Method for breeding thunnus cultured fish, and method for producing processed food of thunnus cultured fish

Abstract

To provide Thunnus cultured fish having a lower selenium content compared to natural Thunnus and a method for breeding the fish, and a processed food of Thunnus cultured fish having a lower selenium content and a method for producing the food.SOLUTION: Provided are Thunnus cultured fish that has either one of a muscle whose selenium content is 90 μg or less per 100 g and a liver whose selenium content is 1,400 μg or less per 100 g, an edible part thereof, and a processed food including the edible part. Also provided is a breeding method in which formula feed containing fish meal 30 wt.% or more of which is constituted of sardine fish meal, an inclusion containing fat, and a shell which wraps the inclusion and is constituted of at least one substance selected from the group consisting of protein and polysaccharides is fed continuously for at least 30 days.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for raising farmed tuna fish and a method for producing processed foods from farmed tuna fish. [Background technology]

[0002] In fish farming, efforts are being made to switch from live feed to compound feed from the perspectives of nutrition, stable supply, preventing environmental pollution, and sustainable aquaculture, and various compound feeds have been developed. In particular, compound feeds tailored to the preferences of fish species have been proposed, so that the switch to compound feed will also progress for highly carnivorous fish species. For example, WO 2010 / 110326 A1 and JP 2012-65565 A disclose fish feed having an outer layer and an inner layer. These fish feeds are used for highly palatable farmed fish such as tuna, and are described as having good feed intake and feed efficiency. JP 2014-45750 A discloses a feed with a double structure consisting of an outer layer and an inner layer containing a protein material and liquid oil, and describes this feed as having high feed intake and suppressing oil leakage.

[0003] Selenium, on the other hand, is a trace element that exerts physiological functions in the form of selenoproteins and is considered important in the antioxidant system and thyroid hormone metabolism. The recommended intake of selenium is 30 μg for adult men and 25 μg for adult women, while the recommended intake of selenium for children is 20 μg, which is lower than the recommended intake for adults. Excessive intake of selenium can be toxic, and excessive intake of selenium is known to cause hair and nail brittleness and loss. On the other hand, tuna is known to contain high concentrations of selenium. For example, the Journal of Food Composition and Analysis, 2001, Vol. 14, pp. 461-467, states that the selenium content of wild tuna is 0.743 mg / kg, and the selenium content of tuna muscle (lean meat) is approximately 110 μg / 100 g according to the 2015 edition (7th revision) of the Standard Tables of Food Composition in Japan. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO 2010 / 110326 A1 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-65565 [Patent Document 3] JP 2014-45750 A [Non-patent literature]

[0005] [Non-Patent Document 1] Journal of Food Composition and Analysis, 2001, Vol.14, pp. 461-467 Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, tuna is known to have a high selenium content. However, because it is relatively easy to eat as sashimi, eating tuna can easily cause selenium intake to exceed the recommended intake. Wild-caught tuna and farmed fish raised on live bait freely eat fish such as horse mackerel and mackerel, making it difficult to control their selenium content. Therefore, it is necessary to develop new farmed tuna fish with low selenium content.

[0007] Therefore, the object of the present disclosure is to provide farmed tuna fish that have a lower selenium content compared to wild tuna fish or farmed tuna fish raised on live bait, a method for raising the same, and edible parts of farmed tuna fish with a low selenium content, processed foods made from the same, and a method for producing the same. [Means for solving the problem]

[0008] The present disclosure includes the following aspects. [1] Farmed tuna fish having either muscle with a selenium content of 90 μg or less per 100 g or liver with a selenium content of 1,400 μg or less per 100 g. [2] A farmed tuna fish according to [1] obtained by raising and managing it with a diet containing compound feed. [3] Farmed tuna fish described in [1] or [2], with a total fish weight of 20 kg or more. [4] A farmed tuna fish according to any one of [1] to [3], having a fork length of 90 cm or more. [5] A farmed tuna fish according to any one of [1] to [4], having a fatness index of 20 or higher. [6] A farmed tuna fish according to any one of [1] to [5], which is a tuna fish of the genus Thunnus, Pectenia, Bonito, Scomber or Skipjack. [7] The tuna species of [6] is albacore, bluefin tuna, southern bluefin tuna, Atlantic bluefin tuna, Atlantic bluefin tuna, yellowfin tuna, bigeye tuna, longfin tuna, bonito, or yellowfin tuna. [8] A farmed tuna fish according to either [6] or [7], which is a tuna fish that mainly feeds on fish native to the Northern Hemisphere. [9] The farmed tuna fish according to [8], which is albacore, bluefin tuna, Atlantic bluefin tuna, yellowfin tuna, bigeye tuna, longfin tuna, bonito or yellowfin tuna.

[10] A farmed tuna fish according to any one of [1] to [9], from which at least one part selected from the group consisting of the gills, internal organs, tail and head has been removed.

[11] A farmed tuna fish according to any one of [1] to

[10] , in which the gills and internal organs have been removed.

[12] A farmed tuna fish according to

[11] , having a total weight of 17 kg or more.

[13] Edible parts of farmed tuna fish that have at least one of muscle with a selenium content of 90 μg or less per 100 g and liver with a selenium content of 1,400 μg or less per 100 g.

[14] An edible portion of the farmed tuna fish described in

[13] , which is at least a portion of the fish meat or internal organs.

[15] The edible portion of the farmed tuna fish described in

[13] , which is lean or fatty.

[16] The edible part of the farmed tuna fish described in

[14] , which is muscle having a selenium content of 90 μg or less per 100 g or liver having a selenium content of 1,400 μg or less per 100 g.

[17] A processed food product of farmed tuna fish, comprising an edible portion of the farmed tuna fish described in any one of

[13] to

[16] and a container for containing the edible portion.

[18] A method for raising farmed tuna fish described in any one of [1] to

[12] , which comprises continuously feeding the fish for at least 30 days a compound feed containing fish meal composed of 30% by weight or more of sardine fish meal, an inclusion containing oil and fat, and an outer skin that encases the inclusion and is composed of at least one substance selected from the group consisting of proteins and polysaccharides.

[19] A method for producing processed foods from farmed tuna fish, comprising: preparing farmed tuna fish obtained by the method for raising farmed tuna fish described in

[18] ; harvesting edible parts from the prepared farmed tuna fish; and placing the edible parts in a container. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide farmed tuna fish that have a lower selenium content compared to wild tuna fish or farmed tuna fish raised on live bait, a method for raising the same, as well as edible parts of farmed tuna fish with a low selenium content, processed foods made from the same, and a method for manufacturing the same. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a cross section in a direction perpendicular to the longitudinal direction of a fish body, showing the location where fish meat was harvested in the example. [Figure 2] FIG. 2 is a graph showing the change in selenium content in the muscle of farmed tuna fish in the example. [Figure 3] FIG. 3 is a graph showing the change in selenium content in the liver of farmed tuna fish in the example. [Figure 4]FIG. 4 is a perspective view showing an example of a processed food product made from farmed tuna fish according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] When referring to a "step" in this disclosure, it is intended that the purpose of that step be achieved, and it does not matter whether that step can be clearly distinguished from other steps. In this disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after it as the minimum and maximum values, respectively. In this disclosure, when the upper limit of a numerical range expressed as a percentage for a certain component is expressed as "less than or equal to" or "less than," unless the lower limit is specifically stated, the lower limit is 0%, meaning that the component is not contained. In this disclosure, when the content of a certain component in a composition is stated, if multiple materials or raw materials constituting the composition each contain the component, the content is expressed as the sum of the component contained in the multiple materials or raw materials, unless otherwise specified.

[0012] In this disclosure, the selenium content is expressed as the content per 100 g of the target object (e.g., muscle or liver). Therefore, it does not necessarily mean that the entire muscle or liver size of a farmed tuna fish, or the entire edible portion of a farmed tuna fish, is 100 g.

[0013] In one embodiment of the present disclosure, the farmed tuna fish has either muscle with a selenium content of 90 μg or less per 100 g or liver with a selenium content of 1,400 μg or less per 100 g. In this specification, such farmed tuna fish may be referred to as "low-selenium farmed tuna fish." It is also possible for the farmed tuna fish to have both such muscle and liver. In one embodiment of the present disclosure, the edible portion of the farmed tuna fish is an edible portion of the farmed tuna fish having at least one of muscle with a selenium content of 90 μg or less per 100 g and liver with a selenium content of 1400 μg or less per 100 g. Note that the farmed tuna fish in one embodiment of the present disclosure may have both such muscle and liver. In one embodiment of the present disclosure, a processed food product of farmed tuna fish includes an edible portion of the farmed tuna fish described above and a container for containing the edible portion.

