Frozen shrimp with head, frozen shrimp feed with head, method for producing frozen shrimp with head, and method for suppressing dropping of head of shrimp with head

Abstract

The present invention provides a frozen lobster with a head and frozen lobster feed that can prevent the head from falling off as compared with commercially available frozen lobsters with a head.SOLUTION: The frozen lobster with the head is obtained by treating lobster with an aqueous solution containing an acidic salt, saccharides and common salt, or a powder containing an acidic salt, saccharides and common salt, and then subjecting the lobster to freezing treatment, wherein the root of the head of the lobster is prevented from softening and falling off by autolysis when thawed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to head-on shrimp, frozen shrimp bait, a method for producing frozen shrimp bait, and a method for suppressing head loss from head-on shrimp, and in particular to head-on shrimp that can suppress the base of the head from softening and falling off due to autolysis, as well as frozen shrimp bait using the same, a method for producing frozen shrimp bait, and a method for suppressing head loss from head-on shrimp. [Background technology]

[0002] Shrimp in the distribution process, whether frozen or not, have high commercial value when they are in a head-on state, with the barbels, legs, and other protruding parts integrated into the body. This is true not only for food, but also for fishing bait, especially for Tenya fishing bait. Tenya fishing is a fishing method for targeting red sea bream by using a tool called red sea bream tenya, which has a large cone-shaped weight attached to the tip of a long-shafted hook (the tip is the hook, and the base of the tip is called the tip), and threading a sea shrimp as bait onto the tool. Tenya fishing itself is a traditional fishing method that has been passed down since the Edo period, but in recent years, the popularity of "hitotsu tenya," which uses the principles of tenya fishing and is easier to use, has been rapidly increasing. There are various baits for Hitotsutenya fishing, but since Hitotsutenya fishing is specialized for red sea bream fishing, sea shrimp is used. Live sea shrimp is the best sea shrimp to use as bait, but since it is difficult and expensive to obtain, frozen shrimp is generally used. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-085535 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-032443 Summary of the Invention [Problem to be solved by the invention]

[0004] In one-tenya fishing, the fish are attracted by a swaying motion, so headless shrimp or peeled shrimp without the head or legs attached look too unnatural and are difficult to catch. However, frozen shrimp often have their heads and legs removed, and the flesh softens due to autolysis, reducing the bait retention.

[0005] An object of the present invention is to provide frozen head-on shrimp and frozen shrimp bait that can suppress head loss compared to commercially available frozen head-on shrimp. [Means for solving the problem]

[0006] The present invention relates to frozen shrimp as described in (1) to (6) below. (1) Frozen head-on shrimp that have been treated with an aqueous solution containing an acid salt, sugars, and salt, or a powder containing an acid salt, sugars, and salt, and then frozen, so that the base of the head is prevented from softening and falling off due to autolysis upon thawing. (2) The frozen head-on shrimp according to (1) above, wherein the aqueous solution or the powder contains burnt alum as the acid salt. (3) The frozen head-on shrimp according to (1) above, wherein the aqueous solution or the powder contains less than 5% by mass of alum as the acid salt. (4) The frozen head-on shrimp according to (1) above, wherein the aqueous solution or the powder contains 1 to 30% by mass of sorbitol as the sugar. (5) The frozen head-on shrimp according to (1) above, wherein the aqueous solution or the powder contains 1 to 15% by mass of salt. (6) The frozen head-on shrimp according to (1) above, wherein the aqueous solution or the powder contains one or more amino acids that are umami components found in crustaceans.

[0007] The present invention also relates to a frozen shrimp bait described in (7) or (8) below. (7) A frozen shrimp bait using the frozen head-on shrimp according to any one of (1) to (6) above. (8) The frozen shrimp bait described in (7) above, which is a shrimp bait exclusively for frozen Tenya. Furthermore, the present invention provides a method for producing frozen head-on shrimp as described in (9) below. (9) A method for producing frozen head-on shrimp, which comprises treating head-on shrimp with an aqueous solution containing burnt alum, sugars and salt, or with a powder containing burnt alum, sugars and salt, and then freezing the shrimp. Additionally, the present invention provides a method for inhibiting head loss in head-on shrimp as described in (10) below. (10) A method for preventing head-on shrimp from losing their heads when frozen head-on shrimp are thawed, which comprises treating the head-on shrimp with an aqueous solution containing baked alum, sugars, and salt, or with a powder containing baked alum, sugars, and salt, and then freezing the shrimp. [Effects of the Invention]

