Frozen headless Pacific white shrimp

Abstract

To provide frozen headless Pacific white shrimp with excellent taste and texture, and a suitable method for producing the same. [Solution] Frozen headless Pacific white shrimp containing 1.0 mg / 100g or more of free guanylic acid, 24 mg / 100g or more of free lysine, and a K value of less than 20%. Preferably, it contains 50 mg / 100g or more of free glutamic acid. It is also preferable that the mass ratio of free glutamic acid to free glycine is 1:16 or less, or the mass ratio of free glutamic acid to free alanine is 1:3.0 or less, or the mass ratio of free glutamic acid to free arginine is 1:16 or less, or the mass ratio of free glutamic acid to free proline is 1:11 or less.

Description

[Technical Field]

[0001] This invention relates to frozen headless Pacific white shrimp and a method for producing the same. [Background technology]

[0002] Shrimp are a widely favored ingredient due to their savory flavor and unique texture, and there is a high demand for technologies to maintain and improve their taste and texture. In particular, frozen headless Pacific white shrimp are inexpensive and widely distributed, so improving them would bring significant economic benefits. For example, Patent Document 1 describes a method for cultivating non-sand-dwelling crustaceans in an aquatic environment under certain light-shielding conditions, using floc containing nitrifying bacteria and aquatic crustaceans with improved taste, in which the content of glycine, alanine, and total free amino acids is above a specific amount. Patent Document 2 describes shrimp with enhanced umami flavor in which the proportion of 5'-inosinic acid (IMP) in ATP-related substances is 50% or more, and IMP is present in greater quantities than AMP, and a method for producing the same. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2019 / 059402 [Patent Document 2] Japanese Patent Publication No. 2011-172598 [Overview of the project] [Problems that the invention aims to solve]

[0004] In recent years, with the increasing consumer demand and rising food prices, there has been a need for technologies related to frozen, headless Pacific white shrimp that offer improved taste and texture, and better freshness, using simpler methods. Patent documents 1 and 2 have not adequately addressed this point.

[0005] Therefore, the object of the present invention is to provide frozen headless Pacific white shrimp with excellent taste and texture, and a suitable method for producing the same. [Means for solving the problem]

[0006] The present invention was discovered to solve the above problems, and provides frozen headless Pacific white shrimp containing 1.0 mg / 100g or more of free guanylic acid, 24 mg / 100g or more of free lysine, and a potassium content of less than 20%.

[0007] Furthermore, the present invention relates to a method for producing frozen headless Pacific white shrimp collected from aquaculture ponds, This invention provides a method for producing frozen headless Pacific white shrimp, comprising an oxygen injection step in which Pacific white shrimp collected from aquaculture ponds are kept alive under conditions of oxygen injection at 18°C ​​to 28°C, and a step in which the heads of the shrimp are removed after the oxygen injection step and then frozen. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide frozen headless Pacific white shrimp with excellent taste and texture. Furthermore, the present invention can provide a method for producing the aforementioned frozen headless Pacific white shrimp in a simple and successful manner. [Modes for carrying out the invention]

[0009] Preferred embodiments of the present invention will be described below. The present invention relates to frozen headless Pacific white shrimp containing 1.0 mg / 100g or more of free guanylic acid, 24 mg / 100g or more of free lysine, and a potassium content of less than 20%.

[0010] In this specification, unless otherwise specified, the free amino acid content or nucleotide content refers to the free amino acid content or free nucleotide content per 100g of deshelled and peeled meat of Pacific white shrimp.

[0011] This invention relates to frozen headless vannamei shrimp. Vannamei shrimp (scientific name: Litopenaeus vannamei) is a species of shrimp belonging to the family Penaeidae, native to the eastern Pacific Ocean, and widely fished and farmed for food. When alive, its body color is a translucent grayish-brown with no particular markings, and its head is relatively small compared to its body. It has high resistance to low salinity, high density, and diseases, and its rapid growth and efficient farming have led to the spread of aquaculture around the world. In Asia, aquaculture began in China in the 1990s, and since the technology was established in 2000, production has increased explosively from southern China to Southeast Asia, and in recent years has surpassed the farming volume of black tiger shrimp. The flesh is soft, and both the taste and color are good, making it a shrimp that goes well with any dish, such as tempura, fried shrimp, salt-grilled shrimp, chili shrimp, and bouillabaisse.

[0012] Compared to spiny lobsters of the Palinuridae family, and prawns of the Penaeidae family such as kuruma prawns and black tiger prawns, Pacific white shrimp (Vannamei) are farmed and widely distributed, making them inexpensive and readily available on the market. In this invention, Pacific white shrimp are headless. Among Pacific white shrimp, those with heads intact are traded at a higher price than headless shrimp due to their more luxurious appearance when used in cooking. However, because headless Pacific white shrimp are inexpensive, manufacturing methods that can improve taste, texture, and freshness at a cost are not employed. Therefore, a technology that can inexpensively improve the taste and texture of headless Pacific white shrimp is expected to have a particularly economic effect.

[0013] The size of Pacific white shrimp, in the case of headless shrimp, is indicated by the number of shrimp per pound (453.6g), which is the international standard. For example, the indication 13 / 15 means that there are 13 to 15 shrimp per pound. In this invention, the size of the shrimp is not particularly limited, but it is preferable that it be larger than the size of 41 to 50 shrimp per pound.

[0014] The frozen headless Pacific white shrimp of the present invention contains 1.0 mg / 100g or more of free guanylic acid, 24 mg / 100g or more of free lysine, and has a potassium (K) value of less than 20%. Free guanylic acid is a component that increases during the breakdown of nucleic acids in Pacific white shrimp. Specifically, nucleic acids (RNA) present in the shrimp's muscles are broken down by enzymes, then inosinic acid is produced, followed by the generation of free guanylic acid. Guanylic acid is primarily produced in large quantities after the shrimp dies. Guanylic acid is a component that enhances the umami flavor. Furthermore, free lysine is a component that increases during the protein breakdown process in Pacific white shrimp. Free lysine is a stable amino acid and is suitable for accurately understanding protein degradation and the behavior of the resulting amino acids. Furthermore, the K value is an indicator of freshness. In the frozen headless Pacific white shrimp of the present invention, the fact that the K value is below a certain level, meaning that the freshness is good, and that the amount of protein and nucleic acid degradation is still below a certain level, while the amount of free guanylic acid and free lysine is above a certain level, means that the outflow of components derived from proteins and nucleic acids that have been degraded after death is suppressed and that they are sufficiently retained in the shrimp. As a result, the frozen headless Pacific white shrimp of the present invention have a good taste. Furthermore, the frozen headless Pacific white shrimp of the present invention have a firm texture and good mouthfeel, reflecting that their internal components are well retained without leakage.

