Method for producing edible catfish

Abstract

To provide a method for producing edible catfish excellent in palate feeling while suppressing muddy smell peculiar to catfish.SOLUTION: The method for producing the edible catfish includes a processing step of processing the catfish into a sliced state, a preparation step of preparing ≥ 0.5 wt.% and ≤ 4.0 wt.% trisodium phosphate, an organic acid and water to obtain a treatment liquid, and a treatment step of immersing the sliced catfish in the treatment liquid for ≥ 1 hr. The catfish in this case may be Pangasius.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing edible catfish. [Background technology]

[0002] Traditionally, freshwater fish have been improved in taste and processed differently from saltwater fish, and catfish have been eaten in some countries or regions, but a sufficient method for producing edible catfish has not yet been developed. Specific prior art documents include the following documents 1 and 2. Patent Document 1 (JP 2022-049366 A) describes a method for producing a decomposed food material that has a desirable taste derived from the raw material and a cooked flavor (such as a baked or stewed flavor). It also provides a method for improving the flavor by adding the decomposed food material to other foods and beverages.

[0003] The manufacturing method described in Patent Document 1 is a method for manufacturing a decomposed food material, which includes a step of crushing at least one of shrimp and / or shrimp processed products, catfish and / or catfish processed products, or residues thereof as a pretreatment, a step of heat-treating the crushed residue at 70 to 350°C in an extruder, and a step of processing the extruded heat-treated material again in an extruder, wherein the processing in the extruder again involves adding an enzyme.

[0004] Patent Document 2 (JP 62-195242 A) discloses that the composition of the present invention can stabilize fish fillets with a significantly lower amount of sorbate than that required in conventional compositions and without the use of citric acid. The composition of the present invention provides effective control of microorganisms, flavor, texture, and appearance at a lower cost than conventional compositions.

[0005] The composition described in Patent Document 2 contains an alkali metal salt of hexametaphosphate, an acidic alkali metal salt of pyrophosphate, and a sorbate antibacterial agent, and is capable of stabilizing the storage and yield of fish fillets without using citric acid and without the taste problems associated with the use of citric acid.

[0006] On the other hand, although saltwater fish have different characteristics, various methods for improving the taste and processing have been investigated. Patent Document 3 (JP 2018-038403 A) provides a method for producing semi-raw frozen fish that can provide safe and secure fish food ingredients that are thoroughly sterilized and that can provide soft, juicy, and delicious fish dishes that are free of fishy odor with little effort and time.

[0007] According to this document, an alkaline aqueous solution containing 1.0% trisodium phosphate, 0.4% sodium bicarbonate, 0.4% sodium carbonate, 0.1% trisodium citrate, and 2.0% other additives was adjusted to a pH of 9.0, and frozen mackerel and salmon were soaked in the solution at room temperature for 30 minutes.

[0008] Patent Document 4 (JP 2007-061059 A) provides a curd inhibitor that inhibits the formation of curd, a meat texture improver that makes meat less likely to become dry, a meat yield improver that improves yield, canned fish meat and processed meat foods containing these improved products, and methods for producing these products.

[0009] Patent Document 4 describes the use of trisodium phosphate as a curd formation inhibitor to inhibit curd formation in fish meat such as mackerel. According to Patent Document 4, when the alkaline agent trisodium phosphate is added to fish meat, it is possible to shift the pH of the fish meat to the alkaline side and denature the proteins. Therefore, when used in canned products, it is described as being able to suppress the elution of soluble proteins from the fish meat and inhibit the formation of curd. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2022-049366 [Patent Document 2] Japanese Patent Application Laid-Open No. 62-195242 [Patent Document 3] Japanese Patent Application Publication No. 2018-038403 [Patent Document 4] Japanese Patent Application Laid-Open No. 2007-061059 Summary of the Invention [Problem to be solved by the invention]

[0011] In recent years, catfish, which grow in a short period of time with little feed, have been attracting attention as a food source with little environmental impact. In particular, efforts are underway to expand the acquisition of MSC and ASC certifications for pangasius, a type of catfish, which are evidence of sustainable seafood that is properly managed with consideration for fishery resources and the marine environment, and it is a fish that is expected to become more popular in Japan in the future as a sustainable seafood product. However, compared to saltwater fish, catfish is a freshwater fish that has a muddy smell characteristic of freshwater fish and is easily affected by osmotic pressure during processing. Therefore, conventional processing methods are unable to suppress the smell, and the texture and flavor tend to deteriorate.

