) into the seawater in which the fish are located, or killing the fish by hitting it on the head. Here, "immobilized yellowtail fish bodies" refers to fish that have been rendered unable to move on their own (i.e., they cannot move unless an external force is applied).

[0021] Then, the tail vein or tail artery (at least one of these) in the tail of the yellowtail fish body (preferably an immobilized yellowtail fish body) is cut. This cutting can be performed, for example, by completely cutting the tail of the yellowtail fish body with a knife or the like, but as long as the tail vein or tail artery is cut, the tail may not be completely cut (for example, by making an incision in the tail). Furthermore, the cutting position is not particularly limited as long as it is a position where the tail vein or tail artery can be cut. In this cutting process, as described above, the tail vein or tail artery in the tail of the yellowtail fish is cut, but it is preferable to leave veins and arteries other than the tail vein or tail artery substantially uncut, as this will make it less likely for oxygen gas to leak in the oxygen gas injection process described below and make it easier for the injected oxygen gas to spread throughout the entire fish.

[0022] <Cooling process> This cooling step is a step of cooling the yellowtail fish bodies whose tail vein or tail artery has been cut in the cutting step described above in order to reduce oxygen consumption in the dark muscle (oxygen consumption in muscle tissue) after oxygen gas injection. The temperature of the fish bodies after this cooling should be a temperature that does not cause them to become frozen, but is more preferably between 0°C and 10°C, even more preferably between 0°C and 5°C, and even more preferably between 0°C and 4°C. As a cooling method, for example, a method is shown in which the body of a yellowtail fish, the tail vein or tail artery of which has been cut, is cooled in ice water or on ice, etc. In this case, direct contact between the body of the fish and the ice water, etc. is avoided.

[0023] Furthermore, by sufficiently reducing the oxygen consumption of the dark muscle and more easily maintaining a predetermined or higher oxygen partial pressure in the dark muscle throughout the fish through the oxygen gas injection process, browning of the dark muscle throughout the frozen yellowtail fish during and after thawing can be more easily suppressed. Therefore, in this cooling process, the yellowtail fish with the caudal vein or caudal artery cut is preferably left to cool for 6 hours or more (cooled while being left to cool), more preferably 12 hours or more, even more preferably 24 hours or more, and even more preferably 36 hours or more. The upper limit of this period is not particularly limited, but it may be, for example, 48 hours or less. Here, this period of time includes the period during cooling from the start of the cooling process, i.e., it includes not only the time after the yellowtail fish reaches the above-mentioned temperature range, but also the time during cooling before the temperature reaches the above-mentioned range.

[0024] <Bleeding process> In the present invention, because it becomes easier to maintain the oxygen partial pressure in the dark muscle at a predetermined level or higher, it is more preferable to include a bleeding step after the cutting step and before the cooling step, in which the severed tail vein or tail artery of the yellowtail fish is bled (exsanguinated) in ice, on ice, in freshwater, in seawater, etc. This bleeding method includes leaving the severed tail vein or tail artery open in ice (buried in ice chips) or on ice, or leaving it immersed in iced freshwater or iced seawater, etc. Furthermore, this bleeding step and the cooling step may be performed consecutively or as a single unit.

[0025] In this bleeding step, it is not preferable to cut the gills or other parts of the body and drain blood from sites other than the tail vein or tail artery. In other words, it is preferable to perform bleeding while leaving veins and arteries other than the tail vein or tail artery substantially intact. This is because, in the oxygen gas injection step described below, oxygen gas will easily leak from the gills (veins or arteries near the gills), making it difficult for the injected oxygen gas to be distributed throughout the fish.

[0026] <Oxygen gas injection process> This oxygen gas injection process involves inserting a thin tube into the tail vein or tail artery of the yellowtail fish body that has been cooled in the cooling process, and injecting oxygen gas with an oxygen concentration of 50% or more into the fish body (through the inserted thin tube) so that the oxygen gas penetrates the blood vessels of the fish body into the entire dark muscle (including the inner side), thereby obtaining fish bodies containing fish meat in which the oxygen partial pressure in at least the dark muscle is 150 mmHg or more. Here, "oxygen gas" refers to the remainder, if any, being at least one selected from nitrogen gas, carbon dioxide gas, and argon gas (the remainder being at least one selected from the group consisting of nitrogen gas, carbon dioxide gas, and argon gas), i.e., a gas consisting of oxygen gas or a mixed gas of oxygen gas and at least one selected from nitrogen gas, carbon dioxide gas, and argon gas. The oxygen concentration (volume percentage of oxygen gas) of the injected oxygen gas is 50% or more, but because this makes it easier to maintain the oxygen partial pressure of the dark muscle at a predetermined level, it is more preferable to inject oxygen gas with an oxygen concentration of 70% or more, even more preferable to inject oxygen gas with an oxygen concentration of 80% or more, even more preferable to inject oxygen gas with an oxygen concentration of 90% or more, and even more preferable to inject oxygen gas with an oxygen concentration of 100% (gas consisting of oxygen gas).