[0008] According to the present invention, head-on shrimp are treated with an aqueous solution containing an acid salt, sugars, and salt, or a powder containing an acid salt, sugars, and salt, before being frozen. This makes it possible to prevent the heads from falling off when the frozen head-on shrimp are thawed, compared to commercially available frozen head-on shrimp. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a table showing the measurement results of the longitudinal shear force and lateral shear force at the base of the neck of head-on shrimp according to the type of acid salt, and the measurement results of the tensile strength at the base of the neck. [Figure 2] 1 is a table showing the composition of the soaking liquid when the condition of the neck of head-on shrimp was visually evaluated according to the type of acid salt. [Figure 3] This table shows the results of visually evaluating the condition of the neck of head-on shrimp according to the number of jerks, while changing the concentration of sorbitol, the concentration of baked alum, and the size of the head-on shrimp, and also shows the measurement results of the tensile strength at the base of the neck. [Figure 4]This table shows the results of visually evaluating the condition of the neck of head-on shrimp according to the number of jerks when additives such as propylene glycol, sodium lactate preparations, bleach, and synthetic coloring agents were added, as well as the results of measuring the longitudinal shear force and lateral shear force at the base of the neck and the tensile strength at the base of the neck. [Figure 5] This table shows the results of visually evaluating the condition of the neck of head-on shrimp according to the number of jerks when additives such as acid meta, malic acid, citric acid, and synthetic coloring were added, as well as the results of measuring the longitudinal shear force and lateral shear force at the base of the neck and the tensile strength at the base of the neck. [Figure 6] 1 is a table showing the measurement results of the longitudinal shear force and lateral shear force at the base of the neck of head-on shrimp according to this example and commercially available head-on shrimp, and the measurement results of the tensile strength at the base of the neck. [Figure 7] 10 is a table showing the results of evaluating the state of head-on shrimp according to the present embodiment and commercially available head-on shrimp according to the number of times the automatic shredder performed the shredder. [Figure 8] 10 is a table showing the results of evaluating the state of the head-on shrimp according to the present embodiment and commercially available head-on shrimp as shrimp bait according to the number of jerking movements in an actual fishing test. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the frozen head-on shrimp according to the present invention will be described.

[0011] (Shrimp) Any type of edible shrimp can be used as shrimp bait in this embodiment. Examples of such shrimp include pistol shrimp, kuruma prawn, black tiger shrimp, vannamei shrimp, shiba shrimp, monkey shrimp, fan shrimp, Japanese tiger shrimp, octopus shrimp, octopus shrimp, otoko shrimp, spiny lobster, snow lobster, cherry shrimp, glass shrimp, northern red shrimp (Panthera crustacea), nephrops prawn, isoparasite shrimp, Pandalus nigricans, koshima grove shrimp, ruffed grass shrimp, freshwater shrimp, striped shrimp, freshwater shrimp, crayfish, and red swamp crayfish. The origin of the shrimp is not particularly limited. In this embodiment, shrimp caught in the Seto Inland Sea of ​​Japan are used as shrimp bait. Hereinafter, shrimp used as shrimp bait will also be referred to simply as "shrimp."

[0012] (immersion liquid) In order to maintain the freshness of the head-on shrimp, the head-on shrimp are frozen in this embodiment. Furthermore, in this embodiment, before freezing the head-on shrimp, the shrimp are pre-treated by immersing them in the immersion liquid according to this embodiment. The immersion liquid according to this embodiment is described below.

[0013] The soaking solution according to this embodiment contains an acid salt, sugars, and salt, and is used to suppress autolysis of heads of head-on shrimp during thawing and to prevent the heads from falling off. The acid salt acts as an inhibitor of the autolytic enzyme in head-on shrimp, suppressing autolysis of the heads. The sugars and salt are also thought to strengthen the muscles in the heads and increase their strength.

[0014] In this embodiment, the acid salt contained in the immersion solution is not particularly limited, but calcium lactate or alum can be used, and alum is more preferred. This is because calcium lactate tends to precipitate at high pH levels. In the present invention, alum refers to a double salt of a sulfate of a monovalent cation and a sulfate of a trivalent metal ion, and includes hydrates and anhydrides. However, it is preferable to use calcined alum, which is an anhydrous alum. Alums include potassium aluminum sulfate or its anhydride, as well as ammonia alum, soda alum, chrome alum, alum sulfate, and their anhydrides. However, potassium aluminum sulfate or its anhydride is preferred. In the present invention, the term "calcined alum" refers to anhydrous potassium aluminum sulfate, and the term "alum" refers to all of the above types of alum.

[0015] The content of the acid salt is not particularly limited, but when the acid salt is alum, it has a bleaching effect but is not desirable to use it at an excessively high concentration, and is preferably less than 5.0% by mass of the entire soaking solution, more preferably 3.0% by mass or less, and even more preferably 2.0% by mass or less. On the other hand, in order to inhibit the action of autolytic enzymes, the acid salt is preferably 0.1% by mass or more of the entire soaking solution, more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more.

[0016] The sugars contained in the immersion liquid are not particularly limited, but include sugar alcohols such as sorbitol and xylitol, monosaccharides such as glucose and fructose, disaccharides such as sucrose, and polysaccharides such as pectin. In this embodiment, a sorbitol solution is used as the sugar. The sugar content is also not particularly limited, but can be 1.0 to 30.0% by mass, more preferably 5.0 to 20.0% by mass, and even more preferably 8.0 to 15.0% by mass of the entire immersion liquid.

[0017] Furthermore, the immersion liquid according to this embodiment may contain salt. The salt content is not particularly limited, but is preferably 0.1 to 15.0% by mass, more preferably 0.5 to 10.0% by mass, and even more preferably 0.8 to 3.0% by mass.

[0018] Furthermore, the soaking liquid may contain the following additives. For example, the soaking liquid may contain shrimp flavor components. Specifically, the soaking liquid may contain shrimp flavor components such as amino acids such as glycine, alanine, glutamic acid, and betaine, nucleotides (nucleic acid-related substances) such as 5'-inosinic acid, and organic acid salts such as lactic acid and succinic acid. In particular, in this embodiment, the soaking liquid may contain one or more amino acids, namely, glycine and alanine, or may contain two or more amino acids. Glycine and alanine are amino acids that have a sweet taste. Soaking shrimp in the soaking liquid improves the taste of the edible parts of the shrimp, synergistically with the saltiness of the alkali salt, which will be described later.