[0012] However, few methods for producing edible catfish have been developed to solve the above problems, and the only prior art documents related to the production of edible catfish are the following documents 1 and 2. The manufacturing method of Patent Document 1 uses an extruder and its processing conditions to achieve a desirable cooked flavor, and therefore does not allow for odor suppression without crushing the catfish.

[0013] The composition of Patent Document 2 is intended to extend the shelf life of catfish, but does not suppress the odor of catfish or improve its texture.

[0014] On the other hand, saltwater fish such as mackerel are prone to producing curd, a soluble protein that elutes from the fish flesh. This can lead to the growth of bacteria, which can cause a fishy smell and reduce the juiciness. The manufacturing method in Patent Document 3 describes that mackerel fillets are immersed for a short time in an alkaline aqueous solution containing trisodium phosphate, then heat-treated with superheated steam and quickly frozen. It also describes that this reduces the amount of dripping (curd formation) when the product is thawed naturally. Patent Document 4 describes that adding trisodium phosphate to mackerel fillets denatures the proteins on the surface of the fish meat, thereby suppressing the formation of curd.

[0015] In addition, since the fishy smell of saltwater fish is caused by trimethylamine, methods have been developed to reduce the smell by neutralizing it with an acidic treatment solution or by denaturing the protein with an alkaline treatment solution.

[0016] However, catfish is a freshwater fish, and no method for treating geosmin and 2-methylisoborneol, which cause its muddy odor, has been clarified. In particular, catfish have a problem in that the muddy odor cannot be reduced even by changing the pH of the treatment solution, making them difficult to use for food. To address this issue, efforts have been made to manage the water quality at farms and to use feed to suppress the odor, but these efforts have been costly and problematic.

[0017] The main object of the present invention is to provide a method for producing edible catfish that has an excellent texture while suppressing the muddy smell peculiar to catfish. Another object of the present invention is to provide a method for producing catfish that has excellent texture and flavor while suppressing the fishy odor specific to catfish. [Means for solving the problem]

[0018] (1) According to one aspect, a method for producing edible catfish (processing method) includes a processing step of processing catfish into fillets, a preparation step of preparing 0.5% by weight to 4.0% by weight of trisodium phosphate, an organic acid, and water to obtain a treatment solution, and a treatment step of immersing the catfish fillets in the treatment solution for one hour or more.

[0019] Catfish grow in a short period of time, so they require less feed than other farmed fish, and because the feed only requires a small amount of protein, they have recently been attracting attention as a food product with low environmental impact. However, catfish generally live in shallow rivers or swamps, and therefore have a problem of retaining a muddy odor inside their bodies, which has prevented them from being fully utilized as food. In particular, catfish have odor components that are different from those of seawater fish, so there has been a problem in that the muddy odor cannot be reduced simply by immersing them in an acidic or alkaline treatment solution. In addition, catfish is a freshwater fish and is more susceptible to osmotic pressure than saltwater fish, so there was a problem in that it was not possible to suppress the muddy smell that is characteristic of catfish without compromising the texture and flavor of the fillets. The inventors then focused on the fact that catfish have a low osmotic pressure in their bodies and are easily affected by water quality (components dissolved in the breeding environment), and discovered that the muddy smell characteristic of catfish can be eliminated by immersing them in a predetermined concentration of trisodium phosphate aqueous solution. It is generally believed that the muddy smell characteristic of catfish is caused by geosmin, and it is thought that the reaction between trisodium phosphate ingested by the catfish and geosmin results in the consumption of geosmin, thereby reducing the muddy smell characteristic of catfish.

