Packaged raw tuna meat, method for manufacturing packaged raw tuna meat, and method for suppressing discoloration of raw tuna chunks.

Abstract

To provide a method for preventing a chunk of raw tuna meat from discoloring during the package.SOLUTION: One aspect of this disclosure provides packaged raw tuna meat comprising an oxygen-impermeable packaging member and a chunk of raw tuna meat packaged by the packaging member along with a gas having an oxygen concentration of 1 vol.% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a packaged raw tuna meat product, a method for producing the packaged raw tuna meat product, a method for inhibiting discoloration of raw tuna chunk meat, a raw tuna chunk meat, and a method for providing the raw tuna chunk meat.

Background Art

[0002] In recent years, consumers' interest in palatability and safety has been increasing, and the freshness and deliciousness of fish meat are being demanded more than ever. As products that maintain the freshness and deliciousness of fish meat for a long time, packaged products with fish meat wrapped therein are widely known. For the purpose of maintaining the freshness of fish meat for a long time, a method of replacing the inside of the packaged product with a predetermined gas is known.

[0003] For example, Patent Document 1 discloses a gas composition for improving the shelf life of fish and shellfish, which comprises a mixed gas of nitrogen gas and carbon dioxide gas at a volume ratio of 7:3 to 4:6, with allyl isothiocyanate gas contained in an amount of 10 to 300 ppm relative to the total of the nitrogen gas, the carbon dioxide gas and the allyl isothiocyanate gas. It is described in Patent Document 1 that by using such a gas composition for improving shelf life, the generation of off-odors in container-packed fish and shellfish can be suppressed for 10 to 14 days, and in particular, the growth of psychrotrophic bacteria, which is a problem in the storage of fish and shellfish, can be effectively suppressed.

[0004] In particular, for large-sized fish such as tuna, instead of distributing the whole fish itself, it is sometimes shaped into chunk meat of a certain size such as a so-called block after landing, and circulated as a processed product. For this reason, it is required to maintain freshness even for such processed products.

[0005] For example, Patent Document 2 discloses a thawing method characterized by packaging or storing highly fresh frozen meat, frozen immediately before rigor mortis, in an oxygen-gas-purged package, and then thawing it. Patent Document 2 also discloses a method for frozen tuna in which the muscle is packaged or stored in an oxygen-gas-purged package to generate bright red oxy-type myoglobin, thereby preventing auto-oxidation of myoglobin, metmyoglobin formation, browning of the meat color, and deterioration of the meat quality. Patent Document 2 states that, as a result of investigating storage conditions that suppress metmyoglobin formation, these methods can improve and maintain the color tone of the muscle of tuna and other fish over a long period of time, promote muscle recovery, suppress drip generation, or improve texture.

[0006] On the other hand, from the perspective of securing marine resources, aquaculture (including livestock farming, hereinafter simply referred to as aquaculture) of tuna and other fish is widely practiced. In aquaculture, fish are raised under controlled environments and feeding conditions, resulting in fish with more fat (abundance) than wild fish, making it possible to provide high-quality processed fish meat. Unlike wild tuna, which can only be obtained in the open ocean, farmed tuna are raised in relatively coastal waters, so they are sometimes processed into blocks and other forms relatively soon after being caught, and shipped as packaged products in a fresh state without freezing.

[0007] The blocks obtained through processing are sometimes tightly packaged in plastic film for distribution. In this case, it has been pointed out that the amount of drip loss increases over time after packaging. To solve this problem, Patent Document 3 proposes cooling the tightly packaged tuna at a temperature of 10°C or lower. According to the technology disclosed in Patent Document 3, it is possible to reduce drip loss during storage and distribution and improve the yield of edible tuna. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 08-070764 [Patent Document 2] Japanese Patent Publication No. 2015-015946 [Patent Document 3] Japanese Patent Publication No. 2006-014630 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, in the case of fresh tuna, even if it is processed into blocks and packaged, the fish meat may discolor if exposed to air for a long time. Also, in recent years, supermarkets and other stores sometimes receive processed products such as blocks, open the packaging at the store, and then further prepare products such as sashimi from the processed product. However, if discoloration has already occurred in the processed product when the packaging is opened, this part cannot be used as a product. Therefore, it becomes necessary to cut off the discolored part, and if there is a lot of discolored part, the product utilization rate, or yield, will decrease.

[0010] This disclosure provides a method for suppressing discoloration of raw tuna chunks, which suppresses discoloration while the tuna is packaged and, in some cases, even after the tuna has been unpacked. [Means for solving the problem]

[0011] This disclosure provides the following: [1] A packaged raw tuna meat product comprising an oxygen-impermeable packaging material and raw tuna meat chunks packaged together with a gas having an oxygen concentration of 1 volume percent or less by the packaging material. [2] The raw tuna meat packaged product according to [1], wherein the gas is an inert gas. [3] The raw tuna meat package according to [2], wherein the inert gas comprises at least one gas selected from the group consisting of nitrogen gas, carbon dioxide gas, helium gas, and argon gas. [4] A packaged raw tuna meat product according to any one of [1] to [3], further comprising a water-absorbing member, wherein part or all of the raw tuna meat is in contact with the water-absorbing member. [5] The oxygen permeability of the above packaging material is 1000 cm 3 / m 2• Raw tuna meat packaged products that are 24hr·atm or less, as described in any of [1] to [4]. [6] The oxygen permeability of the above packaging material is 50 cm 3 / m 2 • Packaged raw tuna meat products that are 24 hours or less per ATM and meet any of the following criteria [1] to [5]. [7] A method for producing a packaged raw tuna product, comprising: cutting up tuna after it has been landed to obtain raw tuna chunks; packaging the raw tuna chunks with an oxygen-impermeable packaging material and performing a gas exchange treatment until the oxygen concentration in the gas inside the packaging is 1 volume% or less; and sealing the packaging material after the gas exchange treatment. [8] A method for producing a packaged raw tuna product according to [7], wherein the gas displacement treatment described above is performed using an inert gas. [9] The method for producing a packaged raw tuna product according to [8], wherein the inert gas is at least one gas selected from the group consisting of nitrogen gas, carbon dioxide gas, helium gas, and argon gas.

[10] A method for producing a packaged raw tuna product according to any one of [7] to [9], further comprising refrigerating the raw tuna block meat until it is packaged with the packaging material described above.

[11] A method for suppressing discoloration of raw tuna chunks, comprising: cutting up tuna after landing to obtain raw tuna chunks; packaging the raw tuna chunks with an oxygen-impermeable packaging material and performing a gas exchange treatment until the oxygen concentration in the gas inside the packaging is 1 volume% or less; and sealing the packaging material after the gas exchange treatment to obtain a packaged raw tuna product.

[12] The method for suppressing discoloration of raw tuna chunks according to

[11] , further comprising refrigerating the raw tuna meat packaged product described above.

[13] The method for suppressing discoloration of raw tuna chunks according to

[12] , wherein the period of refrigerated storage is at least one week.

[14] The method for suppressing discoloration of raw tuna chunks according to

[12] , wherein the period of refrigerated storage is at least 4 weeks.

[15] A packaged raw tuna product comprising an oxygen-impermeable packaging material and raw tuna chunks tightly packaged by the above packaging material, wherein the amount of gas inside the package is 21 mL or less per 1 kg of raw tuna chunks.

[16] The oxygen permeability of the packaging member is 1000 cm 3 / m 2 ·24hr·atm or less, the packaged raw tuna meat according to

[15] .

[17] The oxygen permeability of the packaging member is 200 cm 3 / m 2 ·24hr·atm or less, the packaged raw tuna meat according to

[15] or

[16] .

[18] The packaged raw tuna meat according to any one of

[15] to

[17] , wherein the tensile strength of the packaging member is 80 MPa to 250 MPa.

[19] The packaged raw tuna meat according to any one of

[15] to

[18] , wherein the tensile elastic modulus of the packaging member is 500 MPa to 900 MPa.

[20] A method for producing a packaged raw tuna meat, comprising: cutting tuna after landing to obtain raw tuna chunk meat, and tightly packaging the raw tuna chunk meat with an oxygen-impermeable packaging member, so that the amount of gas in the package is 21 mL or less per 1 kg of the raw tuna chunk meat.

[21] The method for producing a packaged raw tuna meat according to

[20] , further comprising refrigerating and storing the raw tuna chunk meat until it is packaged with the packaging member.

[22] A method for inhibiting discoloration of raw tuna chunk meat, comprising: cutting tuna after landing to obtain raw tuna chunk meat, and tightly packaging the raw tuna chunk meat with an oxygen-impermeable packaging member, so that the amount of gas in the package is 21 mL or less per 1 kg of the raw tuna chunk meat, to obtain a packaged raw tuna meat.

[23] The method for inhibiting discoloration of raw tuna chunk meat according to

[22] , further comprising refrigerating and storing the packaged raw tuna meat.

[24] The method for inhibiting discoloration of raw tuna chunk meat according to

[23] , wherein the period of the refrigerated storage is at least 4 days.

[25] Raw tuna chunk meat taken out from a packaged raw tuna meat that has passed 4 days or more after packaging, wherein the a * value measured by a color difference meter is 14.05 or more and 19 or less 0.5 hours after opening the packaged raw tuna meat, the raw tuna chunk meat.

[26] Raw tuna chunk meat taken out from a packaged raw tuna meat, wherein the a * / b* The value is a 0.5-hour period after opening the raw tuna meat package. * / b * Raw tuna chunks that meet the standard of 99% or higher.

[27] Raw tuna chunks removed from a packaged raw tuna product that has been in packaging for more than four days, and measured with a colorimeter * / b * However, raw tuna chunks that have a pH of 1.29 or higher 0.5 hours after opening the raw tuna meat package.

[28] A method for providing raw tuna chunks, comprising the step of opening a raw tuna meat package, wherein the raw tuna chunks are measured with a colorimeter. * A method of providing raw tuna meat where the value is 17.05 or higher 8 hours after opening the packaged raw tuna meat. [Effects of the Invention]

[0012] According to this disclosure, it is possible to provide packaged raw tuna meat products and a method for suppressing discoloration of raw tuna chunks, in which discoloration is suppressed while the product is packaged and, in some cases, even after the packaging has been removed. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a graph showing the change in the a* value of tuna meat 7 days after packaging according to the embodiment of this disclosure. [Figure 2] Figure 2 is a graph showing the change in the a* / b* value of tuna meat 7 days after packaging according to the embodiment of this disclosure. [Modes for carrying out the invention]

[0014] Preferred embodiments of this disclosure are described below. However, this disclosure is not limited to the embodiments described below.

[0015] In this specification, the time-dependent color changes of raw tuna chunks, as described later, that follow a specific pattern, will be simply referred to as "discoloration" unless otherwise specified. Furthermore, a slowing of the rate of this "discoloration" may be simply referred to as maintaining the color, delaying discoloration, or suppressing discoloration (discoloration suppression). As described later, this "discoloration" refers to a change in color that irreversibly occurs in a specific pattern at room temperature and pressure and in air (oxygen concentration: 21.0 vol%), from a low-saturation red (e.g., dark red) at the time of cutting, to a bright red (e.g., crimson), and then to a red with low brightness and saturation (e.g., dark brown). "Discoloration" does not include temporary color changes of tuna chunks that occur, for example, when exposed to nitrogen gas. In this specification, crimson may be referred to as "bright red" or "pale pink," etc., based on the intensity of its red color.

[0016] In the first embodiment of this specification, when referring to the concentration or quantity of a gas, the concentration or quantity of the gas shall be based on the volume of the gas at room temperature (1 atmosphere) and at temperatures between 0°C and 10°C. In the second embodiment of this specification, when referring to the concentration or quantity of a gas, the concentration or quantity of the gas shall be based on the volume of the gas at room temperature (1 atmosphere) and at temperatures between 18°C ​​and 20°C.

[0017] In this specification, the term "process" includes not only independent processes but also any process that is indistinguishable from other processes, provided that its intended purpose is achieved. In this specification, numerical ranges indicated using "~" represent a range that includes the numbers before and after it as the minimum and maximum values, respectively. In this specification, the amount of each component in a composition means the total amount of multiple substances present in the composition, unless otherwise specified, if multiple substances corresponding to each component exist in the composition. In this specification, the terms "less than" or "less than" with respect to percentages mean a range that includes 0%, i.e., "not present," unless a lower limit is specifically stated, or a value that is undetectable by current means.

[0018] Where this disclosure describes a numerical range that specifies only one or more upper limits and a numerical range that specifies only one or more lower limits for the same subject, unless otherwise specified, a numerical range that is formed by combining an upper limit arbitrarily selected from one or more upper limits and a lower limit arbitrarily selected from one or more lower limits is also included as one embodiment of the present invention. The disclosure is described below.

[0019] <First Embodiment> The first embodiment of the raw tuna meat packaged product according to this disclosure is a raw tuna meat packaged product comprising an oxygen-impermeable packaging member and a block of raw tuna meat packaged by the packaging member together with a gas having an oxygen concentration of 1 volume% or less.

[0020] The first embodiment of the method for manufacturing a packaged raw tuna product according to this disclosure is a method for manufacturing a packaged raw tuna product, which includes: cutting up tuna after it has been landed to obtain chunks of raw tuna meat; packaging the chunks of raw tuna meat with an oxygen-impermeable packaging material; performing a gas exchange treatment until the oxygen concentration in the gas inside the packaging is 1 volume% or less; and sealing the packaging material after the gas exchange treatment.