[0019] The immersion liquid may also contain amino acids other than glycine and alanine. For example, in this embodiment, the immersion liquid may contain free asparagine and free aspartic acid, with the total concentration of the free asparagine and free aspartic acid preferably being 0.002 to 0.3 wt %, more preferably being 0.0025 to 0.2 wt %, and even more preferably being 0.005 to 0.1 wt %. The immersion liquid may also contain citric acid, with the concentration of the citric acid being 0.1 to 20.0 wt %, preferably being 0.14 to 10.0 wt %, and even more preferably being 0.4 to 3.0 wt %. The immersion liquid may also contain malic acid, with the concentration of the malic acid being preferably being 0.02 to 4.0 wt %, more preferably being 0.02 to 2.0 wt %, and even more preferably being 0.05 to 0.5 wt %. The organic acid contained in the immersion liquid is added and adjusted to the above-mentioned concentration when the immersion liquid is prepared.

[0020] Furthermore, the soaking liquid may contain an alkaline salt. In this embodiment, the soaking liquid may contain an inorganic alkaline salt such as sodium chloride or a polyphosphate, or an organic alkaline salt such as a citrate or a lactate. The sodium chloride concentration in the soaking liquid may preferably be up to 5.0% by weight, more preferably 0.1 to 5.0% by weight, and even more preferably 0.4 to 3.5% by weight. The sodium chloride concentration in the soaking liquid may be adjusted depending on the level of saltiness desired for the shrimp bait after soaking. The sodium chloride contained in the soaking liquid is added and adjusted to the above concentration when the soaking liquid is prepared.

[0021] Furthermore, the soaking solution may contain alkali metal salts or alkaline earth metal salts other than sodium chloride. By adding such salts, the pH of the soaking solution can be increased, thereby improving the yield of shrimp pickled and enhancing the effect of inhibiting discoloration. Such salts are preferably edible, and specific examples include sodium salts, potassium salts, calcium salts, and magnesium salts.

[0022] The pH of the soaking solution is not particularly limited, but is preferably 7.0 to 10.0, more preferably 7.0 to 9.7, and even more preferably 7.0 to 9.4. If the pH becomes low, it can be adjusted to within the above pH range using an aqueous sodium hydroxide solution or the like. By adjusting the soaking solution to the alkaline side, the yield of shrimp to be soaked can be improved, or the discoloration suppression effect can be enhanced. The above pH is the value at the temperature during soaking.

[0023] The ionic strength of the soaking solution is not particularly limited, but is preferably 0.5 to 3.0 mol / kg, more preferably 0.55 to 3.0 mol / kg, and even more preferably 0.60 to 3.0 mol / kg. A higher ionic strength of the soaking solution can improve the yield of shrimp to be soaked or enhance the effect of inhibiting discoloration. Note that the above ionic strength refers to the "aqueous solution ionic strength," which is calculated by adding up the molar concentration of each ion and the square of its charge for all ionic species in the solution and dividing the sum by half.

[0024] However, when shrimp are immersed in the immersion solution according to this embodiment, the "total ionic strength" is preferably 0.2 to 1.5 mol / kg, more preferably 0.3 to 1.5 mol / kg, and even more preferably 0.4 to 1.5 mol / kg. This is because even if the aqueous solution ionic strength of the immersion solution is determined, the effect will change if the amount of immersion solution relative to the shrimp changes. The "total ionic strength" is defined as "(aqueous solution ionic strength × amount of aqueous solution) / (amount of aqueous solution + shrimp weight)" assuming that the weight of shrimp is the amount of water.

[0025] The aqueous solution ionic strength and total ionic strength can be adjusted using edible organic acid salts and / or inorganic acid salts, specifically, any one or combination of sodium salts, potassium salts, calcium salts, magnesium salts, or any one or combination of citrates, carbonates, bicarbonates, ascorbic acid, erythorbate, lactates, succinates, acetates, malates, fumarates, gluconates, polymerized phosphates, and hydrochlorides. More specifically, preferred examples include sodium chloride, trisodium citrate, potassium chloride, tripotassium citrate, calcium citrate, sodium lactate, sodium succinate, sodium acetate, sodium malate, sodium fumarate, sodium gluconate, potassium gluconate, calcium gluconate, calcium lactate, magnesium chloride, calcium chloride, sodium erythorbate, and polymerized phosphates.

[0026] (Frozen product) The frozen head-on shrimp bait according to this embodiment is distributed and sold in a frozen state. Compared to conventional frozen head-on shrimp bait, the frozen head-on shrimp bait according to this embodiment is able to prevent heads from falling off after thawing. Furthermore, the frozen head-on shrimp bait according to this embodiment can suppress dripping due to thawing and can also maintain the firm texture of the shrimp meat. Furthermore, the frozen head-on shrimp bait contains high concentrations of salty and flavorful components, and thawing synergistically improves the flavor and allows the shrimp to be restored to a state with improved muscle and body color.

[0027] (Quality assessment of shrimp feed) Many methods for assessing the quality of shrimp feed have been developed, broadly classified as sensory, physical, microbiological, and chemical. Shrimp feed quality assessment involves determining whether shrimp morphology, color, flavor, meat texture, selection, and glaze meet certain standards. In particular, frozen shrimp feed is required to be processed using clean water and to ensure a uniform glaze to prevent the shrimp from drying out. It is also important to ensure that the core temperature of the frozen shrimp is below -10°C, that the content weight matches the labeled weight, that packaging materials are hygienic and strong enough to prevent damage to the contents, that size and other labeling information matches the contents, and that there is no foreign matter present. To assess the level of spoilage, volatile base nitrogen must be below 30 mg per 100 g of sample; there must be no ammonia, trimethylamine, or hydrogen sulfide odor; the bacterial count (viable cell count) must be below 100,000 per 1 g of sample; and the E. coli count must be negative per 100 g.