[0020] In one aspect of the method for producing edible catfish, catfish fillets are immersed in a treatment solution containing 0.5% by weight or more of an aqueous solution of trisodium phosphate for at least one hour, allowing the treatment solution to penetrate the entire fillet. The trisodium phosphate contained in the treatment solution reacts with geosmin, a component that causes the odor, thereby suppressing the muddy odor characteristic of catfish. Furthermore, for catfish, which is easily affected by the processing solution, the use of 0.5% to 4.0% by weight of trisodium phosphate increases the fillet yield, preventing the meat from becoming hard or dry and making it moderately tender, allowing for the production of edible catfish with excellent texture without compromising the appearance of the fillets.

[0021] (2) The method for producing edible catfish according to the second invention is a production method according to one aspect, in which the catfish may be Pangasius.

[0022] By using Pangasius catfish, it is possible to reduce the muddy smell and produce fillets with an excellent texture. Among catfish, Pangasius catfish grow quickly, which reduces the environmental burden of raising them. In addition, Pangasius catfish have thick flesh and a high collagen content, which makes them prone to falling apart, but this can be prevented.

[0023] (3) The method for producing edible catfish according to the third invention is an invention according to one aspect, and may further include a pH adjustment step in the preparation step, in which the pH of the treatment liquid is adjusted to 6 to 10.5 by adjusting the amount of organic acid added.

[0024] By adjusting the pH of the treatment solution to fall within a predetermined range, edible catfish with excellent texture and flavor can be produced. That is, by setting the pH of the treatment liquid to 6 or higher, the acidity is suppressed, allowing the flavor of the food material to be felt. Also, by setting the pH of the treatment liquid to 10.5 or lower, it is possible to prevent jelly formation while maintaining the yield even when heated, resulting in a food material with excellent texture.

[0025] (4) A method for producing edible catfish according to a fourth aspect of the present invention is an invention according to one aspect, and the pH of the treatment liquid in the pH adjustment step may be 7 to 8.

[0026] This allows edible catfish to be stored for a long period of time without discoloration even when frozen.

[0027] (5) The method for producing edible catfish according to the fifth invention is a method for producing edible catfish according to any one of the inventions from one aspect to the third aspect, and the weight of the catfish fillets that have been heat-treated after the processing step may be 0.8 to 0.95 times the weight of the catfish fillets before the processing step.

[0028] This makes it possible to prevent the catfish from shrinking and turning into a jelly even when heated, resulting in a food ingredient with an excellent texture.

[0029] (6) The sixth invention relates to a method for producing edible catfish, which is a method for producing edible catfish according to any one of the first to third inventions, and in the treatment step, the soaking time may be 12 hours or more, allowing the catfish to permeate with the treatment liquid.

[0030] In this case, soaking for 12 hours or more allows the processing solution to penetrate evenly and thoroughly into the entire catfish fillet, allowing trithorium phosphate to react with the odor-causing components and reliably suppress the muddy smell of edible catfish.

[0031] (7) The method for producing edible catfish according to the seventh invention is a method for producing edible catfish according to any one of the first to third inventions, in which in the treatment step, instead of soaking, soaking and shaking may be performed for one hour or more to allow the treatment liquid to penetrate the catfish.

[0032] This allows the fillets to be more easily penetrated by the soaking and shaking method, which reduces the processing time to one hour, thereby improving production rates. DETAILED DESCRIPTION OF THE INVENTION

[0033] The manufacturing method of this embodiment will be described in detail below. Preferred embodiments of the present invention are as follows, but the present invention is not limited thereto. Furthermore, at least a part of the configuration of each embodiment can be appropriately combined with a part of another embodiment without departing from the spirit and scope of the present invention.

