Shell-on edible shrimp

Abstract

To provide shell-on edible shrimp in which the shell is softened while deterioration of the texture of the flesh is suppressed, thereby making it easy to eat.SOLUTION: The invention provides shell-on edible shrimp whose shell calcium content is 1800 mg / 100 g or less, and whose flesh has a breaking strength of 3000 gf or less after boiling. Preferably, the aliphatic oxycarboxylic acid is citric acid. Preferably, the breaking strength of the flesh after boiling is 3000 gf or less. Preferably, the water content of the flesh after boiling is 65 mass % or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to shrimp for eating with shell, which is eaten with the shell. [Background technology]

[0002] Shrimp are generally eaten without the shell, and are popular for their firm texture. However, shrimp shells are rich in calcium, so if shrimp could be eaten with the shell, it would reduce the cost of disposing of the shell, and it would also have the economic advantage of adding volume to the shrimp. Furthermore, it would also add value as a health food rich in minerals such as calcium. Therefore, there is a strong demand for technology that allows shrimp with the shell to be eaten deliciously at low cost.

[0003] Conventionally, when shrimp are eaten with the shell on, the shrimp shells are hard and difficult to eat, and to solve this problem, processes such as soaking in hydrochloric acid (Patent Document 1) and a process of applying reduced pressure and heating under pressure (Patent Document 2) have been proposed as shell softening processes. Although not related to shrimp for eating with the shell on, Patent Document 3 describes soaking shrimp in a solution with a salt concentration of 1.5%, a pH adjuster concentration of 2.0% (mixture ratio: trisodium citrate 75%, sodium bicarbonate 25%), and a pH of 9.5. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-268916 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-20527 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-158285 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the shrimp treated with a strong acid such as hydrochloric acid in Patent Document 1 and the shrimp treated by heating under reduced pressure and heating under pressure in Patent Document 2 both harden and have a significantly deteriorated texture. The inventors also found that the shrimp obtained by soaking in a sodium citrate-containing solution as described in Patent Document 3 also have insufficient shell softening effect.

[0006] An object of the present invention is to provide shelled shrimp for eating, which have softened shells and are easy to eat because the deterioration of the texture of the meat is suppressed. [Means for solving the problem]

[0007] As a result of intensive research into the above-mentioned problems, the present inventors have surprisingly found that the above-mentioned problems can be solved by providing shell-on shrimp for consumption, in which the calcium content in the shell is set to a specific value or less and the breaking strength is set to a specific value or less.

[0008] The present invention is based on the above findings and provides shell-on edible shrimp having a calcium content of 1800 mg / 100 g or less in the shell and a breaking strength of the meat after boiling of 3000 gf or less. [Effects of the Invention]

[0009] According to the present invention, there is provided a shrimp for consumption which has a good texture of meat and in which the hardness of the shell is effectively reduced when eaten with the shell and chewed with the molars. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below based on preferred embodiments thereof.

[0011] The shell-on shrimp for consumption of the present invention has a calcium content of 1800 mg / 100 g or less in the shell. The calcium content of the shell is preferably 1600 mg / 100 g or less, more preferably 1500 mg / 100 g or less, particularly preferably 1300 mg / 100 g or less, and particularly preferably 1100 mg / 100 g or less. By adjusting the calcium content to the above amount, the shell is sufficiently softened, making it easy to eat.

[0012] Furthermore, in the shell-on shrimp of the present invention, the lower the calcium content of the shell, the better, but on the other hand, if the calcium content of the shell is such that calcium leaching due to the presence of aliphatic hydroxycarboxylic acids is below a certain level, deterioration in the texture of the meat due to the aliphatic hydroxycarboxylic acids is prevented, the texture can be maintained, and the shrimp tends to be delicious to eat. From this perspective, the calcium content of the shell may be 550 mg / 100 g or more, 600 mg / 100 g or more, 650 mg / 100 g or more, 700 mg / 100 g or more, or 780 mg / 100 g or more. To achieve the above calcium content, the aliphatic hydroxycarboxylic acid content, pH, amount of carbonate, etc. in the immersion solution may be adjusted in the preferred production method described below, and the immersion time may also be adjusted.