[0021] The first embodiment of the method for suppressing discoloration of raw tuna chunks according to this disclosure is a method for suppressing discoloration of raw tuna chunks, which includes: cutting up tuna after landing to obtain raw tuna chunks; packaging the raw tuna chunks with an oxygen-impermeable packaging material and performing a gas exchange treatment until the oxygen concentration in the gas inside the packaging is 1 volume% or less; and sealing the packaging material after the gas exchange treatment to obtain the raw tuna meat package.

[0022] According to this disclosure, by packaging the cut raw tuna chunks with a gas having an oxygen concentration of 1% by volume or less using the above-mentioned packaging material, it is possible to provide a packaged raw tuna product in which discoloration is suppressed while it is packaged, and in some cases even after the packaging is removed.

[0023] First, let's explain the changes in the color of fish meat. Generally, the color of fish meat varies depending on the state of myoglobin. Fresh raw tuna meat immediately after being caught is dark red due to reduced myoglobin. When the tuna is cut after being caught, the reduced myoglobin near the cut surface combines with oxygen in the air. This causes the reduced myoglobin to change into oxymyoglobin, and consequently, the color of the raw tuna meat changes from dark red to bright red. It is thought that if the oxidation of oxymyoglobin progresses further, it becomes methoglobin, resulting in a dark brown color.

[0024] Furthermore, it is believed that the color of fish meat is determined not only by changes in myoglobin, but also by various other factors, such as lipid oxidation and metabolic products.

[0025] It is known that the color of raw tuna chunks varies depending on factors such as the part of the tuna and the individual fish. However, the color of raw tuna chunks after cutting generally shows a low-luminosity red (e.g., dark red) at the time of cutting, then a bright red (e.g., crimson), and as time passes, it tends to show a low-luminosity and low-saturation red (e.g., dark brown).

[0026] As mentioned above, the color of raw tuna meat is known to change over time according to a certain pattern, but the cause of this change has not been clearly elucidated.

[0027] According to one aspect of this disclosure, since the raw tuna chunks obtained by cutting the tuna after landing are packaged with a gas of a predetermined oxygen concentration, although the detailed mechanism is not clear, the progression of the color change of the raw tuna chunks over time can be delayed. In other words, according to one aspect of this disclosure, it is possible to provide a packaged raw tuna product with good color retention. This tendency to delay color change can be confirmed in the packaged product and can also be confirmed after the packaging is removed.

[0028] Furthermore, in the first embodiment of the raw tuna meat package according to this disclosure, since the raw tuna chunks are packaged with a gas of a predetermined oxygen concentration, the color change of the raw tuna chunks can be delayed for a longer period than conventional raw tuna meat packaged products, both during packaging and, although the details are not clear, possibly even after the packaging has been removed. In addition, the first embodiment of the raw tuna meat package according to this disclosure can maintain a good color for a longer period than conventional products.

[0029] Furthermore, in the first embodiment of the method for suppressing discoloration of raw tuna chunks according to this disclosure, the raw tuna chunks are packaged together with a gas of a predetermined oxygen concentration. Compared to conventional products, this method delays the change in color of the packaged raw tuna chunks for a longer period, and in some cases, maintains a good color for a longer period even after the packaging is removed.

[0030] Furthermore, conventional packaged raw tuna meat products can discolor not only the surface but also the interior of the raw tuna chunks. In contrast, in one embodiment of the packaged raw tuna meat product according to this disclosure, even if discoloration occurs in the raw tuna chunks, the discoloration can be limited to a shallower part of the surface (surface layer) compared to conventional products. Therefore, the amount of discolored portion that needs to be removed when preparing the final product from the raw tuna chunks can be reduced, and the yield of the final product can be increased compared to conventional products.

[0031] [Packaged raw tuna] One embodiment of the raw tuna meat packaging product according to this disclosure comprises an oxygen-impermeable packaging member and a block of raw tuna meat packaged by the packaging member together with a gas having an oxygen concentration of 1 volume percent or less.

[0032] Examples of tuna to which the above-mentioned packaged raw tuna meat can be applied include those belonging to the genus Thunnus. Among the genus Thunnus, relatively large tuna species are preferably used, such as bluefin tuna, southern bluefin tuna, and Atlantic bluefin tuna. Because the above-mentioned tuna species are relatively large, they are often distributed as processed products, and these tuna species are preferably applicable to the packaged raw tuna meat of this disclosure. The above-mentioned tuna species are generally known to contain relatively large amounts of functional unsaturated fatty acids such as docosahexaenoic acid (DHA). In addition to raw tuna chunks, the above-mentioned packaged raw tuna meat may also contain chunks of other fish. Examples of such other fish include swordfish.

[0033] The tuna to which the above-mentioned packaged raw tuna meat applies may be farmed tuna or wild tuna. Farmed tuna tends to discolor more easily than wild tuna because it contains more fat (i.e., it has more fat), but the packaged raw tuna meat of this disclosure can be applied to it. The discoloration-suppressing effect of this disclosure is more pronounced when the raw tuna chunks include farmed tuna.

[0034] In this specification, "farmed tuna" means tuna that has been raised on compound feed, moist pellets, or live feed for a predetermined rearing period. In this specification, "farming" includes not only artificial seedlings or juvenile fish of a size of several hundred g to 5 kg and aged 0 to 1 year, which are caught and raised for 3 to 5 years, but also "stocking," which involves catching juvenile fish of a size of 5 kg to 300 kg and raising them for a short period, for example, six months to one year.

[0035] In this specification, "raw tuna meat" means fish meat obtained by cutting up a tuna fish (tuna meat after cutting). In this specification, "raw" means that it has not been heated from the outside or frozen, or has not been stored frozen. The tuna to which raw tuna meat packages apply is tuna that has not been heated or frozen, or stored frozen, after being caught.

[0036] Cutting, by convention, refers to the process of sequentially cutting a tuna fish at the time of landing into the following stages: the GG form, which is the tuna fish with the gills and internal organs removed; the "dress" (also called "headless"), which is the GG with the head and tail cut off; the "fillet," which is the dress cut into three pieces and the spine removed; and the "loin," which is the fillet further cut into male and female sections. In this specification, "tuna block meat" includes not only the dress, fillet, and loin mentioned above, but also "blocks" (also called "koro") obtained by further cutting the loin into, for example, two to four pieces perpendicular to the longitudinal direction of the flesh.

[0037] The term "tuna chunks" as described above may include, for example, not the entire tuna body at the time of landing, but rather intermediate forms of fish meat from which at least a part of the fish body has been removed, and in some cases, the form of fish meat that is ultimately consumed. However, tuna chunks do not include the form from which the gills and internal organs have been removed, the so-called "GG". "Tuna chunks" may include, for example, parts of an individual fish, which may be in the conventional processing form in cutting (e.g., the dress, fillet, and loin mentioned above), or may be processed into a different shape. There are no particular restrictions on the shape of tuna chunks that are different from the conventional processing form, and may be shapes derived by further removing parts of the dress, fillet, loin, etc., or any shape cut from an individual fish without depending on the processing form of the dress, fillet, loin, etc.

[0038] More specifically, raw tuna chunks may be tuna chunks in a form referred to as blocks. By putting raw tuna chunks into block form, it is possible to create a packaged raw tuna product that is easy to handle.

[0039] Raw tuna chunks can be made from any part of the tuna's body. For example, raw tuna chunks may be made from the lean meat of the back, the medium fatty meat of the back, the lean meat of the belly, the medium fatty meat of the belly, and the fatty meat of the belly.

[0040] Since the parts of the raw tuna block meat in which discoloration is suppressed can be used directly in final products such as sashimi, discoloration can be suppressed by first packaging the raw tuna meat according to this disclosure after the tuna has been landed, minimizing the effort required to cut off discolored parts and increasing the yield of the final product.

[0041] There are no particular restrictions on the size of the raw tuna chunks. The size of the raw tuna chunks can be set appropriately according to the intended use. For example, if the raw tuna chunk is a loin, it may be 65cm to 90cm in length and 25cm to 35cm in width. If the raw tuna chunk is a block, it may be 25cm square. The thickness of the raw tuna chunk may be, for example, 1cm or more, 3cm or more, 5cm or more, 10cm or more, or 20cm or more. The size of the raw tuna chunk may be small, for example, 5cm x 7cm x 1cm square, and the weight may be around 200g or even around 1kg. The shape of the raw tuna chunk is also acceptable as long as it can be packaged with packaging materials.

[0042] Fresh tuna chunks retain their fresh color almost immediately after being cut. "Immediately after cutting" means, for example, within 30 minutes, 10 minutes, or 5 minutes after cutting is completed. Because cutting exposes the surface of the fresh tuna chunks to the surrounding environment, prolonged exposure to air and other ambient elements can significantly alter the color. Therefore, it is preferable to package fresh tuna chunks immediately after cutting. However, the fresh color can be maintained for a longer period by, for example, packaging the tuna chunks to block out the surrounding environment after cutting and storing them under refrigeration. In this case, fresh tuna chunks within 24 hours or 12 hours after cutting can also retain their fresh color and can be used in the manufacture of packaged fresh tuna products. Within this range, a large amount of reduced myoglobin is retained in the fish meat, allowing it to exhibit a dark red color. This dark red color is distinguishable from the bright red of oxymyoglobin or the dark brown of metmyoglobin.

[0043] According to one embodiment of the raw tuna meat packaging product of this disclosure, the packaged raw tuna meat can maintain the color of the tuna meat immediately after cutting (raw color) for a long period of time. Whether or not a product is the raw tuna meat packaging product of this disclosure can be confirmed, for example, by measurement using a colorimeter. Examples of confirmation methods include, but are not limited to, the following methods.

[0044] First, a packaged raw tuna meat product, packaged with air, is prepared as a standard. For both the raw tuna meat product to be measured and the standard product, the packages are opened, and the color change of the surface of the raw tuna meat block that was wrapped in the packaging material is measured using an appropriate colorimeter or similar device. The results of the product to be measured are compared with the results of the standard product to determine whether the progression of discoloration according to the color change pattern is faster or slower. If the progression of discoloration according to the color change pattern is slow, it can be determined that it is a packaged raw tuna meat product according to this disclosure.

[0045] The leakage of moisture from raw tuna chunks is generally referred to as drip. In the raw tuna meat packaged product according to this disclosure, the exposure of moisture from raw tuna chunks tends to be suppressed, and the amount of drip is reduced.

[0046] The raw tuna meat package may further include a water-absorbing material. That is, the raw tuna chunks may be packaged together with a water-absorbing material. In the raw tuna meat package, part or all of the raw tuna chunks may be in contact with the water-absorbing material. For example, only one side of the raw tuna chunks may be in contact with the water-absorbing material, or the entire raw tuna chunks may be in contact with the water-absorbing material (the raw tuna chunks may be wrapped in the water-absorbing material). By bringing the water-absorbing material into contact with the raw tuna chunks, drip from the raw tuna chunks can be further suppressed. Also, by bringing the water-absorbing material into contact with the raw tuna chunks, discoloration of the surface and surface layer (for example, a layer of several mm from the surface) of the raw tuna chunks by blood, etc. can be more reliably prevented, and the decrease in yield when preparing the final product from the raw tuna chunks can be further suppressed.

[0047] The absorbent material is not particularly limited as long as it is used for this purpose, and can be any material that is typically used for water absorption. Examples of absorbent material shapes include sheets and trays. Specifically, an example of an absorbent material is an absorbent sheet (product name: "Fresh Plate," manufactured by Kinsei Paper Co., Ltd.).

[0048] The packaging material used for packaged raw tuna meat is an oxygen-impermeable packaging material. As an oxygen-impermeable packaging material, for example, a packaging material having an oxygen permeability of a predetermined value or less can be used. The oxygen permeability of such a packaging material is, for example, 1000 cm². 3 / m 2 • 24hr • atm or less, and 500cm 3 / m 2 ·24hr・atm or less, 400cm 3 / m 2 ·24hr・atm or less, 320cm 3 / m 2 ·24hr・atm or less, 300cm 3 / m 2 ·24hr・atm or less, 200cm 3 / m 2 ·24hr・atm or less, 100cm 3 / m 2 ·24hr・atm or less, 50cm 3 / m 2 ·24hr·atm or less, 30cm 3 / m 2 ·24hr・atm or less, 25cm 3 / m 2 ·24hr・atm or less, 20cm 3 / m 2 • 24hr • atm or less, and 10cm 3 / m 2The oxygen permeability may be 24hr·atm or less. Packaging materials having the above-mentioned oxygen permeability can be used individually or in combination of two or more types. Using packaging materials with lower oxygen permeability is preferable from the viewpoint of controlling the oxygen concentration of the gas inside the packaging, and when used individually, it may be advantageous to select packaging materials with lower oxygen permeability. The oxygen impermeability shall be the value measured according to the conditions of JIS K 7126 (23℃, 65%RH).

[0049] Examples of packaging materials include films coated with silicon dioxide, aluminum oxide, aluminum, etc., aluminum foil, and resin films such as polyamide (nylon), polyethylene naphthalate, polyvinylidene chloride, ethylene vinyl copolymer, and polyvinyl alcohol.

[0050] There are no particular restrictions on the shape of the packaging material, and it can be appropriately selected according to the shape of the raw tuna block. The shape of the packaging material may be, for example, a bag shape or a box shape, or any other shape commonly used for this purpose. More specifically, the packaging material may be a bag-shaped packaging material made of a soft material, a box-shaped packaging material made of a hard material, or any other type commonly used for this purpose.

