Method for freezing fish

Abstract

To provide high-quality frozen fish with suppressed drip generation.SOLUTION: The method for freezing fish comprises a step of freezing fish whose band intensity of myosin heavy chain in the muscle has been reduced by 1% to 100% compared to that before aging, through aging according to the present invention.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for freezing fish, a method for producing frozen fish, and frozen fish produced thereby. According to the present invention, high-quality frozen fish can be obtained. [Background technology]

[0002] Fish are usually frozen at ultra-low temperatures (e.g., -40°C to -80°C) to maintain their freshness (Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] "Journal of the Japanese Society of Fisheries Science" 2016 (Japan) Vol. 82, p. 953- Summary of the Invention [Problem to be solved by the invention]

[0004] However, freezing is sometimes performed at a temperature of about −20° C. The inventors have noticed that such freezing at about −20° C. causes dripping and other problems, resulting in a deterioration in the quality of the frozen fish. Therefore, an object of the present invention is to provide high-quality frozen fish in which the occurrence of dripping is suppressed. [Means for solving the problem]

[0005] The present inventors have conducted extensive research into high-quality frozen fish with reduced dripping, and have surprisingly found that high-quality frozen fish with reduced dripping can be obtained by freezing fish in which the myosin protein content has been reduced due to degradation. The present invention is based on this finding. Therefore, the present invention provides [1] A method for freezing fish, comprising a step of freezing fish in which the band intensity of myosin heavy chain in the muscle has decreased by 1 to 100% compared to before aging due to aging; [2] A method for producing frozen fish, comprising a step of freezing fish in which the band intensity of myosin heavy chain in the muscle has decreased by 1 to 100% compared to before aging due to aging; and [3] Frozen fish obtained by the manufacturing method described in [2], Regarding. [Effects of the Invention]

[0006] According to the fish freezing method and frozen fish manufacturing method of the present invention, high-quality frozen fish can be obtained, particularly even at relatively high freezing temperatures of about -20°C to -40°C. [Brief explanation of the drawings]

[0007] [Figure 1] 1 shows photographs of SDS-PAGE of proteins in the muscle of frozen amberjack obtained in Example 1 (aged at 1°C for 5 days), Example 3 (aged at 1°C for 14 days), Comparative Example 1 (aged at 1°C for 0 days), and Reference Example 1 (aged at 1°C for 1 day). [Figure 2] 1 is a photograph of SDS-PAGE of proteins in the muscle of aged amberjack obtained in Example 4 (aged at 30°C for 2 hours) and Comparative Example 2 (aged at 30°C for 0 days). DETAILED DESCRIPTION OF THE INVENTION

[0008] [1] Method for freezing fish and method for producing frozen fish The method for freezing fish of the present invention includes a step of freezing fish whose muscle myosin heavy chain band intensity has been reduced by 1 to 100% by aging compared to before aging. The method for producing frozen fish of the present invention includes a step of freezing fish whose muscle myosin heavy chain band intensity has been reduced by 1 to 100% by aging compared to before aging. (Hereinafter, the "method for freezing fish" and "method for producing frozen fish" of the present invention may be collectively referred to as the method of the present invention.) As used herein, the phrase "the band intensity of myosin heavy chain in muscle has decreased by 1 to 100% compared to before aging" means, but is not limited to, that the fish muscle has aged to a certain extent. The lower limit of the reduction rate of myosin heavy chain is, but is not limited to, 1% or more, preferably 5% or more, more preferably 10% or more, more preferably 15% or more, more preferably 20% or more, more preferably 25% or more, and more preferably 30% or more. The upper limit of the reduction rate of myosin heavy chain is also, but is not limited to, 100% or less, preferably 90% or less, more preferably 80% or less, more preferably 70% or less, more preferably 60% or less, more preferably 50% or less, and more preferably 40% or less. The upper and lower limits can be combined as appropriate. The content of myosin heavy chains is thought to decrease in the muscles of aged fish. On the other hand, actin heavy chains are hardly reduced by aging. Therefore, the reduction rate of myosin heavy chains after aging can also be expressed by the ratio of the band intensity of myosin heavy chains to actin heavy chains in muscle. The upper limit of the ratio of myosin heavy chains to actin heavy chains is not limited, but is 200% or less, preferably 190% or less, more preferably 160% or less, more preferably 150% or less, more preferably 140% or less, and more preferably 130% or less. The lower limit of the ratio of myosin heavy chains to actin heavy chains is also not limited, but is 1% or more, preferably 30% or more, more preferably 50% or more, more preferably 70% or more, and more preferably 90% or more. The upper and lower limits can be combined as appropriate. In raw fish before aging, the myosin heavy chain content is the same if the fish is from the same species. Therefore, the myosin content before aging can be determined by SDS-PAGE of the same species of fish. By comparing the SDS-PAGE band intensity of the same species of fish with that of frozen fish, the "decrease rate of myosin heavy chain band intensity in muscle compared to before aging" can be calculated.

