Method for recovering nutrient substances in water for crayfish processing

Abstract

The invention provides a method for recovering nutrient substances in water for crayfish processing, which comprises the following steps: S1, standing and layering the water for crayfish processing, and carrying out primary separation to obtain an upper grease layer, namely a first processed substance, and a lower aqueous solution layer, namely a second processed substance; s2, treating the first processed material by using a hanging bag centrifuge to obtain filter residues, namely a shrimp yellow crude product, and combining the filtrate with the second processed material to obtain a mixed filtrate; s3, treating a prawn yellow crude product and the mixed filtrate: respectively carrying out bubbling cleaning on the prawn yellow crude product by using rice washing water and ultrasonic concussion combined cleaning by using a peracetic acid solution, and filtering by using the hanging bag centrifuge to obtain prawn yellow; and adding chitosan and sodium alginate into the mixed filtrate to flocculate, precipitate and filter the water-soluble protein, and recovering to obtain the recovered water-soluble protein. According to the method, the shrimp yellow and the water-soluble protein in the water for processing the crayfish can be effectively recovered, the recovery efficiency is high, and the method is green and pollution-free.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, and in particular to a method for recovering nutrients in water used for processing crayfish. Background Art

[0002] Most of the crayfish are distributed in the middle and lower reaches of the Yangtze River. They are widely loved for their rich nutrition and delicious meat. The aquaculture industry has developed rapidly and the consumer market has continued to expand. They have become an important resource of freshwater shrimp in China. The processed products of crayfish can be divided into quick-frozen products, pre-prepared dishes, snack foods and deep-processed products. However, a large amount of by-products will be produced during the initial processing of crayfish, among which the by-products such as shrimp heads (including shrimp roe) and shrimp shells account for more than 70% of the raw materials. Further processing can prepare products rich in astaxanthin and protein, which have high utilization value and huge potential. At present, the processing process of finished crayfish is generally as follows: the cleaned crayfish is steamed, the shrimp heads and shrimp tails are separated after steaming, and then cooled with water. On average, about 9.3 tons of water are used to produce 1 ton of crayfish products, especially in the cooking and cooling stages, where a large amount of wastewater is generated. The cooking water contains more protein, and the loss rate of shrimp roe during the cooling process is as high as 60%. The lost shrimp roe enters the cooling water. The water used in crayfish processing contains nutrients such as shrimp roe, protein, chitin, astaxanthin, lipids and trace elements. At present, there is no special recycling and processing equipment for these nutrients, resulting in waste of resources and environmental pollution, which restricts the development of the crayfish industry chain towards a green, healthy and efficient direction.

[0003] Therefore, it is urgent to develop green and efficient recycling technology for nutrients in water used in crayfish processing, solve the environmental pollution problems caused by crayfish production, and increase the added value of crayfish processing. Summary of the invention

[0004] In order to solve the problems existing in the background technology, the present invention provides a method for recovering nutrients in water for processing crayfish. The method can effectively recover shrimp roe and water-soluble protein in water for processing crayfish, and solves the problem of resource waste and non-recyclability in the crayfish industry chain.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] A method for recovering nutrients in water for processing crayfish comprises the following steps:

[0007] S1. Primary separation: The crayfish processing water is allowed to stand for stratification, and the upper layer containing solid and liquid shrimp roe components is initially separated to obtain a first processed product for recovering shrimp roe, and the lower aqueous solution layer is used to recover a second processed product of water-soluble protein;

[0008] S2. The first processed product is processed using a hanging bag centrifuge to obtain a filtrate and a semi-solid residue trapped in the hanging bag, and the filtrate and the residue are recovered, wherein the residue is a crude shrimp roe product, and the filtrate is incorporated into the second processed product separated in step S1 to obtain a mixed filtrate, wherein the hanging bag of the hanging bag centrifuge is provided with a hydrophilic oleophobic coating;

[0009] S3. respectively treating the crude shrimp roe product and the mixed filtrate obtained in step S2: placing the crude shrimp roe product in rice washing water for bubbling washing, filtering using a hanging bag centrifuge provided with a hydrophilic oleophobic coating, then placing the crude shrimp roe product in a peracetic acid solution for ultrasonic shaking combined washing, filtering using a hanging bag centrifuge provided with a hydrophilic oleophobic coating to obtain shrimp roe; adding chitosan and sodium alginate to the filtrate to flocculate and precipitate the water-soluble protein, filtering, and obtaining recovered water-soluble protein.