[0015] From the viewpoint of improving umami and preserving internal components, the free guanylic acid content in 100g of shrimp meat of the present invention is preferably 1.0mg or more, more preferably 2.0mg or more, even more preferably 2.4mg or more, and particularly preferably 3.0mg or more. Furthermore, from the viewpoint of balancing the taste and maintaining freshness, the free guanylic acid content in 100g of shrimp meat of the present invention is preferably 20mg or less, more preferably 15mg or less, and even more preferably 10mg or less.

[0016] From the viewpoints of improving taste and maintaining internal components, in the frozen headless banana prawns of the present invention, the free lysine content in 100 g of prawn meat is 24 mg or more, more preferably 28 mg or more, still more preferably 40 mg or more, and particularly preferably 60 mg or more. Further, from the viewpoints of taste balance and freshness maintenance, the free lysine content in 100 g of the meat of banana prawns is preferably 150 mg or less, more preferably 125 mg or less, and even more preferably 100 mg or less.

[0017] The frozen headless banana prawns of the present invention have a K value of less than 20%. Generally, fishery products are evaluated to have higher quality as their freshness is better. For the freshness determination of fishery products, currently, the K value is used as an objective index for freshness. When fishery products die, the decomposition of adenosine triphosphate (ATP) starts in the muscle, so it can be said that the freshness deteriorates as the decomposition progresses. Based on the fact that the decomposed components change as adenosine triphosphate (ATP) → adenosine diphosphate (ADP) → adenylic acid (AMP) → inosinic acid (IMP) → inosine (HxR) → hypoxanthine (Hx), the K value is calculated by the following formula. K value (%) = (HxR + Hx) / (ATP + ADP + AMP + IMP + HxR + Hx) × 100 It can be evaluated that the smaller the K value, the better the freshness, and the larger the K value, the worse the freshness.

[0018] In the present invention, from the viewpoint of good freshness, the K value is preferably less than 20%, more preferably 15% or less, still more preferably 12.5% or less, even more preferably 10% or less, and particularly preferably 5% or less. Further, from the viewpoint of ease of production, the K value is preferably 1.0% or more, more preferably 1.2% or more, and most preferably 1.5% or more.

[0019] In order to obtain the above-mentioned frozen headless banana prawns, the frozen headless banana prawns may be produced in the examples described below.

[0020] In the frozen headless Pacific white shrimp of the present invention, the free glutamic acid content per 100g of meat is preferably 50mg or more. It is known that when glutamic acid and guanylic acid are combined, the umami flavor is enhanced through a synergistic effect. The frozen headless Pacific white shrimp of the present invention have a high content of both free glutamic acid and free guanylic acid, reflecting that the breakdown products after protein decomposition are sufficiently retained in the body, thus further enhancing the umami flavor. Furthermore, in the present invention, a K value below a certain level and a high amount of free glutamic acid are preferable as they suggest good retention of internal components and the possibility of a good texture. In the frozen headless Pacific white shrimp of the present invention, the free glutamic acid content per 100g of Pacific white shrimp meat is more preferably 75mg or more, and even more preferably 100mg or more. Furthermore, from the viewpoint of taste balance and freshness maintenance, the free glutamic acid content per 100g of Pacific white shrimp meat is preferably 300mg or less, more preferably 250mg or less, and even more preferably 200mg or less. Furthermore, the ratio of free glutamic acid to the total amount of the 18 free amino acids described later is preferably 1.8% by mass or more, more preferably 2.0% by mass or more, even more preferably 2.3% by mass or more, and even more preferably 2.7% by mass or more.

[0021] In this specification, the K value is calculated by measuring the ATP, ADP, AMP, IMP, HxR, and Hx in the flesh of Pacific white shrimp using high-performance liquid chromatography (HPLC) and calculating it using the formula described above. The sample for measurement is the flesh of Pacific white shrimp after decapsulation and shell removal. The preparation of the sample and the measurement method can be carried out by the method described in the examples below. The free amino acid content shall be the value measured by high-performance liquid chromatography. The preparation of the sample for measurement and the measurement method may be carried out by the method described in the examples below. The free nucleotide content shall be the value measured by high-performance liquid chromatography. The preparation of the sample for measurement and the measurement method may be carried out by the method described in the examples below. The above measurement is preferably performed on shrimp in an unheated state (for example, in a state where they have not been heated to 70°C or higher for 2 minutes or more, and more preferably in a state where they have not been heated to 60°C or higher for 1 minute or more).

[0022] Furthermore, as technical features that characterize the intensity of umami in the frozen headless Pacific white shrimp of the present invention, it is preferable that the ratio of free glutamic acid to free glycine; the ratio of free glutamic acid to free alanine; the ratio of free glutamic acid to free arginine; or the ratio of free glutamic acid to free proline is below a predetermined value. Generally, free glycine, free alanine, free arginine, and free proline have functions such as regulating osmotic pressure and originate from sources other than protein degradation. For this reason, the ratio of free glycine, free alanine, free arginine, and free proline to free glutamic acid in the total amount of free amino acids in Pacific white shrimp is often considerably larger than the ratio of glycine, alanine, arginine, and proline to glutamic acid in the protein (amino acid ratio measured after protein degradation). In this regard, it is preferable that the ratio of free glycine, free alanine, and free proline to free glutamine in the frozen headless Pacific white shrimp of the present invention is relatively small. This is because the amount of free glutamic acid, which is easily derived from protein degradation, is thought to reflect the degree of retention of internal components after death more than the amount of free glycine, free alanine, free arginine, and free proline. Rather, high levels of free glycine, free alanine, free arginine, and free proline may reflect rearing under stressful conditions such as high osmotic pressure or large osmotic pressure changes. Therefore, in this invention, it is not a problem if the content of these free amino acids is below a certain level. Furthermore, the frozen Pacific white shrimp of the present invention is preferably particularly superior in umami flavor compared to the sweetness of Pacific white shrimp. From these viewpoints, the content of free glutamic acid and free glycine is preferably 1:16 or less by mass ratio, more preferably 1:14 or less by mass ratio, even more preferably 1:12 or less by mass ratio, and particularly preferably 1:11 or less by mass ratio. Also, from the viewpoint of ease of shrimp production, the content of free glutamic acid and free glycine is preferably 1:0.5 or more by mass ratio, more preferably 1:1.0 or more by mass ratio, and particularly preferably 1:1.5 or more by mass ratio.