[0051] The packaging material may have a sealing mechanism to retain the gas inside the packaged product. The sealing mechanism in the packaging material may be integrated with the packaging material or it may be detachable. Examples of packaging materials having a sealing mechanism include a packaging material composed of a box-shaped body and a sealing lid, and a packaging material having a snap-fit ​​mechanism and an adhesive member on part of the packaging material. The packaging material does not have to be equipped with a sealing mechanism in advance. In this case, it may be sealed separately by a physically sealing mechanism. Examples of such sealing mechanisms include heat sealing, rubber fasteners, adhesives, adhesive sheets, and clips.

[0052] Specific examples of packaging materials include bags made of a composite film of nylon and polyethylene, and boxes made of polypropylene.

[0053] In packaged raw tuna meat, the oxygen concentration of the gas inside the packaging along with the raw tuna chunks is 1 volume percent or less. The gas inside the packaging may contain oxygen below the detection limit, or it may be a gas that contains no oxygen at all. By keeping the oxygen concentration of the gas inside the packaged raw tuna meat within the above range, discoloration of the raw tuna chunks after cutting can be suppressed, and the progression of discoloration of the raw tuna chunks after unpacking can also be suppressed.

[0054] From the viewpoint of further suppressing discoloration, the oxygen concentration in the gas inside the packaged raw tuna meat may be, for example, 0.8% by volume or less, 0.5% by volume or less, 0.4% by volume or less, 0.3% by volume or less, 0.2% by volume or less, and 0.1% by volume or less. A predetermined gas with an oxygen concentration of 1% by volume or less can be obtained by conventionally known methods. This will be described later.

[0055] The oxygen concentration in the gas inside the packaging can be determined by methods commonly applied to this purpose. For example, the oxygen concentration in the gas inside the packaging of a packaged raw tuna product can be determined by taking a predetermined amount (e.g., 10 mL) of gas from inside the packaging using a syringe and measuring it with an oxygen analyzer.

[0056] In packaged raw tuna meat, as long as the oxygen concentration of the gas packaged with the raw tuna meat is 1 volume percent or less, there are no particular restrictions on the amount of gas inside the package. For example, the amount of gas per 1 kg of raw tuna meat can be 10 L (liters) or less. The amount of gas inside the package may also be adjusted depending on the type of gas. By keeping the amount of gas inside the package within the above range, the color tone of the packaged raw tuna meat can be made more desirable, and the packaged raw tuna meat can be made to maintain its color tone by suppressing discoloration for a longer period of time.

[0057] The gas packaged with the raw tuna chunks may contain an inert gas. Including an inert gas further suppresses the progression of discoloration of the raw tuna chunks, both during packaging and after unpacking. Examples of inert gases include those capable of maintaining an oxygen concentration of 1 volume% or less inside the packaging. Such inert gases include, for example, at least one gas selected from the group consisting of nitrogen gas, carbon dioxide gas, helium gas, and argon gas.

[0058] It is particularly preferable that the inert gas include nitrogen gas. By including nitrogen gas as the inert gas, discoloration can be suppressed for a longer period of time compared to conventional products, both in the packaged product and even after the packaging has been removed. Furthermore, even if discoloration occurs in the raw tuna block after the packaging has been removed, the area where discoloration occurs can be limited to a thinner surface layer compared to conventional products. Note that the color of the surface layer of the raw tuna block that comes into contact with nitrogen gas may temporarily change, but this change in color is reversible, and by removing the packaging and exposing the raw tuna block to air, the surface layer of the raw tuna block can return to a color close to the color at the time of cutting, i.e., dark red or light red.

[0059] The raw tuna meat packaging may include, for example, other components and food materials, as long as they do not impair the effects of this disclosure. Examples of such other components include water-resistant paper and non-absorbent trays. Examples of such food materials include meat.

[0060] The raw tuna meat packaged product relating to this disclosure may also be a raw tuna meat packaged product in which raw tuna chunks are packaged with an oxygen-impermeable packaging material together with a gas containing 21 mL or less of oxygen per kg of raw tuna chunks.

[0061] In this specification, the raw tuna meat package described above, in which raw tuna chunks are packaged with a gas having an oxygen concentration of 1 volume% or less, is referred to as the "first raw tuna meat package," and the raw tuna meat package in which raw tuna chunks are packaged with a gas having an oxygen content of 21 mL or less per 1 kg of raw tuna chunks is referred to as the "second raw tuna meat package." When these are not distinguished, they may simply be referred to as "raw tuna meat package."

[0062] In the second packaged raw tuna product, the raw tuna chunks are packaged with a gas containing 21 mL or less of oxygen per kg of raw tuna chunks. Therefore, similar to the first packaged raw tuna product, discoloration of the surface or interior of the raw tuna chunks is suppressed throughout the packaging period and even after the packaging is opened, and the color tone can be maintained for a long period of time.

[0063] In the second packaged raw tuna product, the raw tuna chunks are packaged with a gas containing 21 mL or less of oxygen per kg of raw tuna chunks. By packaging the raw tuna chunks with a gas containing oxygen within the above range, discoloration of the raw tuna chunks can be effectively suppressed, and the color can be maintained over a long period of time.

[0064] The amount of oxygen in the packaging gas can be, for example, 15 mL or less, 10 mL or less, 8 mL or less, 6 mL or less, 4 mL or less, 3 mL or less, 2.5 mL or less, 2 mL or less, 1.5 mL or less, 1 mL or less, 0.5 mL or less, 0.3 mL or less, and 0.2 mL or less per 1 kg of raw tuna meat. The amount of oxygen can be confirmed, for example, using an oxygen analyzer, as described in relation to the first packaged raw tuna meat product.

[0065] As mentioned above, the amount of gas inside the package is not particularly limited as long as it satisfies the requirement of 21 mL or less of oxygen per 1 kg of raw tuna meat. For example, the amount of gas inside the package per 1 kg of raw tuna meat can be 10 L (liters) or less. The amount of gas inside the package can also be adjusted according to the type of gas. For example, the amount of air inside the package can be 100 mL or less per 1 kg of raw tuna meat. The gas inside the package may include an inert gas. The inert gas applicable to the second raw tuna meat package can be the same as that described for the first raw tuna meat package.

[0066] In the second raw tuna meat package, the raw tuna chunks may be packaged with a gas having an oxygen concentration of 1 volume% or less and an oxygen content of 21 mL or less per kg of raw tuna chunk. In this case, the oxygen concentration may be any other concentration described in the first raw tuna meat package, and the oxygen content per kg of raw tuna chunk may be any other oxygen content as described above, and these may be in any combination to the extent possible.

[0067] The provisions described in relation to the first packaged raw tuna product may be applied to the raw tuna chunks and oxygen-impermeable packaging materials in the second packaged raw tuna product. The provisions described in relation to the first packaged raw tuna product may also be applied to other matters concerning the second packaged raw tuna product.

[0068] [Manufacturing method for packaged raw tuna meat] A first embodiment of the method for manufacturing packaged raw tuna meat according to this disclosure includes: cutting up tuna after it has been landed to obtain chunks of raw tuna meat (hereinafter also referred to as the cutting step); packaging the chunks of raw tuna meat with an oxygen-impermeable packaging material and performing a gas replacement treatment until the oxygen concentration in the gas inside the packaging is 1 volume% or less, and / or until the amount of oxygen in the gas inside the packaging is 21 mL or less per kg of raw tuna meat (hereinafter also referred to as the packaging step); and sealing the packaging material after the gas replacement treatment (hereinafter also referred to as the sealing step). The method for manufacturing packaged raw tuna meat according to this disclosure may include other steps as necessary.

[0069] According to this manufacturing method, the aforementioned packaged raw tuna meat product can be obtained efficiently.

[0070] In the cutting process, the tuna after being landed is cut using, for example, a cutting tool. The tuna may be killed using the ikejime method at the time of landing. In this specification, "ikejime" means the process of paralyzing the landed tuna (live fish) to induce brain death, followed by bleeding. The tuna may be paralyzed using methods that are normally employed at the time of landing. Methods for paralysis include, for example, carbon dioxide gas, cold water immersion, and electric shockers. Of these methods, the method using an electric shocker is preferred because it can avoid excessive muscle movement at the time of landing and suppress the occurrence of so-called burnt meat.

[0071] From the time of landing until the tuna is cut, it is preferable to store the tuna in a refrigerated state in order to maintain its fresh condition. In other words, the cutting process may further include refrigerating the tuna after it has been landed. The temperature for refrigeration may be cold, for example, 10°C or below, 4°C or below, 2°C or below, or 0°C or below, and above the freezing point.

[0072] The tuna provided for the cutting process may be either wild tuna or farmed tuna. The wild tuna and farmed tuna may be in their natural form or in the so-called GG form. In the case of farmed tuna, it is preferable that the individual has gained weight and obesity during the rearing period. The weight of the tuna provided for the cutting process is preferably 40 kg or more, more preferably 60 kg or more, and even more preferably 80 kg or more.

[0073] The fatness of the tuna provided for the cutting process is preferably 20 or higher, more preferably 22 or higher, and even more preferably 24 or higher. Such tuna is a so-called fatty fish (toro) with abundant fat throughout the entire individual, and has high commercial value when processed into a product, making it desirable as a food. In this specification, "fatness" means a value calculated from the total weight and fork length of the tuna according to the following formula. Obesity level = {Total body weight (g) / [Fork length (cm)]} 3} × 1000

[0074] Cutting can be carried out at room temperature, for example, at 18-20°C. From the viewpoint of preserving the freshness and preventing discoloration of the raw tuna chunks, it is preferable to cut the tuna as soon as possible after landing, for example, within 24 hours or within 12 hours of landing.

[0075] The cutting can be performed using a cutting tool that can cut the fish into pieces of a predetermined size. There are no particular restrictions on the cutting tool, and examples include kitchen knives, cutters, and cutting machines. As for the cutting tool, a relatively short kitchen knife is preferable. The blade length of such a knife is preferably 50 cm or less, more preferably 20 cm or more and less than 30 cm, and even more preferably 20 cm or more and 28 cm or less. By using such a cutting tool, relatively soft fish bodies, such as fish bodies immediately after being caught, and even farmed tuna immediately after being caught, can be reliably cut.

[0076] When cutting the fish, it is preferable to securely fix the fish body in place. Methods of fixation are not particularly limited and include, for example, holding the fish body with personnel or using fixing devices. The fixing method can be appropriately selected considering the size of the fish, efficiency, etc.

[0077] The cutting process may further include trimming the raw tuna chunks obtained by cutting. Trimming helps to shape the raw tuna chunks and improve efficiency in subsequent processing. Any tool that can shape the raw tuna chunks can be used for trimming without restriction. Such trimming tools may include, for example, the cutting tools used during the cutting process, and scissors.

[0078] From the viewpoint of preserving the freshness and preventing discoloration of the raw tuna, it is preferable to store the raw tuna chunks obtained by cutting in a refrigerator until they are packaged with packaging materials. That is, the method for manufacturing packaged raw tuna according to this disclosure may further include storing the raw tuna chunks in a refrigerator. When raw tuna chunks are stored in a refrigerator, it is possible to maintain the color tone immediately after cutting until packaging, and it is not necessary to package the raw tuna chunks immediately after the cutting process.

[0079] The temperature for refrigerated storage is preferably low, for example, 10°C or below, 4°C or below, 2°C or below, or 0°C or below, and above the freezing point, for example, preferably 0°C ± 2°C. If the temperature for refrigerated storage is within the above range, the raw tuna chunks can be stored without freezing and their fresh color can be preserved more effectively. In addition, if discoloration of the raw tuna chunks can be suppressed, they may be stored at a higher temperature than those exemplified above.

[0080] In the packaging process, the raw tuna chunks after cutting are packaged in an oxygen-impermeable packaging material, and a gas replacement treatment is performed until the oxygen concentration of the gas inside the packaging reaches 1 volume percent. In this specification, "gas replacement" means changing the gas inside the packaging, and includes introducing another type of gas into the packaging to replace the gas inside the packaging, and removing the gas constituting the gas inside the packaging to a desired amount.

[0081] There are no particular restrictions on the packaging method, and it can be appropriately selected depending on the shape of the packaging material and the packaging mechanism, for example. Packaging can be carried out at room temperature, for example, in an environment of 18-20°C. Furthermore, the packaging material can be the same as described above for the packaged raw tuna meat, and multiple types of packaging material may be used to more reliably maintain the type and composition ratio of gas inside the package.

[0082] The packaging process is preferably carried out within 24 hours or 12 hours after cutting, from the viewpoint of suppressing discoloration of the raw tuna chunks, and may be carried out immediately after the cutting process. If the raw tuna chunks are refrigerated after cutting, the packaging process may be carried out immediately after the end of refrigerated storage. If the raw tuna chunks are refrigerated after cutting, the packaging process does not need to be completed within approximately 24 hours of landing, as long as it is carried out after cutting; for example, it may be completed within 5 days, 4 days, 3 days, or 2 days of landing. If packaging is not carried out immediately after cutting, a processing step may be included before packaging, and the product may be further processed into a desired shape suitable for packaging.