[0010] The above-mentioned crayfish processing water comes from the cooking and cooling steps in the crayfish processing process, which contains multiple components such as shrimp roe and water-soluble protein. After standing, it is stratified, wherein the upper layer is a fat layer containing solid and liquid shrimp roe components, and the lower layer is an aqueous solution layer containing water-soluble protein. It is treated by a hanging bag centrifuge with a hydrophilic and oleophobic coating on the hanging bag, which can retain solid shrimp roe and liquid fatty components in the hanging bag to obtain a semi-solid filter residue, i.e., crude shrimp roe. The aqueous solution containing water-soluble protein passes through the hanging bag to form a filtrate. The recovered filtrate is combined with the second processed product obtained by the initial separation to extract the water-soluble protein by flocculation.

[0011] The crude shrimp roe is washed with rice water and peracetic acid solution successively. The rice water can remove dirt and heavy metals, while reducing the fishy smell of shrimp roe and improving the flavor. Peracetic acid, as a high-efficiency disinfectant with antibacterial activity, can destroy microbial proteins and enzymes through hydroxyl free radical oxidation, thereby sterilizing the shrimp roe without producing toxic residues.

[0012] According to the above scheme, after the crayfish processing water is allowed to stand and separate into layers in step S1, the gate is opened to discharge the material and separate the aqueous solution layer as much as possible to obtain a first processed product containing a fat layer and a separated second processed product containing mostly aqueous solution.

[0013] According to the above scheme, after the crayfish processing water is allowed to stand and separate into layers in step S1, the gate is opened to discharge most of the aqueous solution in the lower layer until the liquid level of the aqueous solution layer is 4-6 cm, thereby obtaining a first processed product containing a fat layer and a separated second processed product containing most of the aqueous solution.

[0014] According to the above scheme, the hydrophilic and oleophobic coating is composited by polydopamine and sodium polyacrylate.

[0015] According to the above scheme, the method of providing a hydrophilic and oleophobic coating composed of polydopamine and sodium polyacrylate on the hanging bag is as follows:

[0016] 1) dissolving dopamine in a Tris-HCl buffer solution with a pH of 6.8 to 8.5 to obtain a dopamine solution, and immersing the hanging bag in the dopamine solution for 25 to 40 minutes;

[0017] 2) Add sodium persulfate to the dopamine solution in which the hanging bag is soaked, and continue soaking for 20 to 30 minutes;

[0018] 3) Sodium polyacrylate is added to the solution in which the hanging bag is soaked in step 2) to obtain a mixed solution, the hanging bag continues to be soaked in the mixed solution for 1.5 to 2.5 hours, and then the hanging bag is taken out, cleaned, and dried.

[0019] The present invention uses polydopamine and sodium polyacrylate to obtain a hydrophilic and oleophobic coating, which has good hydrophilicity and oleophobicity. The polydopamine has good adhesion and can enhance the adhesion of the hanging bag surface. The sodium persulfate used in the preparation is used as an initiator to promote the polymerization reaction of dopamine and the rapid formation of a coating by sodium polyacrylate. The coating can be used for the effective separation of crayfish roe, liquid fatty components and other components, and greatly improves the recovery rate of crude roe.

[0020] According to the above scheme, in step 3), after adding sodium polyacrylate, stir at room temperature for 1 to 2 hours, then let it stand and soak for 20 to 40 minutes before taking it out.

[0021] According to the above scheme, the mass concentration of dopamine in the dopamine solution is 0.5% to 4%, the molar concentration of sodium persulfate in the mixed solution is 0.1 to 1 mol / L, and the mass concentration of sodium polyacrylate is 0.1% to 2%.

[0022] According to the above scheme, in step S3, the weight ratio of shrimp roe to rice washing water is 1:10-30, the bubbling flow rate is 200-250L / min, and the bubbling cleaning time is 20-35min.

[0023] According to the above scheme, the concentration of the peracetic acid solution in step S3 is 0.3-1%, the ultrasonic power is 300-500W, the ultrasonic temperature is 40-50°C, and the ultrasonic time is 20-60min.