[0028] The frozen head-on shrimp according to this embodiment can be prevented from losing their heads after thawing by soaking the shrimp in the soaking liquid according to this embodiment. In other words, the present invention provides a method for producing frozen head-on shrimp that can prevent head loss after thawing, and also provides a method for preventing head loss from head-on shrimp. Furthermore, the frozen head-on shrimp according to this embodiment are not only suitable as frozen head-on shrimp bait, because the presence of the heads affects the bite of fish and makes them less likely to fall off even when fishing with a fishing rod, but also suitable for use as shrimp for human cooking. In particular, there is a high demand for head-on shrimp as an ingredient in dishes in which shrimp are served with their heads attached, and these shrimp are suitable for use as shrimp for such dishes.

[0029] (Pickling process) Shrimp for shrimp bait are reared for 2 to 24 hours, preferably 3 to 8 hours, in environmental water with a salinity of 85% to 150% of seawater's salinity (3.4%), preferably 105% to 135% of seawater's salinity (3.4%). The water temperature is preferably 20°C to 45°C, more preferably 25°C to 38°C. Rearing shrimp using this rearing process can increase the content of flavor components in the shrimp. Specifically, the edible parts of the shrimp have improved content of at least one of the flavor components: glycine, alanine, glutamic acid, proline, threonine, and serine, and also have an improved texture. Furthermore, this rearing process imparts a moderate saltiness to the muscles, improving the flavor through a synergistic effect between the saltiness and the flavor.

[0030] Shrimp can be soaked at a temperature that does not affect the quality of the crustaceans, typically 0 to 20°C. The soaking time can be set to 1 second to 48 hours, more preferably 1 second to 24 hours, and even more preferably 1 second to 18 hours, depending on the size and shape of the shrimp, the allowable bacterial count, and the storage period after thawing. If the shrimp after soaking are to be eaten raw, they can be soaked for 1 second to 10 minutes, preferably 1 second to 5 minutes, and even more preferably 1 second to 1 minute. If the shrimp after soaking are to be cooked, they can be soaked for 1 second to 48 hours, preferably 10 minutes to 24 hours, and even more preferably 1 hour to 18 hours. If the shrimp is to be cooked, they will be displayed in supermarkets and the like for several days after thawing, and therefore discoloration must be suppressed for a long period of time. Therefore, it is preferable to soak them for a longer time than if they are to be eaten raw.

[0031] The immersion method may be either immersing the head-on shrimp in the immersion liquid or spraying the immersion liquid on the surface of the head-on shrimp. The immersion liquid may be a seasoning liquid used for pickling fish (miso-pickled, sake lees-pickled, saikyo-zuke, etc.). It is preferable to immerse the head-on shrimp in the immersion liquid while they are still alive, but frozen head-on shrimp or non-living head-on shrimp may also be immersed in the immersion liquid.

[0032] There is no particular upper limit to the soaking time, but it is not necessary to soak the shrimp for longer than necessary so as not to affect the quality of the head-on shrimp, and it is preferable to set an appropriate time in relation to other processes. For example, it is preferable to soak the head-on shrimp in the soaking liquid for 3 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. On the other hand, it is preferable to soak the head-on shrimp in the soaking liquid for 120 minutes or less, more preferably 100 minutes or less, and even more preferably 80 minutes or less.

[0033] The amount of the soaking liquid to be used to soak the head-on shrimp is not particularly limited, but is preferably 10 to 500% by mass, more preferably 50 to 400% by mass, and even more preferably 80 to 250% by mass, of the weight of the head-on shrimp. The temperature at which the head-on shrimp are soaked in the soaking liquid is also not particularly limited, but is preferably -10 to 30°C, more preferably 0 to 20°C, and even more preferably 3 to 10°C.

[0034] The soaking solution according to the present embodiment contains an acid salt, particularly alum, in an amount less than 5% by mass of the total solution. This inhibits the activity of autolytic enzymes when frozen head-on shrimp are thawed, thereby preventing head loss from occurring after thawing. Furthermore, the use of burnt alum among alums can prevent head loss from occurring after thawing by approximately twice as much as using raw alum. Furthermore, the soaking solution according to the present embodiment contains sugars, particularly sorbitol, in an amount less than 5% by mass of the total solution, and further contains salt in the range of 1 to 15% by mass of the total solution, thereby strengthening the muscles at the base of the head and preventing head loss from occurring after thawing. Furthermore, the soaking solution according to the present embodiment can also prevent discoloration due to the reducing effect caused by the reaction of organic acids, such as citric acid and malic acid, with sodium chloride and / or alkali metal salts to generate organic acid salts in the soaking solution. It is also possible that the antioxidant effects of organic acids such as citric acid and malic acid and / or polyphenols may inhibit the oxidation of pigment proteins, carotenoid pigments, or phospholipids, thereby preventing discoloration.

[0035] As used herein, "discoloration" refers to the browning or fading of the shrimp's original red color. Furthermore, "inhibition of discoloration" includes reducing the degree of browning or fading compared to untreated shrimp, slowing its progression, and / or maintaining the original red color. In particular, with regard to shrimp, this includes the inhibition of blackening.

[0036] It has been found that treatment with the soaking solution according to this embodiment can suppress discoloration even after freezing at -30°C to -5°C for 1 day to 12 months and then thawing. Furthermore, if the shrimp after soaking is intended for raw consumption, the suppression of discoloration can be achieved even after storage at 2°C to 15°C for 1 hour to 12 hours after thawing. Furthermore, if the shrimp after soaking is intended for cooking, the suppression of discoloration can be achieved even after storage at 2°C to 15°C for 1 day to 5 days after thawing.