[0013] The calcium content of the shell of the shell-on shrimp for consumption of the present invention can be measured by the method described below.

[0014] The in-shell shrimp for consumption of the present invention has a breaking strength of the meat after boiling of 3000 gf or less. When treated with an acid such as an aliphatic hydroxycarboxylic acid, the shell softens while the breaking strength of the meat after boiling tends to increase. However, in the present invention, by having the breaking strength after boiling be equal to or less than the above-mentioned upper limit, the meat is more likely to be softer and have a good texture. From this viewpoint, the breaking strength of the meat after boiling is more preferably 2800 gf or less, even more preferably 2500 gf or less, even more preferably 2300 gf or less, and particularly preferably 2000 gf or less. Furthermore, from the viewpoints of ease of production and chewiness, the breaking strength of the in-shell shrimp for consumption after boiling is preferably 1500 gf or more, more preferably 1550 gf or more, and even more preferably 1600 gf or more.

[0015] The breaking strength is the breaking strength of the remaining flesh after removing the shells, telson, and tails of the first to sixth abdominal segments. To achieve this breaking strength, the aliphatic hydroxycarboxylic acid content, pH, and carbonate amount in the soaking solution may be adjusted, as well as the soaking time, in the preferred production method described below. The boiling conditions are as follows: 600 parts by mass of shrimp are placed in 2000 parts by mass of boiling water, and the shrimp are boiled at 95°C or higher for 1 minute and 30 seconds.

[0016] The shell-on shrimp of the present invention preferably contains a specific amount or more of an aliphatic hydroxycarboxylic acid, which facilitates a balance between the shell texture and the meat texture. The aliphatic hydroxycarboxylic acid is an aliphatic compound having both a hydroxy group (-OH) and a carboxy group (-COOH) in the same molecule. Preferred aliphatic hydroxycarboxylic acids include citric acid, tartaric acid, malic acid, and lactic acid. Among these, citric acid and lactic acid are more preferred because of their high flavor-imparting and shell-softening effects. Citric acid is particularly preferred because it effectively reduces the hardness of the shell and the feeling of the shell remaining in the mouth when chewed with the molars, and facilitates a good balance with the meat texture.

[0017] The shrimp for eating with shell of the present invention preferably has an aliphatic hydroxycarboxylic acid content of 100 mg / 100 g or more. When the aliphatic hydroxycarboxylic acid content in the shrimp for eating with shell is equal to or higher than this lower limit, the presence of the aliphatic hydroxycarboxylic acid tends to effectively soften the shell. From the viewpoint of further softening the shell, the aliphatic hydroxycarboxylic acid content is more preferably 300 mg / 100 g or more, even more preferably 500 mg / 100 g or more, and particularly preferably 800 mg / 100 g or more. In addition, from the viewpoint of flavor and the like, the aliphatic hydroxycarboxylic acid content of shell-on shrimp for consumption is preferably 3000 mg / 100 g or less, more preferably 2000 mg / 100 g or less, even more preferably 1500 mg / 100 g or less, even more preferably 1300 mg / 100 g or less, and particularly preferably 1100 mg / 100 g or less.

[0018] The above-mentioned aliphatic hydroxycarboxylic acid content is preferable because the shells are easily softened and become more palatable. To achieve the above-mentioned aliphatic hydroxycarboxylic acid content, in the preferred production method described below, the aliphatic hydroxycarboxylic acid content in the soaking solution is adjusted, the soaking time is adjusted, and further, after soaking in the soaking solution, the washing time is shortened or washing is not performed. The content of aliphatic hydroxycarboxylic acids in shell-on shrimp for consumption can be measured by high performance liquid chromatography (HPLC). For example, the content of aliphatic hydroxycarboxylic acids can be measured by the method described in the Examples below.

[0019] This aliphatic hydroxycarboxylic acid content is a value measured after boiling with the shell, telson, and uropods of the first to sixth abdominal segments removed, and is the amount measured with the meat boiled, and can be measured by the method described in the Examples below. If the shrimp meat has legs, the legs are also included in the measurement. The purpose of measuring the aliphatic hydroxycarboxylic acid content after removing the shell is to prevent variation in the content. In shell-on edible shrimp, the presence of aliphatic hydroxycarboxylic acid in the meat means that the shell has been treated with aliphatic hydroxycarboxylic acid. It is preferable that shell-on edible shrimp contain aliphatic hydroxycarboxylic acid not only in the meat but also in the shell. For example, the shrimp shell, telson, and uropod are crushed and extracted with an appropriate solvent, and the aliphatic hydroxycarboxylic acid content of the shell can be measured by HPLC.