[0024] According to the above scheme, in step S3, the deacetylation degree of the chitosan is 80% to 99%. Before using chitosan and sodium alginate, chitosan is first dissolved in 0.5wt% to 2wt% acetic acid solution to prepare a chitosan acetic acid solution with a chitosan concentration of 0.5% to 1%, and sodium alginate is dissolved in water to prepare a sodium alginate aqueous solution with a concentration of 0.3% to 0.6%. The added amounts of chitosan and sodium alginate per liter of mixed filtrate are 2.5g to 5g and 1.5g to 3g, respectively.

[0025] The beneficial effects of the present invention are:

[0026] The method of the present invention can effectively extract shrimp roe and water-soluble protein from crayfish processing water, thereby realizing the recycling of shrimp roe and water-soluble protein. The method is simple, efficient, green and pollution-free, which not only solves the environmental pollution problem caused by the industrial production of crayfish, but also further increases the added value of crayfish and improves the economic benefits of the enterprise.

[0027] The recovery efficiency of the crude shrimp roe of the present invention reaches more than 85%, and the shrimp roe obtained by double washing with rice washing water and peracetic acid solution has no fishy smell, less heavy metal content, high safety, high comprehensive quality, and can effectively recover water-soluble protein. DETAILED DESCRIPTION

[0028] The principles and features of the present invention are described below in conjunction with specific embodiments. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0029] During the crayfish processing, the cleaned crayfish are boiled, the shrimp heads and tails are separated, and then water-cooled. A large amount of water is needed for both the boiling and cooling stages. A large amount of protein will enter the boiling water during the boiling process, and the shrimp roe will be lost in the cooling water during the cooling stage. Therefore, the crayfish processing water produced in the boiling and cooling stages contains shrimp roe and water-soluble protein. Direct discharge will not only cause environmental pollution, but also cause a waste of nutrients. The crayfish processing water is layered after standing, wherein the upper layer is a fat layer containing solid and liquid shrimp roe components, and the lower layer is an aqueous solution layer containing water-soluble protein. In order to better recycle the nutrients in the crayfish processing water, the present invention provides a method for reclaiming the nutrients in the crayfish processing water, and the crayfish processing water can be the processing water for boiling and cooling one or two stages during the crayfish processing.

[0030] The method comprises the following steps:

[0031] S1. The crayfish processing water is allowed to stand for stratification and initial separation to obtain an upper layer containing solid and liquid shrimp roe components, i.e., a first processed product for recovering shrimp roe, and a lower aqueous solution layer, i.e., a second processed product for recovering water-soluble protein;

[0032] S2. The first processed product is processed using a hanging bag centrifuge to obtain a filtrate and a semi-solid residue trapped in the hanging bag, and the filtrate and the residue are recovered, wherein the residue is a crude shrimp roe product, and the filtrate is incorporated into the second processed product separated in step S1 to obtain a mixed filtrate, wherein the hanging bag of the hanging bag centrifuge is provided with a hydrophilic oleophobic coating;

[0033] S3. The crude shrimp roe product and the mixed filtrate obtained in step S2 are treated respectively: the crude shrimp roe product is placed in rice washing water for bubbling washing, filtered using a hanging bag centrifuge provided with a hydrophilic oleophobic coating, then placed in a peracetic acid solution for ultrasonic shaking combined washing, filtered using a hanging bag centrifuge provided with a hydrophilic oleophobic coating to obtain shrimp roe; chitosan and sodium alginate are added to the mixed filtrate to flocculate and precipitate the water-soluble protein, and filtered to obtain the recovered water-soluble protein.

[0034] By using a hanging bag centrifuge with a hydrophilic and oleophobic coating on the hanging bag, solid shrimp roe and liquid fatty components can be retained in the hanging bag to obtain a semi-solid filter residue, i.e., crude shrimp roe. The aqueous solution containing water-soluble protein is passed through the hanging bag as the filtrate and combined with the second processed product obtained by the initial separation to extract the water-soluble protein using a flocculation method.

[0035] The crude shrimp roe is washed with rice water and peracetic acid solution successively. The rice water can remove dirt and heavy metals, while reducing the fishy smell of shrimp roe and improving the flavor. Peracetic acid, as a high-efficiency disinfectant with antibacterial activity, can destroy microbial proteins and enzymes through hydroxyl free radical oxidation, thereby sterilizing the shrimp roe without producing toxic residues.