[0014] The selenium content in the red meat of wild tuna is 110 μg per 100 g, whereas the selenium content in the farmed tuna fish of the present disclosure is 90 μg or less per 100 g in the muscle and 1,400 μg or less per 100 g in the liver, significantly reducing the selenium content in farmed tuna fish. Farmed tuna fish and their edible parts with tissues containing such low selenium content have not been identified to date.

[0015] Therefore, the farmed tuna fish of the present disclosure contain selenium at a much lower concentration than wild tuna that eat live bait, and therefore, even if edible parts such as muscle or liver are eaten, the selenium intake can be reduced compared to wild tuna or farmed tuna fish raised on live bait. As a result, the risk of excessive selenium intake can be reduced compared to wild tuna or farmed tuna fish raised on live bait.

[0016] In one embodiment of the present disclosure, a method for raising farmed tuna fish includes continuously feeding, for at least 30 days, a compound feed containing fish meal composed of 30% or more by weight of sardine fish meal, an inclusion containing oil and fat, and an outer skin that encases the inclusion and is composed of at least one substance selected from the group consisting of proteins and polysaccharides. The method for raising the low-selenium tuna farmed fish described above involves raising the fish using a compound feed containing an inclusion and an outer shell that encases the inclusion, where the inclusion contains fish meal with 30% or more by weight of sardine fish meal and oil. By continuously feeding the fish with this compound feed for at least 30 days, the low-selenium tuna farmed fish described above can be efficiently obtained. Each embodiment will be described in more detail below.

[0017] <Farmed tuna fish> Tunas that are low-selenium tuna farmed fish include the Thunnus and Bonito families. The Thunnus family includes the genus Thunnus, the genus Bonito, the genus Scutellaria, and the genus Bonito, while the genus Bonito includes the genus Dogtooth Thunnus and the genus Bonito. Examples of tunas include albacore, bluefin tuna, southern bluefin tuna, Atlantic bluefin tuna, yellowfin tuna, bigeye tuna, and longfin tuna from the genus Thunnus, skipjack tuna, flathead tuna and roundfin tuna from the genus Scutellaria, and bigfin tuna from the genus Scutellaria, and skipjack tuna from the genus Scutellaria, or albacore, bluefin tuna, southern bluefin tuna, Atlantic bluefin tuna, yellowfin tuna, bigeye tuna, longfin tuna, bonito, or longfin tuna.

[0018] The low-selenium farmed tuna fish is preferably a tuna that can feed primarily on fish native to the Northern Hemisphere, such as albacore, bluefin, Atlantic bluefin, yellowfin, bigeye, longfin tuna, bonito, or spotted tuna.

[0019] The low-selenium farmed tuna fish may be farmed fish obtained by any method, and it is preferable that the fish be obtained by raising and managing them with a feed containing a compound feed. "Formulated feed" means feed that combines ingredients to meet the nutrients such as protein, vitamins, and minerals required for fish growth. "Raising management" means that fish are raised using feed selected to achieve a specific purpose.

[0020] Low-selenium farmed tuna fish have either muscle with a selenium content of 90 μg or less per 100 g or liver with a selenium content of 1,400 μg or less per 100 g. It is also possible for the fish to have both such muscle and liver. Since muscle and liver are common edible parts of farmed tuna fish, if the selenium content of either the muscle or the liver is within the above range, the selenium intake when eaten can be lower than that of farmed tuna fish raised in the wild or on live feed.

[0021] The selenium content in the muscle of low-selenium farmed tuna fish is 90 μg or less per 100 g of muscle. To provide edible portions with even lower selenium content, the content can be 80 μg or less, 70 μg or less, 60 μg or less, 55 μg or less, or 50 μg or less. Lower selenium content tends to further reduce the risk of overconsumption. There is no particular limit on the lower limit of selenium content, and it can be, for example, 30 μg or more or 35 μg / 100 g or more. While this is unlikely in reality, for the purposes of this disclosure, the selenium content per 100 g of muscle may be zero.

[0022] The selenium content in the liver of low-selenium farmed tuna fish is 1400 μg or less per 100 g of liver. To provide edible portions with even lower selenium content, the content can be 1350 μg or less, 1300 μg or less, 1200 μg or less, 1100 μg or less, 1000 μg or less, 900 μg or less, 800 μg or less, 700 μg or less, or 600 μg or less. Lower selenium content tends to further reduce the risk of overdose. There is no particular limit to the lower limit of selenium content, and it can be, for example, 300 μg or more. While this is unlikely in reality, given the objectives of the present disclosure, the selenium content per 100 g of liver may be zero.

[0023] Examples of muscles include dorsal muscles, ventral muscles, dorsal keel muscles, ventral keel muscles, and dark muscles. The dorsal muscles, ventral muscles, dorsal keel muscles, and ventral keel muscles are located relatively deep in the body of the fish and can be divided into lean meat, which has a higher myoglobin content and a reddish color, and fatty meat, which is located relatively shallow in the body of the fish and has a lower myoglobin content and a lighter red color. Fatty meat is also commonly called "fatty tuna," and is called "otoro" (fatty tuna) or "chutoro" (fatty tuna) depending on the amount of fat. Dark muscles are reddish-brown muscles located near the junction of the dorsal and ventral lateral muscles.

[0024] The selenium content in this disclosure refers to a value measured as follows: In the case of muscle, a portion of the muscle, for example, a piece approximately 5 cm square, is cut out to serve as a test piece; in the case of liver, a portion of the liver, for example, the central portion, is cut out to serve as a test piece, for example, a piece 5 cm x 5 cm. The amount of selenium in the test piece is measured by the method based on "(1) Quantitative determination by fluorometry" on page 433 of "Hygienic Test Methods, Commentary 2010" (edited by the Pharmaceutical Society of Japan, published February 20, 2010, Kanehara Publishing).

[0025] Examples of selenium include inorganic selenium and organic selenium, and examples of organic selenium include selenium-containing proteins such as glutathione peroxidase, iodothyronine deiodinase, and thioredoxin reductase, and selenium-containing amino acids such as selenomethionine and selenocystine. Low-selenium farmed tuna fish can contain these inorganic selenium and organic selenium elements alone or in combination of two or more.

[0026] Preferably, the low-selenium farmed tuna fish have a lower selenium content in both muscle and liver than farmed tuna fish raised in the wild or on live feed. For example, the low-selenium farmed tuna fish may have a muscle with a selenium content of 90 μg or less, 80 μg or less, 70 μg or less, 60 μg or less, 55 μg or less, or 50 μg or less per 100 g, and a liver with a selenium content of 1400 μg or less, 1350 μg or less, 1300 μg or less, 1200 μg or less, 1100 μg or less, 1000 μg or less, 900 μg or less, 800 μg or less, 700 μg or less, or 600 μg or less per 100 g.

[0027] More preferably, low-selenium farmed tuna fish may have muscle with a selenium content of 30 μg or more and 70 μg or less, 60 μg or less, 55 μg or less, or 50 μg or less per 100 g, and liver with a selenium content of 300 μg or more and 1000 μg or less, 900 μg or less, 800 μg or less, 700 μg or less, or 600 μg or less per 100 g.

[0028] Low-selenium farmed tuna fish can have a fatness index of preferably 20 or more, more preferably 21 or more, and even more preferably 22 or more. Low-selenium farmed tuna fish with a fatness index of 20 or more can provide more of the so-called fatty edible parts compared to wild fish. Obesity can generally be assessed based on the following formula [1]: Obesity index = weight (g) / [{fork length (cm)} 3 ]×1000···[1]

[0029] Low-selenium tuna farmed fish can have a fork length of 90 cm or more, 100 cm or more, 120 cm or more, 150 cm or more, or 200 cm or more. Low-selenium tuna farmed fish with a fork length of 90 cm or more tend to be more obese than wild fish, and can provide more edible portions. Fork length refers to the distance from the tip of the fish's head to the center of the fin, and is an indicator of external morphology well known to those skilled in the art. Fork length is measured by measuring the linear distance in a plan view from the tip of the fish's head to the center of the fin. There is no particular upper limit for the fork length of low-selenium tuna farmed fish, and it can be, for example, 1,000 cm or less.