[0023] The frozen Pacific white shrimp of the present invention is preferably particularly superior in umami flavor compared to the sweetness of Pacific white shrimp. From these viewpoints, the content of free glutamic acid and free alanine is preferably 1:3.0 or less by mass ratio, more preferably 1:2.4 or less by mass ratio, and even more preferably 1:2.3 or less by mass ratio. Furthermore, from the viewpoint of ease of shrimp production, the content of free glutamic acid and free alanine is preferably 1:0.3 or more by mass ratio, more preferably 1:0.6 or more by mass ratio, and particularly preferably 1:1 or more by mass ratio.

[0024] Arginine is an amino acid that brings out bitterness and a seafood-like flavor in food. In the frozen headless Pacific white shrimp of the present invention, it is preferable that the shrimp have superior umami flavor compared to the bitterness. From this viewpoint, the content of free glutamic acid and free arginine is preferably 1:16 or less by mass ratio, and more preferably 1:12 or less by mass ratio. Furthermore, from the viewpoint of ease of shrimp production, the content of free glutamic acid and free arginine is preferably 1:0.5 or more by mass ratio, more preferably 1:1 or more by mass, and particularly preferably 1:2 or more by mass ratio.

[0025] Proline is an amino acid that contributes to the sweetness of the umami flavor in Pacific white shrimp. In the frozen headless Pacific white shrimp of the present invention, it is preferable that the umami flavor is particularly superior to that of conventional Pacific white shrimp. From this viewpoint, the mass ratio of free glutamic acid to free proline is preferably 1:11 or less, more preferably 1:10 or less, even more preferably 1:8 or less, and particularly preferably 1:7.5 or less. Furthermore, from the viewpoint of ease of shrimp production, the mass ratio of free glutamic acid to free proline is preferably 1:1.0 or more, more preferably 1:2.0 or more, and particularly preferably 1:2.8 or more.

[0026] The preferred range for the content of the free amino acids mentioned above is that any of glycine, alanine, arginine, and proline is below the above-mentioned range / upper limit. Furthermore, it is more preferable that any two combinations of amino acids selected from glycine, alanine, arginine, and proline are below the above-mentioned range / upper limit, even more preferable that three of the amino acids among glycine, alanine, arginine, and proline are below the above-mentioned range / upper limit, and it is preferable that all of glycine, alanine, arginine, and proline are below the above-mentioned range / upper limit.

[0027] Furthermore, in the present invention, the amount of free threonine is preferably 8 mg to 130 mg per 100 g of shrimp meat, more preferably 8 mg to 100 mg, even more preferably 8 mg to 80 mg, and particularly preferably 8 mg to 50 mg. The presence of free threonine within the above range may suggest that decomposition or deterioration has not progressed and that the components are being well retained.

[0028] In the frozen headless Pacific white shrimp of the present invention, the total amount of the following 18 free amino acids is preferably 1700 mg or more, more preferably 1850 mg or more, and particularly preferably 2000 mg or more per 100 g of shrimp meat. As described above, the present invention uses free lysine as one of the indicators of component retention, and a high total amount of the 18 free amino acids under conditions below a certain K value is preferable because it enhances the effects of the present invention. In the frozen headless Pacific white shrimp, the total amount of the 18 free amino acids is preferably 3000 mg or less, more preferably 2750 mg or less, particularly preferably 2500 mg or less, and especially preferably 2400 mg or less per 100 g of shrimp meat. In this specification, the 18 amino acids are lysine, glutamic acid, threonine, histidine, serine, aspartic acid, valine, glycine, arginine, proline, taurine, alanine, methionine, isoleucine, leucine, tyrosine, phenylalanine, and hydroxyproline.

[0029] Furthermore, in the frozen headless Pacific white shrimp of the present invention, it is preferable that the content of free amino acids other than those mentioned above in 100g of Pacific white shrimp meat is within the following range. The amount of free histidine is preferably 12 mg or more, more preferably 14 mg or more, and especially preferably 16 mg or more. There is no upper limit, but from the standpoint of ease of manufacturing and maintaining high freshness, it is preferably 40 mg or less, and more preferably 35 mg or less.

[0030] Serine is an amino acid that contributes to the sweetness and umami of shrimp. In the frozen headless Pacific white shrimp of the present invention, in order to enhance the umami of the shrimp and improve the taste, the free serine content is preferably 12 mg or more, more preferably 15 mg or more, and even more preferably 20 mg or more per 100 g of frozen headless Pacific white shrimp meat. Furthermore, in order to further improve the balance of the taste and maintain high freshness, the free serine content is preferably 70 mg or less, more preferably 60 mg or less, and even more preferably 50 mg or less per 100 g of frozen headless Pacific white shrimp meat.

[0031] Aspartic acid is an amino acid that contributes to the umami and sourness of Pacific white shrimp. In the frozen headless Pacific white shrimp of the present invention, in order to enhance the umami and sourness of the shrimp and improve the taste, the free aspartic acid content is preferably 2 mg or more per 100 g of meat of the frozen headless Pacific white shrimp. Furthermore, in order to further improve the balance of taste and maintain high freshness, the free aspartic acid content is preferably 20 mg or less, more preferably 15 mg or less, and even more preferably 10 mg or less per 100 g of meat of the frozen headless Pacific white shrimp.

[0032] The amount of free valine is preferably 5 mg or more, particularly 10 mg or more, and even more preferably 15 mg or more. There is no upper limit, but from the standpoint of ease of manufacturing and maintaining high freshness, it is preferably 50 mg or less, and more preferably 40 mg or less.

[0033] The amount of free glycine is preferably 310 mg or more, particularly 320 mg or more, and even more preferably 330 mg or more. There is no upper limit, but from the standpoint of ease of manufacturing and maintaining high freshness, it is preferably 600 mg or less, and more preferably 580 mg or less.