[0027] Furthermore, in this oxygen gas injection step, it is more preferable to inject oxygen gas while cooling the yellowtail fish bodies (for example, at an ambient temperature of 10°C or less), but the cooling temperature in this case may be the same as in the cooling step described above. That is, it is sufficient to use a temperature that does not cause the fish to become frozen, but a temperature of 0°C or higher and 10°C or lower is preferable, a temperature of 0°C or higher and 5°C or lower is more preferable, and a temperature of 0°C or higher and 4°C or lower is even more preferable. However, cooling the yellowtail fish bodies is not essential in this oxygen gas injection step, and this oxygen gas injection step may also be carried out at an ambient temperature of, for example, higher than 10°C but lower than 30°C.

[0028] In this oxygen gas injection step, a thin tube is inserted into the cut tail vein or tail artery of the yellowtail fish, and oxygen gas is injected. The thin tube may have any shape that allows it to be inserted into the tail vein or tail artery of the yellowtail fish, and is not particularly limited. An example is a cylindrical thin tube 10 (cannula) with a hollow structure and an opening at one end (terminal end), as shown in FIG. 1(a). Note that this "cylindrical shape" is not limited to a perfectly circular cylindrical shape, but also includes an elliptical cylindrical shape. Furthermore, the thin tube 10 is connected to a hose 30 (e.g., a rubber hose) via a connecting member 20 (the hose 30 and the hollow structure of the thin tube 10 are in communication), and the hose 30 is connected to an oxygen cylinder. Such a thin tube 10 is inserted into the tail vein or tail artery of the tail 52 (e.g., FIG. 1(b)), and oxygen gas is supplied from the oxygen cylinder at a predetermined cylinder pressure. Although Fig. 1(b) shows an embodiment in which oxygen gas is injected directly into the yellowtail fish body (without cooling), oxygen gas may be injected into the fish body while the fish body is in contact with ice, ice water, etc. Furthermore, the orientation and position of the fish body are not particularly limited.

[0029] In particular, because it becomes easier to adjust the oxygen partial pressure of the dark muscle to a predetermined level, it is more preferable that the thin tube used in this oxygen gas injection step be a cannula with an outer diameter of 2 to 5 mm (more preferably 2 to 3 mm), an inner diameter of 1 to 4 mm (more preferably 1 to 2 mm), and a length of 3 to 30 cm. Furthermore, it is more preferable that the oxygen gas be injected under conditions where the pressure of the oxygen gas injection cylinder is 0.1 MPa or more and 0.3 MPa or less, and the injection is carried out for 10 minutes or more. This injection time is more preferably 12 minutes or more, even more preferably 15 minutes or more, even more preferably 20 minutes or more, and even more preferably 30 minutes or more. The upper limit may be, for example, 200 minutes or less, 180 minutes or less, 100 minutes or less, 60 minutes or less, or 40 minutes or less. Here, the "inner diameter of the cannula tube" refers to the diameter of its internal hollow structure (the inner diameter in a direction approximately perpendicular to the longitudinal direction of the cannula), and the "outer diameter of the cannula tube" refers to the outer diameter in a direction approximately perpendicular to the longitudinal direction of the cannula, both of which are the average values ​​measured at 10 random locations. Furthermore, the "length of the cannula tube" refers to the length from the tip of the cannula to the part where it is connected to a connecting member or the like.

[0030] The material from which the capillary tube is made is not particularly limited, but is preferably made of plastic or metal. Examples of the metal mentioned above include stainless steel and brass. However, the capillary tube may be made of a metal other than the above (e.g., aluminum) or a hard resin material. Furthermore, the capillary tube may have an opening at the end as described above, or may have one or more, more preferably multiple, openings on its side (the surface that forms the longitudinal direction of the capillary tube).