[0030] In the case of individual low-selenium farmed tuna fish, the weight of the whole fish, i.e., the total fish body weight, of the low-selenium farmed tuna fish is preferably 20 kg or more, more preferably 25 kg or more, even more preferably 30 kg or more, even more preferably 35 kg or more, and particularly preferably 40 kg or more. Low-selenium farmed tuna fish with a heavier total fish weight have the advantage of being able to obtain more edible portions. There is no particular upper limit on the weight of the whole fish of low-selenium farmed tuna fish, and it can be set at, for example, 500 kg or less.

[0031] To measure the weight of individual fish, after landing, they are first bled, then the gills and internal organs are removed, and the weight of the fish after these are removed, i.e., the GG tuna described below, is measured. The total weight of the removed internal organs and gills plus the weight of the GG tuna is taken as the "total fish weight." To measure the weight, a measuring device normally used for measuring fish weight can be used.

[0032] The forms of low-selenium farmed tuna fish include those that include all parts from the head to the tail, i.e., "individual fish," and "processed forms" in which parts of the individual fish have been removed. Examples of processed low-selenium farmed tuna fish include those from which at least one part selected from the group consisting of gills, internal organs, tail, and head has been removed. Internal organs include the esophagus, stomach, intestines, liver, pyloric caeca, testes, ovaries, pancreas, heart, swim bladder, etc. The processed form is appropriately selected, for example, depending on the convenience of distribution, and includes a form from which the gills and internal organs have been removed. Tuna from which the gills and internal organs have been removed is generally referred to as GG (gilled and gutted) tuna. In other words, "GG tuna" refers to a form from which the gills and internal organs, specifically the esophagus, stomach, intestines, liver, pyloric caeca, gonads (testes or ovaries), spleen, heart, and swim bladder, have been removed. Farmed tuna fish processed in this manner may also be referred to as "processed tuna products."

[0033] It is known that the weight of GG tuna corresponds to approximately 85 to 89% of the total fish body weight. In one embodiment of the present disclosure, the weight of GG tuna is preferably 17 kg or more, more preferably 21 kg or more, even more preferably 26 kg or more, and even more preferably 34 kg or more. The heavier the weight, the greater the advantage of being able to obtain more edible portions. The length of GG tuna is approximately the same as the fork length of the low-selenium tuna farmed fish described above; that is, GG tuna can have a length of 90 cm or more, 100 cm or more, or 120 cm or more. GG tuna with a length of 90 cm or more are larger than wild fish, and can provide more edible portions.

[0034] Other processed forms include, for example, the so-called headless form, in which the head and tail are further removed from GG tuna, and the so-called loin form, in which the headless form is divided into left and right halves and dorsal and ventral sides and cut into quarters.

[0035] A processed form of low-selenium farmed tuna fish from which at least one part selected from the group consisting of gills, internal organs, and head has been removed can have at least one of muscle with a selenium content of 90 μg or less, 80 μg or less, 70 μg or less, 60 μg or less, 55 μg or less, or 50 μg or less per 100 g, and liver with a selenium content of 1400 μg or less, 1350 μg or less, 1300 μg or less, 1200 μg or less, 1100 μg or less, 1000 μg or less, 900 μg or less, 800 μg or less, 700 μg or less, or 600 μg or less per 100 g. As mentioned above, the selenium content in the muscle or liver of processed low-selenium farmed tuna fish is not particularly limited, but in the case of muscle, it can be, for example, 30 μg or more per 100 g, and in the case of liver, it can be, for example, 300 μg or more or 350 μg or more per 100 g.

[0036] Examples of low-selenium farmed tuna fish according to one embodiment of the present disclosure include: (1) Low-selenium farmed tuna fish with muscle containing 30 μg or more, but not more than 70 μg, 60 μg, 55 μg, or 50 μg per 100 g, and with a body mass index of 21 or more, a total fish weight of 25 kg or more, or a fork length of 90 cm or more; (2) Low-selenium farmed tuna fish with muscle that has a selenium content of 30 μg or more, but not more than 70 μg, 60 μg or less, 55 μg or less, or 50 μg or less per 100 g, and a body mass index of 20 or more, a total fish weight of 20 kg or more, or a fork length of 100 cm or more; (3) Low-selenium farmed tuna fish that are GG tuna with a muscle selenium content of 30 μg or more, 70 μg or less, 60 μg or less, 55 μg or less, or 50 μg or less per 100 g, and a body mass index of 21 or more, a total weight of 21 kg or more, or a fork length of 90 cm or more; and (4) Low-selenium farmed tuna fish, GG tuna, with muscles containing 30 μg or more and 70 μg or less, 60 μg or less, 55 μg or less, or 50 μg or less of selenium per 100 g, and with a body mass index of 20 or more, a total weight of 17 kg or more, or a fork length of 100 cm or more:

[0037] (5) Low-selenium farmed tuna fish with a liver containing 300 μg or more, but not more than 1000 μg, 900 μg, 800 μg, 700 μg, or 600 μg of selenium per 100 g, and with a body mass index of 21 or more, a total body weight of 25 kg or more, or a fork length of 90 cm or more; (6) Low-selenium farmed tuna fish with a liver containing 300 μg or more, but not more than 1000 μg, 900 μg or less, 800 μg or less, 700 μg or less, or 600 μg or less of selenium per 100 g, and with a body mass index of 20 or more, a total body weight of 20 kg or more, or a fork length of 100 cm or more; (7) Low-selenium farmed tuna fish, which are GG tuna, having a liver with a selenium content of 300 μg or more, but not more than 1000 μg, 900 μg or less, 800 μg or less, 700 μg or less, or 600 μg or less per 100 g, and having a body mass index of 21 or more, a total weight of 21 kg or more, or a fork length of 90 cm or more; and (8) Low-selenium farmed tuna fish, GG tuna, with a liver containing 300 μg or more, but not more than 1000 μg, 900 μg or less, 800 μg or less, 700 μg or less, or 600 μg or less of selenium per 100 g, and with a body mass index of 20 or more, a total weight of 17 kg or more, or a fork length of 100 cm or more:

[0038] The low-selenium farmed tuna fish (1) to (8) have a low selenium content, so when used as food, it is possible to provide food with a reduced selenium intake. The muscle-related forms (1) to (4) and the liver-related forms (5) to (8) may be independently combined with each other to the extent possible.

[0039] <Edible parts and processed foods> One embodiment of the present disclosure is an edible portion of a farmed tuna fish having at least one of muscle with a selenium content of 90 μg or less per 100 g and liver with a selenium content of 1,400 μg or less per 100 g. In other words, the edible portion of the farmed tuna fish may be the edible portion of the low-selenium farmed tuna fish described above. As described above, low-selenium farmed tuna fish have a low selenium content per individual. Therefore, the edible portion obtained from the low-selenium farmed tuna fish can also have a lower selenium content than edible portion obtained from wild-caught tuna or farmed tuna fish that eat live food. Therefore, when the edible portion according to one embodiment of the present disclosure is provided as food, the selenium intake can be kept lower than that of the same edible portion of wild-caught or farmed tuna fish raised on live food, thereby reducing the risk of excessive selenium intake. Such edible parts of farmed tuna fish may also be referred to as edible parts of tuna.

[0040] "Edible parts" refer to parts of a fish that can be eaten, such as fish meat, internal organs, eyeballs, skin, brain, and blood. In the case of tissues or organs, it may be the entire tissue or organ, or even a part thereof. For example, in the case of the liver, it may be the entire liver or a part thereof. Note that "edible" here refers not only to food for humans, but also to food for animals other than humans.

[0041] The edible part may be fish meat or at least a part of the internal organs. The edible fish meat is muscle and is generally eaten uncooked (raw) or cooked. Examples of fish meat include the lean meat, fatty meat, and dark muscle described above, with lean meat or fatty meat being preferred.

[0042] Examples of edible internal organs include the liver, pyloric caeca, stomach, esophagus, intestines, gonads (testes or ovaries), spleen, heart, swim bladder, etc. These internal organs can generally be cooked and eaten. The eyeballs as edible parts may have surrounding muscles attached.