[0020] The moisture content of the shell-on shrimp meat after boiling is preferably 65% ​​by mass or more. When shell-on shrimp is treated with an acid such as an aliphatic hydroxycarboxylic acid, the moisture content of the boiled meat tends to decrease. However, when the shell-on shrimp meat of the present invention has a moisture content of not less than the above-mentioned lower limit, it is more likely to be perceived as softer and with a good texture. From this perspective, the moisture content is more preferably 68% by mass or more, and particularly preferably 70% by mass or more. On the other hand, from the viewpoints of ease of production and a chewy texture, the moisture content of the boiled meat is preferably 77% by mass or less, more preferably 76% by mass or less, even more preferably 75% by mass or less, and particularly preferably 73% by mass or less.

[0021] The moisture content is measured after removing the shells, telson, and tails from the first to sixth abdominal segments and boiling the remaining meat. If the shelled shrimp for eating has legs, the legs are also measured. To achieve this moisture content, the aliphatic hydroxycarboxylic acid content, pH, and carbonate amount in the soaking solution may be adjusted, as well as the soaking time, in the preferred production method described below.

[0022] The shell-on shrimp for consumption of the present invention has abdominal meat and a shell covering the abdominal meat. The shell may cover only a portion of the abdominal meat, or may cover the entire abdominal meat. The abdominal meat has six abdominal segments, from the first abdominal segment to the sixth abdominal segment. As shell parts covering each of these, the abdominal shell has the first abdominal segment lateral carapace to the sixth abdominal segment lateral carapace. The shell-on shrimp for consumption of the present invention may or may not have the cephalothorax removed, but having the cephalothorax is preferred in that it allows for the production of voluminous shrimp with a good shell texture as well as the texture of the abdominal meat at low cost. The legs of the shell-on shrimp may be removed, or may not be removed, but it is preferable that the legs are not removed in terms of volume.

[0023] In addition, shrimp species of the present invention are preferably shrimp of the genera Penaeidea, Caridea, and Stenopodidea, and more preferably shrimp of the family Penaeidae. Examples of the family Penaeidae include Litopenaeus vannamei, Black tiger shrimp (Penaeus monodon), Kuruma shrimp (Marsupenaeus japonicus), Shiba shrimp (Metapenaeus joyneri), Poovaran shrimp (Metapenaeus dobsoni), Endeavor shrimp (Metapanaeus endeavouri), Bangladesh brown shrimp (Metapenaeus onoceros), Asian king shrimp (Fenneropenaeus chinensis), and banana shrimp (Fenneropenaeus merguiensis). In particular, in the present invention, it is particularly preferable to use vannamei shrimp, which are commonly available on the market, because the shells can be softened at low cost and this has an excellent economic effect.

[0024] The edible shrimp with shells of the present invention can be eaten with the shells, and when they are in an uncooked state, they can be used for various cooking methods such as frying, boiling, steaming, and grilling, resulting in cooked edible shrimp with shells. The uncooked edible shrimp with shells can be distributed and sold for cooking.

[0025] For example, unheated shrimp for eating with shells may be stored in a frozen state. When unheated shrimp for eating with shells are heated to obtain cooked shrimp with shells, the shrimp may be subjected to various cooking methods (frying, boiling, steaming, grilling, etc.) in either a frozen or chilled state, or the shrimp for eating with shells may be stored frozen or chilled after cooking. A frozen state generally refers to storage at a temperature range of less than 10°C, and freezing is generally carried out at a temperature lower than -3°C and higher than -45°C. For example, when the frozen shrimp for eating with shells of the present invention are thawed by heating in a microwave oven or by natural thawing and eaten, effects such as reduced shell hardness and reduced feeling of shell remaining when chewed with molars can be obtained. The shell-on shrimp for eating of the present invention can be used as various processed foods such as frozen foods, foods for microwave heating, diet foods, oil-based products such as fried foods, chilled foods, and the like, or as raw materials for producing such processed foods.