[0037] After marinating, the shrimp can be frozen at -80 to -5°C, preferably -70 to -10°C, and more preferably -65 to -20°C. Freezing can be slow or rapid, with rapid freezing being preferred. The shrimp can be frozen after the marinating liquid has been removed, or with the marinating liquid still attached to the shrimp.

[0038] The frozen shrimp can be stored at -60°C to -5°C, preferably -50°C to -20°C, and more preferably -45°C to -25°C, for 1 day to 12 months. Frozen storage can include storage in a freezer, transportation at frozen temperatures, and product display at frozen temperatures. The frozen shrimp can be thawed at 0 to 40°C by thawing with air, thawing under running water, thawing in standing water, or natural thawing.

[0039] By such a treatment, frozen head-on shrimp or frozen head-on shrimp feed can be obtained that has been pickled and then frozen or frozen-stored.Furthermore, head-on shrimp or head-on shrimp feed can be obtained by thawing frozen head-on shrimp or frozen head-on shrimp feed that has been pickled and then frozen or frozen-stored. [Example]

[0040] The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0041] In this example, monkey shrimp, which are abundant in the Seto Inland Sea, were used as head-on shrimp. Monkey shrimp are relatively small shrimp with a body length of about 10 cm. In the following description, the monkey shrimp with a head used in this example will be simply referred to as "head-on shrimp."

[0042] In this example, first, the immersion solutions of Examples 1 to 3 and Comparative Examples 1 and 2 were prepared. As shown in FIG. 1, the immersion solutions of Examples 1 to 3 all contained 3 mass% salt and 10 mass% sorbitol. Also, as shown in FIG. 1, the immersion solution of Example 1 contained 1 mass% burnt alum as an acid salt, the immersion solution of Example 2 contained 1 mass% citric acid (anhydrous) as an acid salt, and the immersion solution of Example 3 contained 1 mass% fumaric acid as an acid salt. Also, as shown in FIG. 1, Comparative Examples 1 and 2 both contained no acid salt and 3 mass% salt. Furthermore, Comparative Example 1 did not contain sorbitol, and Comparative Example 2 contained 5 mass% sorbitol. FIG. 1 shows the test results of Examples 1 to 3 and Comparative Examples 1 and 2.

[0043] Live head-on shrimp were then immersed in the immersion liquids of Examples 1 to 3 and Comparative Examples 1 and 2 at a ratio of head-on shrimp to immersion liquid of 1:2. In Examples 1 to 3 and Comparative Example 2, the shrimp were immersed in the immersion liquid at 4°C for 30 minutes, while in Comparative Example 1, the shrimp were immersed in the immersion liquid at 4°C for 15 minutes. The head-on shrimp were then stored frozen at -20°C for one month while still immersed in the immersion liquid. The frozen head-on shrimp of Examples 1 to 3 and Comparative Examples 1 and 2 were then thawed, and a rheometer was used to measure the longitudinal shear force and lateral shear force at the base of the head-on shrimp's neck, as well as the tensile strength at the base of the head-on shrimp's neck. In these examples, a "sun RHEO METER CR-100" manufactured by Sun Scientific Co., Ltd. was used as the rheometer.

[0044] FIG. 1 shows the results of measuring the longitudinal shear force, lateral shear force, and tensile strength of the base of the neck of head-on shrimp in Examples 1 to 3. As shown in FIG. 1, in Examples 1 to 3, the tensile strength and longitudinal shear force were more than twice as high as those of Comparative Examples 1 and 2 because the soaking solution contained an acid salt. In particular, the tensile strength and longitudinal shear force were greatest when alum was used as the acid salt. This indicates that it is preferable for the soaking solution to contain an acid salt, and it is more preferable to use alum as the acid salt, which can increase the tensile strength and longitudinal shear force of the base of the neck of thawed head-on shrimp and prevent the heads from falling off.

[0045] In Examples 4 and 5, the condition of frozen head-on shrimp after thawing was visually evaluated using a soaking solution containing components other than acid salts, sugars, and salt, as shown in Figure 2. Specifically, the soaking solutions for Examples 4 and 5 both contained 25% by mass of sorbitol, 2.5% by mass of glycine, 1.5% by mass of alanine, 1.5% by mass of monosodium glutamate, 0.2% by mass of sodium inosinate, 1.0% by mass of a curing agent (a complex preparation primarily composed of alkaline polyphosphate), and 3.0% by mass of salt. Example 4 contained 2.5% by mass of burnt alum as the acid salt, and Example 5 contained 2.5% by mass of calcium lactate as the acid salt. The curing agent used was "Curing Agent HP" manufactured by Hamada Food Systems Co., Ltd.

[0046] In Examples 4 and 5, head-on shrimp were immersed in a 4°C immersion solution for 30 minutes at a shrimp:soaking solution ratio of 1:2. The shrimp were then frozen at -20°C for one month while still immersed in the immersion solution. The frozen shrimp of Examples 4 and 5 were then thawed, and the condition of the base of the neck of each thawed shrimp was visually inspected and evaluated. Specifically, in both Examples 4 and 5, no gaps were formed between the heads and the base of the neck, and no head loss was observed. However, in Example 5, calcium lactate reacted with the phosphate curing agent, resulting in precipitation, indicating that calcined alum is preferable as the acid salt.