[0034] The amount of free arginine is preferably 210 mg or more, particularly 280 mg or more, and even more preferably 340 mg or more. There is no upper limit, but from the standpoint of ease of manufacturing and maintaining high freshness, it is preferably 650 mg or less, and more preferably 630 mg or less.

[0035] The amount of free proline is preferably 160 mg or more, particularly 250 mg or more, and even more preferably 340 mg or more. There is no upper limit, but from the standpoint of ease of manufacturing and maintaining high freshness, it is preferably 600 mg or less, and more preferably 580 mg or less. In particular, it is preferable that the amount of free proline is less than 500 mg per 100 g of frozen headless Pacific white shrimp meat, or that the weight ratio of free glutamic acid to free proline is less than 1:5.

[0036] The amount of free taurine is preferably 15 mg or more, more preferably 20 mg or more, and even more preferably 25 mg or more. There is no upper limit, but from the standpoint of ease of manufacturing and maintaining high freshness, it is preferably 45 mg or less, and more preferably 40 mg or less.

[0037] The amount of free alanine is preferably 80 mg or more, particularly 95 mg or more, and even more preferably 110 mg or more. There is no upper limit, but from the standpoint of ease of manufacturing and maintaining high freshness, it is preferably 250 mg or less, and more preferably 200 mg or less.

[0038] The amount of free methionine should be 0 mg or more. However, from the standpoint of maintaining high freshness, the upper limit is preferably 20 mg or less, and more preferably 15 mg or less.

[0039] The amount of free isoleucine is preferably 8 mg or more. While there is no upper limit, it is preferably 25 mg or less, and more preferably 20 mg or less, from the standpoint of ease of manufacturing and maintaining high freshness.

[0040] The amount of free leucine is preferably 12 mg or more. While there is no upper limit, it is preferably 40 mg or less, and more preferably 35 mg or less, from the standpoint of ease of manufacturing and maintaining high freshness.

[0041] The amount of free tyrosine is preferably 11 mg or more. While there is no upper limit, it is preferably 30 mg or less, and more preferably 25 mg or less, from the standpoint of ease of manufacturing and maintaining high freshness.

[0042] The amount of free phenylalanine is preferably 8 mg or more, and more preferably 9 mg or more. There is no upper limit, but from the standpoint of ease of manufacturing and maintaining high freshness, it is preferably 20 mg or less, and more preferably 15 mg or less.

[0043] The amount of free hydroxypronin is preferably 1 mg or more. There is no upper limit, but from the standpoint of ease of manufacturing and maintaining high freshness, it is preferably 100 mg or less, and more preferably 75 mg or less.

[0044] Furthermore, in the frozen headless Pacific white shrimp of the present invention, the amount of free inosinic acid per 100g of Pacific white shrimp meat is preferably 15mg or more, and more preferably 20mg or more. From the viewpoint of ease of manufacture and maintaining high freshness, the upper limit is preferably 50mg or less, and more preferably 40mg or less.

[0045] The frozen Pacific white shrimp of the present invention preferably have a firm texture. A firm texture makes the shrimp appear closer to larger, higher-priced shrimp, thereby increasing its commercial value. In the frozen Pacific white shrimp of the present invention, from the viewpoint of having a firm texture, the brittle load / breaking strength value is preferably 0.1 or less, more preferably 0.095 or less, and particularly preferably 0.092 g or less. Furthermore, from the viewpoint of easily obtaining a firm texture, the brittle load / breaking strength value is preferably 0.002 or more, more preferably 0.005 or more, and even more preferably 0.01 or more. Here, brittle load refers to the degree of decrease in load (stress) after the sample fractures, and is the difference in test force between the maximum peak in the stress-displacement curve and the bottom point at fracture (the minimum value immediately after the initial sharp drop). Fracture strength refers to the maximum test force just before the material fractures during the test. The preparation and measurement methods for samples to be measured for brittle load and fracture strength can be carried out according to the examples described later.

[0046] The frozen headless Pacific white shrimp of the present invention preferably has a breaking strength of 900 gf or more, which provides a good chewy texture, and more preferably 1000 gf or more. Furthermore, in the frozen headless Pacific white shrimp of the present invention, from the viewpoint of good chewiness, the breaking strength is preferably 3000 gf or less, more preferably 2500 gf or less, and even more preferably 2000 gf or less.

[0047] The brittle load / breaking strength ratio and the breaking strength value described above can be obtained by producing frozen headless Pacific white shrimp using a suitable manufacturing method described later.

[0048] Next, the method for producing frozen headless Pacific white shrimp according to the present invention will be described. The method for producing frozen headless Pacific white shrimp according to the present invention is a preferred method for producing frozen headless Pacific white shrimp according to the present invention. The present invention is a method for producing frozen Pacific white shrimp, The process involves oxygen injection to keep live Pacific white shrimp, harvested from aquaculture ponds, under conditions of 18°C ​​to 28°C, and maintaining them in this state. The process includes the steps of removing the heads of the shrimp after the oxygen injection step and freezing them.

[0049] The inventors of the present invention have found that conventional methods for producing frozen headless Pacific white shrimp have problems such as insufficient flavor and a tendency for the texture to soften. Further investigation led to the following conclusions. Generally, in the processing of Pacific white shrimp, the distance from the aquaculture pond to the processing plant is several tens of kilometers or more. Traditionally, Pacific white shrimp harvested from aquaculture ponds and sold frozen and headless were usually frozen in ice at the pond and then transported to the processing plant in ice water. The inventor focused on this point and, as an alternative to the above-mentioned transport method, attempted to transport live shrimp from the aquaculture pond to the processing plant while injecting oxygen at a predetermined temperature. Surprisingly, they found that this method yielded frozen Pacific white shrimp with high free lysine and free guanylic acid content, superior freshness, and a low K value. The reason for the high free lysine and free guanylic acid content in this method is not entirely clear, but conventional methods involve ice-freezing the shrimp immediately after harvesting from the aquaculture pond and transporting them to the factory in that state, during which free amino acids and free nucleotides leak out of the body. In contrast, this method, by transporting the shrimp alive while injecting oxygen under predetermined conditions, prevents the reduction of free lysine and free guanylic acid content in Pacific white shrimp during transport, maintains high levels, and improves taste. Furthermore, as mentioned above, free lysine and free guanylate are components produced by protein degradation and nucleic acid degradation / metabolism. Under the specified oxygen injection conditions, the enzyme activity responsible for protein degradation and nucleic acid degradation / metabolism in Pacific white shrimp is maintained, and this is also considered to be the reason why the free lysine content and free guanylate content are improved or maintained. Furthermore, it is believed that the oxygen injection during transport helps preserve the internal components of the Pacific white shrimp, and that various internal activities are well maintained during transport, making the tissue less prone to softening. This improves resistance to damage from subsequent freezing and thawing, and maintains the texture, including firmness and chewiness.