[0083] The gas displacement treatment can be performed by any method that can reduce the oxygen concentration of the gas inside the packaging material to a predetermined value or lower. Examples of gas displacement treatment methods include degassing, gas filling, and combinations thereof. More specifically, gas displacement treatment methods include degassing the inside of the packaging to a desired amount of gas, filling the inside of the packaging material with an inert gas, degassing the inside of the packaging and then filling with an inert gas, and performing these multiple times in succession. Degassing may be performed, for example, using a vacuum packaging machine or by applying pressure from the outside.

[0084] The gas displacement treatment is preferably carried out by repeating a set of filling and degassing treatments with an inert gas multiple times. By performing the gas displacement treatment in this manner, the oxygen concentration of the gas inside the packaging can be more reliably reduced to below a predetermined value. In addition to the above, other methods such as using an oxygen absorber may also be used as the gas displacement treatment method.

[0085] As the inert gas used in the gas displacement treatment, as described above for the packaged raw tuna meat, at least one gas selected from the group consisting of nitrogen gas, carbon dioxide gas, helium gas, and argon gas can be mentioned. The inert gas preferably includes nitrogen gas, and more preferably consists of nitrogen gas.

[0086] In the sealing process, the packaging material is sealed after the gas replacement treatment. That is, the sealing process is a process in which the raw tuna chunks, after being cut, are sealed with a gas having an oxygen concentration of 1 volume% or less using the packaging material. The sealing method can be appropriately selected depending on the type of packaging material. From the viewpoint of retaining the gas inside the packaging, the sealing method is preferably, for example, heat sealing. Through the sealing process, the above-described packaged raw tuna meat product can be obtained in which the raw tuna chunks are packaged together with a predetermined gas.

[0087] The method for producing packaged raw tuna meat may further include refrigerating the packaged raw tuna meat obtained after the sealing process. By further including refrigeration, discoloration of the raw tuna meat can be suppressed for a longer period of time.

[0088] [Method to prevent discoloration of raw tuna chunks] The first embodiment of the method for suppressing discoloration of raw tuna meat according to this disclosure includes: cutting up tuna after landing to obtain raw tuna meat (hereinafter also referred to as the cutting step); packaging the raw tuna meat with an oxygen-impermeable packaging material and performing a gas replacement treatment until the oxygen concentration of the gas inside the packaging is 1 volume% or less, and / or until the amount of oxygen in the gas inside the packaging is 21 mL or less per kg of raw tuna meat (hereinafter also referred to as the packaging step); and sealing the packaging material after the gas replacement treatment to obtain the raw tuna meat package described above (hereinafter also referred to as the sealing step). The above method for suppressing discoloration of raw tuna meat may further include refrigerated storage of the obtained raw tuna meat package (hereinafter also referred to as the refrigerated storage step). The above method for suppressing discoloration of raw tuna meat may include other steps as needed.

[0089] In other words, the method for suppressing discoloration of raw tuna chunks according to this disclosure includes a cutting step, a packaging step, and a sealing step, similar to the method for manufacturing packaged raw tuna meat described above. Therefore, it is possible to delay the change in the color tone of raw tuna chunks in packaged raw tuna meat and maintain the color tone, suppressing discoloration of the raw tuna chunks and maintaining the color tone during packaging, and in some cases even after the packaging has been removed, thereby maintaining a good color tone for a longer period than conventional products. The above method for suppressing discoloration of raw tuna chunks may further include refrigerating the obtained packaged raw tuna meat. By refrigerating the packaged raw tuna meat, the change in the color tone of the raw tuna chunks in packaged raw tuna meat can be further delayed and the color tone can be maintained more sufficiently, suppressing discoloration of the raw tuna chunks and maintaining the color tone more sufficiently during packaging, and in some cases even after the packaging has been removed, thereby maintaining a good color tone for a longer period than conventional products.

[0090] The method for suppressing discoloration of raw tuna chunks according to this disclosure can delay the progression of discoloration and maintain the color tone, thereby suppressing the occurrence of discolored areas in the raw tuna chunks. Furthermore, even if areas of discoloration do occur in the raw tuna chunks, the distance of the discolored area from the surface can be reduced compared to packaged products packaged with air. As a result, the method for suppressing discoloration of raw tuna chunks can increase the yield of the product.

[0091] Up to the sealing step in the method for suppressing discoloration of raw tuna chunks, the entirety of the previously described method for manufacturing packaged raw tuna can be applied.

[0092] In the refrigerated storage process, the packaged raw tuna meat obtained after the sealing process is stored under refrigeration. The temperature in the refrigerated storage process is preferably low, for example, 10°C or below, 4°C or below, 2°C or below, or 0°C or below, and above the freezing point, for example, preferably 0°C ± 2°C. If the temperature in the refrigerated storage process is within the above range, discoloration of the raw tuna meat block can be more suppressed and the color tone can be better maintained until the package is unpacked, and in some cases even after the package is unpacked, allowing for a longer period of good color tone compared to conventional products.

[0093] The refrigerated storage process allows the packaged product to be stored until it is unpacked and the raw tuna block is used or consumed. From the viewpoint of maintaining the freshness, color, and texture of the raw tuna block, the refrigerated storage period can be, for example, at least one week, or at least four weeks. The refrigerated storage period can be terminated within a range where the color and other characteristics of the raw tuna block can be maintained.

[0094] A method for suppressing discoloration of raw tuna chunks may further include the step of unpacking the refrigerated raw tuna meat package. The method of unpacking can be selected depending on the packaging method, and can be applied without limitation, for example, opening, cutting, peeling, and releasing fasteners.

[0095] The packaged raw tuna meat obtained through the method for suppressing discoloration of raw tuna chunks exhibits suppressed discoloration even after the packaging is removed, allowing the color of the raw tuna chunks to be maintained for a longer period than conventional products. Furthermore, the packaged raw tuna meat obtained through the method for suppressing discoloration of raw tuna chunks exhibits suppressed discoloration of the raw tuna chunks, and if discoloration does occur, the affected area is reduced, preferably limited to the shallow surface layer. This allows for higher yields when preparing the final product, even after long-term storage. When an inert gas is used during packaging, discoloration can be suppressed for an even longer period compared to conventional products, not only in the packaged product but also after the packaging is removed.

[0096] The raw tuna meat obtained by the raw tuna meat package product and raw tuna meat discoloration suppression method described herein is raw tuna meat that maintains a good color tone as raw tuna meat and maintains good freshness.

[0097] The fact that this disclosure pertains to raw tuna chunks can be confirmed by the following evaluation method.

[0098] (Checking the discolored area) In raw tuna chunks obtained from the raw tuna meat packaged product relating to this disclosure, the identifiable discolored areas on the surface or inside the meat are fewer compared to raw tuna chunks obtained from conventionally packaged products packaged with air. Therefore, whether or not a target raw tuna meat packaged product is the raw tuna meat packaged product relating to this disclosure can be confirmed by examining the discolored areas of the obtained raw tuna chunks.

[0099] The evaluation method involves unpacking the product, removing the raw tuna block, cutting off a portion of it, and using it as an evaluation sample. The evaluation sample is then cut in the middle, and the cut surface is observed. As the color changes from dark red at the time of cutting to bright red and then dark brown, it is possible to determine whether the product is a raw tuna block from the raw tuna meat packaged product according to this disclosure or a comparative product packaged under air, based on the presence or absence of discoloration from the color at the time of cutting, the presence or absence of discoloration on the surface or inside, or the thickness of the discolored portion.

[0100] Specifically, the packaged product is placed under conditions of room temperature of 18°C ​​and relative humidity of 60-90%, the raw tuna block is removed from the packaging and cut in the middle, and the thickness from the surface of the discolored portion is measured at predetermined intervals. If multiple layers with distinctly different color tones are formed in the thickness direction, the thickness of each layer can be measured. If the thickness of the discolored portion is less than that of a conventional product packaged with air, it can be confirmed that it is the raw tuna block according to this disclosure.

[0101] The raw tuna chunks contained in the raw tuna meat package according to this disclosure, even after being unpacked, exhibit suppressed discoloration and can maintain a good color tone for a longer period compared to conventional products. Therefore, it is possible to obtain raw tuna chunks with a good color tone over a long period, even after being cut from the tuna's catch. Furthermore, after storing these raw tuna chunks with a good color tone for a long period, they can be further processed to provide high-value processed tuna products.

[0102] <Second Embodiment> A second embodiment of the raw tuna meat packaged product according to this disclosure comprises an oxygen-impermeable packaging member and a block of raw tuna meat tightly packaged by the packaging member, wherein the amount of gas inside the package is 21 mL or less per 1 kg of raw tuna meat block.

[0103] A second embodiment of the method for manufacturing packaged raw tuna meat according to this disclosure is a method for manufacturing packaged raw tuna meat, which includes cutting up tuna after it has been landed to obtain chunks of raw tuna meat, tightly packaging the chunks of raw tuna meat with an oxygen-impermeable packaging material, and keeping the amount of gas inside the packaging to 21 mL or less per 1 kg of raw tuna chunks of meat.

[0104] A second embodiment of the method for suppressing discoloration of raw tuna chunks according to this disclosure is a method for suppressing discoloration of raw tuna chunks, which includes cutting up tuna after it has been landed to obtain raw tuna chunks, and tightly packaging the raw tuna chunks with an oxygen-impermeable packaging material, and keeping the amount of gas inside the packaging to 21 mL or less per 1 kg of raw tuna chunks to obtain the packaged raw tuna product.

[0105] The second embodiment will be described below, but the descriptions of common and optional configurations in the second embodiment and the first embodiment described above can be applied to each other. The second embodiment will mainly be described in terms of the parts that differ from the first embodiment described above.

[0106] According to one aspect of this disclosure, since the raw tuna chunks are tightly packaged with the above-mentioned packaging material, and the amount of gas inside the packaging is 21 mL or less per 1 kg of raw tuna chunks, it is possible to provide a packaged raw tuna product in which discoloration is suppressed while it is packaged, and even after the packaging is removed.

[0107] According to one aspect of this disclosure, since the raw tuna chunks obtained by cutting the tuna after landing are tightly packaged in a near-vacuum or vacuum state with a predetermined amount of gas or less, the progression of the color change of the raw tuna chunks over time can be delayed. In other words, according to one aspect of this disclosure, it is possible to provide a packaged raw tuna product with good color retention. This tendency to delay color change can be confirmed in the packaged product and can also be confirmed after the packaging is removed.

[0108] Furthermore, in the second embodiment of the raw tuna meat packaging according to this disclosure, since the raw tuna chunks are tightly packaged in a near-vacuum or vacuum state as described above, the color change of the raw tuna chunks can be delayed for a longer period than conventional raw tuna meat packaging, both during packaging and, in some cases, after unpacking. In addition, in the second embodiment of the raw tuna meat packaging according to this disclosure, a good color condition can be maintained for a longer period than conventional products.

[0109] Furthermore, in the second embodiment of the method for suppressing discoloration of raw tuna chunks according to this disclosure, the raw tuna chunks are tightly packaged in a near-vacuum or vacuum state as described above. Compared to conventional products, this method delays the change in color of the packaged raw tuna chunks for a longer period, and in some cases, maintains a good color for a longer period even after the packaging is removed.

[0110] [Packaged raw tuna] A second embodiment of the raw tuna meat packaged product according to this disclosure comprises an oxygen-impermeable packaging member and a block of raw tuna meat tightly packaged by the packaging member, wherein the amount of gas inside the package is 21 mL or less per 1 kg of raw tuna meat block.

[0111] The packaging material used for packaged raw tuna meat is preferably a film material with mechanical properties of low elongation and high flexibility. When raw tuna chunks are tightly packaged while still fresh, rigor mortis may occur after packaging, causing a phenomenon known as bulging. If a packaging material with high elongation is used, this bulging may create a gap between the raw tuna chunk and the packaging material. Gas inside the packaging can accumulate in this gap, and contact with this accumulated gas may cause discoloration around the bulged portion of the raw tuna chunk. Packaging materials with low elongation are less likely to create the gap caused by the bulging, and therefore tend to suppress discoloration around the bulged portion more effectively. Furthermore, highly flexible packaging materials can conform to the shape of the raw tuna chunk with high precision and uniformly wrap it without crushing it. In other words, highly flexible packaging materials can achieve a higher degree of adhesion to the raw tuna chunk. In this way, by using packaging materials that have mechanical properties such as low elongation and high flexibility, raw tuna chunks can be tightly packaged with a higher degree of vacuum.

[0112] The elongation of the packaging material can be evaluated using tensile strength or elongation at the breaking point as indicators. Tensile strength and elongation at the breaking point shall be values ​​measured under conditions of 23°C and 50%RH in accordance with JIS K 7127.

[0113] The tensile strength of the packaging material may be, for example, 250 MPa or less, and may be between 80 MPa and 250 MPa, or between 100 MPa and 200 MPa. The tensile strength of the packaging material may differ in the longitudinal and transverse directions, and the tensile strength in the longitudinal and transverse directions can be adjusted depending on the shape and material of the packaging material, for example. For example, if the packaging material is a film material prepared by extrusion molding, and the longitudinal direction during extrusion molding is the longitudinal direction of the packaging material and the width direction is the transverse direction of the packaging material, the tensile strength in the longitudinal direction can be 80 MPa to 200 MPa, or 100 MPa to 150 MPa, and the tensile strength in the transverse direction can be 100 MPa to 250 MPa, or 130 MPa to 200 MPa. The tensile strength in the longitudinal and transverse directions can be adjusted by controlling the extrusion speed and winding speed of the film material during extrusion molding, respectively.