[0034] (catfish) Various studies have been conducted on the pretreatment of saltwater fish. For example, one method known is to denature proteins on the surface of the fish using an alkaline treatment solution to reduce the amount of exposed curd (fish body fluids). A major difference between saltwater and freshwater fish is the method of adjusting the osmotic pressure that arises from the difference in concentration between the fish body and its surroundings. Freshwater fish have a low osmotic pressure in their bodies, making them susceptible to the effects of water quality (components dissolved in the breeding environment). Therefore, it has been pointed out that raising the pH of the treatment solution too much can affect the taste. On the other hand, catfish has a problem in that the muddy smell cannot be reduced even when the pH is increased, making it difficult to use for food.

[0035] In recent years, amid growing concerns about global food shortages, catfish are gaining attention as a food product with less environmental impact because they grow in a short period of time and therefore require less feed than other farmed fish, and because the feed also requires only a small amount of protein. However, because catfish live in shallow rivers or swamps, they have a muddy smell, which is a problem, and they have not been fully utilized as food. From the viewpoints of growth potential and ease of rearing, catfish of the families Pangasiiidae, Giggidae, and Pimelodontidae are preferably used.

[0036] The catfish in this embodiment is not particularly limited, and examples thereof include pangasius, American catfish, channel catfish, pangasius, rock catfish, Biwa giant catfish, char, longfin catfish, and striped catfish. Among these, Pangasius has seen an expansion in aquaculture in Southeast Asia, including Vietnam, in recent years, and the catch is increasing. It also grows quickly, can grow in a short period of time with little feed, and is omnivorous, being able to use plant debris as feed, which makes it a desirable food source with a low environmental impact, and it has been attracting attention as a food ingredient in Japan as well. Examples of catfish in the Pangasius family include the Basa, Parma, Kai Yang (Char), Mekong giant catfish, and Pra Thepaw.

[0037] (Processing liquid) The treatment liquid prepared in this embodiment contains at least trisodium phosphate, an organic acid, and water. In addition, seasonings and food additives such as organic acid salts, antioxidants, preservatives, coloring agents, and stabilizers can be added as appropriate within the scope of the present invention. Examples of seasonings include salt, vinegar, sugar, soy sauce, miso, mirin, sodium glutamate, and potassium chloride. Examples of organic acid salts include trisodium citrate, monosodium fumarate, and sodium gluconate. Adding organic acid salts to the treatment solution can improve food preservation and pH buffering effects.

[0038] (trisodium phosphate) The trisodium phosphate used in the treatment solution may be any that can be added to food, and may be anhydrous (Na3Po4) or a hydrate (Na3Po4·12H2O, etc.). The lower limit of the concentration of the trisodium phosphate aqueous solution used in the treatment solution is preferably 0.5% by weight or more, more preferably 1.0% by weight or more, and even more preferably 1.5% by weight or more. The upper limit of the concentration is preferably 4.0% by weight or less, more preferably 3.0% by weight or less, and even more preferably 2.5% by weight or less. By using a trisodium phosphate aqueous solution at a concentration equal to or greater than the lower limit, the solution reacts with geosmin, the component responsible for the odor of freshwater fish, thereby suppressing the odor characteristic of catfish. Furthermore, increasing the concentration of the trisodium phosphate aqueous solution can improve yield and water retention. On the other hand, by using a trisodium phosphate aqueous solution with a concentration of not more than the upper limit, precipitation of organic acids is unlikely to occur even when refrigeration / freezing treatment is carried out, and pH adjustment becomes easy. Therefore, by using an aqueous solution of trisodium phosphate of an appropriate concentration, it is possible to produce edible catfish with excellent texture by increasing the yield of fillets while suppressing the muddy smell.

[0039] (organic acid) Examples of organic acids added to the treatment solution to adjust the pH include citric acid, fumaric acid, acetic acid, lactic acid, tartaric acid, adipic acid, gluconic acid, ascorbic acid, and mixtures thereof. Among these, citric acid and fumaric acid are preferred, and citric acid is more preferred because of its solubility in the treatment solution and its minimal effect on taste. This allows the pH of the treatment solution to be adjusted, inhibiting mold and bacterial growth and preventing discoloration.