[0043] As described above, the edible parts of farmed tuna fish in one embodiment of the present disclosure are edible parts of low-selenium farmed tuna fish, i.e., muscle with a selenium content of 90 μg or less per 100 g or liver with a selenium content of 1,400 μg or less per 100 g. Regarding the selenium content in the edible fish meat (muscle) and liver, the same matters as those described above for low-selenium farmed tuna fish apply. Similarly to muscle and liver, other edible parts also have a lower selenium content compared to wild-caught tuna, and therefore can have a lower content than the corresponding part of wild-caught tuna. For example, the stomach may have a selenium content of 250 μg or less per 100 g.

[0044] The edible portion of farmed tuna fish may include the fish meat or parts surrounding the internal organs. For example, the "edible portion" of this disclosure also includes "aro" (rough part). "Aro" generally refers to the head, bones, gills, fins, or a combination of two or more of these that remain after the fish is filleted and removed, along with the meat and skin attached to them.

[0045] The edible parts of farmed tuna fish are preferably used as processed foods, such as the following heated and uncooked foods, and can also be used as animal feed. The processed food and animal feed according to one embodiment can contain the edible parts of low-selenium farmed tuna fish. The present disclosure provides foods and animal feed that can easily prevent excessive selenium intake.

[0046] Examples of animal feed include cat food, dog food, farmed fish feed, poultry feed, and livestock feed. There are no particular restrictions on the proportion of the edible portion of low-selenium farmed tuna fish in the animal feed, and it can be 0.1% to 100% by weight, for example. In addition to the edible portion of low-selenium farmed tuna fish, the animal feed can also contain other nutrients such as vitamins, carriers acceptable for animal feed such as water, and other additives such as excipients, as needed, depending on the type of animal. The animal feed may be contained in a container as described below. Examples of foods include uncooked foods and cooked foods.

[0047] One embodiment of the present disclosure includes a processed food product of farmed tuna fish, including an edible portion of low-selenium farmed tuna fish and a container for housing the edible portion. The processed food product may include both cooked and uncooked products. Processed food products of farmed tuna fish including such a container may also be referred to as a processed tuna product. Unheated products refer to edible parts that have not been cooked with heat, and examples thereof include surimi, sashimi, fillets, blocks, and fillets, as well as frozen, chilled, freeze-dried, dried, and pickled products. The fact that a product has not been cooked with heat can be determined by the color tone of the surface of the edible part. In this specification, "heating" means applying heat to a state in which actomyosin is denatured to a visible extent. When the edible parts of farmed fish are heat-treated, the edible parts discolor due to the denaturation of actomyosin, so the discoloration of the edible parts can be determined based on the discoloration of the edible parts. The term "heated food" refers to edible parts that have been cooked by heating, and examples thereof include boiled food, baked food, steamed food, fried food, paste products, canned food, and the like.

[0048] The shape of the edible part contained in the processed food is not particularly limited, and may have a shape specific to the part of the edible part, may be an irregular shape obtained by shredding, or may be molded into a specific shape.

[0049] The processed food may optionally contain at least one selected from the group consisting of other foods, food ingredients, and accessories. Examples of other foods include rice, garnish (radish, seaweed, etc.), shiso leaves, ginger, sprouts, and condiments. Examples of food ingredients include green onions for negitoro. Examples of accessories include, for example, scales, labels, ice packs, cooling agents, absorbent sheets, ice, dry ice, and sherbet ice. The accessories may be contained within the container together with the edible portion, or may be located on the outside of the container. They may be integrally integrated with the container or detachably attached. Each of the other foods, food ingredients, and accessories may be a combination of one or more.

[0050] The container may be any suitable container for containing the edible portion, and examples of such materials include polystyrene foam, paper, vinyl, soft plastic, hard plastic, metal, and glass. The container may be any suitable shape capable of containing the edible portion, and examples of such containers include packaging sheets, trays with or without lids, bags, and cans. For example, as shown in FIG. 4, a processed tuna-like farmed fish food product 10 can be produced by placing slices 11 of tuna muscle as the edible portion on a tray 12 as a container and then wrapping the whole in plastic wrap 13 as a container. The container for this processed tuna-like farmed fish food product 10 also contains other foods, such as shiso leaves 14 and condiments 15, and an accessory water-absorbent sheet 16.

[0051] The above-mentioned low-selenium tuna farmed fish, the edible portions of the above-mentioned low-selenium tuna farmed fish, and the low-selenium tuna farmed fish for use as edible portions in processed foods may be obtained by any method. The low-selenium tuna farmed fish are preferably low-selenium tuna farmed fish produced by the following rearing method.

[0052] <Breeding method> The rearing method in one embodiment of the present disclosure includes continuously feeding a compound feed containing fish meal composed of 30% or more by weight of sardine fish meal, an inclusion containing oil and fat, and an outer shell that encases the inclusion and is composed of at least one substance selected from the group consisting of proteins and polysaccharides, for at least 30 days, and may include other processes as necessary. In the above-described rearing method, a double-layered compound feed having a specific inner shell and a specific outer shell containing fish meal and fats and oils composed of a relatively large amount of sardine fish meal is fed to tunas continuously for at least 30 days, thereby efficiently producing low-selenium farmed tuna fish according to an embodiment of the present disclosure, with reduced selenium content in the muscles or livers. From this perspective, in this specification, the term "method for rearing low-selenium farmed tuna fish" is synonymous with "method for producing low-selenium farmed tuna fish" or "method for producing low-selenium farmed tuna fish," and can be interpreted interchangeably.

[0053] The compound feed used in the rearing method of this embodiment has a double structure including an outer shell and an inner shell. In the present disclosure, this compound feed used in the rearing method of this embodiment may be referred to as low-selenium tuna farmed fish rearing feed. The low-selenium tuna farmed fish feed is mainly composed of fish meal and oils, and the fish meal is made up of sardine fish meal at least 30% by weight of the total weight. Sardines, which are the raw material for sardine fish meal, belong to the order Clupeidae, and include species such as Sardinops and Etrumeus in the Clupeidae family, and Anchovy in the Engraulidae family. Sardines are marine fishes that are approximately 10 to 30 cm in size and are typically found in the genus Engraulis or Sarudina. Sardine fish meal can be produced by the steam-drying method or the hot air method, but can also be produced by other methods.

[0054] The sardine fish meal content in the fish meal may be 30% by weight or more, 40% by weight or more, or 50% by weight or more. There is no particular upper limit to the proportion of sardine fish meal in the fish meal, and it can be, for example, 95% by weight or less, 98% by weight or less, or 100% by weight. If the proportion of sardine fish meal in the fish meal is within this range, farmed tuna fish with a low selenium content can be efficiently obtained. Other fishmeals that can be contained in the fishmeal include various fishmeals commonly used as ingredients in fish farming feed, such as those from horse mackerel, bonito, threadfin bream, and menhaden, as well as crustacean powder such as krill, and materials derived from squid, etc. Sardine fishmeal is particularly suitable as the fishmeal contained in low-selenium tuna farming feed, and if other fishmeals are added, threadfin bream fishmeal and / or bonito meal may be mixed in. Feeding farmed tuna with such fishmeals can contribute to keeping the selenium content in the muscle of farmed tuna to 90 μg or less per 100 g and the selenium content in the liver to 1,400 μg or less per 100 g.

[0055] The fish meal content can be 30% to 70% by weight of the total weight of the inclusion, preferably 30% by weight or more, more preferably 35% by weight or more, and most preferably 45% by weight or more. From the viewpoint of maintaining the shape, it is preferable to add an excipient such as a polysaccharide with binding properties, hardened oil, or emulsifier to the inclusion.

[0056] The encapsulation can contain raw materials used in conventional compound feed for farmed fish, such as proteins such as raw fish, squid meal, krill meal, soybean oil cake, and corn gluten meal, oils and fats such as krill oil, whale oil, soybean oil, corn oil, rapeseed oil, and hardened oil, starches such as starch, wheat flour, rice flour, tapioca flour, and corn flour, polysaccharides such as alginic acid and its salts, sodium carboxymethylcellulose (CMC), guar gum, dextrin, chitosan, curdlan, pectin, carrageenan, mannan, gellan gum, gum arabic, and edible water-soluble cellulose, vitamins, and minerals.

[0057] The inclusions may contain 20 to 70% by weight of the oil or fat of the total weight of the inclusions, and when feeding particularly large farmed fish, the oil or fat may be blended so that it is preferably 30% by weight or more, more preferably 35% by weight or more, and most preferably 45% by weight or more of the total weight of the inclusions. A large amount of oil or fat content can have an excellent effect on the growth and growth efficiency of farmed fish, and if it is 70% by weight or less, it becomes easy to select and blend other preferred ingredients.