[0050] The present invention's method for producing Pacific white shrimp typically involves first cultivating Pacific white shrimp. The cultivation method can be any method commonly used for Pacific white shrimp cultivation, and is not particularly limited. The cultivation facility can be any suitable facility equipped with necessary equipment such as temperature control equipment and water supply and drainage systems for the tanks. Brackish water is preferred. The water temperature in the cultivation facility is preferably maintained at 20°C to 30°C.

[0051] It is preferable to maintain the pH of the water in the aquaculture facility between pH 6 and pH 8 using pH adjusters or the like.

[0052] The density of Pacific white shrimp in aquaculture is 100-200 shrimp / m³ relative to the volume of water in the aquaculture pond at the time of release. 3 This is preferable. The cultivation period can be appropriately adjusted to the period until the average individual mass of a randomly selected juvenile shrimp grows to 15g to 30g.

[0053] The manufacturing method of the present invention includes an oxygen injection step in which oxygen is injected into live Pacific white shrimp harvested from aquaculture ponds under conditions of a water temperature of 18°C ​​to 28°C. Preferably, in the oxygen injection step, the Pacific white shrimp harvested from the aquaculture ponds are placed alive in tanks, and the tanks are transported from the aquaculture ponds to the processing plant by a vehicle. At the processing plant, the shrimp are usually frozen, their heads and shells are removed, and their intestines are removed. There are no particular restrictions on the method used to transfer live Pacific white shrimp collected from aquaculture ponds to aquariums; any method can be used.

[0054] In this specification, injecting oxygen does not simply mean injecting air into the shrimp tank, but requires injecting a gas containing a high concentration of oxygen into the shrimp tank. Here, the gas containing a high concentration of oxygen preferably contains 60 mol% or more of oxygen, more preferably 70 mol%, even more preferably 80 mol% or more, and even more preferably 85 mol% or more.

[0055] The amount of oxygen injected into the tank is 5-80 cm³ per minute and per 1 kg of shrimp mass. 3 Preferably, 10-70cm 3 It is more preferable that it be 20-60cm 3 It is even more preferable that the oxygen injection amount is maintained within the above range, thereby keeping the Pacific white shrimp alive in good condition, and successfully obtaining frozen Pacific white shrimp in which free lysine and free guanylic acid are above the lower limit and the K value is below the upper limit.

[0056] In the present invention, in order to maintain the living environment of the banana prawns and make it easier to maintain freshness, the height of the water surface from the bottom of the water tank is preferably 50 to 150 cm, more preferably 70 to 100 cm. In addition, the area of the bottom of the water tank is preferably 1,500 cm 2 or more in order to maintain the living environment of the banana prawns and maintain freshness, and more preferably 3,000 cm 2 or more. The upper limit is not limited. For example, 12000 cm 2 is preferably mentioned, more preferably 9,000 cm 2 or less, and even more preferably 6,000 cm 2 or less. By setting the water surface height and the water tank area within the above ranges, it becomes easier to adjust the density of the banana prawns and the oxygen concentration, and it becomes even easier to transport the banana prawns while maintaining their freshness. The shape of the water tank can be arbitrarily selected from a rectangular shape, a cylindrical shape, an elliptical shape, a linear shape, etc. From the viewpoint of uniformly distributing oxygen throughout the water tank, a rectangular shape, a cylindrical shape, and an elliptical shape are preferred.

[0057] An oxygen discharge member is installed in the water tank. The method of injecting oxygen is preferably a method that can inject while maintaining a certain injection rate, and particularly preferably a method that can inject in the form of bubbles (oxygen bubbles). By injecting in the form of bubbles, the water in the water tank can be circulated, the water quality can be stabilized, and the living environment of the banana prawns can be maintained in a good state. Examples of oxygen discharging members that inject oxygen in the form of bubbles include air stones, tube-type air diffusers using silicone tubes with fine holes, and pipe-type diffusers using pipes made of metal or the like with fine slits inside. Examples of air stones include those made from porous materials such as ceramics, wood, sand, and ore. In particular, in the present invention, it is preferable to use an air stone because it is easy to increase the oxygen concentration in the water. The shape of the oxygen discharging member can be any shape that can distribute bubbles throughout the entire tank, and examples include square, spherical, and cylindrical shapes. If the oxygen discharging member has pores, the size of the pores can be in the range of 10 to 1000 μm, more preferably in the range of 10 to 500 μm, and even more preferably in the range of 10 to 300 μm.

[0058] The size of the oxygen discharge member can be selected to any size depending on the amount of water in the tank. In this invention, in order to ensure a sufficient supply of oxygen to the tank, the total volume of the oxygen discharge member is preferably 0.005 to 10%, more preferably 0.01 to 5%, even more preferably 0.02 to 3%, and particularly preferably 0.02 to 1% of the volume of water in the tank. The oxygen discharge component can be installed at any position in the water tank, such as the top, bottom, or side. In this invention, it is preferable to install it at the bottom of the water tank from the viewpoint of distributing the injected oxygen throughout the entire water tank.

[0059] The oxygen discharge component is preferably located inside the water tank and connected to oxygen supply equipment such as an oxygen tank via piping.

[0060] The aquarium can be set up in either a light-emitting or light-blocking state during transport. In this invention, it is preferable that the aquarium be in a light-blocking state from the viewpoint of maintaining the water temperature in the aquarium, keeping the shrimp calm and reducing oxygen consumption, and preventing damage from collisions and cannibalism.

[0061] From the viewpoint of maintaining a good environment for the growth of Pacific white shrimp, the density of Pacific white shrimp in the tank is preferably 50 to 200 shrimp / 10 liters, more preferably 60 to 170 shrimp / 10 liters, and even more preferably 70 to 140 shrimp / 10 liters per volume of water in the tank.