[0026] Next, a preferred method for producing the shell-on shrimp for eating of the present invention will be described. A preferred method for producing edible shrimp with shells of the present invention involves immersing unheated shrimp with shells in an immersion liquid containing an aliphatic hydroxycarboxylic acid and a carbonate and having a pH of 7 or less.

[0027] In this method, unheated shelled shrimp are immersed in a immersion solution containing an aliphatic hydroxycarboxylic acid and a carbonate, such as sodium carbonate, potassium carbonate, sodium bicarbonate, or potassium bicarbonate.

[0028] In this production method, an immersion liquid is prepared by mixing an aliphatic hydroxycarboxylic acid and a carbonate in the presence of water. In the present invention, the amount of the aliphatic hydroxycarboxylic acid used in the immersion liquid is preferably 1.5 parts by mass or more, more preferably 2% by mass or more, even more preferably 4% by mass or more, even more preferably 5% by mass or more, and particularly preferably 6% by mass or more. The amount of the aliphatic hydroxycarboxylic acid used in the immersion liquid is preferably 10% by mass or less, more preferably 9% by mass or less. The amount of the aliphatic hydroxycarboxylic acid referred to here may be any amount as long as it is the ratio of the amount of the aliphatic hydroxycarboxylic acid added to the mass of the resulting immersion liquid. Examples of the aliphatic hydroxycarboxylic acid include those mentioned above.

[0029] In this production method, the amount of carbonate used in the immersion liquid is preferably 1.5 parts by mass or more, more preferably 2% by mass or more, even more preferably 4% by mass or more, and particularly preferably 6% by mass or more. The amount of carbonate used in the immersion liquid is preferably 10% by mass or less, more preferably 9% by mass or less. The amount of carbonate referred to here may be any amount as long as it is the ratio of the amount of carbonate added to the mass of the resulting immersion liquid.

[0030] In this production method, the amount of aliphatic hydroxycarboxylic acid and carbonate used in the immersion solution is preferably such that the mass ratio of aliphatic hydroxycarboxylic acid:carbonate is 100:80-130, more preferably 100:90-130, even more preferably 100:90-120, and most preferably 100:95-115, as solid content.

[0031] The immersion liquid used in this production method may contain salt, and in that case, the amount of salt in the immersion liquid is preferably 1 to 4 mass %, more preferably 1.5 to 3 mass %.

[0032] The soaking method can be carried out by mixing an aliphatic hydroxycarboxylic acid, a carbonate, and other ingredients, if necessary, in the presence of water. Mixing the aliphatic hydroxycarboxylic acid and the carbonate in the presence of water causes foaming. The uncooked shell-on shrimp may be added immediately after mixing the aliphatic hydroxycarboxylic acid and the carbonate in the presence of water, or may be added after a certain time has elapsed since mixing the aliphatic hydroxycarboxylic acid and the carbonate, once foaming has ceased to a certain extent.

[0033] The pH of the soaking liquid is preferably 7 or less, and more preferably 4 to 7. In particular, the pH is preferably 4 to 6, more preferably 4.5 to 5.5, and particularly preferably 5.0 to 5.2. The pH of the soaking liquid referred to here is the pH when the temperature of the soaking liquid is 20°C. The measurement is carried out without adding shrimp, and the average of three measurements taken every 30 minutes after at least one and a half hours has passed since the aliphatic hydroxycarboxylic acid and carbonate were mixed is taken.

[0034] The amount of soaking liquid is preferably 100 to 120 parts by mass per 100 parts by mass of shell-on shrimp, from the viewpoints that the entire shrimp can be soaked and from the viewpoint of economy, and more preferably 100 to 115 parts by mass.

[0035] The state of the shell-on shrimp to be subjected to the immersion treatment of this production method, whether or not it contains shells, legs, and heads, can be the same as that of the shell-on shrimp for consumption of the present invention described above.

[0036] The immersion treatment in the immersion liquid is preferably 4 hours or more, more preferably 8 hours or more, more preferably 12 hours or more, and particularly preferably 14 hours or more, and is preferably 24 hours or less, more preferably 20 hours or less, and particularly preferably 18 hours or less.