[0040] (Processing process) In the processing step of this embodiment, the catfish fillets to be processed may be those that have been filleted into three pieces for eating. In detail, it is preferable to drain the blood of the caught catfish [bleeding process], then, if necessary, soak it in fresh water to remove mud [mud removal process], remove the slime with salt or the like, and wash it with fresh water [slime removal process], remove the head and internal organs [removing process], fillet it into three pieces to make fillets [filleting process], remove the backbone and wash it [bone removing process], remove the epidermis (the mucus layer where the scales have degenerated) from the fillets [skinning process], further remove unnecessary parts such as the blood vessels [trimming process], and then wash it. Furthermore, if necessary, the catfish may then be frozen [freezing process] before being transported or stored. In order to ensure that the catfish odor is removed, it is preferable to perform a bleeding process.

[0041] (Preparation process) In the preparation step of this embodiment, the pH is adjusted by adding an appropriate organic acid to an aqueous solution of trisodium phosphate having a predetermined concentration. The preferred concentration of the aqueous solution of trisodium phosphate used in the treatment liquid is as described above. The amount of organic acid to be added to the aqueous trisodium phosphate solution varies depending on the type of organic acid, but it is preferable to use a pH meter to adjust the solution to the following suitable pH. That is, the lower limit of the pH of the treatment solution for soaking the fillets is preferably 5.8 or higher, more preferably 6.5 or higher, and even more preferably 7.0 or higher. The upper limit of the pH is preferably less than 12.0, more preferably 11.0 or lower, even more preferably 10.5 or lower, and most preferably 8.0 or lower. The pH of the treatment solution may be selected appropriately depending on the type of catfish. Generally, a pH of 5.8 or higher reduces the sourness, and a pH of 6.8 or higher reduces the saltiness and sourness, and can suppress the muddy odor while maintaining excellent flavor and texture. A pH of less than 12.0 can prevent the catfish fillets from turning into a jelly, and a pH of 10.5 or lower is preferred because it allows the fillets to be stored for long periods of time without discoloration even when frozen.

[0042] (Processing process: immersion) The amount of treatment solution used to immerse catfish fillets in the treatment liquid should be sufficient to immerse the entire fillet, and is preferably 2 parts by weight or more, more preferably 4 parts by weight or more, per part by weight of catfish fillet. This allows sufficient treatment liquid to penetrate the catfish fillet even if the treatment liquid near the catfish fillet is partially neutralized, thereby effectively suppressing odor. The temperature of the treatment solution during immersion is preferably 10° C. or lower, more preferably 7° C. or lower, and even more preferably 5° C. or lower. This makes it possible to maintain freshness while preventing spoilage and bad odors. The immersion time in the treatment solution can be selected depending on the type of catfish, but is preferably 2 hours or more, more preferably 10 hours or more, and even more preferably 15 hours or more. This allows the treatment solution to penetrate deep into the catfish fillets, allowing trithorium phosphate to fully react with odor-causing components and effectively suppress the muddy smell of catfish.

[0043] (Processing step: immersion and shaking) Shaking methods include stirring the treatment solution, placing the fillets in a rotating barrel and immersing them in the treatment solution while stirring, shaking the immersion container with a sieve, and rotating the fillets themselves on a stand in the treatment solution. The temperature of the treatment solution during immersion is preferably 10° C. or lower, more preferably 7° C. or lower, and even more preferably 5° C. or lower. This makes it possible to maintain freshness while preventing spoilage and bad odors. The immersion and shaking time can be selected depending on the type of catfish, but is preferably 60 minutes or more, more preferably 80 minutes or more, more preferably 100 minutes or more, and even more preferably 120 minutes or more, which allows the solution to penetrate the fillets more easily, thereby shortening the processing time and improving productivity.

[0044] (heat treatment) The heat treatment of catfish is appropriately selected depending on the cooking method, and can be carried out using, for example, an oven, a microwave oven (microwave heating), grill heating, steam heating, heated steam, or the like. In the following examples, a microwave oven (microwave heating) was used. Microwave heating has high heating efficiency, can heat the entire fillet evenly, and can easily adjust the temperature because the microwave output can be freely controlled.