[0114] The elongation at the breaking point of the packaging material may be, for example, 200% or less, and may be between 110% and 200%, or between 120% and 180%. The elongation at the breaking point of the packaging material may differ in the longitudinal and transverse directions depending on, for example, the shape and material of the packaging material. For example, if the packaging material is a film material prepared by extrusion molding, and the longitudinal direction during extrusion molding is the longitudinal direction of the packaging material and the width direction is the transverse direction of the packaging material, the elongation at the breaking point in the longitudinal direction can be 120% to 200%, or 130% to 180%, and the elongation at the breaking point in the transverse direction can be 110% to 180%, or 110% to 150%. The tensile strength in the longitudinal direction and the elongation at the breaking point in the transverse direction can be adjusted by controlling the extrusion speed and winding speed of the film material during extrusion molding, respectively.

[0115] The flexibility of packaging materials can be evaluated using Young's modulus (tensile modulus) as an indicator. The tensile modulus (Young's modulus) shall be the value measured under conditions of 23°C and 50%RH in accordance with JIS K 7127.

[0116] The tensile modulus of the packaging material may be, for example, 900 MPa or less, and may be between 500 MPa and 900 MPa, or between 650 MPa and 850 MPa. The tensile modulus of the packaging material may differ in the longitudinal and transverse directions, and the tensile strength in the longitudinal and transverse directions can be adjusted, for example, by the shape and material of the packaging material. For example, if the packaging material is a film material prepared by extrusion molding, and the longitudinal direction during extrusion molding is the longitudinal direction of the packaging material and the width direction is the transverse direction of the packaging material, the Young's modulus in the longitudinal direction can be 500 to 800 MPa or 650 to 700 MPa, and the Young's modulus in the transverse direction can be 550 to 850 MPa or 650 to 850 MPa. The tensile strength in the longitudinal direction and the tensile modulus of the transverse direction can be adjusted by controlling the extrusion speed and winding speed of the film material during extrusion molding, respectively.

[0117] The thickness of the packaging material is preferably, for example, 15 μm to 80 μm, 20 μm to 70 μm, 30 μm to 60 μm, or 35 μm to 50 μm, in order to exhibit the above-mentioned mechanical properties.

[0118] Packaging materials having the above-mentioned oxygen permeability and mechanical properties are preferred from the viewpoint of more securely packaging raw tuna chunks, and can be used without particular limitations as long as they satisfy the above-mentioned conditions. Examples of packaging materials having the above-mentioned oxygen permeability and mechanical properties include co-extruded multilayer films containing ethylene vinyl alcohol (EVOH). Examples of co-extruded multilayer films containing EVOH include "Kurehalon ML40G" (product name, manufactured by Kureha Corporation). Kurehalon ML40G has a multilayer structure (PET / PA / EVOH / PO multilayer structure) in which polyethylene terephthalate (PET), polyamide (PA), EVOH, and polyolefin (PO) are laminated in this order, and has a thickness of 40 μm.

[0119] The sealing mechanism in the packaging material may be integrated with the packaging material or it may be detachable. Examples of packaging materials having a sealing mechanism include packaging materials that have a snap-fit ​​mechanism, adhesive member, etc., on a part of the packaging material. The packaging material does not have to be equipped with a sealing mechanism from the beginning. In this case, it may be sealed separately by a physically sealing mechanism. Examples of such sealing mechanisms include heat sealing, rubber fasteners, adhesives, adhesive sheets, and clips.

[0120] Specific examples of packaging materials include bags made of a composite film of nylon and polyethylene, and boxes made of polypropylene.

[0121] In packaged raw tuna meat, the amount of gas inside the packaging is 21 mL or less per 1 kg of raw tuna meat. By keeping the amount of gas inside the packaged raw tuna meat within the above range, discoloration of the raw tuna meat after cutting can be suppressed, and the progression of discoloration of the raw tuna meat after the packaging is removed can also be suppressed.

[0122] The amount of gas inside the packaging can be confirmed by, for example, the following method: After packaging, the packaged product is left to stand for 10 minutes, then pressure is applied to the entire package by placing it in a container filled with a liquid such as water, causing air bubbles to accumulate in one place on the upper surface of the tuna chunk inside the package. The air bubbles accumulated on the surface are visually observed and drawn into a syringe, and the amount collected in the syringe is measured. This amount is taken as the amount of gas. The measurement should be performed at room temperature (18°C to 20°C).

[0123] The amount of gas inside the packaging may be, for example, 15 mL or less, 10 mL or less, 8 mL or less, 6 mL or less, 4 mL or less, 3 mL or less, 2.5 mL or less, 2 mL or less, 1.5 mL or less, 1 mL or less, 0.5 mL or less, 0.3 mL or less, or 0.2 mL or less per 1 kg of raw tuna meat, and may be below the detection limit, for example, 0 mL. The less gas inside the packaging, the more effectively discoloration can be suppressed.

[0124] The type of "gas" in the second embodiment is not particularly limited and can include, for example, air, oxygen gas, inert gas, and mixtures thereof. Examples of inert gases include nitrogen gas, carbon dioxide gas, helium gas, and argon gas.

[0125] [Manufacturing method for packaged raw tuna meat] A second embodiment of the method for manufacturing packaged raw tuna meat according to this disclosure includes cutting up tuna after it has been landed to obtain raw tuna chunks (hereinafter also referred to as the cutting process), tightly packaging the raw tuna chunks with an oxygen-impermeable packaging material, and keeping the amount of gas inside the packaging to 21 mL or less per kg of raw tuna chunks (hereinafter also referred to as the packaging process), and including other processes as necessary. According to this manufacturing method, the above-mentioned packaged raw tuna meat can be efficiently obtained.

[0126] In the packaging process, the raw tuna chunks are tightly packaged with oxygen-impermeable packaging material, and the amount of gas inside the packaging is kept to 21 mL or less per kg of raw tuna chunks. There are no particular restrictions on the packaging method, and it can be carried out as appropriate depending on the shape of the packaging material and the packaging mechanism. In addition, multiple types of packaging material may be used to more reliably maintain the type and composition ratio of gas inside the packaging. Packaging can be carried out at room temperature, for example, in an environment of 18-20°C.

[0127] Tight packaging can be performed by wrapping the raw tuna block with the packaging material so that it conforms to the shape of the raw tuna block. In this case, it is preferable to package the raw tuna block in such a way that no gas remains between it and the packaging material. By tightly packaging the raw tuna block, the amount of gas inside the resulting packaged raw tuna can be reduced.

[0128] The amount of gas inside a packaged raw tuna product can be reduced to 21 mL or less per kg of raw tuna by, for example, tight packaging as described above. Furthermore, a method to reduce the amount of gas inside the packaging can be used to more reliably keep it below a predetermined level. The method for reducing the amount of gas inside the packaging to a predetermined level or less may be any method known in the industry for this purpose, such as degassing. Degassing may be performed using, for example, a vacuum packaging machine, or by applying external pressure. In addition to the above, methods using oxygen absorbers may also be used to reduce the amount of gas inside the packaging to a predetermined level or less.

[0129] The method for manufacturing a packaged raw tuna product may further include sealing the packaging material after tight packaging (hereinafter also referred to as the sealing step) in order to maintain the amount of gas inside the packaged product for a long period of time after tight packaging. The sealing method can be appropriately selected depending on the type of packaging material. From the viewpoint of maintaining the gas inside the packaging, the sealing method is preferably, for example, heat sealing. The sealing step makes it possible to store the packaged raw tuna product according to this disclosure, in which the raw tuna block meat is packaged so that the amount of gas inside the packaging is below a predetermined amount, for a longer period of time.

[0130] The method for manufacturing packaged raw tuna meat may further include refrigerating the packaged raw tuna meat obtained after the packaging or sealing process. By further including refrigeration, discoloration of the raw tuna meat can be suppressed for a longer period of time.

[0131] [Method to prevent discoloration of raw tuna chunks] A second embodiment of the method for suppressing discoloration of raw tuna chunks according to this disclosure includes cutting up tuna after landing to obtain raw tuna chunks (hereinafter also referred to as the cutting step), and tightly packaging the cut raw tuna chunks with an oxygen-impermeable packaging material, and keeping the amount of gas inside the packaging to 21 mL or less per 1 kg of raw tuna chunks to obtain the raw tuna meat packaged product described above (hereinafter also referred to as the packaging step). The above method for suppressing discoloration of raw tuna chunks may further include refrigerating the obtained raw tuna meat packaged product (hereinafter also referred to as the refrigerated storage step). The above method for suppressing discoloration of raw tuna chunks may include other steps as needed.

[0132] Up to the packaging step in the method for suppressing discoloration of raw tuna chunks, the entirety of the previously described method for manufacturing packaged raw tuna can be applied.

[0133] The refrigerated storage process allows the packaged product to be stored until it is unpacked and the raw tuna chunks are used or consumed. From the viewpoint of maintaining the freshness, color, and texture of the raw tuna chunks, the refrigerated storage period can be, for example, at least 3 days, at least 4 days, at least 5 days, at least 6 days, at least 1 week, at least 2 weeks, at least 3 weeks, or at least 4 weeks. The refrigerated storage period can also be terminated, for example, when the color and other characteristics of the raw tuna chunks can be maintained.

[0134] The raw tuna meat obtained by the raw tuna meat package product and raw tuna meat discoloration suppression method described herein is raw tuna meat that maintains a good color tone as raw tuna meat and maintains good freshness.

[0135] The fact that this disclosure pertains to raw tuna chunks can be confirmed by the following evaluation method.

[0136] (1) Color evaluation The raw tuna meat blocks relating to this disclosure are tightly packaged, and the amount of gas inside the packaging is extremely small or even vacuum-sealed, so the transition from bright red to dark brown is delayed and color change is well suppressed. This color change is measured, for example, by a colorimeter, to measure the change over time from processing to unpacking, and the change over time from opening the sealed package until a predetermined time has elapsed. * value, and a * / b * It can be evaluated and confirmed based on values, etc.

[0137] a of raw tuna meat measured with a colorimeter * The values ​​may be, for example, 14.05 or higher, 15.00 or higher, 16.00 or higher, 17.00 or higher, 17.00 or higher, 17.30 or higher, 17.50 or higher, or 17.7 or higher for the raw tuna meat package that has been packaged for four days or more (for example, four days, five days, six days, or seven days), immediately after opening the raw tuna meat package, 0.5 hours after opening, 2 hours after opening, 4 hours after opening, or 8 hours after opening. * There are no specific restrictions on the upper limit of the value; for example, it can be 20 or less, or 19 or less.

[0138] a of raw tuna meat measured with a colorimeter * / b * The values ​​are measured immediately after opening the raw tuna meat package, 0.5 hours after opening, 2 hours after opening, 4 hours after opening, or 8 hours after opening the raw tuna meat package, which has been in the packaging for 4 days or more (for example, 4 days, 5 days, 6 days, or 7 days, etc.), and the value measured 0.5 hours after opening the raw tuna meat package. * / b * Based on the value, for example, it may be 96% or higher, 99% or higher, 100% or higher, 101% or higher, or 102% or higher, and it may be 120% or lower, 110% or lower, or 105% or lower.

[0139] a of raw tuna meat measured with a colorimeter * / b *In the above-mentioned packaged raw tuna meat product that has been packaged for four days or more (for example, four days, five days, six days, or seven days), the ratio may be 1.46 or higher, 1.48 or higher, 1.50 or higher, 1.60 or higher, or 1.70 or higher immediately after opening the packaged raw tuna meat product, and may be 1.29 or higher, 1.30 or higher, 1.31 or higher, 1.34 or higher, 1.40 or higher, or 1.45 or higher 0.5 hours, 2 hours, 4 hours, or 8 hours after opening the packaged raw tuna meat product. * / b * There are no particular restrictions on the upper limit; for example, it can be 1.90 or less, or 1.80 or less.

[0140] (2) K value The K value is an index represented by the following formula (1), which measures the degree of ATP (adenosine triphosphate) breakdown and quantifies the evaluation of freshness.

[0141] K value =(HxR+Hx) / (ATP+ADP+AMP+IMP+HxR+Hx)×100...(1) In the above formula, ATP represents the adenosine triphosphate content, ADP represents the adenosine diphosphate content, AMP represents the adenosine monophosphate content, IMP represents the inosinic acid content, HxR represents the inosine content, and Hx represents the hypoxanthine content.

[0142] ATP in fish meat is broken down after the fish dies, gradually breaking down into ADP, AMP, IMP, HxR, and Hx. ADP, AMP, IMP, HxR, and Hx are compounds produced during the ATP breakdown process and are also called ATP-related substances. A smaller K value means that the ratio of the total amount of HxR and Hx to the total amount of ATP and ATP breakdown-related substances in the sample is small, indicating that the breakdown from IMP to HxR or Hx has not progressed sufficiently. In other words, a smaller K value means that a larger amount of ATP breakdown-related substances up to IMP (i.e., ATP, ADP, AMP, and IMP) remain, indicating that the fish meat is fresher.

[0143] The K value of the raw tuna block meat obtained by the above method for suppressing discoloration of raw tuna block meat can be, for example, 35% or less, preferably 15% or less, and more preferably 10% or less.

[0144] One embodiment of the method for providing raw tuna chunks according to this disclosure is a method for providing raw tuna chunks that includes the step of opening a raw tuna package. In this method for providing raw tuna chunks, a colorimeter is used to measure the raw tuna chunks. * The value may be 17.05 or higher or 17.38 or higher 8 hours after opening the raw tuna meat package, and the K value of the raw tuna block meat represented by formula (1) above may be 35% or less.