[0036] In some specific embodiments, after the crayfish processing water is allowed to stand and separate into layers in step S1, the gate is opened to discharge the material and separate the aqueous solution layer as much as possible to obtain a first processed product including a fat layer and a separated second processed product containing mostly aqueous solution.

[0037] In some specific embodiments, after the crayfish processing water is allowed to stand and separate into layers in step S1, the gate is opened to discharge the lower aqueous solution until the liquid level of the aqueous solution layer is 4-6 cm, and the lower aqueous solution is separated and removed as much as possible to obtain a first processed product containing a fat layer and a separated second processed product containing most of the aqueous solution.

[0038] In some specific embodiments, the hydrophilic-oleophobic coating is composited by polydopamine and sodium polyacrylate.

[0039] Further, the method of providing a hydrophilic and oleophobic coating composed of polydopamine and sodium polyacrylate on the hanging bag is:

[0040] 1) dissolving dopamine in a Tris-HCl buffer solution with a pH of 6.8 to 8.5 to obtain a dopamine solution, and immersing the hanging bag in the dopamine solution for 25 to 40 minutes;

[0041] 2) Add sodium persulfate to the dopamine solution in which the hanging bag is soaked, and continue soaking for 20 to 30 minutes;

[0042] 3) Sodium polyacrylate is added to the solution in which the hanging bag is soaked in step 2) to obtain a mixed solution, the hanging bag continues to be soaked in the mixed solution for 1.5 to 2.5 hours, and then the hanging bag is taken out, cleaned, and dried.

[0043] The present invention uses polydopamine and sodium polyacrylate to obtain a hydrophilic and oleophobic coating, which has good hydrophilicity and oleophobicity. The polydopamine has good adhesion and can enhance the adhesion of the hanging bag surface. The sodium persulfate used in the preparation is used as an initiator to promote the polymerization reaction of dopamine and the rapid formation of a coating by sodium polyacrylate. The coating can be used for the effective separation of crayfish roe, liquid fatty components and other components, and greatly improves the recovery rate of crude roe.

[0044] According to the above scheme, in step 3), after adding sodium polyacrylate, stir at room temperature for 1 to 2 hours, then let it stand and soak for 20 to 40 minutes before taking it out.

[0045] Furthermore, the mass concentration of dopamine in the dopamine solution is 0.5% to 4%, the molar concentration of sodium persulfate in the mixed solution is 0.1 to 1 mol / L, and the mass concentration of sodium polyacrylate is 0.1% to 2%.

[0046] In some specific embodiments, in step S3, the weight ratio of shrimp roe to rice washing water is 1:10-30, the bubbling flow rate is 200-250 L / min, and the bubbling cleaning time is 20-35 min.

[0047] In some specific embodiments, the concentration of the peracetic acid solution in step S3 is 0.3% to 1%, the ultrasonic power is 300 to 500 W, the ultrasonic temperature is 40 to 50° C., and the ultrasonic time is 20 to 60 min.

[0048] In some specific embodiments, in step S3, the deacetylation degree of the chitosan is 80-90%. Before using chitosan and sodium alginate, chitosan is first dissolved in 0.5wt%-2wt% acetic acid solution to prepare a chitosan acetic acid solution with a chitosan concentration of 0.5%-1%, and sodium alginate is dissolved in water to prepare a sodium alginate aqueous solution with a concentration of 0.3%-0.6%. The added amounts of chitosan and sodium alginate per liter of filtrate are 2.5g-5g and 1.5g-3g, respectively.

[0049] The following are specific embodiments.

[0050] Example 1 A method for recovering nutrients from crayfish processing water

[0051] The crayfish processing water in this embodiment is the processing water generated in the crayfish steaming and cooling process, and the recovery method comprises the following steps:

[0052] (1) Preparation of hydrophilic and oleophobic hanging bags: Weigh 5 g of dopamine and dissolve it in a 10 mM Tris-HCl buffer solution with a pH of 8.5 to prepare a dopamine solution with a mass concentration of 0.5%. Soak the hanging bag in the solution for 30 minutes, then add sodium persulfate to make the concentration of sodium persulfate in the solution 0.1 mol / L, and continue soaking for 30 minutes. Then weigh sodium polyacrylate and add it to the solution to make the mass concentration of sodium polyacrylate in the solution 0.3%, stir at room temperature for 2 hours, let it stand for 30 minutes, then take out the hanging bag, wash it with clean water and ethanol respectively, and dry it at 50°C to obtain a hydrophilic and oleophobic hanging bag.