[0045] Example 1 We prepared farmed Pangasius fillets (Kuraray Co., Ltd. Pangasius hypophtalmus, Vietnam, frozen product) of the Pangasius family, thawed them at room temperature, and then cut them into fillets weighing approximately 25g each (processing process).The Pangasius fillets (frozen product) prepared here are fillets of Pangasius that have undergone the processes of bleeding, removing blood, filleting, deboning, skinning, trimming, and freezing. Next, trisodium phosphate (anhydrous trisodium phosphate manufactured by Mitejima Chemical Co., Ltd.) was prepared, and purified water was added to prepare an aqueous solution of trisodium phosphate so that the concentration of trisodium phosphate was 2.0% by weight. Citric acid (manufactured by RZBC) was added to the aqueous solution of trisodium phosphate thus obtained using a pH meter (pH METER F-13 manufactured by Horiba Ltd.) to adjust the pH to 7.0, thereby preparing a treatment solution (preparation step). Next, 1 part by weight of the pangasius fillets obtained in the processing step was prepared, and the fillets were immersed in 1 part by weight of the processing solution prepared in the preparation step, and left to stand in a refrigerated environment at 5°C for 16 hours (processing step). Next, the soaked Pangasius fillets were removed from the treatment solution and washed with pure water. Then, the fillets were placed in a plastic heat-resistant storage container, sealed with food wrap, and placed in a microwave oven (Hitachi Microwave Oven, Healthy Chef MRO-MBK3000) at 500W for 2.5 minutes to produce Pangasius fillets (heat treatment).

[0046] (Examples 2 to 4) Pangasius fillets were produced in the same manner as in Example 1, except that the concentration of trisodium phosphate was changed from 0.5% by weight to 4% by weight in the preparation process.

[0047] Examples 5 to 10 Pangasius fillets were produced in the same manner as in Example 1, except that the pH of the treatment solution was changed from 5 to 12 in the preparation step.

[0048] (Comparative Examples 1 and 2) Pangasius fillets were produced in the same manner as in Example 1, except that trisodium phosphate was replaced with sodium polyphosphate or disodium phosphate in the preparation process. (Comparative Examples 3 to 10) The same steps as in Example 1 were carried out, except that the fish species was changed from Pangasius of the order Siluriformes to horse mackerel or yellowtail, both of which are marine fish, and the type of alkali was changed to trisodium phosphate or sodium carbonate. The concentrations of trisodium phosphate or sodium carbonate and the pH of the treatment solution were as shown in Table 4.

[0049] (Weight measurement) The weight of the Pangasius fillets was measured using a weighing scale (A&D HF-2000). In Tables 1 to 4, the weight of the fillets obtained in the processing step is referred to as the "initial weight (g)," the weight of the fillets obtained in the soaking step divided by the initial weight is referred to as the "post-soaking yield (%)," the weight of the fillets obtained in the heating step divided by the initial weight is referred to as the "post-heating yield (%)," and the weight of the fillets obtained in the heating step divided by the weight of the fillets obtained in the soaking step is referred to as the "weight before and after heating (%)."

[0050] (Odor evaluation test) After the heating process, the fillets were removed, the moisture on the surface was wiped off, and then the fillets were cut into three pieces. Each fillet was then smelled and subjected to an odor evaluation test. As a result, samples that still had a muddy smell were rated as "X", samples that had a sufficiently reduced smell were rated as "△", and samples that had no detectable smell were rated as "◯".

[0051] (Texture evaluation test) After the heating process, the fillets were removed, the moisture on the surface was wiped off, and then the fillets were cut into three pieces. Each fillet was then eaten to evaluate its texture. As a result, fillets that had turned into jelly and had a bad texture (sticky) were rated as "X", and fillets that were moderately soft, plump, and elastic were rated as "O".