[0062] The water temperature in the tank should preferably be maintained at 18-28°C. The water temperature can be adjusted by any method. Furthermore, the sodium chloride concentration should preferably be maintained at 15,000-35,000 ppm by mass. The tank itself can be appropriately selected to allow for easy temperature adjustment; for example, a plastic tank is suitable.

[0063] Under the above oxygen injection conditions, it is preferable to maintain the oxygen concentration dissolved in the water in the tank at 3 to 11 mg / L, more preferably at 3.5 to 10 mg / L, and even more preferably at 4 to 9 mg / L.

[0064] The time for oxygen injection (the time spent transporting while injecting oxygen) can be arbitrarily selected. In this invention, from the viewpoint of maintaining the freshness of the Pacific white shrimp, the transport time is preferably 24 hours or less, more preferably 10 hours or less, and particularly preferably 5 hours or less. By keeping the transport time below the above upper limit, the condition of the Pacific white shrimp after transport can be kept in good condition, and frozen headless Pacific white shrimp with excellent taste and texture can be provided. On the other hand, from the viewpoint of exhibiting the effects of this invention, the transport time may be 10 minutes or more, 30 minutes or more, or 1 hour or more.

[0065] During the oxygen injection process, feeding the Pacific white shrimp is optional, but not feeding them is preferable in terms of maintaining water quality.

[0066] The pH of the water in the tank during the oxygen injection process is preferably 6 to 8.5, and more preferably 6 to 8.

[0067] After the oxygen injection process, the Pacific white shrimp are frozen after their heads are removed. The Pacific white shrimp after the oxygen injection process are then placed in water between 1°C and 5°C and frozen, which causes them to freeze to death by supercooling. The time spent in the water at the above temperature range can be adjusted as appropriate depending on the condition of the Pacific white shrimp, but 5 to 20 minutes is preferred, and 5 to 10 minutes is particularly preferred.

[0068] The head can be removed manually. By freezing Pacific white shrimp, they can be made into frozen headless Pacific white shrimp. Rapid freezing is preferable from the standpoint of maintaining the freshness of the Pacific white shrimp. Rapid freezing refers to a method in which the core temperature of the food passes through the maximum ice crystal formation temperature range (-1°C to -5°C) within 30 minutes when freezing food.

[0069] The frozen headless Pacific white shrimp obtained through the above process can be used in various cooking methods such as deep-frying, boiling, steaming, and grilling due to their excellent taste, texture, and high freshness. They can also be used as a raw material for various processed foods such as frozen foods, microwaveable foods, retort foods, diet foods, deep-fried products such as fried foods, and chilled foods.

[0070] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to what is described above. [Examples]

[0071] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. <Examples 1-5> (Cultivation process) In aquaculture ponds, Pacific white shrimp larvae are raised at a rate of 100-200 individuals / m². 3They were released into the tank at a density of [density] and reared. They were reared for 40 to 70 days under conditions of water temperature of 20-30°C, water pH of 6-8, and sodium chloride concentration of 20,000-30,000 ppm by mass. Feeding was done 1-2 times a day. The feed consisted of commercially available compound feed (protein content 20-60% by mass, carbohydrates 0.1-3% by mass, fat 1-10% by mass, minerals 1-15% by mass).

[0072] (Transportation process (oxygen injection process)) The aforementioned Pacific white shrimp were collected alive from the aquaculture pond and transferred to cylindrical tanks with a water volume of 50 to 300 liters, installed in a vehicle. The aquarium had a bottom diameter of 60 cm and a water surface height of 70-80 cm. The density of Pacific white shrimp in the aquarium was 100-120 shrimp / 10 liters relative to the volume of water in the aquarium. The water temperature in the aquarium was maintained at 18-28°C. Brackish water was used for the aquarium water, with a sodium chloride concentration of 15,000-25,000 ppm by mass. The pH of the water in the aquarium was in the range of 6-8. Nine to twelve cylindrical air stones (size: 3 cm in diameter, 5 cm in length, pore size 50-100 μm) were placed at the bottom of the tank, and oxygen-containing gas (oxygen purity 90% or higher) was injected by connecting the air supply pipe of the oxygen tank mounted on the vehicle to the air stones. The oxygen injection rate is 20-60 cm³ per minute and per kg of shrimp mass. 3 The dissolved oxygen concentration in the water was maintained at 4-9 mg / L. Maintaining the aforementioned conditions, the Pacific white shrimp were transported by vehicle under the distance and time conditions listed in Table 1. After transport, the Pacific white shrimp were placed in a tank of water between 1°C and 5°C for 5-10 minutes to freeze. Afterward, the heads, shells, and legs were removed. After that, the stretching process (removal of intestinal tract, cutting of muscle tissue, and flattening of the shrimp) was carried out.

[0073] (Water retention process) The obtained Pacific white shrimp were immersed in a water-retaining solution (pH 7.8-8.8, 2% by mass of sodium chloride, no amino acids or nucleic acids) at 10°C or below for 30 minutes to retain water.

[0074] The obtained Pacific white shrimp were rapidly frozen at -18°C or below using a freezer.

[0075] <Comparative Example 1> Vannamei shrimp, farmed using the same method as in Examples 1-5 (aquaculture process), were harvested alive from the aquaculture ponds, placed in a tank filled with water between 1°C and 5°C for 5-10 minutes to freeze, and then transported to a processing plant in that state. There, the heads, shells, and legs were removed. After that, the stretching process (removal of intestinal tract, cutting of muscle tissue, and flattening of the shrimp) was carried out.

[0076] (Water retention process) The obtained Pacific white shrimp were immersed in a water-retaining solution (pH 7.5-8.5, containing 2% by mass of sodium chloride and 0.4% by mass of glycine, without nucleic acids) at a temperature of 10°C or below for 3 to 5 hours to retain water.

[0077] The obtained Pacific white shrimp were rapidly frozen at -18°C or below using a freezer.

[0078] <Comparative Examples 2 and 3> Pacific white shrimp, farmed using the same method as in Examples 1-5 (aquaculture process), were harvested alive from the aquaculture ponds, placed in a tank filled with water between 1°C and 5°C for 5-10 minutes to freeze, and then transported to a processing plant in that state. Comparative Example 2 was transported 100 km for 2 hours and 30 minutes, and Comparative Example 3 was transported 200 km for 4 hours and 30 minutes. At the processing plant, the heads, shells, and legs were removed. After that, the stretching process (removal of intestinal tract, cutting of muscle tissue, and flattening of the shrimp) was carried out.