[0053] (2) Initial separation: First, the crayfish processing water is discharged by opening the valve to separate a portion of the lower aqueous solution and inject it into the hanging bag centrifuge (without the hanging bag at this time), and the liquid level of the aqueous solution layer is 5 cm, and then the separation is stopped to obtain a first processed product containing a fat layer and a separated second processed product containing most of the aqueous solution;

[0054] (3) Raw material recovery: The first processed product is poured into a bag centrifuge having the above-mentioned hydrophilic and oleophobic bag placed therein, at a speed of 1500 r / min, to obtain a filtrate and a filter residue trapped in the hydrophilic and oleophobic bag, wherein the filter residue is a crude shrimp roe product and is recovered for later use; the filtrate is combined with the second processed product obtained by the initial separation to obtain a mixed filtrate, and chitosan-sodium alginate is added to the mixed filtrate at a feed rate of 4 g / L, wherein the mass ratio of chitosan to sodium alginate is 5:3, wherein: chitosan is dissolved in 500 mL of 2% acetic acid solution to prepare a chitosan acetic acid solution in advance, sodium alginate is dissolved in deionized water to prepare a sodium alginate aqueous solution in advance, the chitosan acetic acid solution and the sodium alginate aqueous solution are mixed and set aside, the water-soluble protein is flocculated, allowed to stand for 30 min, filtered, and the recovered water-soluble protein is placed in a -80°C refrigerator for later use.

[0055] (4) Raw material cleaning and processing: soak the crude shrimp roe product recovered in step (3) in rice washing water for bubbling cleaning, wherein the weight ratio of the crude shrimp roe product to the rice washing water during the cleaning process is 1:10 (m:m), the bubbling flow rate is 220 L / min, the bubbling cleaning time is 30 min, and the raw material is filtered in a hanging bag centrifuge equipped with a hydrophilic and oleophobic hanging bag, and then placed in a hanging bag centrifuge equipped with a 0.3% peracetic acid solution for ultrasonic and oscillation combined cleaning for 20 min, and filtered in a hanging bag centrifuge equipped with a hydrophilic and oleophobic hanging bag to obtain shrimp roe, which is placed in a -80°C refrigerator for freezing and standby use;

[0056] Example 2 A method for recovering nutrients from crayfish processing water

[0057] The crayfish processing water in this embodiment is the processing water generated in the crayfish steaming and cooling process, and the recovery method comprises the following steps:

[0058] (1) Preparation of hydrophilic and oleophobic hanging bags: Weigh 5 g of dopamine and dissolve it in a 10 mM Tris-HCl buffer solution with a pH of 8.5 to prepare a dopamine solution with a mass concentration of 1.0%. Soak the hanging bag in the solution for 30 minutes, then add sodium persulfate to make the concentration of sodium persulfate in the solution 0.3 mol / L, and continue soaking for 30 minutes. Then weigh sodium polyacrylate and add it to the solution to make the mass concentration of sodium polyacrylate in the solution 0.6%, stir at room temperature for 2 hours, let it stand for 30 minutes, then take out the hanging bag, wash it with clean water and ethanol respectively, and dry it at 50°C to obtain a hydrophilic and oleophobic hanging bag.

[0059] (2) Initial separation: First, the crayfish processing water is discharged by opening the valve to separate a portion of the lower aqueous solution and inject it into the hanging bag centrifuge (without the hanging bag at this time), and the liquid level of the aqueous solution layer is 5 cm, and then the separation is stopped to obtain a first processed product containing a fat layer and a separated second processed product containing most of the aqueous solution;