[0047] In the example shown in Figure 3, Examples 6 to 13 were prepared by varying the sorbitol concentration, the baked alum concentration, and the size of the head-on shrimp. The condition of the head-on shrimp's neck was visually inspected and evaluated according to the number of times the shrimp was jerked, and the tensile strength of the base of the head-on shrimp's neck immediately after thawing was measured. The soaking solutions in Examples 6 to 13 all contained 3.0 wt% salt, 1.0 wt% glycine, 1.0 wt% monosodium glutamate, and 0.1 wt% disodium inosinate. Examples 6, 7, 10, and 11 contained 10.0 wt% sorbitol, while Examples 8, 9, 12, and 13 contained 5.0 wt% sorbitol. Furthermore, Examples 6 to 9 contained 1.0 wt% baked alum, and Examples 10 to 13 contained 0.5 wt% baked alum. Additionally, medium-sized head-on shrimp were used in Examples 6, 8, 10, and 12, while large-sized head-on shrimp were used in Examples 7, 9, 11, and 13. In Comparative Examples 3 and 4, head-on shrimp soaked in seawater without the addition of sorbitol or burnt alum were used.

[0048] In the example shown in Figure 3, live head-on shrimp were procured from a fishery company and immersed in immersion liquid for two hours in a cooler box (5-10°C) at a head-on shrimp to immersion liquid ratio of 1:2. The shrimp were then frozen and stored at -30°C for one month while still immersed in the immersion liquid. In the example shown in Figure 3, thawed frozen head-on shrimp were attached to a fishing rod, and the fishing rod with the head-on shrimp attached was jerked up and down alternately using an automatic jerker and by hand in tap water at a temperature of 26°C (125 jerks using the automatic jerker followed by 10 jerks by hand, repeated). The condition of the gap at the base of the head of each head-on shrimp was evaluated by comparing it with that of fresh, raw shrimp. The evaluation of the neck condition of head-on shrimp according to the number of jerks was as follows: if the condition was the same as that of raw head-on shrimp, it was given 100 points; if the gap at the base of the head was slightly wider than that of raw head-on shrimp but the base was strong, it was given 80 points; if the gap at the base of the head was wider than that of raw head-on shrimp but the base was strong and the head had not fallen off, it was given 60 points; if the gap at the base of the head was wider than that of raw head-on shrimp and the head was on the verge of falling off, it was given 40 points; if the gap at the base of the head was significantly wider and the head was on the verge of falling off, it was given 20 points; and if the head had fallen off, it was given 0 points.

[0049] As shown in Figure 3, it was found that large head-on shrimp tended to have less head loss than medium-sized shrimp. Regarding the amount of sorbitol added, there was a slight tendency for the heads to be less likely to fall off when added at 10.0 wt% compared to 5.0 wt%, but the difference was not significant. The amount of burnt alum added also showed similar results when added at 0.5 wt% and 1.0 wt%. From these results, it was found that a sorbitol content of 5.0 wt% or more is preferable, and a burnt alum content of 0.5 wt% or more is also preferable. Furthermore, when comparing head-on shrimp of the same size, the tensile strength of the necks of head-on shrimp was greater in Examples 6 to 13 than in Comparative Examples 3 and 4.

[0050] Next, in Figure 4, Examples 14 to 21 were prepared by varying the sorbitol concentration and adding a sodium lactate preparation, bleach, and synthetic coloring. The condition of head-on shrimp necks was visually inspected and evaluated according to the number of jerks, and the vertical shear force, horizontal shear force, and tensile strength of the neck base of head-on shrimp immediately after thawing were measured. Specifically, the soaking solutions in Examples 14 to 21 shown in Figure 4 all contained 3.0 wt% salt, 1.0 wt% glycine, 1.0 wt% monosodium glutamate, 0.1 wt% disodium inosinate, and 1.0 wt% baked alum. The soaking solutions in Examples 14, 15, 18, and 21 contained 10.0 wt% sorbitol, and the soaking solutions in Examples 16, 17, 19, and 20 contained 20.0 wt% sorbitol. Furthermore, the soaking solutions of Examples 15, 17, 19 to 21 contain 1.0 wt% of a sodium lactate preparation, the soaking solutions of Examples 18 and 19 contain 0.3 wt% of a bleaching agent, and the soaking solutions of Examples 20 and 21 further contain 0.1 wt% of a coloring synthetic agent.

[0051] In the example shown in Figure 4, head-on shrimp were immersed in a 5°C immersion solution for 30 minutes at a shrimp:soaking solution ratio of 1:2, and then frozen and stored at -30°C for one month. The evaluation of the neck condition of head-on shrimp according to the number of jerks was performed in the same manner as in the example shown in Figure 3. The jerking motion was also performed in tap water at 26°C using an automatic jerker 125 times, followed by 10 manual jerks, as in the example shown in Figure 3.

[0052] As shown in Figure 4, there was no significant difference between Examples 14, 15, 18, and 21, which contained 10.0 wt% sorbitol, and Examples 16, 17, 19, and 20, which contained 10.0 wt% sorbitol, indicating that a sorbitol content of 10.0 wt% or more is preferable. Furthermore, there was no significant difference between the presence or absence of sodium lactate preparations and the presence or absence of bleaching agents. Furthermore, when synthetic coloring agents were added, there was a tendency for the heads to fall off more easily.