[0052] (Flavor evaluation test) After the heating process, the fillets were removed, the moisture on the surface was wiped off, and then the fillets were cut into three pieces. Each fillet was then eaten to conduct a taste evaluation test. As a result, those that could be tasted as sour and salty were rated as "X", those that could be tasted as the flavor of the ingredients with reduced sourness were rated as "△", and those that could be tasted as the flavor of the ingredients without any sour or salty taste were rated as "◯".

[0053] Table 1 shows the results of the above evaluation tests carried out on Examples 1 to 4, where the pH of the treatment solution was kept constant and the concentration of trisodium phosphate was varied.

[0054] [Table 1]

[0055] The test results showed that when the trisodium phosphate concentration was 0.5 wt%, the odor was sufficiently reduced (△), and when the trisodium phosphate concentration was 2.0 wt%, the muddy odor was not noticeable (◯). This is presumably because geosmin, the component of the muddy odor in the catfish, was consumed by trisodium phosphate, eliminating the catfish odor. Note that, as will be described later, when salts other than trisodium phosphate were used on pangasius, such a deodorizing effect was not obtained (Comparative Examples 1 and 2), and the deodorizing effect of trisodium phosphate was not observed on marine fish (Comparative Examples 3 to 10).

[0056] In Examples 1 to 4, the higher the concentration of trisodium phosphate, the greater the weight before and after heating, and the smaller the weight loss due to heating. This is thought to be because trisodium phosphate easily penetrates the body of the catfish and has water-retaining properties, so evaporation of water is suppressed even after heat treatment, reducing the weight loss. This allows for edible catfish with an excellent texture even after heating. Furthermore, in Table 1, although a larger amount of citric acid was added in Example 4 compared to Examples 1 and 2, the pH of the treatment solution was adjusted to around 7, so the sourness and bitterness specific to citric acid were suppressed, and the taste was also superior.

[0057] Furthermore, instead of the immersion step in Example 1, an immersion and shaking step was performed in which the fillets were placed in a shaker (Taitec Plus Shaker EP-1) in the treatment solution and shaken (30 times / minute) and an evaluation test was conducted. As a result, the same effect as in Example 1 was obtained in about 2 hours. Therefore, it is thought that shaking during immersion promotes the penetration of the treatment solution and its reaction with odorous components.

[0058] Furthermore, mass production tests of Pangasius were carried out as follows. That is, 250 g of pangasius fillets were prepared after the steps of bleeding, removing, filleting, deboning, skinning and trimming (processing step). Next, trisodium phosphate (6 parts by weight), citric acid (3 parts by weight) as an organic acid, sodium chloride (1 part by weight) as a seasoning, and trisodium citrate (0.5 parts by weight) as an additive were prepared and mixed with pure water to obtain a treatment solution with a pH of 7.0 and 2.0% by weight of trisodium phosphate (preparation process). Next, six fillets of Pangasius obtained in the processing step (total of 1500 g) and 3000 g of the processing liquid prepared in the preparation step were placed in a rotating barrel, and the fillets were immersed in the liquid while being stirred for 60 minutes, 80 minutes, and 100 minutes (immersion and shaking step). Next, the soaked pangasius fillets were removed from the treatment solution and washed with pure water, then frozen in a freezer (SANYO MDR-U333), and after a few days, thawed naturally at room temperature. Then, one fillet was placed in a plastic heat-resistant storage container, sealed with food wrap, and placed in a microwave oven (Hitachi Healthy Chef MRO-MBK3000) at 500W for 20 minutes (heat treatment). The resulting pangasius fillets were then subjected to an evaluation test. The results showed that the muddy smell was sufficiently reduced (△) when the soaking and shaking time was 60 minutes, but the muddy smell was completely absent (◯) when the soaking and shaking time was 80 or 100 minutes.

[0059] Table 2 shows the results of the above evaluation tests for Examples 5 to 10, where the concentration of trisodium phosphate used in the treatment solution was constant and the pH of the treatment solution was changed.