[0031] After obtaining fish meat containing fish meat with a predetermined or higher oxygen partial pressure in the dark muscle through this oxygen gas injection process, the fish meat may be frozen as is in the freezing process described above. However, as described above, the fish may be semi-dressed by removing the internal organs or dressed by removing the head, and then frozen in the freezing process described above. The fish may also be further processed into fillets, loins, fillets, or other processed products before freezing. In other words, a freezing process is performed in which fish meat containing yellowtail fish meat or processed products thereof with an oxygen partial pressure in the dark muscle of yellowtail fish meat of 150 mmHg or higher is frozen to obtain frozen yellowtail fish meat (fish meat or processed fish product containing frozen fish meat). Even if the fish meat is processed, such as by cutting it into pieces, as described above, by keeping it at a low temperature (for example, 5°C or below), the oxygen partial pressure in the dark muscle of fillets, etc., will not drop below 150 mmHg in a short period of time.

[0032] The above-described embodiment provides a method for producing frozen yellowtail fish meat that is capable of producing frozen yellowtail fish meat that is resistant to browning of the dark muscle during and after thawing (i.e., a decrease in the intensity of the red color in the dark muscle). Furthermore, the frozen yellowtail fish meat obtained by this method is resistant to browning of the dark muscle during and after thawing, and therefore can be of high quality with a high intensity of red color in the dark muscle even when thawed and eaten raw. Furthermore, depending on the conditions, it is possible to achieve a ratio of metmyoglobin to the total myoglobin in the dark muscle immediately after cold thawing of less than 30%, or even less than 25%, or even 20% or less, or even 10% or less. Here, the percentage of metmyoglobin in the total myoglobin (oxygenated myoglobin, reduced myoglobin, and metmyoglobin) in the dark muscle is calculated by extracting the water-soluble components in the minced dark muscle in water, filtering the extract, adjusting the pH to near neutral with phosphate buffer, measuring the absorbance (503 nm, 525 nm, 540 nm, 557 nm, 582 nm) using a monochromator microplate reader, and then calculating according to the method of Tang et al. (Tang et al., Journal of Food Science, Vol. 69, No. 9, C717-720, 2004). The same applies below.

[0033] It should be noted that the embodiment described above is merely an example for facilitating understanding of the present invention and does not limit the present invention. In other words, the steps described above may be changed, improved, combined, etc. without departing from the spirit of the present invention.

[0034] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples, and various modifications and the like are possible within the technical concept of the present invention. [Example]

[0035] Example 1 After sedate- ing whole yellowtail fish on an electric mat, the tail was partially cut so that the tail vein could be severed and the fish was cooled in ice for 48 hours. A cylindrical metal (stainless steel) cannula (outer diameter 2.5 mm, inner diameter 1.5 mm, length 8 cm, as shown in Figure 1(a)) was inserted into the tail vein of the cooled fish. The cannula was connected to a pressure-adjustable oxygen tank via a connector and hose. Then, while the fish was cooled in freshwater ice, 100% oxygen gas was injected from the oxygen tank at a pressure of 0.2 MPa for 15 minutes.

[0036] Then, fillets (including dark muscle) approximately 1 cm thick were taken from the upper body near the head of the yellowtail fish after oxygen gas injection and from yellowtail fish treated in the same manner except that oxygen gas injection was not performed. The intensity of redness (a * ) was measured, and the internal oxygen partial pressure was also measured using an oxygen monitor (BAS, FireSting) and a sensor (BAS, OXF1100 fixed needle O2 mini sensor). These fillets were vacuum-packed in oxygen-impermeable film (TOPPAN) using a vacuum packaging device (TOSEI, TOSPACK V-930), frozen in a -40°C freezer for one week, and then thawed under running water (water temperature 14°C) for 5 minutes. The redness intensity (a) of the dark muscle was measured using the spectrophotometer described above at 0, 1, 3, and 8 hours after thawing. * ) and the proportion of metmyoglobin in total myoglobin (metMb, %) was measured using a microplate reader (Multiskan SkyHigh, manufactured by ThermoFisher Scientific). The redness intensity, oxygen partial pressure, and metmyoglobin ratio of the dark muscle measured and calculated above are shown in graphs in Figure 2. In Figure 2, data from samples that received oxygen gas injection are labeled "oxygen gas injection," and data from samples that did not receive oxygen gas injection are labeled "untreated" (the same applies below). The upper row of Figure 2 shows data before freezing, and the lower row shows data after freezing and thawing.