[0060] (3) Raw material recovery: the first processed product is poured into a hanging bag centrifuge in which the above-mentioned hydrophilic and oleophobic hanging bags are placed, and the speed is 1500r / min to obtain a filtrate and a filter residue trapped in the hydrophilic and oleophobic hanging bags, wherein the filter residue is a crude shrimp roe product and is recovered for later use; the filtrate is combined with the second processed product obtained by the initial separation in step (2) to obtain a mixed filtrate, and chitosan-sodium alginate is added to the mixed filtrate at a feed rate of 5g / L, and the mass ratio of chitosan to sodium alginate is 5:3, wherein: chitosan is dissolved in 500mL of 2% acetic acid solution to prepare a chitosan acetic acid solution in advance, and sodium alginate is dissolved in 500mL of deionized water to prepare a sodium alginate aqueous solution in advance, and the chitosan acetic acid solution and the sodium alginate aqueous solution are mixed and set aside, and the water-soluble protein is flocculated, left to stand for 30min, filtered, and the recovered water-soluble protein is placed in a -80°C refrigerator for later use.

[0061] (4) Raw material cleaning and processing: The shrimp roe recovered in step (3) is soaked in rice washing water for bubbling cleaning, wherein the weight ratio of the crude shrimp roe to the rice washing water is 1:15 (m:m), the bubbling flow rate is 225 L / min, the bubbling cleaning time is 30 min, and the raw material is filtered in a hanging bag centrifuge equipped with a hydrophilic and oleophobic hanging bag, and then placed in a hanging bag centrifuge equipped with a 0.5% peracetic acid solution for ultrasonic and oscillation combined cleaning for 40 min, and filtered in a hanging bag centrifuge equipped with a hydrophilic and oleophobic hanging bag to obtain shrimp roe, which is placed in a -80°C refrigerator for freezing and standby use;

[0062] Example 3 A method for recovering nutrients from crayfish processing water

[0063] The crayfish processing water in this embodiment is the processing water generated in the crayfish steaming and cooling process, and the recovery method comprises the following steps:

[0064] (1) Preparation of hydrophilic and oleophobic hanging bags: Weigh 5 g of dopamine and dissolve it in a 10 mM Tris-HCl buffer solution with a pH of 8.5 to prepare a dopamine solution with a mass concentration of 1.5%. Soak the hanging bag in the solution for 30 minutes, then add sodium persulfate to make the concentration of sodium persulfate in the solution 0.5 mol / L, and continue soaking for 30 minutes. Then weigh sodium polyacrylate and add it to the solution to make the mass concentration of sodium polyacrylate in the solution 0.9%, stir at room temperature for 2 hours, let it stand for 30 minutes, then take out the hanging bag, wash it with clean water and ethanol respectively, and dry it at 50°C to obtain a hydrophilic and oleophobic hanging bag.

[0065] (2) Initial separation: First, the crayfish processing water is discharged by opening the valve to separate a portion of the lower aqueous solution and inject it into the hanging bag centrifuge (without the hanging bag at this time), and the liquid level of the aqueous solution layer is 5 cm, and then the separation is stopped to obtain a first processed product containing a fat layer and a separated second processed product containing most of the aqueous solution;

[0066] (3) Raw material recovery: the first processed product is poured into a bag centrifuge having the above-mentioned hydrophilic and oleophobic bag placed therein, at a speed of 1500 r / min, to obtain a filtrate and a filter residue trapped in the hydrophilic and oleophobic bag, wherein the filter residue is a crude shrimp roe product and is recovered for later use; the filtrate is incorporated into the second processed product obtained by initial separation in step (2) to obtain a mixed filtrate, and chitosan-sodium alginate is added to the mixed filtrate at a feed rate of 4 g / L, wherein the mass ratio of chitosan to sodium alginate is 5:3, wherein: chitosan is dissolved in 500 mL of 2% acetic acid solution to prepare a chitosan acetic acid solution in advance, sodium alginate is dissolved in 500 mL of deionized water to prepare a sodium alginate aqueous solution in advance, the chitosan acetic acid solution and the sodium alginate aqueous solution are mixed and set aside, the water-soluble protein is flocculated, allowed to stand for 30 min, filtered, and the recovered water-soluble protein is placed in a -80°C refrigerator for later use.