[0009] 《Fish》 The fish used in the method of the present invention is not limited, and any fish having myosin protein in the muscle can be used, for example, saltwater fish or freshwater fish. Fish bodies may be in a state of suspended animation or paralysis, but non-living fish bodies can also be used. The effects of the present invention can also be obtained using fish that have been landed and transported to a wholesale market or the like. Specific fish species include, for example, rockfish, red grouper, red sea bream, horse mackerel, Atlantic salmon, conger eel, sweetfish, monkfish, grunt, threadfin tuna, sardine, char, eel, ray, lizardfish, stonefish, jack mackerel, scorpionfish, sculpin, swordfish, bonito, blacktip tuna, barracuda, flounder, filefish, amberjack, whiting, golden amberjack, silver-stripe herring, coho salmon, croaker, flathead, bighead carp, salmon, mackerel, shark, saury, Spanish mackerel, halfbeak, grass carp, and yellowtail. Examples include cren, pangasius, flounder, loach, sea bass, cod, sea bream, hairtail, flying fish, loach, trout salmon, Nile tilapia, catfish, herring, rainbow trout, goby, grouper, conger eel, flounder, yellowtail amberjack, pufferfish, crucian carp, yellowtail (including yellowtail, amberjack, Japanese Spanish mackerel, Japanese horse mackerel, Japanese white-eye, etc.), Atka mackerel, hoki, black rockfish, tuna, carp, milkfish, rockfish, mackerel, Japanese carp, tilapia, and rohu.

[0010] 《Aging process》 The "fish in which the band intensity of myosin heavy chain in the muscle has been reduced by 1 to 100% by aging compared to before aging" is not limited to, but is preferably a fish obtained by an aging process. However, even if the practitioner of the present invention does not perform an aging process, the "method for freezing fish" and "method for producing frozen fish" of the present invention can be carried out and the effects of the present invention can be obtained by freezing "fish in which the band intensity of myosin heavy chain in the muscle has been reduced by 1 to 100% compared to before aging." When aging is carried out, the procedure is not limited as long as it results in "fish in which the band intensity of myosin heavy chain in the muscle has been reduced by 1 to 100% by aging compared to before aging." The upper limit of the aging temperature is, for example, 50° C. or lower, in one embodiment 30° C. or lower, and in one embodiment 20° C. or lower. The lower limit of the aging temperature is −1° C. or higher, in one embodiment 0° C. or higher, and in one embodiment 1° C. or higher. The upper limit of the aging time is, for example, 90 days or less, in one embodiment, 30 days or less, and in one embodiment, 15 days or less. The lower limit of the aging time is, for example, 10 minutes or more, in one embodiment, 30 minutes or more, in one embodiment, 1 hour or more, in one embodiment, 5 hours or more, in one embodiment, 10 hours or more, in one embodiment, 1 day or more, in one embodiment, 3 days or more, and in one embodiment, 4 days or more. The aging temperature and aging time can be adjusted as appropriate by those skilled in the art, and it is possible to obtain "fish in which the band intensity of myosin heavy chain in muscle has been reduced by 1 to 100% by aging compared to before aging." That is, when the aging temperature is low, the aging time can be extended to obtain the desired degree of aging, and when the aging temperature is high, the aging time can be shortened to obtain the desired degree of aging. That is, by combining the aging temperature and aging time, it is possible to obtain "fish in which the band intensity of myosin heavy chain in muscle has been reduced by 1 to 100% by aging compared to before aging." Furthermore, the aging can be accelerated by using, for example, enzymes. That is, by immersing fish in a solution of a protease and aging it, the aging can be accelerated even at the same aging temperature and aging time. Furthermore, the ripening can be accelerated by applying pressure or by subjecting the mixture to ultrasonic treatment.