[0037] As a result, it was revealed that the dark muscle of the fillets injected with oxygen gas was sufficiently oxygenated. Specifically, the intensity of redness of the dark muscle of the fillets before freezing (a * The oxygen partial pressure was approximately 3 mmHg for the untreated fish and approximately 680 mmHg for the oxygen-injected fish. * ) was approximately 16 for the untreated fillet, while the oxygen gas injection fillet was approximately 28, resulting in a stronger reddish color, and remained at a higher level than the untreated fillet for at least 8 hours after thawing. Furthermore, the metmyoglobin content of the dark muscle in the fillet after freezing and thawing was approximately 30% for the untreated fillet, while the oxygen gas injection fillet was less than 10%, and remained at a lower level than the untreated fillet for at least 8 hours after thawing. These results confirm that oxygen gas injection allows oxygen gas to penetrate and oxygenate the entire dark muscle, including the inner part, maintaining the reddish color even after freezing and thawing, making browning less likely to progress.

[0038] Example 2 For yellowtail (whole fish), the medulla oblongata was destroyed and immobilized, and then the tail was completely cut. Blood was exsanguinated from the tail vein in iced tap water (fresh iced water), and the fish was left to stand for 3 hours to keep cold. Immediately after this, the water adhering to the fish was wiped off, the fish was placed in a plastic bag, and the fish was left to stand in iced fresh water for 24, 36, or 48 hours without coming into contact with water (all of these times included the initial 3 hours of keeping cold), and a metal cannula similar to that in Example 1 was inserted into the tail vein. Then, while the fish were cooled in iced fresh water, 100% oxygen gas was injected from an oxygen tank at a pressure of 0.2 MPa for 30 minutes (the amount of oxygen gas used per fish was approximately 1 m). 3 ).

[0039] First, fillets (including dark muscle) approximately 1 cm thick were harvested from the area from the tip of the gill cover to the center of the cut tail (the center). Similarly, fillets were harvested from the area between the center and the cut tail (the tail) and from the area between the tip of the gill cover and the center (the head). Photographs of the surface and cross-sections of these fillets (surface and cross-sections in the thickness direction including the dark muscle) were taken with a digital camera (Nikon, D3400). From these images, the percentage of the oxygenated area (%) relative to the dark muscle was calculated using image analysis software Fiji (Rasband, WS, ImageJ, US National Institutes of Health, Bethesda, Maryland, USA, https: / / imagej.nih.gov / ij / , 1997-2018). The graph showing the results is shown in Figure 3. The intensity of redness (a * The oxygen partial pressure on the inner side was also measured. The graph showing these results is also shown in Figure 3. In addition, these fillets were frozen by immersing them in brine at -20°C or below, and then thawed. The intensity of redness of the dark muscle (a * ) was measured. The results are shown in a graph in Figure 4.

[0040] As a result, before freezing, when the cooling time before oxygen gas injection was 24 hours, the percentage of the area of ​​the oxygenated part in the dark muscle of the central and tail was approximately 90%. When the cooling time was increased to 36 hours, the oxygenated area increased further, and when the cooling time was increased to 48 hours, it became clear that the dark muscle of the entire fish was oxygenated. The partial oxygen pressure in the dark muscle of the head was 700mmHg or higher under all conditions, and in the central part was 650mmHg or higher under all conditions. In the tail, the partial oxygen pressure in the dark muscle increased as the cooling time was longer. The intensity of the redness of the dark muscle (a * ) showed roughly the same trend as the oxygenated area. In addition, the results after freezing and thawing showed that the browning of the dark muscle was generally suppressed as the cooling time increased, and the intensity of the redness (a *) tended to increase. In particular, when the cooling time was 48 hours, browning of the dark muscle was suppressed overall from the head to the tail, and the redness increased. In other words, the progression of browning of the dark muscle and the decrease in redness after freezing and thawing tended to be roughly inversely proportional to the efficiency of oxygenation (i.e., oxygen partial pressure) before freezing, and it was shown that the efficiency of this oxygenation before freezing increased when the cooling time before oxygen gas injection was longer.