[0037] The temperature of the soaking liquid during the soaking treatment in this production method is preferably 2 to 10°C, particularly preferably 4 to 8°C, from the viewpoint of hygiene when soaking for a long period of time and efficiency in softening the shells.

[0038] In this production method, after immersion in the immersion solution containing the aliphatic hydroxycarboxylic acid and carbonate, a washing treatment may be performed, or may not be performed. In this case, water is usually used for the washing treatment. Specific examples of the washing treatment include washing with running water and washing with stored water. From the viewpoint of shortening the production time, when washing with water, the washing time is preferably, for example, 10 minutes or less, more preferably 5 minutes or less, and particularly preferably 1 minute or less. The washing time here refers to the total time of each washing when washing is performed intermittently.

[0039] In the present invention, the shrimp may be immersed in a water-retaining agent before the immersion treatment with the aliphatic oxycarboxylic acid and carbonate. Examples of the water-retaining agent include alkaline agents, such as sodium bicarbonate, sodium carbonate, etc. The water-retaining agent may be one of these alone or a combination of two or more thereof. [Example]

[0040] 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 such examples. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass."

[0041] Example 1 An immersion solution was prepared by mixing 8 parts by mass of citric acid (Fujifilm Wako Pure Chemical Industries, Ltd., Citric Acid), 8 parts by mass of sodium bicarbonate (baking soda, Pax Baking Sodium F, Taiyo Yushi Co., Ltd.), and 2 parts by mass of salt with 82 parts by mass of water at 5°C. Five minutes after mixing the citric acid and baking soda into the water, unheated, shelled vannamei shrimp with their cephalothorax and legs removed and their abdominal shells still attached were added. Frozen vannamei shrimp were thawed under running water before use. The white shrimp were left to stand in the soaking liquid in a refrigerator for 16 hours. The amount of soaking liquid was 100 parts by mass per 100 parts by mass of white shrimp. The soaked shrimp were drained on a colander for 180 seconds to obtain shell-on shrimp for consumption. The pH of the soaking liquid at 20°C was 5.0.

[0042] Example 2 The amount of citric acid was changed from 8 parts by mass to 4 parts by mass, sodium bicarbonate from 8 parts by mass to 4 parts by mass, and the amount of water at 5°C was changed from 82 parts by mass to 90 parts by mass. Except for this, shell-on shrimp for consumption were obtained in the same manner as in Example 1. The pH of the soaking liquid at 20°C was 5.2.

[0043] Example 3 The amount of citric acid was changed from 8 parts by mass to 1.5 parts by mass, sodium bicarbonate from 8 parts by mass to 1.5 parts by mass, the amount of salt was changed from 2 parts by mass to 1.5 parts by mass, and the amount of water at 5°C was changed from 82 parts by mass to 95.5 parts by mass. Except for these points, the same procedure as in Example 1 was followed to obtain shell-on shrimp for consumption. The pH of the soaking liquid at 20°C was 5.1.

[0044] Example 4 The amount of citric acid was changed from 8 parts by mass to 10 parts by mass, the amount of sodium bicarbonate was changed from 8 parts by mass to 10 parts by mass, and the amount of water at 5°C was changed from 82 parts by mass to 78 parts by mass. Except for this, shell-on shrimp for consumption were obtained in the same manner as in Example 1. The pH of the soaking liquid at 20°C was 5.2.

[0045] (Comparative Example 1) Instead of the soaking liquid, water was used, and other than that, the same procedure as in Example 1 was carried out to obtain shrimp for eating with shells.

[0046] (Comparative Example 2) No sodium bicarbonate was used, and the amount of water was 90 parts by mass. Except for this, the same procedure as in Example 1 was carried out to obtain shell-on shrimp for eating.

[0047] (Comparative Example 3) This is a comparative example corresponding to Patent Document 3. A mixed solution of 1.5 mass % of salt, 1.5 mass % of trisodium citrate, 0.5 mass % of sodium bicarbonate, and 96.5 mass % of water was prepared (pH 9.5 at 20° C.). The above-mentioned mixed solution was used as the soaking solution. The soaking time was 3 hours and the soaking temperature was 10° C. Other than that, the same procedures as in Example 1 were carried out to obtain shelled shrimp for eating.