[0053] Next, in Figure 5, Examples 22 to 31 were prepared by varying the concentration of sorbitol and adding acidic metaphosphoric acid, malic acid, citric acid, and synthetic coloring. The condition of head-on shrimp necks was visually inspected and evaluated according to the number of jerks, and the vertical shear force, horizontal shear force, and tensile strength of the neck base of head-on shrimp immediately after thawing were measured. In the examples shown in Figure 5, two freezing and preservation methods were performed: one in which head-on shrimp were immersed in an immersion solution and then frozen while still immersed, and the other in which head-on shrimp were removed from the immersion solution, vacuum-packaged, and frozen. Specifically, the immersion solutions in Examples 22 to 31 shown in Figure 5 all contained 3.0 wt% salt, 1.0 wt% glycine, 1.0 wt% monosodium glutamate, 0.1 wt% disodium inosinate, and 1.0 wt% roasted alum. The soaking solutions of Examples 22, 23, 26, 29, and 31 contained 10.0 wt% sorbitol, and those of Examples 24, 25, 27, 28, and 30 contained 20.0 wt% sorbitol. The soaking solutions of Examples 24 and 25 contained 1.0 wt% acidic metaphosphoric acid, those of Examples 26 and 27 contained 0.5 wt% malic acid, those of Examples 28 and 29 contained 0.5 wt% citric acid, and those of Examples 30 and 31 contained 0.04 wt% synthetic coloring agent (R106). In Examples 22, 24, 26, and 28, the head-on shrimp were immersed in the soaking solution and frozen while still immersed, while in Examples 23, 25, 27, 29 to 31, the head-on shrimp were removed from the soaking solution, vacuum-packed, and frozen. In this example, Liquid Ultra (50% metaphosphoric acid solution) manufactured by Polyphos Chemical Laboratory was used as the acidic metaphosphoric acid.

[0054] In the example shown in Figure 5, head-on shrimp were immersed in a 5°C immersion solution for 30 minutes at a shrimp:soaking solution ratio of 1:2, and then frozen and stored at -30°C for one month. The evaluation of the neck condition of head-on shrimp according to the number of jerks was performed in the same manner as in the examples shown in Figures 3 and 4. The jerking motion was also performed in tap water at 26°C using an automatic jerking machine 125 times, followed by 10 manual jerks, as in the examples shown in Figures 3 and 4.

[0055] As shown in Figure 5, Examples 22, 24, 26, and 28, in which head-on shrimp were immersed in the immersion liquid and frozen while still immersed, tended to suppress head loss compared to Examples 23, 25, 27, and 29-31, in which head-on shrimp were removed from the immersion liquid, vacuum-packaged, and frozen. Furthermore, while it is preferable to use burnt alum as an acid salt, adding organic acids such as acid methyl cellulose, malic acid, or citric acid in addition to burnt alum did not have a significant effect on head loss.

[0056] In addition, in the example shown in Figure 6, the vertical shear force, horizontal shear force, and tensile strength of the neck base of head-on shrimp immediately after thawing were measured for Example 32, a frozen head-on shrimp according to the present embodiment, and commercially available frozen head-on shrimp (Comparative Examples 5 to 11). As shown in Figure 6, the vertical shear force at the neck base of the head-on shrimp of Example 32 was the highest among Example 32 and Comparative Examples 5 to 11, and the horizontal shear force at the neck base of the head-on shrimp was the second highest among Example 32 and Comparative Examples 5 to 11. Furthermore, the tensile strength at the neck base of the head-on shrimp of Example 32 was the highest among Example 32 and Comparative Examples 5 to 11. Specifically, the vertical shear force at the neck base of the head-on shrimp of Example 32 was approximately 1.2 times the average of Comparative Examples 5 to 11, and the horizontal shear force at the neck base was approximately 1.3 times the average of Comparative Examples 5 to 11. Furthermore, the tensile strength of the head-on shrimp of Example 32 at the base of the neck was approximately 3.15 times the average value of Comparative Examples 5 to 11, which was a significant improvement over Comparative Examples 5 to 11. As such, it was found that the frozen head-on shrimp of this embodiment has a strength of the meat that is closer to that of live head-on shrimp and has the property of making the head less likely to come off compared to commercially available frozen head-on shrimp.

[0057] Next, in the example shown in Figure 7, the head-on shrimp of Example 32 and the head-on shrimp of Comparative Examples 5 to 10 were visually inspected and evaluated for the condition of their necks according to the number of jerks. The evaluation of the condition of the head-on shrimp's neck according to the number of jerks was performed in the same manner as in the examples shown in Figures 3 to 5. The jerking motion was also performed in the same manner as in the examples shown in Figures 3 to 5. As shown in Figure 7, in Example 32 and Comparative Example 5, even before the jerking motion began (zero jerking motions), the head-on shrimp were in a state similar to raw head-on shrimp and were rated 100 points. However, in Comparative Examples 6 to 10, when thawed, there was a small gap at the base of the head compared to raw head-on shrimp, and they were rated 80 points. In Comparative Examples 8 and 10, the head fell off after 250 scooping movements with the automatic scooping machine and 10 hand movements. In Comparative Example 7, the head fell off after 375 scooping movements with the automatic scooping machine and 10 hand movements. In Comparative Example 9, the head fell off after 1000 scooping movements with the automatic scooping machine. In Comparative Example 2, the head fell off after 1000 scooping movements with the automatic scooping machine and 10 hand movements. Furthermore, in Comparative Example 1, the head fell off after 1250 scooping movements with the automatic scooping machine and 10 hand movements. In contrast, in the Examples, even after 1450 scooping movements with the automatic scooping machine and 10 hand movements, the gap at the base of the head widened significantly, and the head was on the verge of falling off, but it did not fall off. From this, it was found that the heads of the headed shrimp of Example 32 were less likely to come off even when the jerking motion was performed, compared to the headed shrimp of Comparative Examples 5 to 10, and that tenaya fishing could be performed in a state similar to that of raw headed shrimp.