[0145] Although several embodiments have been described above, the descriptions of common configurations can be applied to each other. Furthermore, this disclosure is not limited in any way to the embodiments described above. [Examples]

[0146] The contents of this disclosure will be described in more detail below with reference to examples and comparative examples. However, this disclosure is not limited to the examples described below.

[0147] <First aspect> [Preparing for the exam] (1) Tuna farming 1500 tuna, each weighing approximately 3 kg and having a fork length of approximately 55 cm, were housed in a 40m x 45m Aba-style holding pen to begin rearing. Mackerel and sardines were used as feed, and the tuna were normally fed once a day, and once every two days during the winter. Rearing began in July and continued for more than three years, after which they were paralyzed using an electric shocker and harvested. Immediately after harvesting, the tuna were bled and killed using the ikejime method, and the gills and internal organs were removed using the usual method to obtain tuna GG (Gross Weight). The weight of the obtained tuna GG was over 80 kg, and the obesity score was over 24.

[0148] (2) Juwari The cutting was carried out in a cutting room with a room temperature of 18°C ​​to 20°C. A cutting board known for its non-slip surface was selected. The fish were only held in place by hand, and no special securing devices were used. The worker wore vinyl gloves on both hands, and an additional cut-resistant glove on the hand not holding the knife.

[0149] Immediately after obtaining the tuna gill fillets as described above, the head and tail were first cut off using a knife with a blade length of 20cm to 28cm. Then, following the usual procedure, the fish meat was cut into loins by making cuts along the back and then the belly.

[0150] During the cutting process, when first making cuts along the centerline of the back of the tuna loin, the surface of the loin was cut to a depth of a few millimeters. Then, the knife blade was held at an angle of approximately 10° to 30° relative to the fish's body, and the cuts were made gradually and carefully until the nerve spines were visible. When cutting, the separated pieces of flesh were gently held to prevent tearing, and the process was carried out carefully. The belly side was cut in the same manner. Because it had been caught within a few hours, the flesh was still firm, but by carefully cutting with a relatively short knife, it was possible to reliably obtain four loins.

[0151] Next, trimming was performed to shape the loin. During trimming, the knife was operated so that it was almost parallel to the tuna flesh, at an angle of 5° or less. As described above, the loin was obtained 3 hours after the tuna was killed. The length of the loin was 65cm to 90cm, and the thickness was 15cm to 23cm.

[0152] When storing the obtained loins, they were wrapped in absorbent paper and then placed directly into a plastic bag. The plastic bag containing the loins was then submerged in a 500L polyethylene container box filled with ice water (water temperature 0°C ± 2°C) so that the entire bag was submerged in the ice water. The loins were then refrigerated in this state until use.

[0153] When preparing blocks from the obtained loins, roughly cubic blocks weighing approximately 200g to 3.5kg and with a thickness of approximately 5cm to 25cm were cut from the loins obtained by cutting or from loins that had been stored in the refrigerator, using a knife with a blade length of 20cm to 28cm.

[0154] (3) Packaging materials and absorbent sheets, etc. The following tests were conducted using the loin or block prepared as described above. When preparing sashimi as evaluation samples, fillets measuring approximately 4cm-10cm x 5cm-20cm x 1cm-2cm were prepared from the lean or medium fatty portion on the back side of the loin or block, and then slices approximately 0.5cm-1.0cm thick were prepared to serve as evaluation samples.

[0155] Table 1 shows the packaging types used for evaluation. Table 1 also shows the oxygen permeability of each packaging material. In Table 1, "*1" means that there is almost no oxygen permeability, and "*2" means that packaging of 40.0cm × 20.0cm, 40.0cm × 30cm, or 40.0cm × 50.0cm was appropriately selected and used based on the size of the sample. In Table 1, PE is an abbreviation for polyethylene, and NY is an abbreviation for nylon.

[0156] The products used in Table 1 are as follows: Plastic container: "KeepLock Easy Clean" (deep airtight container, product name, manufactured by Pearl Metal Co., Ltd.) Freezer bags: "Ziploc®" (registered trademark) (product name, manufactured by Asahi Kasei Home Products Corporation) Nylon poly bag: "Shinjumon" (product name, manufactured by Chlorin Kasei Co., Ltd.) Absorbent sheet: "Fresh Plate" (product name, manufactured by Kinsei Paper Co., Ltd.) Cooking sheet: "Fuji Cooking Paper" (product name, manufactured by Fujinap Co., Ltd.) Water-resistant paper: "Sample Roof (registered trademark) G" (cut paper) (product name, manufactured by Asahi Kasei Home Products Corporation)

[0157] [Table 1]

[0158] [Example 1-1] (1) Preparation of Sample 1 and Control Sample Within 24 hours of landing, the tuna GG was cut and processed into blocks, producing six blocks of approximately 1 kg each. These were then divided into three blocks for sample 1 preparation and three blocks for control sample preparation.

[0159] As described above, the blocks for preparing Sample 1 (weights: 1.14 kg, 1.14 kg, and 1.26 kg) were further divided into smaller blocks (size: approximately 7 cm long, 7 cm wide, and 1 cm to 2 cm thick), and packaged using Type I packaging material and absorbent sheets as follows to obtain Sample 1.

[0160] The blocks were sandwiched between absorbent sheets and then placed in a plastic container with a lid. The plastic container was then placed in a freezer bag. Next, with the zipper of the freezer bag mostly closed, a plastic pipette for gas injection was inserted between the plastic container and its lid, and nitrogen gas was injected. When the freezer bag inflated due to the nitrogen gas leaking from the plastic container, the nitrogen gas was released, and the freezer bag was compressed by hand to remove the gas from inside the freezer bag. The process was then repeated until the freezer bag inflated again due to the nitrogen gas leaking from the plastic container. This operation was repeated four times to perform gas exchange inside the plastic container and the freezer bag.

[0161] Finally, once the freezer bag had inflated with nitrogen gas, the pipette was removed from the plastic container and the lid of the plastic container was closed. Next, the freezer bag was slowly compressed to release the gas, the pipette was removed from the freezer bag, and then the zipper of the freezer bag was closed to seal it. In this way, Sample 1, a packaged raw tuna product consisting of a block of raw tuna meat, was prepared. In Sample 1, the oxygen concentration of the gas inside the packaging was 0.1 volume% or less, and the oxygen amount was 0.2 mL to 1.5 mL per 1 kg of raw tuna meat. It was also confirmed that the amount of gas inside the packaging of Sample 1 was 5 L or less per 1 kg of raw tuna meat. The prepared Sample 1 was placed in a polystyrene storage box and stored in a refrigerator kept at approximately 0°C to 2°C until evaluation.

[0162] Furthermore, control samples were prepared using Type IV packaging materials and absorbent sheets for blocks weighing 0.92 kg, 1.24 kg, and 1.58 kg, respectively. First, the entire block was wrapped in cooking paper, then wrapped in waterproof paper, and placed in a plastic bag. Next, the plastic bag was filled with air instead of nitrogen gas, and the opening of the plastic bag was sealed with a rubber band to obtain the control sample. In the control sample, the oxygen concentration of the gas inside the packaging was 0.1 volume% or higher, and the oxygen amount was 200 mL per 1 kg of raw tuna block. It was also confirmed that the amount of gas inside the packaging of the control sample was 1000 mL per 1 kg of raw tuna block. The prepared control samples were placed in a polystyrene storage box and stored in a refrigerator kept at approximately 0°C to 2°C until evaluation.

[0163] (2) Evaluation As described above, one package of raw tuna meat was opened for each sample (Sample 1 and Control Sample) 5 days and 8 days after landing. Sashimi was prepared from the removed raw tuna chunks, and the color tone of the surface and interior of the sashimi, as well as its changes over time, were confirmed and evaluated.

[0164] In Sample 1, packaging with nitrogen gas caused the surface in contact with nitrogen to turn dark purple or reddish-purple during packaging. However, upon unpacking and exposure to air, this discolored surface changed back to the same reddish-purple or bright red color as when the tuna was cut. After 5 and 8 days following landing, no discoloration was observed on the surface or inside of the sashimi prepared from the opened raw tuna meat package of Sample 1. In contrast, in the control sample, discoloration to dark red was observed on the surface and approximately 5 mm from the surface of the sashimi prepared from the opened package after 5 days following landing. Furthermore, discoloration to dark brown was observed on the surface and approximately 15 mm from the surface of the sashimi prepared from the opened package after 8 days following landing.

[0165] As shown in the results above, the raw tuna chunks obtained from Sample 1 showed less discoloration than the raw tuna chunks obtained from the control sample, both during the preparation of the package and after the package was opened. Therefore, in Sample 1, discoloration of the raw tuna chunks was suppressed compared to the control sample, and even if there was discoloration, it was limited to a smaller area closer to the surface compared to the control sample. This means that with the raw tuna meat package from Sample 1, when obtaining final products such as sashimi from the raw tuna meat package, less discoloration can be removed compared to the control sample, resulting in a higher yield. Furthermore, when the sashimi obtained from Sample 1 was tasted, it was confirmed to have a good flavor.

[0166] For Sample 1, the storage period was further extended, and the packaged product was opened 11 days after landing. Sashimi was prepared as described above, and the surface and internal color of the sashimi were checked. Even though the sashimi was prepared from a packaged product 11 days after landing, only the surface layer of about 1 mm from the surface showed irreversible discoloration, but no discoloration was observed inside.

[0167] [Implementation 1-2] (1) Preparation of Sample 2 and Control Sample Within 24 hours of landing, the tuna GG was cut and processed into blocks, producing two blocks of approximately 2 kg each. These blocks were then cut in half to prepare two blocks for sample 2 and two blocks for the control sample.

[0168] As described above, the block for preparing sample 2 was packaged using a type II packaging material and an absorbent sheet as follows to obtain sample 2.

[0169] An absorbent sheet was attached to the surface of the block used for preparing sample 2, and then it was placed in a Type II nylon poly bag. Next, with as much gas as possible removed from the nylon poly bag, a plastic pipette for gas injection was inserted into the nylon poly bag, and nitrogen gas was injected while the opening of the nylon poly bag was constricted. Once the nylon poly bag had inflated, the constricted opening of the nylon poly bag was loosened while the nitrogen gas was still being vented, and the nylon poly bag was compressed by hand to push out as much gas as possible from inside the bag. The opening of the nylon poly bag was then constricted again and left until the nylon poly bag inflated. This operation was repeated four times to replace the gas inside the nylon poly bag.

[0170] Subsequently, with some nitrogen gas remaining inside the nylon poly bag, the plastic pipette was removed, and the squeezed portion of the nylon poly bag was sealed with a rubber band. In this way, Sample 2, a packaged raw tuna product consisting of a block of raw tuna meat, was prepared. In Sample 2, the oxygen concentration of the gas inside the packaging was 0.1 volume% or less, and the oxygen amount was 0.2 mL to 1.5 mL per kg of raw tuna meat. Furthermore, it was confirmed that the amount of gas inside the packaging of Sample 2 was 5 L or less per kg of raw tuna meat. The prepared Sample 2 was placed in a polystyrene storage box and stored in a refrigerator kept at approximately 0°C to 2°C until evaluation.

[0171] Furthermore, for the control sample preparation blocks, Type IV packaging materials and absorbent sheets were used to prepare the control samples. First, the entire block was wrapped in cooking paper, then waterproof paper was wrapped around it, and this was placed in a plastic bag. Next, the plastic bag was filled with air instead of nitrogen gas, and the opening of the plastic bag was sealed with a rubber band to obtain the control sample. In the control sample, the oxygen concentration of the gas inside the packaging was 0.1 volume% or higher, and the oxygen amount was 200 mL per 1 kg of raw tuna block. It was also confirmed that the amount of gas inside the packaging of the control sample was 1000 mL per 1 kg of raw tuna block. The prepared control samples were placed in a polystyrene storage box and stored in a refrigerator kept at approximately 0°C to 2°C until evaluation.

[0172] (2) Evaluation As described above, one package of raw tuna meat was opened for each of the two samples (Sample 2 and the control sample) four and six days after landing (corresponding to three, five, and five days after packaging, respectively). Sashimi was prepared from the removed raw tuna chunks, and the color tone of the surface or interior of the sashimi and its changes over time were confirmed and evaluated.

[0173] As a result, in Sample 2, packaging with nitrogen gas caused the surface in contact with nitrogen to turn dark purple or reddish-purple during packaging. However, upon unpacking and exposure to air, this discolored surface changed back to the same reddish-purple or bright red color as when the tuna was cut. In Sample 2, no discoloration was observed on the surface or inside of the sashimi prepared by opening the raw tuna meat package, neither after 4 days nor 6 days had elapsed since landing. In contrast, in the control sample, discoloration was observed on the surface and in the top 5-10 mm of the sashimi prepared after opening the package 4 days after landing, and discoloration was also observed on the surface and in a portion of the top 5-10 mm of the sashimi prepared after opening the package 6 days after landing.

[0174] As shown above, the discoloration to dark brown was suppressed more in sample 2 than in the control sample, resulting in a favorable outcome. This indicates that similar effects can be obtained regardless of the shape of the packaging material, as long as it has low oxygen permeability.