[0011] <<Measurement of myosin heavy chain band intensity>> The method for measuring the band intensity of myosin heavy chain is not particularly limited, but can be performed as follows. For example, fish meat is solubilized in 8 M urea-2% SDS-2% mercaptoethanol-20 mM Tris HCl (pH 8.8) solution and electrophoresed using a 5-20% gradient polyacrylamide gel. The gel is then stained with CBB, and the intensity of the myosin heavy chain is calculated by image analysis. An ATTO CS Analyzer was used for image analysis.

[0012] 《Freezing process》 The method for freezing fish and the method for producing frozen fish of the present invention include a freezing step. The freezing temperature and time are not particularly limited as long as the effects of the present invention can be obtained. In the freezing step, fish whose muscle myosin heavy chain band intensity has decreased by 1 to 100% compared to before aging due to the aging process is placed in a freezer, whereby the fish can be frozen. The upper limit of the freezing temperature is, for example, −10° C. or lower, in some embodiments −15° C. or lower, and in some embodiments −20° C. or lower. The lower limit of the freezing temperature is −100° C. or higher, in some embodiments −8° C. or higher, in some embodiments −60° C. or higher, in some embodiments −50° C. or higher, and in some embodiments −40° C. or higher. The freezing time is not particularly limited as long as the quality of the fish is not deteriorated. The lower limit of the freezing time is, for example, one day or more, in one embodiment, five days or more, and in one embodiment, ten days or more. The upper limit of the freezing time is not particularly limited, but is, for example, two years or less, in one embodiment, one year or less, in one embodiment, six months or less, and in one embodiment, three months or less.

[0013] <<Compression drip rate>> Drip rate is one of the quality indicators that shows the water retention capacity of fish muscle, and an increase in drip rate due to freezing leads to a decrease in quality. The squeezed drip rate of the frozen fish obtained by the method of the present invention is not limited, but is 4.0 to 8.0%, preferably 4.5 to 7.8%, and more preferably 5.0 to 7.4%. The upper and lower limits can be combined as appropriate.

[0014] The drip rate in this specification can be determined as follows: Cut fish meat (2 cm long, 2 cm wide, 1 cm thick) is sandwiched between three pieces of filter paper, a weight (2 kg) is placed on top, and the drip rate is calculated from the change in weight before and after the two minutes.

[0015] <Breaking strength> The breaking strength is a value obtained from the breaking point obtained by an experiment in which a plunger is pushed into fish muscle, and indicates the stress required to bite through food. The breaking strength of the frozen fish obtained by the method of the present invention is not limited, but is, for example, 20 to 50 kPa, preferably 25 to 45 kPa, and more preferably 25 to 40 kPa. The upper and lower limits can be combined as appropriate.

[0016] The breaking strength in this specification can be calculated as follows: It is obtained from the breaking point on the stress-strain curve obtained when a spherical plunger with a diameter of 5 mm is pressed into fish meat cut into 1.5 cm cubes at a rate of 1 mm / sec.

[0017] "Break Dent" The breaking depression is a value obtained from the breaking point obtained by an experiment in which a plunger is pressed into fish muscle, and is related to the flexibility of the food. The breaking depth of the frozen fish obtained by the method of the present invention is not limited, but is, for example, 4.7 to 6.0 mm, preferably 4.7 to 5.5 mm, and more preferably 4.7 to 5.3 mm. The upper and lower limits can be combined as appropriate.