[0067] (4) Raw material cleaning and treatment: The crude shrimp roe product recovered in step (3) is soaked in rice washing water for bubbling cleaning, wherein the weight ratio of the crude shrimp roe product to the rice washing water is 1:20 (m:m), the bubbling flow rate is 250 L / min, the bubbling cleaning time is 30 min, and the raw material is filtered in a hanging bag centrifuge equipped with a hydrophilic and oleophobic hanging bag, and then placed in a hanging bag centrifuge equipped with a 0.8% peracetic acid solution for ultrasonic and oscillation combined cleaning for 60 min, and filtered in a hanging bag centrifuge equipped with a hydrophilic and oleophobic hanging bag to obtain shrimp roe, which is placed in a -80°C refrigerator for freezing and standby use;

[0068] Comparative Example 1

[0069] The difference between this comparative example and Example 1 is that the surface of the hanging bag is not coated with a hydrophilic oleophobic coating.

[0070] Comparative Example 2

[0071] The difference between this comparative example and Example 1 is that: in step (3), no flocculation is performed, the mixed filtrate is allowed to stand for 30 minutes, filtered, and the precipitate is obtained and placed in a -80°C refrigerator for freezing for later use.

[0072] Comparative Example 3

[0073] The difference between this comparative example and Example 1 is that rice washing water and peracetic acid solution are not used for cleaning, and the specific operation of step (4) is: soaking the crude shrimp roe recovered in step (3) in ultrapure water at a weight ratio of 1:10 (m:m) for 30 minutes, filtering, and freezing in a -80°C refrigerator for later use.

[0074] The performance of the hydrophilic and oleophobic hanging bag in Example 1 was tested. The wettability water contact angle of the coating reached 7.52°, and the underwater oil contact angle reached 163°, which showed good hydrophilic and oleophobic properties.

[0075] The amounts of shrimp roe and water-soluble protein recovered in Examples 1-3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were measured, and the odor, microorganisms and heavy metal content of the recovered shrimp roe were tested.

[0076] 1) The evaluation criteria for the smell of shrimp roe are as follows:

[0077] 5 points: Full of shrimp flavor, no rancid smell

[0078] 3-4 points: Shrimp smell, no peculiar smell or obvious rancid smell

[0079] 1-2 points: There is a peculiar smell and a distinct rancid smell

[0080] 2) The test method for the crude shrimp roe yield is as follows:

[0081] Yield of crude shrimp yellow product = (weight of crude shrimp yellow product / weight of first processed product)*100%

[0082] 3) The recovery test method of water-soluble protein is as follows:

[0083] Water-soluble protein recovery rate = (1-water-soluble protein mass concentration in the supernatant obtained after flocculation / protein mass concentration in the mixed filtrate before flocculation) * 100%

[0084] Water-soluble protein content = (mass of water-soluble protein in recovered water-soluble protein / mass of recovered water-soluble protein) * 100%

[0085] Table 1

[0086]

[0087]

[0088] It can be seen from the above table that the recovery efficiency of shrimp roe using the method of the present invention can reach more than 85%. In Comparative Example 1, the hanging bag is not coated with a hydrophilic oleophobic coating, and the recovery efficiency of shrimp roe is only 51.25%. It can be seen that coating a hydrophilic oleophobic coating can greatly improve the recovery efficiency of shrimp roe, and the combined cleaning of rice washing water and peracetic acid can efficiently sterilize, remove heavy metal ions, remove the fishy smell of shrimp roe, and improve the quality of shrimp roe.

[0089] The lower aqueous solution after the crayfish processing water is left to stand contains not only water-soluble proteins but also insoluble nutrients such as shrimp meat scraps that enter the cooking water after cooking. In Comparative Example 2, which is not flocculated, the insoluble nutrients can be directly obtained by precipitation filtration, and the water-soluble proteins cannot be recovered. In Examples 1-3, the recovered water-soluble proteins obtained by flocculation contain not only recovered water-soluble proteins but also insoluble shrimp meat scraps, etc., wherein the content of water-soluble proteins is above 53%. The recovered water-soluble proteins can be used as raw materials to prepare animal food such as feed.