[0041] Example 3 After destroying the medulla oblongata and immobilizing the whole yellowtail fish, the tail was completely cut off and the fish was bled from the tail vein in iced tap water (freshwater iced water) and left to cool for 3 hours. Immediately afterwards, the fish was wiped to remove any moisture and placed in a plastic bag. The fish was then stored in iced freshwater for up to 48 hours (for cooling) without coming into contact with water, after which a metal cannula similar to that used in Example 1 was inserted into the tail vein. While the fish were cooled in iced freshwater, 100% oxygen gas was infused from an oxygen cylinder at a pressure (cylinder pressure) of 0.05 MPa, 0.1 MPa, or 0.2 MPa for 30 minutes.

[0042] Then, in the same manner as in Example 2, fillets (fillets including dark muscle) about 1 cm thick were taken from the center, tail, and head, and photographs of the surface and cross section were taken to calculate the ratio (%) of the area of ​​the oxygenated part to the dark muscle. In addition, the intensity of redness (a * The oxygen partial pressure on the inner side was also measured. The graph showing these results is shown in Figure 5. In addition, these fillets were frozen by immersing them in brine at -20°C or below, and then thawed. The intensity of redness of the dark muscle (a * ) was measured. The results are shown in a graph in FIG.

[0043] As a result, before freezing, at a pressure of 0.05 MPa, oxygenation of the dark muscle from head to tail was poor, and was approximately 50% overall. At pressures of 0.1 MPa to 0.2 MPa, oxygenation of the dark muscle from head to tail was over 90%. At a pressure of 0.05 MPa, the oxygen partial pressure of the dark muscle was low, at approximately 100 mmHg or less, from head to tail. At a pressure of 0.1 MPa, the head was fairly high at approximately 700 mmHg, and even the middle and tail were over 200 mmHg. At a pressure of 0.2 MPa, it was over 500 mmHg from head to tail. The intensity of redness of the dark muscle (a * ) was less than 20 at a pressure of 0.05 MPa, but was more than 20 at a pressure of 0.1 MPa to 0.2 MPa. On the other hand, when oxygen gas was not injected, the dark muscle was not oxygenated, and the oxygen partial pressure of the dark muscle was low at about 4 mmHg, and the intensity of redness of the dark muscle (a * ) was generally low. In addition, after freezing and thawing, the browning of the dark muscle progressed at a pressure of 0.05 MPa, and the intensity of the redness (a * ) was low, but it was mostly dependent on the cylinder pressure, and the browning of the dark muscle was suppressed, resulting in a * ) increased, and at 0.2 MPa, the browning of the dark muscle from the head to the tail was suppressed, resulting in a high redness. On the other hand, when oxygen gas was not injected, the intensity of redness (a * ) was low.

[0044] Example 4 For whole yellowtail fish, the medulla oblongata was destroyed and immobilized, and then the tail was completely cut. The fish was bled from the tail vein in iced tap water (fresh iced water) and left to cool for 3 hours. The water adhering to the fish was then wiped off, the fish was placed in a plastic bag, and the fish was stored in iced fresh water for up to 48 hours (for static cooling), without contact with water. After that, a metal cannula similar to that used in Example 1 was inserted into the tail vein. While the fish were cooled in iced fresh water, 100% oxygen gas was infused from an oxygen tank at a pressure of 0.2 MPa for 5, 15, or 30 minutes.

[0045] Then, in the same manner as in Example 2, fillets (fillets including dark muscle) about 1 cm thick were taken from the center, tail, and head, and photographs of the surface and cross section were taken to calculate the ratio (%) of the area of ​​the oxygenated part to the dark muscle. In addition, the intensity of redness (a * The oxygen partial pressure on the inner side was also measured. The graph showing these results is shown in Figure 7. In addition, these fillets were frozen by immersing them in brine at -20°C or below, and then thawed. The intensity of redness of the dark muscle (a * ) was measured. The results are shown in a graph in FIG.