[0175] [Examples 1-3] (1) Preparation of sample 3-1, sample 3-2 and control sample Within 24 hours of landing, the tuna GG was cut and processed into blocks, producing blocks weighing approximately 1.4 kg to 1.7 kg. After storing the prepared blocks at 0°C for several hours, they were packaged using Type III packaging materials and absorbent sheets as follows, yielding Sample 3-1 (raw tuna meat package containing a 1.72 kg block) and Sample 3-2 (raw tuna meat package containing a 1.74 kg block).

[0176] First, the entire block was wrapped in cooking paper, then waterproof paper was wrapped over it, and it was placed in a nylon poly bag. For sample 3-1, the inside of the nylon poly bag was then degassed using a vacuum packaging machine (V610G series, manufactured by Fuji Impulse Co., Ltd.), and then nitrogen gas was injected. This degassing and nitrogen gas injection was repeated 2 to 4 times, and finally, with only a small amount of gas remaining inside the nylon poly bag, the nylon poly bag was sealed using the sealer attached to the vacuum packaging machine to prepare sample 3-1. For sample 3-2, the degassing and nitrogen gas injection was repeated 2 to 4 times in the same manner as for sample 3-1, and then the inside of the nylon poly bag was degassed as much as possible using the vacuum packaging machine, and the nylon poly bag was sealed using the sealer attached to the vacuum packaging machine to prepare sample 3-2.

[0177] Samples 3-1 and 3-2 were gases with an oxygen concentration of 0.1% by volume or less, and the oxygen content was 0.2 mL to 1.5 mL per kg of raw tuna meat. Furthermore, it was confirmed that the amount of gas inside the packaging of each of samples 3-1 and 3-2 was 5 L or less per kg of raw tuna meat. Each prepared sample was placed in a polystyrene storage box and stored in a refrigerator kept at approximately 0°C to 2°C until evaluation.

[0178] For the control sample preparation block (weight: 1.46 kg), the control sample was prepared using Type IV packaging material and an absorbent sheet. First, the entire block was wrapped in cooking paper, then wrapped again with waterproof paper, and placed in a plastic bag. Next, the plastic bag was filled with air instead of nitrogen gas, and the opening of the plastic bag was sealed with a rubber band to obtain the control sample. In the control sample, the oxygen concentration of the gas inside the packaging was 0.1 volume% or higher, and the oxygen amount was 200 mL to 600 mL per 1 kg of raw tuna block. It was also confirmed that the amount of gas inside the packaging of the control sample was 1000 mL to 3000 mL per 1 kg of raw tuna block. The prepared control sample was placed in a polystyrene storage box and stored in a refrigerator kept at approximately 0°C to 2°C until evaluation.

[0179] (2) Evaluation As described above, for samples 3-1, 3-2, and the control sample, the raw tuna meat packages were opened 5 days after landing (corresponding to 4 days after packaging), sashimi was prepared from the removed raw tuna chunks, and the sashimi was stored under storage conditions of 0°C to 2°C. The color of the sashimi was checked 6 hours and 72 hours after preparation.

[0180] As a result, in samples 3-1 and 3-2, packaging with nitrogen gas caused the surface in contact with nitrogen to turn dark purple or reddish-purple during packaging. However, upon unpacking and exposure to air, this discolored surface changed back to the same reddish-purple or bright red (crimson) color as when the samples were cut. Both samples 3-1 and 3-2 exhibited a brighter red (crimson) color compared to the control sample when unpacked. Comparing sample 3-1 and sample 3-2, sample 3-1 exhibited a brighter red color. Furthermore, sample 3-1 maintained a brighter red color for a longer period compared to the control sample even after unpacking.

[0181] Furthermore, sample 3-1 exhibited a brighter red color compared to the control sample both 6 hours and 72 hours after the preparation of the sashimi. In contrast, with the control sample, the surface of the raw tuna block was already discolored when the package was opened, and it was confirmed that the color changed to a dark brown from the part closest to the surface of the sashimi as time passed, 6 hours and 72 hours after the preparation of the sashimi. Similarly, sample 3-2 also exhibited a brighter red color compared to the control sample, just like sample 3-1.

[0182] As shown above, packaged products kept in a low-oxygen gas environment were found to have reduced discoloration during storage. Furthermore, gas-purged packaging using nitrogen gas was found to extend the color retention period compared to a control sample filled with air.

[0183] [Examples 1-4] (1) Preparation of Sample 4-1, Sample 4-2, Sample 4-3, Sample 4-4 and Control Sample Within 12 hours of landing, the tuna GG was cut and processed into loins. The loins were placed in plastic bags and cooled and stored in ice water. After several hours, the loins were removed from the ice water, cut into blocks, and approximately 1 kg blocks were prepared. Sample 4-1 was obtained by packaging the prepared blocks using Type II packaging material and absorbent sheets in the same manner as Sample 2 of Example 1-2.

[0184] Furthermore, sample 4-2 was obtained by using a Type III packaging material and an absorbent sheet to degas the inside of a nylon poly bag as much as possible, in the same manner as sample 3-2 in Example 1-3, and sealing the nylon poly bag with a sealer attached to a vacuum packaging machine. Sample 4-3 was obtained by packaging the block prepared as described above, in the same manner as sample 4-1 except that helium gas was used instead of nitrogen gas. Furthermore, sample 4-4 was obtained by packaging the block prepared as described above, in the same manner as sample 4-1 except that carbon dioxide was used instead of nitrogen gas.

[0185] Samples 4-1, 4-2, 4-3, and 4-4 had an oxygen concentration of 0.1% by volume or less in the gas inside the packaging, and the oxygen content was 0.2 mL to 1.5 mL per kg of raw tuna meat. Furthermore, it was confirmed that the amount of gas inside the packaging of each of the samples 4-1, 4-2, 4-3, and 4-4 was 5 L or less per kg of raw tuna meat. Each of the prepared samples 4-1, 4-2, 4-3, and 4-4 was placed in a polystyrene storage box and stored in a refrigerator kept at approximately 0°C to 2°C until evaluation.

[0186] As described above, a portion of the prepared block was used as the control sample preparation block, and the control sample was prepared using Type IV packaging material and absorbent sheet. First, the entire block was wrapped in cooking paper, then wrapped in waterproof paper, and placed in a plastic bag. Next, the plastic bag was filled with air instead of nitrogen gas, and the opening of the plastic bag was sealed with a rubber band to obtain the control sample. In the control sample, the oxygen concentration of the gas inside the packaging was 0.1 volume% or higher, and the oxygen amount was 100 mL to 200 mL per 1 kg of raw tuna block. It was also confirmed that the amount of gas inside the packaging of the control sample was 500 mL to 1000 mL per 1 kg of raw tuna block. The prepared control sample was placed in a polystyrene storage box and stored in a refrigerator kept at approximately 0°C to 2°C until evaluation.

[0187] (2) Evaluation For samples 4-1, 4-2, 4-3, and the control sample prepared as described above, each block was opened 5 days after landing, and the color of the removed raw tuna block was checked.

[0188] As a result, in the control sample, the surface and top layer of the block, extending to a depth of approximately 5mm to 8mm, had turned dark brown. In contrast, no changes were observed in samples 4-1 and 4-2. In sample 4-3, discoloration was observed in the surface and top layer of the block, extending to a depth of approximately 5mm, but it was less severe than in the comparison samples. When sample 4-4 was evaluated in the same way as sample 4-1, it was confirmed that the color tone was preserved.

[0189] [Examples 1-5] (1) Preparation of sample 5 and control sample Within 24 hours of landing, the tuna GG was cut and processed into loins. The loins were then placed in plastic bags and stored in a refrigerator set to 0°C. Two days after landing, the loins were removed from the plastic bags, and two blocks of approximately 1 kg each were prepared. These blocks were divided into one block for preparing sample 5 and another block for preparing the control sample.

[0190] As described above, the block for preparing sample 5 was packaged using Type II packaging material and an absorbent sheet in the same manner as sample 2 in Example 1-2 to obtain sample 5. The oxygen concentration of the gas inside the packaging of sample 5 was 0.1 volume% or less, and the oxygen amount was 0.2 mL to 1.5 mL per 1 kg of raw tuna block meat. Furthermore, it was confirmed that the amount of gas inside the packaging of sample 5 was 5 L or less per 1 kg of raw tuna block meat. The prepared block of sample 5 was placed in a polystyrene storage box and stored in a refrigerator kept at approximately 0°C to 2°C until evaluation.

[0191] For the control sample preparation blocks, Type IV packaging materials and absorbent sheets were used to prepare the control samples. First, the entire block was wrapped in cooking paper, then waterproof paper was wrapped around it, and this was placed in a plastic bag. Next, the plastic bag was filled with air instead of nitrogen gas, and the opening of the plastic bag was sealed with a rubber band to obtain the control sample. The prepared control samples were placed in a polystyrene storage box and stored in a refrigerator kept at approximately 0°C to 2°C until evaluation.

[0192] (2) Evaluation As described above, one package of raw tuna meat was opened for each of the two samples (Sample 5 and the control sample) 5 days after landing (corresponding to 3 days after packaging) and 8 days after landing (corresponding to 6 days after packaging). The block of raw tuna meat removed was cut in half, and the color of the cross-section was checked and evaluated.

[0193] As a result, in the control sample, when sashimi was prepared from a block of raw tuna meat that had been opened 5 days after landing, it was confirmed that the surface and the top 5-10 mm of the sashimi discolored 5 hours after preparation. Furthermore, when the control sample was opened 8 days after landing, a block of raw tuna meat was removed and cut in the middle, the cut surface of the block was divided into three layers by color. Specifically, the top 7-8 mm of the block was discolored to a light pink color, the layer below that was discolored to a light green color over a thickness of about 3-10 mm, and no discoloration was observed further inside. The light green discoloration indicates that the discoloration is more advanced than the light pink discoloration.

[0194] In contrast, in sample 5, after opening the package five days after landing, a block of raw tuna meat was removed and cut in the middle. The surface and top 7-8 mm of the block were discolored to a light pink color, similar to the control sample, but no discoloration was observed below that point. Furthermore, in sample 5, after opening the package eight days after landing, a block of raw tuna meat was removed and cut in the middle. Only the surface and top 7-8 mm of the block were discolored, and there was no significant change in the thickness of the discoloration in the surface layer, nor was there any discoloration inside. From this, it was confirmed that the progression of color change was more suppressed in sample 5 compared to the control sample.

[0195] As shown in the results above, even when packaging is done approximately 24 hours after cutting, it was confirmed that good results can be obtained by refrigerating the material after cutting, similar to when packaging is done immediately after cutting. In other words, it was confirmed that sample 5 tends to have a better color tone compared to the control sample. Furthermore, it was confirmed that once discoloration occurs, the discoloration accelerates and expands over time, centered on the discolored area. From this, it is expected that the discolored area will expand earlier in the control sample compared to sample 5, potentially leading to a significant decrease in yield. In the case of sample 5, even if the discolored area is removed, the amount to be removed can be reduced to about half compared to the control sample, resulting in a significantly higher yield than the control sample.

[0196] [Examples 1-6] (1) Preparation of sample 6 and control sample Within 12 hours of landing, the tuna GG was cut and processed into loins. The loins were then placed in plastic bags and stored in a refrigerator at approximately 0°C to 2°C. Approximately 24 hours after landing, the loins were removed from the plastic bags and 200g blocks were prepared. These blocks were divided into blocks for preparing sample 6 and blocks for preparing the control sample.

[0197] As described above, the block for preparing sample 6 was packaged using Type II packaging material and an absorbent sheet in the same manner as in Example 2 to obtain sample 6. The oxygen concentration of the gas inside the packaging of sample 6 was 0.1 volume% or less, and the oxygen amount was 0.2 mL to 1.5 mL per 1 kg of raw tuna block meat. Furthermore, it was confirmed that the amount of gas inside the packaging of sample 6 was 5 L or less per 1 kg of raw tuna block meat. The prepared sample 6 was stored in a refrigerator at a relatively high temperature setting of 5°C until evaluation.

[0198] For the control sample preparation blocks, Type IV packaging materials and absorbent sheets were used to prepare the control samples. First, the entire block was wrapped in cooking paper, then wrapped again with waterproof paper, and placed in a plastic bag. Next, the plastic bag was filled with air instead of nitrogen gas, and the opening of the plastic bag was sealed with a rubber band to obtain the control sample. The prepared control samples were placed in a polystyrene storage box and stored in a refrigerator at a relatively high temperature of 5°C until evaluation.

[0199] (2) Evaluation As described above, one package of raw tuna meat was opened from each of the sample 6 and control samples four days after landing (corresponding to three days after packaging), and sashimi was prepared from the removed raw tuna blocks. The color of the sashimi was then checked and evaluated.

[0200] As a result, similar to the other evaluation results, when comparing the color tone of the surface and the top 3-5 mm of sample 6 and the control sample with the color tone of the layer below, it was confirmed that sample 6 exhibited a relatively brighter color tone in all cases. It was also confirmed that there was no significant change in the color tone of sample 6 even after one day had passed since the sashimi was prepared. It was found that the color change was delayed in sample 6. From the above results, it was confirmed that by providing a period of refrigerated storage before packaging, even when the refrigeration temperature after packaging is set to a relatively high temperature (e.g., 5°C), sample 6 tends to have a better color tone compared to the control sample.