[0018] The breaking depression in this specification can be calculated as follows: It is obtained from the breaking distance on the stress-strain curve obtained when a spherical plunger with a diameter of 5 mm is pressed into fish meat cut into 1.5 cm cubes at 1 mm / sec.

[0019] <Young's modulus> Young's modulus is obtained as the initial slope of the stress-strain curve obtained by an experiment in which a plunger is pressed into fish muscle, and is related to the hardness of the food. The Young's modulus of the frozen fish obtained by the method of the present invention is not limited, but is, for example, 20.0 to 24.0 kPa, preferably 20.5 to 23.5 kPa, and more preferably 20.6 to 23.3 kPa. The upper and lower limits can be combined as appropriate.

[0020] The Young's modulus in this specification can be calculated as follows: It is calculated as the slope at a strain rate of 5% in the stress-strain curve obtained when a spherical plunger with a diameter of 5 mm is pressed into fish meat cut into 1.5 cm cubes at a rate of 1 mm / second.

[0021] [2] Frozen fish The frozen fish of the present invention is obtained by the manufacturing method of the present invention. The frozen fish of the present invention exhibits a superior drip rate, etc., compared to frozen fish obtained by conventional methods. Specifically, frozen fish frozen at -20°C to -40°C without aging has a high drip rate, but frozen fish frozen at -20°C to -40°C after aging has a low drip rate and exhibits an excellent drip rate. The frozen fish of the present invention exhibits excellent effects. These excellent effects are thought to be due to the physical properties of the muscle of the frozen fish. However, at present, the physical properties of conventional frozen fish frozen at a low level of ripening, such as -20°C to -40°C, and frozen fish frozen at a more mature level, such as -20°C to -40°C, are not clear. It is believed that extensive experiments are necessary to clarify these differences in physical properties.

[0022] 《Action》 In the fish freezing method and frozen fish manufacturing method of the present invention, the mechanism by which high-quality frozen fish can be obtained by freezing fish in which the band intensity of myosin heavy chains in the muscle has decreased by 1 to 100% compared to before aging due to aging has not been clearly analyzed, but can be assumed as follows. However, the present invention is not limited to the following assumption. Myosin is one of the major myofibrillar proteins and plays a role in physically holding muscle fibers together. However, when myosin is decomposed, the structure of the muscle fibers physically collapses, and water molecules held inside are released. [Example]

[0023] The present invention will be specifically described below with reference to examples, but these examples are not intended to limit the scope of the present invention.

[0024] Examples 1 to 3 and Comparative Example 1 In Examples 1 to 3, amberjack was aged at 1°C for 5 days (Example 1), 7 days (Example 2), or 14 days (Example 3), and then frozen at -20°C. In Comparative Example 1, amberjack was frozen at -20°C without aging. Amberjack was aged at 1°C for 1 day (Reference Example 1), and then frozen at -20°C. Specifically, the dorsal muscle of amberjack was aged for 14 days at 1°C. Unfrozen fish was stored as is, while frozen fish was stored frozen at -20°C after aging, and then thawed in ice water before being subjected to various analyses.

[0025] <Analysis by SDS-PAGE> In this analysis, myosin in the muscle of the frozen amberjack obtained in Examples 1 to 3 and Comparative Example 1 was measured by SDS-PAGE. Figure 1 shows a photograph of SDS-PAGE. The band intensities of myosin heavy chain and actin were measured using a CS Analyzer (ATTO).

[0026] [Table 1] As shown in Table 1, Example 1 (5 days of aging) reduced the band intensity of myosin heavy chain by 5.3% compared to Comparative Example 1 (0 days of aging). Also, Example 3 (14 days of aging) reduced the band intensity of myosin heavy chain by 27.3% compared to Comparative Example 1 (0 days of aging).