[0090] The invention adopts a hanging bag coated with polydopamine and sodium polyacrylate to separate fat-soluble shrimp roe components, adopts rice washing water combined with peracetic acid for cleaning, can efficiently recover shrimp roe, retain its nutritional components to the greatest extent and ensure the safety of nutrients, and adopts a flocculation method to recover water-soluble protein components in the aqueous solution, so as to fully recycle and utilize the nutrients, and the obtained shrimp roe and water-soluble protein floccules are rich in nutrition, safe and reliable, and can be used for the preparation of animal food such as feed.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for recovering nutrients from water used in crayfish processing, characterized in that: The steps include: S1. Primary separation: The crayfish processing water is allowed to stand for stratification, and the upper layer containing solid and liquid shrimp roe components is initially separated to obtain a first processed product for recovering shrimp roe, and the lower aqueous solution layer is used to recover a second processed product of water-soluble protein; S2. The first processed product is processed using a hanging bag centrifuge to obtain a filtrate and a semi-solid residue trapped in the hanging bag, and the filtrate and the residue are recovered, wherein the residue is a crude shrimp roe product, and the filtrate is incorporated into the second processed product separated in step S1 to obtain a mixed filtrate, wherein the hanging bag of the hanging bag centrifuge is provided with a hydrophilic oleophobic coating; S3. respectively treating the crude shrimp roe product and the mixed filtrate obtained in step S2: placing the crude shrimp roe product in rice washing water for bubbling washing, filtering using a hanging bag centrifuge provided with a hydrophilic oleophobic coating, then placing the crude shrimp roe product in a peracetic acid solution for ultrasonic shaking combined washing, filtering using the hanging bag centrifuge provided with a hydrophilic oleophobic coating to obtain shrimp roe; adding chitosan and sodium alginate to the mixed filtrate to flocculate and precipitate the water-soluble protein, filtering, and obtaining the recovered water-soluble protein.

2. The method for recovering nutrients from crayfish processing water according to claim 1, characterized in that: The hydrophilic and oleophobic coating is composited from polydopamine and sodium polyacrylate.

3. The method for recovering nutrients from crayfish processing water according to claim 2, characterized in that: The method for providing a hydrophilic and oleophobic coating composed of polydopamine and sodium polyacrylate on a hanging bag is as follows: 1) dissolving dopamine in a Tris-HCl buffer solution with a pH of 6.8 to 8.5 to obtain a dopamine solution, and immersing the hanging bag in the dopamine solution for 25 to 40 minutes; 2) Add sodium persulfate to the dopamine solution in which the hanging bag is soaked, and continue soaking for 20 to 30 minutes; 3) Sodium polyacrylate is added to the solution in which the hanging bag is soaked in step 2) to obtain a mixed solution, the hanging bag continues to be soaked in the mixed solution for 1.5 to 2.5 hours, and then the hanging bag is taken out, cleaned, and dried.

4. The method for recovering nutrients from crayfish processing water according to claim 3, characterized in that: The mass concentration of dopamine in the dopamine solution is 0.5% to 4%, the molar concentration of sodium persulfate in the mixed solution is 0.1 to 1 mol / L, and the mass concentration of sodium polyacrylate is 0.1% to 2%.

5. The method for recovering nutrients from crayfish processing water according to claim 1, characterized in that: In step S3, the weight ratio of shrimp roe to rice washing water is 1:10-30, the bubbling flow rate is 200-250L / min, and the bubbling cleaning time is 20-35min.

6. The method for recovering nutrients from crayfish processing water according to claim 1, characterized in that: In step S3, the concentration of the peracetic acid solution is 0.3% to 1%, the ultrasonic power is 300 to 500 W, the ultrasonic temperature is 40 to 50° C., and the ultrasonic time is 20 to 60 min.

7. The method for recovering nutrients from crayfish processing water according to claim 1, characterized in that: In step S3, the deacetylation degree of the chitosan is 80% to 99%. Before using chitosan and sodium alginate, chitosan is dissolved in 0.5wt% to 2wt% acetic acid solution to prepare a chitosan acetic acid solution with a chitosan concentration of 0.5% to 1%, and sodium alginate is dissolved in water to prepare a sodium alginate aqueous solution with a concentration of 0.3% to 0.6%. The addition amounts of chitosan and sodium alginate per liter of mixed filtrate are 2.5g to 5g and 1.5g to 3g, respectively.

8. The method for recovering nutrients from crayfish processing water according to claim 1, characterized in that: In step S1, after the crayfish processing water is allowed to stand for stratification, the gate is opened to discharge the material to separate the aqueous solution layer as much as possible, thereby obtaining a first processed product including a fat layer and a separated second processed product containing most of the aqueous solution.

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