[0201] [Examples 1-7] (1) Preparation of sample 7 and control sample Within 72 hours of landing, the tuna GG was cut and processed into loins. The loins were then placed in plastic bags and stored in a refrigerator set to 0°C. Approximately 96 hours (4 days) after landing, the loins were removed from the plastic bags and 100g to 200g blocks were prepared. These blocks were divided into blocks for preparing sample 7 and blocks for preparing the control sample.

[0202] As described above, the block for preparing sample 7 was packaged using Type I packaging material and an absorbent sheet in the same manner as in Test 1 of Example 1 to obtain sample 7. The oxygen concentration of the gas inside the packaging of sample 7 was 0.1 volume% or less, and the oxygen amount was 0.2 mL to 1.5 mL per 1 kg of raw tuna block meat. Furthermore, it was confirmed that the amount of gas inside the packaging of sample 7 was 5 L or less per 1 kg of raw tuna block meat. The prepared sample 7 was stored in a refrigerator maintained at approximately 0°C to 2°C.

[0203] For the control sample preparation blocks, Type IV packaging materials and absorbent sheets were used to prepare the control samples. First, the entire block was wrapped in cooking paper, then waterproof paper was wrapped around it, and this was placed in a plastic bag. Next, the plastic bag was filled with air instead of nitrogen gas, and the opening of the plastic bag was sealed with a rubber band to obtain the control sample. The prepared control samples were placed in a polystyrene storage box and stored in a refrigerator maintained at approximately 0°C to 2°C until evaluation.

[0204] (2) Evaluation As described above, one package of raw tuna meat was opened from each of the sample 7 and control samples 25 days after landing (corresponding to 21 days after packaging), and sashimi was prepared from the removed raw tuna meat blocks. The color of the sashimi was then confirmed and evaluated.

[0205] As a result, in sample 7, only the surface and the top 1 mm of the sashimi were irreversibly discolored, but no discoloration was observed inside. In contrast, in the control sample, the discoloration of the sashimi extended to the inside, resulting in the flesh being divided into three layers, with only the center remaining undiscolored. Furthermore, when each sashimi was stored in a refrigerator maintained at 0°C to 2°C and the changes over time were observed, sample 7 maintained a good color tone even 48 hours after opening, confirming that the quality could be maintained up to 27 days after landing.

[0206] Table 2 below summarizes the outlines of Examples 1-1 to 1-7.

[0207] [Table 2]

[0208] Furthermore, in samples 1 to 7, the amount of drip generated from the raw tuna chunks after opening the package tended to be less compared to the control sample.

[0209] As shown in the above embodiments, according to this disclosure, it is possible to obtain a packaged raw tuna product having raw tuna chunks in which discoloration is suppressed and color changes are delayed during packaging and, in some cases, even after the packaging has been removed. Furthermore, the color of the raw tuna chunks can be well maintained during packaging and, in some cases, even after the packaging has been removed. In addition, when preparing products such as sashimi from the packaged product, the amount of discolored portion that needs to be removed can be reduced, and the yield of the product can be improved compared to conventional products.Therefore, according to this disclosure, it is possible to provide a packaged raw tuna product in which discoloration is suppressed and a method for suppressing discoloration of raw tuna chunks.

[0210] <Second aspect> [Example 2-1] Three farmed bluefin tuna were immediately killed after being landed, their gills and internal organs removed, and placed in ice water. The resulting GG weights of the tuna were 68.4 kg, 74.8 kg, and 82.0 kg, respectively, and their body mass index (BMI) was 20.3, 22.6, and 23.3, respectively.

[0211] After processing farmed tuna into a GG (presumably a type of fatty tuna), filleting was performed 24 to 28 hours later. The filleting was carried out in a filleting room at room temperature of 18°C ​​to 20°C. The head and tail were cut off from the tuna's GG, and then, following the usual procedure, the flesh was cut from the dorsal side, and then the ventral side, to obtain a 9 kg dorsal loin. Furthermore, the dorsal loin was divided into five blocks weighing 1 kg to 2 kg each (labeled A, B, C, D, and E from the head side), and of these, A to D, which correspond to the medium fatty tuna on the dorsal side, were used for the test. Each test sample was further processed into a 20 cm × 8 cm × 2.5 cm block.

[0212] The packaging has an oxygen permeability of 20 cm at a temperature of 23°C and a humidity of 80% RH. 3 / m 2 Plastic film pouches (manufactured by Kureha Corporation, product name: "Kurehalon ML40G") with a 24hr·atm rating were used. Each sample was placed in a film pouch and vacuum-sealed to a pressure of 10 millibars or less using a chamber-type vacuum packaging machine (product name: C-200, MULTIVAC), and then sealed by heat sealing. The pouches were then packed with ice in a styrofoam box and stored for one day, and from the second day onward, they were stored in a refrigerator set to 5°C.

[0213] The Kurehalon ML40G used had the following characteristics: Resin composition: PET / PA / EVOH / PO (PET: polyethylene terephthalate, PA: polyamide, EVOH: ethylene-vinyl alcohol copolymer, PO: polyolefin) Total thickness: 40 μm Tensile strength (JIS K 7127 (23℃-50%RH): 130MPa / 160MPa (vertical / horizontal) Elongation at breaking point (JIS K 7127 (23℃-50%RH): 160% / 130% (height / width) Tensile modulus of elasticity (JIS K 7127 (23℃-50%RH): 650MPa / 700MPa (vertical / horizontal)

[0214] The amount of gas inside the packaging after packaging was measured to be 5 mL or less. This packaged product will also be referred to as the "vacuum-sealed product" below.

[0215] For comparison, a packaged product (hereinafter referred to as "standard product") was used, which was obtained in the same manner as the vacuum-sealed product, except that it was wrapped in a water-absorbing sheet, packaged with "CANS FILM® Barrier 7" (product name, manufactured by Shikoku Kako Co., Ltd.), and sealed.

[0216] (Color evaluation) Three days after packaging (equivalent to four days after landing), regular and vacuum-packed fillets, made from the same left and right sides of the same individual fish, were opened simultaneously. Two 10mm thick slices of sashimi, cut perpendicular to the vertebrae of each of the regular and vacuum-packed fillets, were placed in airtight containers with the cut surfaces facing upwards and stored at 4°C. The color of one point in the center of each sashimi slice was measured using a colorimeter (product name: CR-400, manufactured by Konica Minolta Japan, Inc.) at 0 hours (immediately after opening), 0.5 hours, 2 hours, 4 hours, and 8 hours after storage. Regular and vacuum-packed fillets stored unopened at 4°C for seven days after packaging (equivalent to eight days after landing) were evaluated in the same manner.

[0217] The results are shown in Tables 3 and 4, and Figures 1 and 2. In Tables 3 and 4, Figures 1 and 2, "D+3" and "D+7" refer to samples that have been packaged for 3 days and 7 days, respectively. Also, in Tables 3 and 4, Figures 1 and 2, "Normal" refers to a normal product, and "Vacuum" refers to a vacuum-sealed product.

[0218] [Table 3]

[0219] [Table 4]

[0220] As shown in Tables 3 and 4, Figures 1 and 2, for both the regular and vacuum-sealed products, in samples taken 3 days after packaging, a was observed from immediately after unpacking to 0.5 hours later. * While the value is increasing, a * / b * The value decreases, but then remains relatively constant. This result indicates that the color changes from a dark red to a bright red, indicating high freshness, and that this condition is well maintained. Samples taken 7 days after packaging, both regular and vacuum-sealed, showed a * Value and a * / b *Regarding the values, although the values ​​immediately after unpacking differed, a similar trend was observed as with the samples taken three days after packaging.

[0221] On the other hand, when comparing samples that had been packaged for 3 days with samples that had been packaged for 7 days, the normal product showed a * Value and a * / b * In both values, it was confirmed that the sample after 7 days showed a greater decrease in numerical value than the sample after 3 days. This means that, after packaging, the redness dulls and the yellowness becomes slightly stronger over time, and it transitions to a dark brown color. In particular, a * In terms of values, immediately after unpacking, the a of the sample after 7 days. * The value is a of the sample after 3 days. * The value was significantly lower than expected. This means that, even in its regular packaging, the color of the raw tuna chunks had changed.

[0222] In contrast, with vacuum-sealed products, a * Value and a * / b * In both values, immediately after unpacking, the a of the sample after 3 days * Value and a * / b * Value of the sample after 7 days * Value and a * / b * The decrease in each value is small, especially a * Regarding the values, it can be seen that they have hardly decreased even in samples that have been used for 7 days. Furthermore, a * Value and a * / b * Both values ​​remained relatively high even after the packaging was removed, and did not decrease to the same extent as regular products. This suggests that vacuum-sealed products can delay color changes not only while still in their packaging but also after the packaging has been removed.

[0223] (Drip evaluation) Three days after packaging (equivalent to 4 days after landing), the normal product and the vacuum product of block meat prepared from the same site on the left and right of the same individual were opened at the same time. Two pieces of 10 mm-thick sashimi cut perpendicularly to the vertebra of each of the normal product and the vacuum product were prepared, placed in a container whose weight had been measured in advance, the weight was measured, and the weight of the sashimi before storage was calculated by subtracting the weight of the container from the obtained measured value. Thereafter, the two pieces of sashimi were placed in the container, arranged with the cut surfaces of the sashimi facing upward, the container was sealed, and stored at 4°C. After 6 hours of storage, each piece of sashimi was taken out of the container, the total weight of the container and the drip remaining in the container was measured, the amount of drip was calculated by subtracting the weight of the container from the obtained measured value, and the amount of drip from the two pieces of sashimi was evaluated. The drip amount was calculated by the following formula. The same measurement was performed using block meat obtained from 3 farmed bluefin tuna as samples. The results are shown in Table 5. Drip amount [%] = [Weight of drip] / [Weight of sashimi before storage] × 100

[0224]

Table 5

[0225] As shown in Table 5, it was confirmed that the drip amount was smaller in the vacuum product than in the normal product. This means that the vacuum product can delay the change in quality of raw tuna block meat compared to the normal product not only in the packaged state but also after the package is opened.

[0226] In addition, in the vacuum product, compared with the normal product, the raw tuna block meat taken out after opening the packaged product tended to be softer and easier to cut during processing. The vacuum product also tended to have less off-flavor transfer, which is relatively common in farmed fish, compared to the normal product.

[0227] From these results, it is found that the present disclosure can provide a packaged raw tuna meat product with delayed color tone change and suppressed discoloration even after the package is opened during the packaged period, and a method for suppressing discoloration of raw tuna block meat.

Claims

1. Oxygen-impermeable packaging material, The packaging material comprises raw tuna chunks packaged together with a gas having an oxygen concentration of 1 volume% or less (except in cases where the oxygen concentration is less than 0.1 volume%), Packaged raw tuna meat with an oxygen content of 0.2 mL to 1.5 mL per kg of raw tuna chunks.

2. The raw tuna meat package according to claim 1, wherein the gas comprises an inert gas.

3. The raw tuna meat package according to claim 2, wherein the inert gas comprises at least one gas selected from the group consisting of nitrogen gas, carbon dioxide gas, helium gas, and argon gas.

4. It further comprises a water-absorbing component, A packaged raw tuna meat product according to any one of claims 1 to 3, wherein part or all of the raw tuna meat block is in contact with the water-absorbing member.

5. The oxygen permeability of the aforementioned packaging material is 1000 cm². ３ / m ２ - A packaged raw tuna product according to any one of claims 1 to 4, wherein the humidity is 24hr·atm or less.

6. The oxygen permeability of the aforementioned packaging material is 50 cm². ３ / m ２ - A packaged raw tuna product according to any one of claims 1 to 5, wherein the humidity is 24hr·atm or less.

7. After the tuna is landed, it is cut up to obtain raw tuna chunks. The raw tuna chunks are packaged in an oxygen-impermeable packaging material, and a gas exchange treatment is performed until the oxygen concentration in the gas inside the packaging is 1 volume% or less (except when the oxygen concentration is less than 0.1 volume%), and the amount of oxygen is 0.2 mL to 1.5 mL per kg of raw tuna chunks, and After the gas displacement treatment, the packaging material is sealed. A method for manufacturing packaged raw tuna meat products, including [the specified ingredient].

8. The method for producing a packaged raw tuna product according to claim 7, wherein the gas displacement treatment is performed using an inert gas.

9. The method for producing a packaged raw tuna product according to claim 8, wherein the inert gas comprises at least one gas selected from the group consisting of nitrogen gas, carbon dioxide gas, helium gas, and argon gas.

10. A method for producing a packaged raw tuna product according to any one of claims 7 to 9, further comprising refrigerating the raw tuna block until it is packaged with the packaging material.

11. After the tuna is landed, it is cut up to obtain raw tuna chunks. The raw tuna chunks are packaged in an oxygen-impermeable packaging material, and a gas exchange treatment is performed until the oxygen concentration in the gas inside the packaging is 1 volume% or less (except when the oxygen concentration is less than 0.1 volume%), and the amount of oxygen is 0.2 mL to 1.5 mL per kg of raw tuna chunks, and After the gas displacement treatment, the packaging material is sealed to obtain a packaged raw tuna product. A method for suppressing discoloration of raw tuna chunks, including [the specified ingredient].

12. The method for suppressing discoloration of raw tuna chunks according to claim 11, further comprising refrigerating the raw tuna meat package.

13. The method for suppressing discoloration of raw tuna chunks according to claim 12, wherein the period of refrigerated storage is at least one week.

14. The method for suppressing discoloration of raw tuna chunks according to claim 12, wherein the period of refrigerated storage is at least four weeks.

Images