[0060] [Table 2]

[0061] The test results showed that when the pH of the treatment solution was 6.0, the sourness was suppressed while the saltiness was still noticeable and jelly formation was prevented, and when the pH of the treatment solution was 7.0 to 10.5, both the sourness and saltiness were sufficiently suppressed while jelly formation was prevented, resulting in fillets with excellent flavor and texture. Furthermore, when the organic acid added to the treatment solution was changed from citric acid to fumaric acid, the distinctive catfish odor was not detected.

[0062] Furthermore, when the appearance of the cross section of each fillet was checked, when the pH was 10.5 or less, the appearance was the same as that of fillets that had not been subjected to the soaking step, whereas when the pH was 11, the fillets had a slightly transparent appearance and a slightly yellowish appearance. Furthermore, when the pH was 12 or more (Example 7), the entire fillet was transparent and had turned yellow. This transparency remained the same after the heat treatment step; when the pH was 11, the appearance of the fillets was somewhat transparent, and when the pH was 12 or higher (Example 7), the entire fillet was transparent. Furthermore, when each fillet was frozen (in a Sanyo refrigerator for 24 to 48 hours), yellowing was more advanced when the pH was high than before freezing.

[0063] Furthermore, fillets of pangasius that were not immersed in any treatment solution had a muddy odor and had a hard, dry texture after cooking.

[0064] Table 3 shows the results of the above evaluation tests for Comparative Examples 1 and 2, in which trisodium phosphate was changed to sodium polyphosphate or disodium phosphate in the treatment liquid.

[0065] [Table 3]

[0066] The test results showed that the muddy smell of catfish could not be suppressed when sodium polyphosphate and disodium phosphate were used. Therefore, it was found that the muddy smell characteristic of catfish can be significantly eliminated when trisodium phosphate is used. Furthermore, similar to Comparative Examples 1 and 2, an evaluation test was conducted using sodium carbonate instead of trisodium phosphate, and the odor remained muddy (odor suppression: poor), and the entire fillet became transparent after soaking and turned into a sticky jelly (texture: poor).

[0067] The results of the evaluation tests carried out on Comparative Examples 3 to 10 are shown in Table 4.

[0068] [Table 4]

[0069] The test results showed that the saltwater fish horse mackerel and yellowtail did not have the fishy smell that is characteristic of saltwater fish when the treatment solution had a high pH, ​​regardless of the type of sodium salt contained in the treatment solution. This is presumably because the trimethylamine, which is the component that gives saltwater fish its fishy smell, is deodorized by protein denaturation and decomposition due to the pH of the treatment solution. Furthermore, in the case of saltwater fish, no significant difference was found in the trends of the evaluation results between trisodium phosphate and sodium carbonate. Therefore, it is believed that the effect of trisodium phosphate in the present invention is significant for catfish.

Claims

1. A method for producing edible catfish, comprising: A processing process in which catfish is cut into fillets; a preparation step of preparing 0.5% by weight to 4.0% by weight of trisodium phosphate, an organic acid, and water to obtain a treatment solution; A method for producing edible catfish, comprising a treatment step of immersing the catfish fillets in the treatment solution for one hour or more.

2. The method for producing edible catfish according to claim 1, wherein the catfish is Pangasius.

3. The method for producing edible catfish according to claim 1, further comprising a pH adjustment step of adjusting the amount of organic acid added in the preparation step to make the pH of the treatment solution 6 to 10.

5.

4. The method for producing edible catfish according to claim 1, wherein the pH of the treatment solution in the pH adjustment step is set to 7 to 8.

5. A method for producing edible catfish according to any one of claims 1 to 3, wherein the weight of the catfish fillets that have been heat-treated after the treatment step is 0.8 to 0.95 times the weight of the catfish fillets before the treatment step.

6. The method for producing edible catfish according to any one of claims 1 to 3, wherein in the treatment step, the soaking time is 12 hours or more, and the treatment solution is allowed to penetrate the catfish.

7. The method for producing edible catfish according to any one of claims 1 to 3, wherein in the treatment step, immersion and shaking is performed for one hour or more instead of the immersion, thereby allowing the catfish to permeate the treatment solution.

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