[0058] Fish oils and other vegetable oils and fats can be used as they are, or preferably, they can be used after reducing their fluidity using oil-absorbing polysaccharides such as dextran, such as Vitacel (registered trademark, hereinafter the same) WF200, Vitacel WF600, or Vitacel WF600 / 30 (manufactured by Rettenmeyer), Oil Q No. 50 or Oil QS (manufactured by Nippon Starch Chemical Co., Ltd.), or Pine Flow (manufactured by Matsutani Chemical Industry Co., Ltd.), oil-absorbing proteins such as fermented soybean and isoflavones, or hardened oils obtained by hydrogenating oils and fats such as soybean oil, rapeseed oil, or palm oil.

[0059] Fish oil can also be used after reducing its fluidity by emulsification. From the viewpoint of fish digestibility, it is desirable that these fluidity-reducing components be contained in an amount of preferably 10% by weight or less, more preferably 5% by weight or less, of the total weight of the encapsulation. Fish oil is the most preferred oil. Fish oil can also be partially replaced with other vegetable oils.

[0060] The encapsulation may be stabilized by blending polysaccharides, hardened oils, etc., and emulsifying them. This can prevent leakage of fish meal or liquid oils. When compound feed is produced by machine, the encapsulation preferably has fluidity or physical properties suitable for machine use. Examples of oil and fat adsorbents include Oil Q (manufactured by Nippon Starch Chemical Co., Ltd.), and examples of hardened oils include Unishort K (manufactured by Fuji Oil Co., Ltd.). Furthermore, New Fujipro SEH (manufactured by Fuji Oil Co., Ltd.) can be used for emulsification.

[0061] The outer shell of the low-selenium tuna farmed fish feed is composed of at least one substance selected from the group consisting of proteins and polysaccharides. If necessary, the outer shell may contain substances other than proteins and polysaccharides as additives or other blending ingredients. There are no particular limitations on the outer shell, as long as it can encase the contents. For example, the outer shell may be formed under non-heating conditions, regularly or irregularly, from at least one substance selected from the group consisting of proteins and polysaccharides, or the outer shell may be formed from a heated gel obtained by heat treatment or a cooled gel obtained by cooling treatment, using at least one substance selected from the group consisting of proteins and polysaccharides as a raw material.

[0062] When using raw materials containing protein raw materials and / or polysaccharide raw materials that form a gel upon heating, the raw materials gel upon heating and exhibit a certain degree of elasticity, extensibility, and adhesiveness. The use of such a heated gel is preferable because it ensures that the inclusions are encapsulated. Hereinafter, raw material compositions containing protein raw materials and / or polysaccharide raw materials that form a gel upon heating will be referred to as exoskeleton compositions and will be explained below. A gel produced by heating refers to a gel produced by heating at least one raw material selected from the group consisting of proteins and polysaccharides to 60°C or higher, or by heating to 60°C or higher and then cooling, and also refers to a gel produced by adding water to a polysaccharide such as starch and heating it to 60°C or higher to gelatinize it.

[0063] Preferred proteins for use in the outer shell include gel-forming proteins such as fish meat, surimi, krill, gluten, collagen, soy protein, enzymatically hydrolyzed soy protein, gelatin, and egg white, either alone or in mixtures of two or more of these proteins. Proteins also include alginic acid and its salts. Examples of polysaccharides include starch, alginic acid and its salts, sodium carboxymethylcellulose (CMC), guar gum, dextrin, chitosan, curdlan, pectin, carrageenan, mannan, gellan gum, gum arabic, and edible water-soluble cellulose. Preferred starches for use in the outer shell include tapioca starch, wheat starch, potato starch, corn starch, soybean starch, waxy cornstarch, and modified starches thereof. Food materials containing large amounts of these proteins and / or starches can also be used. The outer shell, which contains these proteins and / or polysaccharides, forms a gel that is fixed by heating, has flexibility, and also has the ability to retain the inner layer composition, giving it a certain level of strength. Among these, gels formed by heating protein or gels formed by heating starch are preferred in terms of their physical properties, such as flexibility and extensibility.

[0064] For example, when using fish paste as the raw material, it can be produced using a general method for producing kamaboko or other paste products. Specifically, 2% by weight or more of salt is added, and the mixture is left to stand at 10°C or higher, preferably 30°C to 40°C, for 10 minutes or more, and then heated at 80°C to 90°C for 10 minutes or more. When using egg white, a composition with desired physical properties can be obtained by mixing egg white, starch, fish meal, and water in a weight ratio of 1:1:2:6 and heating the mixture.

[0065] Various auxiliary ingredients can be added to the composition for skin as long as they do not affect gel formation. For example, fish meal or oils and fats can also be added to the composition for skin as long as they do not affect the gelation of the skin. Depending on the type of gel used, in the case of fish meal, the skin can contain up to about 60% by weight of fish meal, and in the case of oils and fats, the skin can contain up to 30% by weight of oil and fat based on the total weight of the composition for skin. When both fish meal and oil and fat are included, the skin preferably contains about 20 to 30% by weight of fish meal and about 5 to 10% by weight of oil and fat based on the total weight of the composition for skin.

[0066] To improve the gel quality of the outer skin, additives used as quality improvers for fish paste products and the like can be added to the outer skin composition. Examples of additives include starch, thickening polysaccharides, isolated soy protein, sodium bicarbonate, polymerized phosphate, egg white, transglutaminase, and various protease inhibitors. In particular, the outer skin can contain a thickener such as agar, gellan gum, pullulan, starch, mannan, carrageenan, xanthan gum, locust bean gum, curdlan, pectin, alginic acid and its salts, gum arabic, chitosan, dextrin, or edible water-soluble cellulose to enhance gel strength.

[0067] Another preferred embodiment of the outer shell is a heated gel composed primarily of starch, which is excellent in terms of elasticity and flexibility. A gel obtained by adding water to starch, kneading the mixture, and heating it exhibits good elasticity, flexibility, and extensibility. In particular, various modified starches each have their own characteristics, and by combining two or more types, an outer shell with better properties such as elasticity, flexibility, and extensibility can be obtained. For example, it is preferable to combine different types of modified starches, such as a combination of etherified starch and phosphate cross-linked starch. Adding proteins such as gluten or soy protein to starch can produce a stronger gel. Gluten-containing wheat flour can also be used instead of gluten. Other secondary ingredients include cereal flours such as wheat flour; proteins such as soy protein, gluten, and egg white; sugars or sugar alcohols such as sugar and starch syrup; thickeners such as carrageenan, agar, gellan gum, pullulan, mannan, xanthan gum, locust bean gum, curdlan, pectin, alginic acid and its salts, gum arabic, chitosan, dextrin, and edible water-soluble cellulose; and salts such as phosphates. For example, adding wheat flour to starch can strengthen the outer shell. Furthermore, adding a certain amount of protein can reduce surface stickiness after heating.

[0068] The starch used in the outer skin is not particularly limited, but tapioca starch, wheat starch, potato starch, corn starch, soybean starch, etc. can be used, with processed starches such as etherified, acetylated, acetyl-crosslinked, ether-crosslinked, phosphate-crosslinked, and pregelatinized hydroxypropyl phosphate-crosslinked starches being particularly preferred. The outer skin of low-selenium tuna farmed fish feed contains a combination of tapioca starch acetate and etherified tapioca starch. This type of low-selenium tuna farmed fish feed is preferred from the standpoints of suppressing surface stickiness and making the feed easier to eat. The combination of tapioca starch acetate and etherified tapioca starch can be, for example, a weight ratio of 1:1 to 1:20, preferably 1:2 to 1:15, and more preferably 1:8 to 1:12.

[0069] Low-selenium tuna farmed fish feed can be produced by adding water to a skin composition made from starch, the raw material for the skin, and other auxiliary ingredients such as protein, mixing and kneading the mixture, wrapping the contents in a filling machine, and then heating.

[0070] Preferably, the outer shell composition and the inclusions are supplied to a double-nozzle extruder, and the outer shell composition is mixed and heat-treated while being extruded so that the inclusions are wrapped in the outer shell, and the product can be produced by a method including other steps as necessary. For example, an extruder equipped with a double nozzle can be used to simultaneously heat-treat the composition for the outer shell by extrusion cooking and coat the inner shell with the outer shell; for example, the cylindrical extruded product can be cut to a certain length with a shutter mechanism that moves up and down in accordance with the speed of extrusion, and the cut surface can be covered with the outer shell to obtain a double-structured compound feed.