[0027] <<Compression drip rate>> In this analysis, the squeeze drip rates of the frozen amberjack obtained in Examples 1 to 3 and Comparative Example 1 were measured. Cut fish meat (2 cm long, 2 cm wide, 1 cm thick) was sandwiched between three pieces of filter paper, a weight (2 kg) was placed on top, and the weight was held for two minutes. The weight was calculated from the change before and after the sandwich.

[0028] [Table 2] The "untreated sample" in the table refers to feed for which the squeeze drip rate was measured without being frozen at -20°C. The rate of change indicates the rate of change between the untreated sample and the frozen sample. As shown in Table 2, the drip rate of Comparative Example 1 was 9.6%, while the drip rates of Examples 1 to 3 were excellent, ranging from 5.8 to 7.8%.

[0029] <Breaking strength> In this analysis, the breaking strength of the frozen amberjack obtained in Examples 1 to 3 and Comparative Example 1 was measured. The breaking strength was calculated from the breaking point on the stress-strain curve obtained when a spherical plunger with a diameter of 5 mm was pressed into fish meat cut into 1.5 cm cubes at a rate of 1 mm / sec.

[0030] [Table 3] The "untreated sample" in the table refers to feed whose breaking strength was measured without being frozen at -20° C. The rate of change indicates the rate of change between the untreated sample and the frozen sample. As shown in Table 3, the breaking strength of Comparative Example 1 was 63.5 kPa, whereas the breaking strengths of Examples 1 to 3 were excellent, ranging from 29.2 to 38.3 kPa.

[0031] "Break Dent" In this analysis, the fracture dents of the frozen amberjack obtained in Examples 1 to 3 and Comparative Example 1 were measured. The fracture depression was obtained from the fracture distance on the stress-strain curve obtained when a spherical plunger with a diameter of 5 mm was pressed into fish meat cut into 1.5 cm cubes at a rate of 1 mm / sec.

[0032] [Table 4] The "untreated sample" in the table refers to feed for which the breaking depression was measured without being frozen at -20° C. The rate of change indicates the rate of change between the untreated sample and the frozen sample. As shown in Table 4, the fracture dent in Comparative Example 1 was 4.3 mm, whereas the fracture dent in Examples 1 to 3 were excellent, ranging from 4.8 to 5.1 mm.

[0033] <Young's modulus> In this analysis, the Young's modulus of the frozen amberjack obtained in Examples 1 to 3 and Comparative Example 1 was measured. The stress-strain curve was calculated as the slope at a strain rate of 5% when a spherical plunger with a diameter of 5 mm was pressed into fish meat cut into 1.5 cm cubes at 1 mm / sec.

[0034] [Table 5] The "untreated sample" in the table refers to the feed for which Young's modulus was measured without being frozen at -20° C. The rate of change indicates the rate of change between the untreated sample and the frozen sample. As shown in Table 5, the Young's modulus of Comparative Example 1 was 25.1 kPa, whereas the Young's moduli of Examples 1 to 3 were 20.7 to 23.0 kPa, which was superior.

[0035] Example 4 and Comparative Example 2 In this example, amberjack was aged for 2 hours (Example 4) at 30° C. The aging procedures of Examples 1 to 3 were repeated except that the aging temperature and time were changed.

[0036] [Table 6] As shown in Table 6, the amount of myosin decreased after 2 hours of treatment at 30°C. That is, Example 4 (aging at 30°C for 2 hours) reduced the band intensity of the myosin heavy chain by 16.4% compared to Comparative Example 2 (no aging). [Industrial Applicability]

[0037] The fish freezing method and frozen fish manufacturing method of the present invention can be used for freezing and preserving fish, and can provide high-quality frozen fish.

Claims

1. A method for freezing fish, comprising the step of freezing fish whose muscle myosin heavy chain band intensity has decreased by 1 to 100% as compared with that before aging due to aging.

2. A method for producing frozen fish, comprising a step of freezing fish whose muscle myosin heavy chain band intensity has been reduced by 1 to 100% by aging compared to before aging.

3. Frozen fish obtained by the method according to claim 2.

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