[0048] The shelled shrimp for eating obtained in the examples and comparative examples were evaluated as follows.

[0049] (Quantitative determination of calcium content in shells) Calcium was quantified in the shells of the first to sixth abdominal segments, the telson and the uropod. For each of Examples 1 to 3 and Comparative Examples 1 to 3, the bodies and legs of 30 shelled shrimp for eating were removed, and the remaining shells, telson segments and tails of the first to sixth abdominal segments were frozen. The frozen shrimp shells, tails, and tail limbs were placed in a zippered plastic bag and thawed under running water. The shrimp were then placed in a grind mix (Retsch GM200) for 1 minute, and the contents of 30 shrimp were mixed, crushed, and homogenized to obtain the test sample. The calcium content of the obtained samples was measured as follows.

[0050] < <1> >Reagent preparation Preparation of 1% hydrochloric acid solution 50 mL of 20% hydrochloric acid (Wako Pure Chemical Industries, Ltd., for precision analysis) was diluted to 1000 mL with ion-exchanged water. Preparation of 5% strontium solution In a 300 mL Duran bottle that had been washed in the same manner as in the preparation of the specimen extract, 30.43 g of strontium chloride (e.g., strontium chloride hexahydrate for atomic absorption spectrometry, manufactured by Kanto Chemical Co., Ltd.) was weighed out, and 200 mL of the 1% hydrochloric acid solution prepared above was added and stirred to dissolve (5% (w / v) as strontium). Preparation of 12% nitric acid solution 1 L of 60% nitric acid (e.g., Junsei Chemical Co., Ltd. Grade 1 nitric acid) and 4 L of ion-exchanged water were placed in a PP cup with handle (5 L) and stirred.

[0051] < <2> >Preparation of sample extract <1> A 50 mL glass volumetric flask and a 30 mL glass beaker with brown printed numbers were filled with 12% nitric acid solution and left to stand for at least 30 minutes. The volumetric flask was fitted with a stopper, which was also washed with nitric acid at the same time. After the nitric acid solution was returned to the flask, the 30 mL beaker and 50 mL volumetric flask (including the stopper) were washed three times with ion-exchanged water and then thoroughly drained. <2> The homogenized test sample was weighed into a clean beaker (several grams; the sampling amount was adjusted based on previous data and the data listed in the Standard Tables of Food Composition in Japan, with a calcium content of approximately 10 to 50 mg). <3> The mixture was placed on a stainless steel tray and dried at 105°C overnight. <4> After drying, the sample was pre-ashed using a gas burner (oxidizing flame: orange) until no more smoke was emitted. <5> The mixture was incinerated overnight in an electric muffle furnace at 500°C. It was confirmed that the incineration was normal and that the ash was white. <6> After incineration, the sample was handled carefully to prevent the ash from scattering and to prevent dust from getting into it, and then allowed to cool to room temperature. <7> A small amount of ion-exchanged water was carefully added to the beaker to moisten the ash, taking care not to scatter it. Approximately 2 mL of 20% hydrochloric acid (Wako Pure Chemical Industries, precision analysis grade) was added to dissolve the ash. The amount of 20% hydrochloric acid added was adjusted appropriately. <8> The mixture was heated in a copper pot over a boiling water bath for several hours to evaporate and dry up, taking care not to let the water in the copper pot dry up during heating. <9> Remove the beaker from the copper pot and <10> Care was taken to prevent dust and other debris from getting into the device before it was operated. <10> 2.5 mL of 20% hydrochloric acid from the same lot as above was added to dissolve the dried product. 5 mL of the 5% strontium solution was placed in a 50 mL glass volumetric flask that had been previously washed with nitric acid, and the solubilized product in the beaker was washed with ion-exchanged water, and the solution was made up to the desired concentration with ion-exchanged water (final hydrochloric acid concentration: 1%, final strontium concentration: 0.5%). <11> The flask was stoppered and the solution was mixed by inversion to make it uniform. The solution was filtered through filter paper (No. 5B) and used as the specimen extract.