[0046] As a result, before freezing, when the oxygen gas injection time was 5 minutes, the dark muscle from the head to the center was oxygenated by about 60-80%, but the tail tended to be less oxygenated, and the dark muscle in the tail was oxygenated by about 50%. When the oxygen gas injection time was 15 minutes, the overall oxygenation rate increased. When the oxygen gas injection time was 30 minutes, the oxygenation rate increased further, and it became clear that the dark muscle throughout the entire fish was oxygenated. When the oxygen gas injection time was 5 minutes, the oxygen partial pressure in the dark muscle from the head to the center was about 300mmHg, but in the tail it was extremely low, well below 150mmHg. When the oxygen gas injection time was 15 minutes or more, the head and center were above 600mmHg under all conditions, and the tail was above 500mmHg under all conditions. The intensity of redness of the dark muscle (a * ) was approximately 17 when oxygen gas was not injected, but after 5 minutes of oxygen gas injection, it was approximately 25 in the head and less than 20 in the tail. After 15 minutes or more of oxygen gas injection, it was approximately 25 from head to tail. Regarding the results after freezing and thawing, when oxygen gas was not injected, the intensity of redness of the dark muscle (a * ) was about 15, but when the oxygen gas injection time was 5 minutes, it rose to over 20 on the head. As the oxygen gas injection time increased, the intensity of redness (a * ) tended to increase (generally to 20 or more).

[0047] FIG. 9 shows the intensity of redness of the dark muscle before freezing (a * ), or the intensity of redness of the dark muscle after freezing and thawing (a * The relationship between the oxygen partial pressure of the dark muscle and the temperature of the frozen meat is shown in a scatter diagram. In the diagram, the dark muscle that was injected with oxygen gas is shown as a black circle (oxygen injected), and the dark muscle that was not injected with oxygen gas is shown as a white circle (untreated). From these results, the intensity of redness of the dark muscle before freezing (a * The correlation coefficient between the oxygen partial pressure of the dark muscle and the oxygen partial pressure of the dark muscle before freezing is R 2 = 0.7085, which was a high correlation. * The correlation coefficient between the oxygen partial pressure of the dark muscle and the oxygen partial pressure of the dark muscle before freezing is R 2 =0.5432, which was also a sufficient correlation.

[0048] Example 5 After destroying the medulla oblongata and immobilizing the whole yellowtail fish, the tail was completely cut and cooled in iced seawater for approximately 1 hour until immobile. A metal (brass) cannula measuring 2.3 mm in outer diameter, 1.3 mm in inner diameter, and 30 cm in length with ten 0.5 mm diameter holes drilled along its lateral side (the longitudinal surface) was inserted into the tail vein of each cooled yellowtail fish. Then, while the fish were cooled in ice, oxygen gas (20-100% oxygen, consisting of nitrogen gas) was infused at a pressure of 0.2 MPa for 30 minutes from an oxygen cylinder filled with oxygen at concentrations ranging from 20 to 100%. After these treatments, fillets (including dark muscle) approximately 1 cm thick were taken from the upper body near the head of each yellowtail. The intensity of redness (a * ) and the internal oxygen partial pressure were measured in the same manner as in Example 1. The results are shown in the upper graph of Figure 10. In addition, the redness intensity (a * ) and the oxygen partial pressure on the inner side were measured in the same manner as in Example 1. A graph showing these results is also shown in the lower part of FIG.

[0049] As a result, the higher the oxygen gas concentration injected, the higher the oxygen partial pressure in the dark muscle. When 100% oxygen gas was injected, the oxygen partial pressure in the dark muscle was 740mmHg, with 80% oxygen gas it was 440mmHg, with 50% oxygen gas it was 166mmHg, and with 20% oxygen gas, the same as air, it was 2.5mmHg. It was shown that by injecting oxygen gas with a concentration of 50% or more, the oxygen partial pressure in the dark muscle can be raised above a specified level. In addition, the intensity of redness (a) of the dark muscle before freezing and after freezing and thawing was * ) also increased generally depending on the oxygen gas concentration.

[0050] Example 6 After destroying the medulla oblongata and immobilizing the whole yellowtail fish, the tails were completely cut and the fish were cooled in iced seawater for approximately 1 hour until they became immobile. A metal cannula similar to that used in Example 5 was then inserted into the tail vein of the cooled yellowtail fish. Then, while the fish were cooled in ice, 100% oxygen gas was injected from an oxygen tank at a pressure of 0.2 MPa for 30 minutes. Fillets (including dark muscle) approximately 1 cm thick were taken from the upper body near the head of the oxygen-injected yellowtail fish. The time-dependent changes in the oxygen partial pressure inside the dark muscle were then examined. Specifically, the fillets were stored in an incubator at 4°C or 20°C, and the time-dependent changes in the oxygen partial pressure inside each dark muscle were measured using the same method as in Example 1. The results are shown in a graph in Figure 11.