[0079] (Water retention process) The obtained Pacific white shrimp were immersed in water using the same procedure as in Examples 1-5 to retain moisture.

[0080] The obtained Pacific white shrimp were rapidly frozen at -18°C or below using a freezer.

[0081] In the following tests, Pacific white shrimp with sizes ranging from 13 / 15 to 21 / 25 were used. (Measurement of free amino acid content) (1) Preparation of the sample for measurement The Pacific white shrimp from Examples 1-5 and Comparative Example 1 were prepared as samples for measurement by grinding the frozen flesh portion (the entire remaining part after removing the head, shell, and tail, and so on) using Grind Mix GM 200 (Retsch) and homogenizing it. Approximately 3 g of the pulverized material obtained above was sampled into a homogenizing cup, 40 mL of 5% by mass trichloroacetic acid aqueous solution was added, and the mixture was stirred (3000 rpm, 5 min) before being transferred to a 100 mL volumetric flask. After making up the volume with a 5% by mass trichloroacetic acid aqueous solution and stirring, the mixture was left to stand overnight in a refrigerator. After stirring again, the solution was filtered through filter paper (Advantec No. 5B) and subjected to an amino acid analyzer.

[0082] (2) Measurement of free amino acid content A 20 μL sample was analyzed using a high-speed amino acid analyzer (manufactured by Hitachi High-Tech Science Corporation). The instrument configuration is as follows. Measurement device: High-speed amino acid analyzer LA8080 AminoSAAYA (manufactured by Hitachi High-Tech Science Corporation) Ammonia removal column: #2650L column (inner diameter: 4.6mm ID x 40mm) (manufactured by Hitachi High-Tech Science Co., Ltd.) Separation column: #2622PF column (inner diameter: 4.6mm ID x 60mm) (manufactured by Hitachi High-Tech Science Co., Ltd.) Reaction coil: TDE2 REACTOR (852-7700) (manufactured by Hitachi High-Tech Fielding Co., Ltd.) Buffer solution: MCI BUFFER L-8500 PF Kit (Mitsubishi Chemical Corporation) Standard sample: Amino acid mixed standard solution, AN-2 type (Fujifilm Wako Pure Chemical Corporation) Amino acid mixed standard solution, type B (Fujifilm Wako Pure Chemical Corporation) Ninhydrin: Ninhydrin color development solution kit for Hitachi (Fujifilm Wako Pure Chemical Industries, Ltd.) Detection wavelengths: 570, 440 nm Tables 1 and 2 show the measurement results of the free amino acid content (mg) per 100g of Pacific white shrimp meat.

[0083] (Measurement of guanylic acid and inosinic acid levels) (1) Preparation of the sample for measurement After freezing the Pacific white shrimp from Examples 1-5 and Comparative Example 1, the flesh was ground using a grind mix GM 200 (Retsch) while still frozen, and homogenized to prepare the samples for measurement. Approximately 10 g of the obtained sample was mixed with 20 ml of 20% trichloroacetic acid aqueous solution to separate the proteins. The sample obtained after protein separation was diluted to 50 ml with water, filtered using No. 5B filter paper, and 10 ml was taken from the resulting filtrate. The pH was adjusted to 6.5-7.5 with a 20% sodium hydroxide aqueous solution, and the solution was diluted to 50 ml with water. The sample was then filtered using a filter (Millex-LG 0.20 μm) to obtain the sample for measurement.

[0084] (2) Measurement of guanylic acid content A 50 μL sample was measured using high-performance liquid chromatography (Agilent) via HPLC. The instrument configuration and measurement conditions are as follows. Measurement device: 1260 Infinity II (manufactured by Agilent) Autosampler: Model G7129A Pump: Model G7111B Column oven: Model G7129A UV-YIS detector: Model G7115A Measurement conditions: Column: CAPCELL PAK NH2UG80 S5, Φ4.6mm × 250mm (particle size 5μm) Mobile phase: 50 mmol / L ammonium phosphate buffer (pH 3.0) Flow rate: 1ml / min Detection wavelength: 260nm Column temperature: 40 degrees Sample injection volume: 50 μL Analysis time: 25 minutes / sample

[0085] (3) Measurement of inosinic acid content A 50 μL sample was measured using high-performance liquid chromatography (HPLC) with an Agilent instrument. The instrument configuration and measurement conditions are as follows. Measurement device 1260 InfinityII (manufactured by Agilent) Autosampler: Model G7129A Pump: Model G7111B Column oven: Model G7129A UV-YIS detector: Model G7115A Measurement conditions: Column: CAPCELL PAK NH2UG80 S5, Φ4.6mm × 250mm (particle size 5μm) Mobile phase: 50 mmol / L ammonium phosphate buffer (pH 3.0) Flow rate: 1ml / min Detection wavelength: 260nm Column temperature: 40 degrees Sample injection volume: 50 μL Analysis time: 25 minutes / sample

[0086] (Calculation of K value) (1) Preparation of the sample for measurement After freezing the Pacific white shrimp from Examples 1-5 and Comparative Example 1, the flesh was ground using a grind mix GM 200 (Retsch) while still frozen, and homogenized to prepare the samples for measurement. Approximately 10 g of the obtained sample was mixed with 20 ml of 20% trichloroacetic acid aqueous solution to separate the proteins, and the volume was then adjusted to 50 ml with water. The sample obtained after protein separation was filtered using No. 5B filter paper, and approximately 25 ml of the filtrate was taken and prepared with a 20% sodium hydroxide solution to a pH of around 6.8. The resulting solution was diluted to 100 ml with water. Then, it was filtered using a filter (Millex-LG 0.20 μm) to obtain the sample for measurement.