[0071] An apparatus equipped with a double nozzle and suitable for obtaining such a double-structured compound feed may be either a single-screw or twin-screw apparatus, as long as it has an extrusion mechanism and a heating mechanism. A device suitable for obtaining a double-structured compound feed is preferably a co-rotating, intermeshing twin-screw type apparatus. The use of such an apparatus offers advantages such as the ability to thoroughly mix the feed in a short period of time. An example of such an apparatus is one manufactured by Buhler, as disclosed, for example, in WO 2013 / 061892.

[0072] This device is equipped with an extruder with a heating function connected to a skin composition supplying device, and a nozzle that feeds the encapsulation into the center of the skin composition is located near the extruder's discharge port. An encapsulation supplying device is connected to this nozzle. A conveyor is adjacent to the extruder, and a shutter mechanism is located at the end of the conveyor's transport path. The skin composition supplying device mixes the skin composition and sends it to the extruder with a pump. The encapsulation supplying device pumps encapsulations that have been separately mixed and prepared through a nozzle into the extruder's discharge port. The skin composition is kneaded within the extruder and then heated to form a heated gel. At the discharge port, the skin is extruded into a cylindrical shape, its interior filled with encapsulations inserted through the nozzle, and it is discharged in the form of a double-structured column. The discharged double-structured column is transported by a conveyor and inserted vertically downward into the shutter mechanism. The shutter mechanism cuts the envelope to a certain length, resulting in a double-structured molded product.

[0073] Mixing in the extruder can be performed at a screw rotation speed of 300 to 800 rpm, preferably 350 to 700 rpm. The heating temperature may be at or above the temperature at which starch, added proteins, etc. gel, and the product temperature may be approximately 60 to 110°C, preferably 70 to 100°C, and more preferably 80 to 95°C. The discharge temperature may be 80 to 110°C, preferably 85 to 105°C. The outlet pressure may be 2 MPa to 10 MPa, preferably 4 MPa to 8 MPa.

[0074] The weight ratio of the encapsulation composition to the outer shell composition can be 4:6 to 9:1, and preferably 5:5 to 8:2. Combining at such a weight ratio is preferable from the viewpoints of the elasticity of the resulting low-selenium tuna farmed fish feed, the strength of the outer shell, etc.

[0075] The water activity of the compound feed may be adjusted in consideration of its shelf life. This adjustment of water activity can be made by adjusting the composition of the inclusion and / or the shell. For example, the water activity of the inclusion can be lowered by adjusting the amount of water added. The water activity of the composition may be adjusted by adding a water activity regulator such as salts (table salt, sodium malate, sodium lactate, etc.), sugars (sugar, lactose, maltose, sorbitol, etc.), sugar alcohols, amino acids, nucleic acid-related substances, organic acids, alcohols, propylene glucose, glycerin, starches, or proteins.

[0076] The amount of water added to the skin composition may be an amount that is compatible with the encrusting machine or extruder, and is suitably approximately 30 to 50% by weight. For example, the moisture content of the skin, which is formed by encasing the inclusions in a heated starch gel, can be approximately 25 to 50% by weight. Low-selenium tuna farmed fish feed can be stored for long periods by refrigerating or freezing it. This feed can be further dried to a moisture content of 10 to 20% by weight, further improving shelf life. By combining drying the skin with adding an additive to the skin composition to reduce the water activity, a feed that can be stored for long periods at room temperature can be produced. From the perspective of long-term storage, the skin of the compound feed preferably has a moisture content of 10 to 20% by weight and a water activity of 0.8% or less, particularly 0.75% or less, or 0.7% or less. In the present disclosure, the moisture content is measured using a room temperature heating and drying method, and the water activity is measured using a water activity measuring device.

[0077] In low-selenium tuna farmed fish feed, for example, various formulation patterns for starch-containing skin compositions are possible. The nutritional and calorie requirements of feed vary depending on the fish species and growth stage. The higher the fish meal and fish oil content, the more strict the skin composition needs to be adjusted. However, when the fish meal and fish oil content is lower, there is considerable flexibility in the skin composition. It is preferable that starch be contained in at least 20-80 wt% of the total skin weight, calculated on a dry matter basis. For skins containing 25-50 wt% fish meal (dry matter basis), it is preferable to add 20-65 wt% starch, 5-20 wt% wheat flour, and a total of approximately 5-15 wt% protein, oils, thickeners, salts, etc., calculated on a dry matter basis. For skins containing fish oil, it is preferable to add approximately 1-5 wt% fish oil, 1-2 wt% phosphate, 1-5 wt% protein, and 1-5 wt% thickener. When used as a secondary ingredient, wheat flour is preferably strong flour with a high gluten content, but weak flour is also acceptable. To improve the quality of the outer skin, additives used as quality improvers for starch foods can be added.

[0078] Considering the feeding preferences of tuna farmed fish, the shape of the low-selenium tuna farmed fish breeding samples can be similar to the spindle shape of small fish such as sardines that tuna farmed fish prefer. Specific examples of such shapes include a shape in which the outer surface is made up of an outer skin and an inner shell enclosed by the outer skin, giving the sample a roughly cylindrical side, with both ends covered and closed by the outer skin, and at least one of the ends having a tapered protrusion where the outer skin protrudes toward the end. Furthermore, this shape may further be such that the thickness of the outer skin increases toward the end at the protruding portion, or such that the protruding portion is formed at both of the end portions, or such that the protruding portion has a reduced diameter portion whose diameter gradually decreases from the side surface toward the end portion with an outwardly convex curve, the protruding portion is formed at the end of the reduced diameter portion, and an inflection portion whose diameter gradually decreases with an outwardly concave curve toward the end portion is formed between the reduced diameter portion and the protruding portion. The shape of the low-selenium tuna farmed fish breeding samples described above can contribute to achieving a selenium content of 90 μg or less in muscle and 1,400 μg or less in liver in farmed tuna fish.

[0079] The method for producing a compound feed can include drying the double-layered compound feed obtained by cutting with the shutter mechanism, that is, a drying step. There are no particular limitations on the drying method as long as it can dry the compound feed. Drying conditions should be set so that the moisture content of the outer skin of the feed reaches the above-mentioned level.

[0080] The drying conditions are preferably gentle, allowing the moisture content of the outer skin to reach 10 to 20% by weight. When gentle drying conditions are used, the moisture content of the outer skin decreases during the drying process, while the moisture content of the inclusions tends to be higher than the moisture content immediately after cutting due to the migration of moisture from the outer skin. This allows for the production of low-selenium tuna farmed fish feed with good physical properties that meet the preferences of farmed fish. The gentle drying conditions can be appropriately set based on the relative humidity, for example, at a temperature of 20°C to 45°C for 6 to 48 hours, and within a relative humidity range of 20% to 50%. Any drying method that can achieve such gentle drying conditions can be used, and examples include drying by placing the material on a mesh conveyor, mesh container, or sheet.

[0081] A method for raising farmed tuna fish according to one embodiment of the present disclosure includes feeding the tuna fish the above-described low-selenium farmed tuna fish feed for at least 30 consecutive days. By continuing to raise the tuna fish with the low-selenium farmed tuna fish feed for at least 30 consecutive days, the selenium content of the tuna fish being raised can be reduced. Whether the farmed fish have been raised and managed can be confirmed by checking the components of the low-selenium farmed tuna fish feed fed to the tuna fish during the rearing period for characteristic components that are not contained in live feed but can remain in the fish, such as vegetable oils.

[0082] The rearing period using the low-selenium tuna farmed fish feed can be longer, for example, 45 days or more, 60 days or more, 90 days or more, 120 days or more, 150 days or more, 6 months or more, or 1 year or more. By feeding the low-selenium tuna farmed fish breeding material for a longer period, the selenium content in the farmed fish can be further reduced. The effect of reducing the selenium content in the farmed fish does not have to be uniform throughout the fish. For example, if the rearing period using the low-selenium tuna farmed fish feed is 30 days or more, the effect of reducing the selenium content in the muscle can be obtained, and if it is 60 days or more, the effect of reducing the selenium content in the liver can be obtained.