[0052] < <3> >Absorbance measurement using an atomic absorption spectrophotometer <1> The standard stock solution (Ca1000 manufactured by Kanto Chemical Co., Ltd., stored in a refrigerator) was allowed to return to room temperature (left to stand at room temperature for at least 2 hours). <2> Preparation of 10x Ca dilution: Using a Pipetman (P-5000), 4,000 μL of 1% hydrochloric acid solution was measured out. Using a Pipetman (P-1000), 500 μL of 5% strontium solution and 500 μL of Ca standard stock solution were measured out and added, and the mixture was thoroughly stirred to prepare a 10-fold diluted solution (100 ppm, final strontium concentration 0.5%). <3> Preparation of Ca standard solution: Calcium was prepared using a 5% strontium solution and a 1% hydrochloric acid solution to final concentrations of 0, 1, 2.5, 5, 7.5, and 10 ppm (see the preparation example in Table 1 below; final strontium concentration: 0.5%). Strontium was added as an interference agent to prevent calcium from binding with phosphate during measurement, resulting in the formation of calcium phosphate, a difficult-to-dissociate molecule.

[0053] [Table 1]

[0054] <4> In the same manner as in the preparation of the standard solution, the sample extract was independently diluted in two or more stages in the range of 2 to 5 times using a 5% strontium solution and a 1% hydrochloric acid solution to prepare sample measurement solutions. <5> The absorbance was measured using an atomic absorption spectrophotometer according to the instrument manual, and the amount of Ca was calculated using the following formula. Ca (mg / 100g) = (fixed volume (mL) ÷ sample volume (g)) × dilution factor × measured concentration (ppm) × Ca standard solution factor ÷ 10 In the formula, the fixed volume is basically 50 mL.

[0055] (Quantitative determination of aliphatic hydroxycarboxylic acid (citric acid) content) For Examples 1 to 3 and Comparative Examples 1 to 3, the shells, telson, and tail limbs of the first to sixth abdominal segments were removed from 10 shrimp each, and the remaining meat and legs were frozen. The resulting frozen shrimp were placed in a zippered plastic bag and thawed under running water. 600 parts by mass of the thawed shrimp, without wiping off the moisture, were placed in 2000 parts by mass of boiling water and boiled at 95°C or higher for 1 minute and 30 seconds, then placed in a colander and left to cool for 3 minutes to remove surface moisture. The heated shrimp sample was crushed and homogenized in a mixer to prepare the prepared sample. A portion of the prepared sample was taken, purified water was added, and the mixture was shaken. After centrifugation, the supernatant was filtered, purified water was added to the residue, and the same procedure was repeated. The supernatants were combined, adjusted to the specified volume, and diluted appropriately to prepare the test solution. The test solution was injected into an HPLC system, and a chromatogram was obtained. The citric acid content per 100 g of sample was calculated from the peak areas of citric acid in the citric acid standard solution and the test solution. The HPLC used was a Prominence model manufactured by Shimadzu Corporation.

[0056] (Measurement of breaking strength) For each of Examples 1 to 3 and Comparative Examples 1 to 3, the shells, telons, and tails of the first to sixth abdominal segments were removed from 10 shelled shrimp for consumption, and the remaining meat and legs were frozen in a -40°C freezer. The resulting frozen shrimp were placed in a zippered plastic bag and thawed under running water. 600 parts by mass of the thawed shrimp, without wiping off the moisture, were placed in 2000 parts by mass of boiling water and boiled at 95°C or higher for 1 minute 30 seconds, then transferred to a colander and allowed to cool for 3 minutes to remove surface moisture. The breaking strength of the resulting boiled shrimp was measured as a physical property using the method described below.

[0057] (Breaking strength measurement method) The cooked peeled shrimp were placed horizontally and evaluated using a texture analyzer (Eiko Seiki, TA XT plus). Measurement conditions included a wedge-shaped plunger made of plastic (polyacetal resin) (a flat wedge with a 13 mm long, 1 mm wide rectangular tip and a 30° angle at the tip), a plunger thrust speed of 0.5 mm / sec, and a load applied from the top of the sample to 99% of the sample height. Measurements were performed with the shrimp positioned so that the longitudinal direction of the plunger's flat tip was perpendicular to the longitudinal direction of the shrimp. The measurement site for the shrimp sample was the third abdominal segment. The breaking strength of each of the 10 shrimp was measured and the average value was calculated.