[0051] The results revealed that the oxygen partial pressure in dark muscle decreased depending on the time elapsed after oxygen gas injection. When stored at 4°C, it remained above 500mmHg for 6 hours after oxygen injection, but decreased to 1.5mmHg 12 hours after oxygen gas injection. When stored at 20°C, it decreased to 320mmHg 1 hour after oxygen injection, and then rapidly decreased to 1.2mmHg 2 hours after oxygen injection. These results demonstrate that the oxygen partial pressure in dark muscle is significantly dependent on storage temperature.

[0052] Example 7 After destroying the medulla oblongata and immobilizing the whole amberjack fish, the tails were completely cut and the fish were cooled in iced seawater for approximately 1 hour until they were immobile. A metal cannula similar to that used in Example 1 was then inserted into the tail vein of the cooled amberjack fish. While the fish were cooled in ice, 100% oxygen gas was infused from an oxygen cylinder at a pressure (cylinder pressure) of 0.1 to 0.4 MPa for 180 minutes. Fillets (including dark muscle) approximately 1 cm thick were taken from the upper body of the oxygen-injected amberjack fish. The intensity of redness (a * ) was measured in the same manner as in Example 1. The graph showing the results is shown in the upper right of Figure 12. In addition, the intensity of redness (a * ) was measured in the same manner as in Example 1. A graph showing these results is also shown in the upper left of Figure 12. From these results, it became clear that roughly the same effects as those of yellowtail could be obtained with amberjack.

[0053] Furthermore, for the whole amberjack fish, the medulla oblongata was destroyed and immobilized, and then the tail was completely cut off and cooled in iced seawater for approximately 1 hour until immobile. A metal cannula similar to that used in Example 1 was then inserted into the tail vein of the cooled amberjack fish. Then, while these amberjack fish were cooled in ice, 100% oxygen gas was injected from an oxygen tank at a pressure of 0.1 MPa for 30 to 180 minutes. Fillets (including dark muscle) approximately 1 cm thick were taken from the upper body of the oxygen-injected amberjack fish. The intensity of redness (a * ) was measured in the same manner as in Example 1. The graph showing the results is shown in the lower right of Figure 12. In addition, the intensity of redness (a *) was measured in the same manner as in Example 1. The graph showing the results is also shown in the lower left of Figure 12. From these results, it is clear that roughly the same effects as those for yellowtail can be obtained. [Explanation of symbols]

[0054] 100 Oxygen gas injection equipment 10. Cannula 20 Connection 30 Oxygen gas supply unit (hose) 50 Yellowtail fish 52 Tail

Claims

1. A method for producing frozen yellowtail fish meat, comprising: A freezing step of freezing yellowtail fish meat having an oxygen partial pressure of 150 mmHg or more in the dark muscle to obtain the frozen fish meat, A method for producing frozen yellowtail fish meat.

2. A cutting step of cutting the tail vein or tail artery in the body of a yellowtail fish; a cooling step of cooling the fish whose tail vein or tail artery has been cut in the cutting step; an oxygen gas injection step of inserting a thin tube into the tail vein or tail artery of the fish body cooled in the cooling step, and injecting oxygen gas with an oxygen concentration of 50% or more into the fish body through the thin tube, thereby obtaining the fish body containing the fish meat having an oxygen partial pressure of 150 mmHg or more in the dark muscle. The method for producing frozen yellowtail fish meat according to claim 1.

3. 3. The method for producing frozen yellowtail fish meat according to claim 2, wherein the cutting step is a step of cutting the tail vein or the tail artery in the immobilized yellowtail body.

4. 4. The method for producing frozen yellowtail fish meat according to claim 2 or 3, wherein the thin tube used in the oxygen gas injection step is a cannula having an outer diameter of 2 to 5 mm, an inner diameter of 1 to 4 mm, and a length of 3 to 30 cm, and further wherein the oxygen gas is injected under conditions in which the pressure of the oxygen gas injection cylinder is set to 0.1 MPa or more and 0.3 MPa or less for 10 minutes or more.

5. The method for producing frozen yellowtail fish meat according to claim 2 or 3, wherein the fish body is allowed to cool statically for 24 hours or more and 48 hours or less in the cooling step.

6. The fish meat having an oxygen partial pressure in the dark muscle of 150 mmHg or more is obtained, and then the fish meat is frozen in the freezing step while being maintained at 5 ° C. or less within 6 hours to obtain the frozen fish meat. The method for producing frozen yellowtail fish meat according to any one of claims 1 to 3.

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