[0083] The rearing conditions can be the same as those normally used for rearing tuna. For example, the water temperature during the rearing period can be 10°C to 32°C, and feeding can be once a day at a satiating rate during normal times and once every two days during winter. As mentioned above, limiting feeding to once every two days during winter can contribute to keeping the selenium content of farmed tuna muscle at 90 μg or less per 100 g, or the selenium content of liver at 1,400 μg or less per 100 g. Note that winter can be, for example, a period when the average daily water temperature is 20°C or less.

[0084] In this rearing method, as long as the fish are fed with the low-selenium tuna farmed fish feed for the above-mentioned rearing period before landing, there may be a period during which other feed is fed. Examples of other feed include live feed (horse mackerel, mackerel, etc.) and moist pellets. The longer the period of feeding with the low-selenium tuna farmed fish feed before landing, the more reliably the selenium content can be reduced.

[0085] For example, rearing can be started with fish individuals with a total weight of 200 g, or fish individuals with a total weight of 500 g, 1 kg, or 10 kg or more. By starting rearing at such a stage, the fish can be maintained in a healthy state as they grow until the desired age.

[0086] The rearing period may be any period from the start of rearing to the final desired period, such as shipping or spawning. For example, the rearing period may be the period immediately before shipping. In this case, it is possible to provide low-selenium farmed tuna fish and their edible parts with a stably reduced selenium content.

[0087] Low-selenium farmed tuna fish may be produced by methods other than the above-mentioned rearing methods, as long as they have the characteristics described in this disclosure.

[0088] <Method of manufacturing edible parts> A method for producing edible parts according to one embodiment of the present disclosure includes preparing low-selenium tuna farmed fish obtained by the breeding method of the above-described embodiment, harvesting edible parts from the prepared low-selenium tuna farmed fish, and placing the edible parts in a container, and may include other processes as necessary. In this method for producing edible parts, edible parts are collected from farmed tuna fish raised using the rearing method in one embodiment described above, so that edible parts containing selenium at a lower content than edible parts of farmed tuna fish raised in the wild or on live bait can be efficiently obtained.

[0089] The farmed tuna fish may be whole fish or may be processed as described above. There are no particular limitations on the method for collecting the edible parts, and those skilled in the art can collect the edible parts by a conventional method using tools commonly used to cut out the desired edible parts from whole fish or parts thereof.

[0090] <Application> Low-selenium farmed tuna fish and their edible parts are preferred as foods that make it relatively easy to avoid excessive selenium intake due to their low selenium content. Because the selenium content of low-selenium farmed tuna fish and their edible parts has been adjusted to be low, they can also be used as animal feed for livestock such as cows, pigs, and poultry, other farmed fish, and pet food. [Example]

[0091] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited thereto.

[0092] [Example 1] (1) Preparation of low-selenium tuna farmed fish feed 35-40 wt% fish meal, 17-23 wt% starch (etherified tapioca starch: hydroxypropyl starch, manufactured by Nippon Starch Chemical Co., Ltd., G-800), 7 wt% wheat flour, 2 wt% starch (acetate tapioca starch: manufactured by Nippon Starch Chemical Co., Ltd., Z-300), 2 wt% fish oil, 3 wt% salt, 2.5 wt% sugar, 1 wt% gluten, and the remainder water were mixed in an extruder under conditions of a screw rotation speed of 450 rpm, a discharge temperature of 90°C, and an outlet pressure of 50 bar (5 MPa) to give a composition for outer skins. 59% by weight of fish meal, 36% by weight of fish oil, 1.965% by weight of hardened oil, 2% by weight of vitamins, 1% by weight of minerals, and 0.035% by weight of α-tocopherol were mixed using an extruder at 60°C and encapsulated.

[0093] The fish meal used for the encapsulation was made by steam-drying sardines from Chile or Peru, and mixing it with threadfin bream fish meal made in the same way. The sardine fish meal content in the fish meal used for the encapsulation was 55% by weight of the total fish meal.

[0094] To produce low-selenium tuna farmed fish feed by combining the outer shell composition and the inclusions, a co-rotating, fully intermeshing, twin-screw extruder (manufactured by Buhler) with a double nozzle at the tip and an extrusion capacity of 1 t / h was used. Both the outer shell composition and the inner shell were granulated from the double nozzle at the tip of the extruder, and a shutter device was used to obtain low-selenium tuna farmed fish feed in which the inner shell was enclosed by the outer shell. The weight ratio of inner shell to outer shell was 65:35.

[0095] The newly formed mixed feed was then placed on a conveyor and dried naturally for 24 hours at 30-40°C and a relative humidity of 20-50%. This process resulted in good mixed feed with almost no cracks or other defects. The moisture content of the outer skin of the obtained low-selenium tuna farmed fish feed was 12% to 17%, and the water activity was less than 0.8. The moisture content of the inner shell is estimated to be about 4.7% immediately after molding. The moisture content was measured using a Drying Oven DX300 (manufactured by Yamato Scientific Co., Ltd.), and the water activity was Measurement was performed using Aqua Love CX-3 (Milestone General).

[0096] (2) Rearing The prepared low-selenium tuna farmed fish feed was used to raise bluefin tuna. The group raised using the low-selenium tuna farmed fish feed is designated as Example. Approximately 3,000 tuna weighing approximately 16 kg and with a fork length of approximately 90 cm were placed in an oval ocean surface cage with a diameter of 70 m and reared on live feed, and rearing began. The water temperature during the rearing period was 13°C to 29°C. Feeding was normally provided once a day with a satiation feeding, and once every two days in winter. Throughout the test period, feed intake was 30-50% by weight of the live feed. Rearing began in March and continued for 18 months.

[0097] (3) Comparison group As a control group, bluefin tuna were used that were reared under the same conditions as in (2) above, except that they were fed mackerel or sardines as live bait. The group reared using live bait was used as a comparative example.

[0098] (4) Fish body measurements For each of the Examples and Comparative Examples, after the rearing period, the body temperature (°C) of eight tuna from each group was measured immediately after they were removed from the fishponds, and then the weight (kg) and fork length (cm) of the GG tuna were measured, from which the degree of obesity was calculated. The results are shown in Table 1. In each of the following tables, a Student's t-test was performed between the Examples and Comparative Examples for each item, and the resulting T value (t) is also shown.

[0099] [Table 1]

[0100] The above results show that no significant differences were observed between the average values ​​of the Example and Comparative Examples for body temperature, GG weight, fork length, or obesity index, with t<0.05. Therefore, it can be said that the Example fish raised using the low-selenium tuna farmed fish feed exhibited growth comparable to the Comparative Example fish raised on live food. Specifically, the tuna in the Example fish weighed approximately 16 kg at the start of the test, and although there were individual differences, it was confirmed that after approximately 18 months, the average GG weight exceeded 50 kg. The average fork length was approximately 141 cm, and the average obesity index was approximately 22, which were also nearly equivalent to the tuna in the live food group.

[0101] (5) Selenium and Vitamin Contents Figure 1 shows a cross section of the tail side of a tuna cut vertically from the rear end of the first dorsal fin. In this cross section, region A represents the central deep dorsal region, region B represents the central superficial dorsal region, region C represents the central dorsal keel muscle, and region D represents the dark muscle. In Figure 1, E represents the abdominal cavity.

[0102] For each of the tuna samples from the Examples and Comparative Examples described above, a 5 cm square piece of muscle was cut from the opposite side of the cut surface of the tail end shown in Figure 1, i.e., the area of ​​the cut surface of the head end corresponding to region B in Figure 1, and sampled as a test piece from the shallow central dorsal region (chutoro). The selenium content was measured using this test piece. The selenium content was measured according to "(1) Quantification by Fluorescence Spectroscopy" on page 433 of "Hygienic Testing Methods - Commentary 2010" (edited by the Pharmaceutical Society of Japan, published February 20, 2010, Kanehara Publishing). The vitamin A, vitamin B, and vitamin E contents were also measured using the same test piece according to standard methods. The results are shown in Table 2.

[0103] [Table 2]

[0104] As shown in Table 2 above, the selenium content in the muscle of all tuna in the Comparative Example exceeded 80 μg / 100 g. In contrast, the selenium content in the muscle of all tuna in the Example was 50 μg / 100 g or less. Thus, the selenium content in the muscles of the tuna in the fed group was lower than that in the tuna in the live-feed group.