[0058] <Moisture content of the flesh> Ten shrimp from each of the examples and comparative examples were used for eating, and the shells, telson, and tails of the first to sixth abdominal segments were removed. The remaining meat and legs were frozen in a freezer at -40°C. The frozen shrimp were placed in a plastic bag with a zipper and thawed under running water. 600 parts by mass of the thawed shrimp, without wiping off the moisture, were placed in 2000 parts by mass of boiling water and boiled at 95°C or higher for 1 minute and 30 seconds. The shrimp were then placed in a colander and allowed to cool for 3 minutes to remove surface moisture. Ten of the boiled shrimp were homogenized in a grind mix (GM200 manufactured by Retsch) for 1 minute to obtain a measurement sample, and the moisture content was measured.

[0059] (Moisture content measurement method) The shell and flesh samples obtained above were measured by the following methods. <1> An aluminum cup (No. 5) was placed inside an aluminum weighing can, and the can was dried with a lid on (105°C for at least 2 hours). <2> The contents were transferred to a desiccator lined with silica gel and allowed to cool to room temperature (18-28°C). The lid was removed and the contents were weighed accurately, and the mass A (tare weight) was recorded. <3> The homogenized sample was weighed accurately to approximately 2 g, and the mass B (tare weight + sample) was recorded. The lid was placed lightly on top. <4> The mixture was placed on a stainless steel tray and dried overnight (16 hours) at 105°C. <5> After drying, the sample was transferred to a desiccator filled with silica gel and allowed to cool to room temperature for at least 20 minutes. <6> The lid was removed, and the mass C (tare weight after drying + sample) was precisely weighed. The moisture content was calculated using the following formula: Moisture content = (B-C) / (BA) x 100 (mass%)

[0060] (Evaluation of shell and meat texture) The shelled shrimp for eating obtained in each Example and Comparative Example were frozen for days in a freezer at −40° C. Then, they were placed in a zippered plastic bag and thawed under running water from above the bag. The thawed shrimp were then immersed in batter (30% by mass of starch, cereal flour, or modified starch, with other ingredients such as salt and vegetable oil, and the remainder being water) and seasoned with 180° C. cooking oil for 3 minutes. After the oiling, five panelists tasted the product and evaluated it according to the following criteria. Table 2 shows the average evaluation scores.

[0061] (Shell texture: hardness of the shell when chewed with molars) In this evaluation, the lower the evaluation score, the better the evaluation. 10 Extremely strong. 9: Very strong. 8: Strong. 7: Somewhat strong. 6: Neither. 5: Somewhat weak. 4: Weak. 3: Very weak. 2: Very weak. 1: Very weak.

[0062] (Texture of the flesh) The higher the evaluation score, the better the evaluation. 5: It feels firm and very soft. 4: It feels firm and soft. 3: It is a little hard, but within the acceptable range. 2: There is a strong fibrous feel. 1: Mumbling.

[0063] [Table 2]

[0064] A comparison of Comparative Example 1 with Examples 1 to 4 shows that when the calcium content of the shell is 1800 mg / 100 g or less and the breaking strength of the meat after boiling is 3000 gf or less, the texture of the shell can be softened while improving the texture of the meat. On the other hand, as in Comparative Example 2, when the calcium content of the shell is 1800 mg / 100 g or less but the breaking strength of the meat after boiling the shell exceeds 3000 gf, the texture of the meat is deteriorated. Furthermore, when the calcium content of the shell exceeds 1800 mg / 100 g as in Comparative Example 3, the effect of improving the texture of the shell is poor.

Claims

1. The shelled shrimp for eating has a calcium content of 1800 mg / 100 g or less and a breaking strength of the meat after boiling of 3000 gf or less.

2. 2. The shell-on shrimp for eating according to claim 1, wherein the content of an aliphatic hydroxycarboxylic acid is 100 mg / 100 g or more.

3. 3. The shell-on shrimp for eating according to claim 2, wherein the aliphatic hydroxycarboxylic acid is citric acid.

4. 3. The shelled shrimp for eating according to claim 1 or 2, wherein the moisture content of the flesh after boiling is 65% by mass or more.

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