[0058] Furthermore, in the example shown in Figure 8, tenaya fishing was conducted at an actual fishing spot using head-on shrimp from Example 32 and Comparative Examples 5 to 11, and the condition of the head-on shrimp bait was evaluated for each number of jerking movements. Figure 3 is a table showing the evaluation results of the number of jerking movements and the condition of the shrimp bait in the actual fishing test. Specifically, jerking movements were performed vertically on sandy ground at a depth of 20 to 30 meters off the coast of Shido Bay in Kagawa Prefecture, and the condition of the head of each head-on shrimp was evaluated using the same evaluation method as in the examples shown in Figures 3 to 5 and 7. In the example shown in Figure 8, a single-stage jerking was performed for the head-on shrimp from Comparative Examples 5 to 10, and a two-stage jerking was performed for the head-on shrimp from Example 32.

[0059] As shown in Figure 8, even in the actual fishing test, the head-on shrimp of Example 32 was less likely to fall off and retained the bait better than the head-on shrimp of Comparative Examples 5 to 10, despite the two-stage jerking technique, which places more strain on the head-on shrimp than the one-stage jerking technique of Comparative Examples 5 to 10. Specifically, the shrimp bait of Example 32 was rated 70 points, indicating that the base was strong enough and the head did not fall off even after 70 two-stage jerks. Furthermore, the shrimp bait of Example 32 attracted more fish, such as red sea bream, when used in tenaya fishing than the head-on shrimp of Comparative Examples 5 to 10. Furthermore, the actual fishing test revealed that the shrimp bait of Example 32 can be used appropriately in action tenaya fishing using two-stage jerking and casting tenaya fishing from a hill (shore).

[0060] Thus, the frozen head-on shrimp according to the present embodiment are frozen shrimp that have been immersed in an immersion solution and then frozen. The immersion solution is an aqueous solution containing an acid salt, sugars, and salt, which prevents the base of the head from softening and falling off due to autolysis upon thawing. In particular, the immersion solution according to the present embodiment contains less than 5% by mass of alum as an acid salt, based on the total amount of the immersion solution, thereby further preventing head loss from occurring in the frozen head-on shrimp. In particular, the use of alum promotes protein denaturation and deactivation of autolytic enzymes in the head-on shrimp. Furthermore, when the alum is potassium aluminum sulfate, it is expected that aluminum ions will form a crosslinked structure. As a result, the frozen head-on shrimp treated with the immersion solution containing alum according to the present embodiment have increased meat elasticity and firmness compared to conventional shrimp, thereby further preventing head loss from occurring in the frozen head-on shrimp. Furthermore, in the case of the frozen head-on shrimp according to this embodiment, the soaking liquid contains 1 to 30% by mass of sorbitol and 1 to 15% by mass of salt, which further prevents the heads from falling off from the frozen head-on shrimp. The frozen head-on shrimp according to this embodiment is suitable for use as shrimp bait for tenaya fishing and the like, but is also intended to be used for food.

[0061] Although the preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the above-described embodiments. Various modifications and improvements can be made to the above-described embodiments, and such modifications and improvements are also included in the technical scope of the present invention.

[0062] For example, in the above-described embodiment, head-on shrimp are immersed in a immersion solution containing alum, sugars, and salt, or the immersion solution is sprayed onto the induced shrimp, but the present invention is not limited to this configuration. Frozen head-on shrimp can be produced by covering head-on shrimp with a powder containing alum, sugars, and salt, leaving the shrimp to stand for 10 minutes or more, and then freezing the shrimp. In this case, the powder can contain alum, sugars, and salt in the same ranges as the immersion solution in the above-described embodiment.

Claims

1. Frozen head-on shrimp, which is obtained by treating head-on shrimp with an aqueous solution containing an acid salt, sugars, and salt, or with a powder containing an acid salt, sugars, and salt, and then freezing the treated shrimp, Frozen head-on shrimp that is prevented from softening and falling off due to autolysis when thawed.

2. 2. The frozen head-on shrimp according to claim 1, wherein the aqueous solution or the powder contains burnt alum as the acid salt.

3. 2. The frozen head-on shrimp according to claim 1, wherein the aqueous solution or the powder contains less than 5% by mass of alum as the acid salt.

4. 2. The frozen head-on shrimp according to claim 1, wherein the aqueous solution or the powder contains 1 to 30% by mass of sorbitol as the sugar.

5. The frozen head-on shrimp according to claim 1, wherein the aqueous solution or the powder contains 1 to 15% by mass of salt.

6. 2. The frozen head-on shrimp according to claim 1, wherein the aqueous solution or the powder contains one or more amino acids that are umami components contained in crustaceans.

7. A frozen head-on shrimp bait using the frozen head-on shrimp according to any one of claims 1 to 6.

8. The frozen head-on shrimp bait according to claim 7, which is a shrimp bait exclusively for frozen Tenya.

9. This method for producing frozen head-on shrimp involves treating head-on shrimp with an aqueous solution containing burnt alum, sugars and salt, or with a powder containing burnt alum, sugars and salt, and then freezing the shrimp.

10. A method for suppressing head loss of head-on shrimp, which suppresses head loss of head-on shrimp when frozen head-on shrimp is thawed, comprising: This method for preventing head loss in head-on shrimp comprises treating head-on shrimp with an aqueous solution containing burnt alum, sugars and salt, or with a powder containing burnt alum, sugars and salt, and then freezing the treated shrimp.

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