[0105] The average vitamin D content in muscle for the Example was 9.4 μg / 100 g, which was higher than the average of 6.5 μg / 100 g for the Comparative Example, but this difference was not significant (t>0.05). However, the average vitamin A content in muscle for the Example was 834.5 μg / 100 g, which was significantly lower than the average of 1855.0 μg / 100 g for the Comparative Example (t<0.05). Furthermore, the average vitamin E content in muscle for the Example was 13.5 μg / 100 g, which was significantly higher than the average of 1.5 μg / 100 g for the Comparative Example (t<0.05).

[0106] By the way, when I ate the fatty part (chutoro) used in the measurements as sashimi, it was delicious.

[0107] (6) Fatty acid content The contents of various fatty acids were measured using the same test pieces as above according to standard methods. Table 3 shows those in which a significant difference (t<0.05) was observed between the Examples and Comparative Examples.

[0108] [Table 3]

[0109] As described above, it was found that the content of unsaturated fatty acids such as oleic acid, linoleic acid, and α-linolenic acid in the muscle was significantly (t<0.05) higher in the Examples than in the Comparative Examples.

[0110] (7) Free amino acid content The contents of various free amino acids were measured using the same test pieces as above according to standard methods. Tables 4, 5, and 6 show those in which significant differences (t<0.05) were observed between the Examples and Comparative Examples.

[0111] [Table 4]

[0112] [Table 5]

[0113] [Table 6]

[0114] Of the various free amino acids, as shown in Tables 4, 5 and 6 above, it was found that the muscle contents of threonine, glutamic acid, glycine, alanine, valine, isoleucine, leucine, anserine, carnosine and proline in the Examples were significantly (t<0.05) higher than those in the Comparative Examples.

[0115] In particular, as shown in Table 4 above, the content of free amino acids such as glutamic acid, glycine, and alanine was significantly (t<0.05) higher in the Examples than in the Comparative Examples, suggesting that the taste of tuna muscle raised using low-selenium tuna farmed fish samples may be improved compared to tuna muscle raised on live feed.

[0116] Furthermore, as shown in Table 5 above, the content of the branched-chain amino acids (BCAAs) valine, isoleucine, and leucine, which are essential amino acids, was significantly (t<0.05) higher in the Examples than in the Comparative Examples, suggesting that tuna muscle raised using low-selenium tuna farmed fish samples may also be effective as a nutritional supplement.

[0117] Furthermore, as shown in Table 6 above, the content of anserine, which is said to have anti-fatigue effects, active oxygen scavenging ability, blood pressure lowering effect, anti-inflammatory effect, and uric acid level lowering effect, was significantly (t<0.05) higher in the Examples than in the Comparative Examples, suggesting that the muscles of tuna raised using low-selenium tuna farmed fish samples also have a positive effect on these effects.

[0118] [Example 2] Next, we investigated the changes in selenium content due to the change in the type of feed as follows. The animals were reared in the same manner as in Example 1, except that for some of the feed groups and live feed groups, the diet was switched after rearing for 6 months or more. The group that switched from formula feed to live feed was designated the "live feed switching group," and the group that switched from live feed to low-selenium tuna farmed fish feed was designated the "formula feed switching group." After a specified period, the selenium content of the muscle (medium fatty tuna) and liver was measured. The livers were extracted as internal organs at the time of harvest and then minced into small pieces to prepare test pieces. The selenium content of the livers was measured in the same manner as above. The weight and obesity index were measured according to standard methods. The selenium content was measured at the times shown in Table 7 up to 7.5 months after the switch. The results are shown in Table 7 and Figures 2 and 3. In Figures 2 and 3, the black circles indicate the selenium content in the group switched to the raw feed, and the white circles indicate the selenium content in the group switched to the compound feed.

[0119] [Table 7]

[0120] As shown in Table 7 and Figures 2 and 3, the selenium content in muscle and liver of both the raw feed-switched group and the formula feed-switched group changed rapidly after the diet change, and about two months after the diet change, the selenium content in both muscle and liver of the formula feed-switched group was lower than that of the raw feed-switched group. This indicates that selenium content changes rapidly depending on the type of diet. In addition, in the group switched to formula feed, the selenium content rapidly decreased, reaching 90μg / 100g in muscle 1.5 months after the start of feeding and below 1000μg in liver after 3 months. After 4.5 months, the selenium content in both muscle and liver was almost the same as that of the feed group at the start of the test. On the other hand, in the group switched to raw feed, the selenium content rapidly increased, reaching about 80% of the value of the feed group at the start of the test after 7.5 months. This shows that switching to low-selenium tuna farmed fish feed is effective in rapidly reducing the selenium content in farmed tuna.

[0121] [Example 3] Next, the effects of the fish meal ratio and selenium content in the compound feed were examined. Inclusion A with a normal selenium content was obtained in the same manner as in Example 1 (1), except that 91.63 wt% sardine fish meal, 3.88 wt% vitamins, 0.1 wt% α-tocopherol (50 wt%), and 4.45 wt% other ingredients were used. The selenium content of Inclusion A was 1.72 mg / kg. Inclusion B with a high selenium content was obtained in the same manner as in Example 1 (1), except that 33.56 wt% sardine fish meal, 58 wt% bonito meal, 3.88 wt% vitamins, 0.1 wt% α-tocopherol (50 wt%), 0.07 wt% selenium yeast, and 4.45 wt% others were used. The selenium yeast used was "ALKOSEL Selenium Yeast" manufactured by Miwa Pharmaceutical Co., Ltd. The selenium content of Inclusion B was 3.04 mg / kg.

[0122] Formula feed A or B having an inclusion and an outer shell was obtained in the same manner as in Example 1(1), except that inclusion A or inclusion B was used. Formula feed A contains inclusion A with a normal selenium content, and formula feed B contains inclusion B with a high selenium content.

[0123] Tuna weighing 41 kg (GG) were reared in an oval ocean surface pen with a diameter of 70 m using either compound feed A or compound feed B for four months from August to November. The water temperature during the rearing period was between 13°C and 29°C. The fish were fed satiation five or six days a week. Throughout the test period, the feed intake was 30-50% by weight of the live feed. After the specified period, the selenium content in the muscle and liver was measured or calculated. The results are shown in Table 8.

[0124] [Table 8]

[0125] After 4 months of feeding on formula feed A or formula feed B, both groups showed significantly lower values ​​below 90 μg / 100 g in muscle and below 1400 μg / 100 g in liver. Furthermore, as shown in Table 8, no significant difference was observed in the selenium content in the tuna muscle and liver whether formula feed B containing encapsulated B with a high selenium content was used or formula feed A containing encapsulated A with a normal selenium content was used. This shows that, regardless of the selenium content in the compound feed, low-selenium farmed tuna fish can be obtained as long as the fish meal blending ratio is 30% by weight or more.

[0126] From the above examples, it is clear that it is possible to produce low-selenium farmed tuna fish that have a lower selenium content than farmed tuna fish that eat live feed. Therefore, it is clear that low-selenium farmed tuna fish and their edible parts or processed foods can provide a lower selenium intake than farmed tuna fish or wild tuna fed live feed. [Explanation of symbols]

[0127] 10. Processed foods made from farmed tuna fish 11 Saku 12 trays 13 laps 14 Perilla 15 Condiments 16 Water-absorbing sheet A deep central dorsal region B Median dorsal superficial part C. Median dorsal keel muscle D. Dark muscle E peritoneal cavity

Claims

1. Inclusions containing fish meal composed of sardine fish meal in an amount of 30% by weight or more and oil and fat; An outer shell that encases the inclusions and is composed of at least one substance selected from the group consisting of proteins and polysaccharides; A method for raising farmed tuna fish, comprising continuously feeding the fish for at least 30 days a compound feed comprising: The content of the fish meal is 30% by weight or more and 70% by weight or less of the total weight of the inclusion, The content of the oil or fat is 20% by weight or more and 70% by weight or less of the total weight of the inclusion. A method for raising farmed tuna fish having muscles with an oleic acid content of 29.35 g / 100 g or more and 35.34 g / 100 g or less, a linoleic acid content of 5.87 g / 100 g or more and 7.73 g / 100 g or less, and an alpha-linolenic acid content of 1.08 g / 100 g or more and 1.80 g / 100 g or less.

2. Preparing farmed tuna fish obtained by the method for raising farmed tuna fish according to claim 1; Harvesting edible portions from the prepared tuna farmed fish; Placing the edible portion in a container; A method for producing processed foods from farmed tuna fish, comprising:

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