[0087] (2) Measurement of ATP, ADP, AMP, IMP, HxR and Hx The ATP, ADP, AMP, IMP, HxR, and Hx levels in shrimp flesh were measured using high-performance liquid chromatography (HPLC). The HPLC system configuration and measurement conditions were as follows. Measurement device: 1260 InfinityII (manufactured by Agilent) Autosampler: Model G7129A Pump: Model G7111B Column oven: Model G7129A UV-YIS detector: Model G7115A Measurement conditions: Column: Shodex Asahipak GS-320, Φ7.5mm x 500mm (particle size 6μm) Mobile phase (Solution A): 200 mmol / L sodium phosphate buffer (pH 3.0) Flow rate: 1ml / min Detection wavelength: 260nm Column temperature: 30℃ Sample injection volume: 20 μL Analysis time: 40 minutes / sample

[0088] The K value was calculated using the following formula with the ATP, ADP, AMP, IMP, HxR, and Hx values ​​measured by HPLC. The results are shown in Tables 1 and 2. K value (%)=(HxR+Hx) / (ATP+ADP+AMP+IMP+HxR+Hx)×100

[0089] [Table 1]

[0090] As shown in Table 1, the Pacific white shrimp of Examples 1-5, which were transported while injecting oxygen and then chilled with ice, had higher levels of free amino acids such as free lysine, free guanylic acid, and free glutamic acid, as well as free nucleic acids, compared to the Pacific white shrimp of Comparative Example 1, which was obtained through a process without oxygen injection. It was also found to have a lower K value.

[0091] (Measurement of breaking strength) For the Pacific white shrimp used in Examples 1-5 and Comparative Example 1, the frozen Pacific white shrimp were transferred to a container and thawed at room temperature (25°C) with a fan for approximately 30 minutes. After removing the shells, 20 Pacific white shrimp were placed in 4L of boiling water and boiled at over 100°C for 2 minutes and 30 seconds. After boiling, they were cooled in ice water and then left to stand in a colander for approximately 1 minute to remove surface moisture. The breaking strength of the boiled shrimp was measured using the following method. Heated peeled shrimp were placed horizontally and evaluated using a texture analyzer (Shimadzu Corporation, EZ-SX). Measurement conditions included a wedge-shaped plunger made of plastic (acrylic resin) (with a 30mm wide tip and a 30° angle), compression mode, plunger entry speed of 10mm / sec, and a load applied from the top of the sample up to 70% of the sample's height. Measurements were performed with the longitudinal direction of the plunger's tip plane perpendicular to the longitudinal direction of the shrimp. The measurement site for the shrimp sample was the midpoint of its total length, and the breaking strength and brittle load were measured. Five samples were measured for each of Examples 1-5 and Comparative Example 1, and the average values ​​are shown in Table 2.

[0092] [Table 2]

[0093] As shown in Table 2, the Pacific white shrimp of each example have a higher breaking strength compared to the Pacific white shrimp of the comparative example. Furthermore, the ratio of brittle load to breaking strength is smaller.

[0094] (Sensory evaluation) The frozen headless Pacific white shrimp from Example 5 and Comparative Example 1, which were frozen after being chilled with ice, were thawed under running water, dipped in batter, and then fried in 170°C edible oil for 2 minutes.

[0095] After the oil-cooking process, five panelists tasted the food and evaluated its flavor, chewiness, and texture on a 5-point scale. The evaluation was conducted according to the following criteria. The results are shown in Table 3. (1) Taste 5: I can really taste the umami. 4: I strongly taste the umami. 3: I can taste the umami. 2: I don't really taste much umami. 1: I can't taste any flavor at all.

[0096] (2) Chewiness (texture) 5: It is dense and has a very strong fibrous texture. 4: It is dense and has a strong fibrous texture. 3: I can feel the texture of the fibers. 2: The flesh is brittle and doesn't have much of a fibrous texture. 1: The flesh is brittle and has absolutely no fibrous texture.

[0097] (3) Texture 5: It has a firm texture and a strong shrimp flavor. 4: It has a firm texture and you can taste the shrimp. 3: It has a firm texture. 2: It's watery and doesn't have much texture. 1: It's watery and has absolutely no texture.

[0098] [Table 3]

[0099] As can be seen from Table 3, the frozen headless shrimp obtained in the example was superior to the frozen headless shrimp obtained in the comparative example in terms of taste, chewiness, and texture.

Claims

1. Frozen headless Pacific white shrimp containing 1.0 mg / 100g or more of free guanylic acid, 50 mg / 100g or less of free inosinic acid, 24 mg / 100g or more of free lysine, 20 mg / 100g or more of free serine, and a potassium (K) value of less than 12.5%.

2. Frozen headless Pacific white shrimp according to claim 1, containing 50 mg / 100 g or more of free glutamic acid.

3. The frozen headless Pacific white shrimp according to claim 1 or 2, satisfying any of the following conditions: (1), (2), (3), or (4). (1) The mass ratio of free glutamic acid to free glycine is 1:16 or less. (2) The content of free glutamic acid and free alanine shall be 1:3.0 or less by mass ratio. (3) The mass ratio of free glutamic acid to free arginine is 1:16 or less. (4) The mass ratio of free glutamic acid to free proline is 1:11 or less.

4. Frozen headless Pacific white shrimp according to claim 1 or 2, wherein the free threonine content is 8 mg / 100 g or more and 130 mg / 100 g or less.

5. The frozen headless Pacific white shrimp according to claim 1 or 2, wherein the ratio of brittle load (gf) to breaking strength (gf) is 0.1 or less.

6. The frozen headless Pacific white shrimp according to claim 1 or 2, wherein the breaking strength is 900 gf or more.

7. Unheated, frozen headless Pacific white shrimp according to claim 1 or 2.

8. A farmed shrimp, the frozen headless Pacific white shrimp according to claim 1 or 2.

9. A heated frozen headless Pacific white shrimp according to claim 1 or 2.

10. A method for producing frozen headless Pacific white shrimp, The process involves an oxygen injection step in which Pacific white shrimp collected from aquaculture ponds are kept alive under conditions of oxygen injection at a water temperature of 18°C ​​to 28°C, and A method for producing frozen headless Pacific white shrimp, comprising the steps of removing the heads of the shrimp after the oxygen injection step and freezing them, wherein the water level in the tank is 50 to 150 cm above the bottom of the tank, and in the oxygen injection step, a gas containing 60 mol% or more of oxygen is injected into the shrimp tank, with the oxygen injection rate per minute and per 1 kg of shrimp mass being 5 to 80 cm³.

11. The method for producing frozen headless Pacific white shrimp according to claim 10, wherein the oxygen injection step is a transport step from the aquaculture pond to the processing plant.

12. The method for producing frozen headless Pacific white shrimp according to claim 10 or 11, wherein the time for the oxygen injection step is 24 hours or less.

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