Method for recovering protein in surimi rinse water by combining cationic hydrogel with electric field

Abstract

The invention provides a method for recovering protein in surimi rinse water by combining cationic hydrogel with an electric field, which comprises the following steps of: adding a tannic acid-dextran copolymer while applying a low-voltage electric field to the surimi rinse water to obtain protein flocculate, then adding the cationic hydrogel, and performing in-situ gelation on the surface of the protein flocculate to obtain the protein flocculate. The volume of protein flocculate is increased, protein sedimentation and solid-liquid separation are promoted, and finally, the protein in the surimi rinsing water is recycled.

Description

Technical Field

[0001] The invention belongs to the technical field of protein recovery, and in particular relates to a method for recovering protein in fish paste rinsing water by combining cationic hydrogel with electric field. Background Art

[0002] Rinsing is an essential process in the production and processing of frozen surimi. Rinsing can effectively remove the fishy smell, residual fish scraps, fat, pigments and other substances in the fish meat, and improve the gel properties of surimi and surimi products. However, a large amount of organic water containing water-soluble protein will be produced during the rinsing process. It is estimated that it takes about 25-40 tons of water to produce 1 ton of surimi, and the protein concentration in the discharged surimi rinsing water is as high as 5-30 mg / mL. How to recycle this part of protein is also one of the hot topics studied by scientists.

[0003] As for the methods of recycling protein in fish surimi rinsing water, isoelectric precipitation method, resistance heating method, flocculation method and membrane separation method have been reported so far, but these methods have their own advantages and disadvantages. Patent application number CN202410451379.1 discloses a method for recovering protein in fish surimi rinsing water by combining low-voltage electric field with thermal flocculation. After research, it was found that the protein recovery effect of treating fish surimi rinsing water with low-voltage electric field is equivalent to that of chitosan flocculation method-isoelectric precipitation method, but there is still a lot of room for improvement. Therefore, how to recover protein in fish surimi rinsing water more efficiently and improve water resources and the utilization rate of recovered protein has become an urgent problem to be solved. Summary of the invention

[0004] Technical problem to be solved: In view of the above problems, the purpose of the present invention is to provide a method for recovering protein in fish paste rinsing water by combining cationic hydrogel with electric field. Tannic acid-dextran copolymer is added while treating with low-voltage electric field to obtain protein flocs, and then cationic hydrogel is added to gelate in situ on the surface of protein flocs, which is beneficial to increase the volume of protein flocs, promote protein sedimentation and solid-liquid separation, and realize the recovery and utilization of protein in fish paste rinsing water by low-voltage electric field and cationic hydrogel treatment.

[0005] Technical solution: A method for recovering protein in surimi rinsing water by combining cationic hydrogel with electric field, comprising the following steps: S1. Collecting surimi rinse water; S2. Place the surimi rinse water in a low-voltage electric field protein recovery tank and perform electric field treatment at 25-30°C and 30-40V. At the same time, add tannic acid-dextran copolymer to the recovery tank, mix evenly, react for 30-60 minutes, then add cationic hydrogel, mix evenly, react for 15-30 minutes, collect the lower protein sedimentation layer to obtain protein solids and supernatant, adjust the pH of the protein solids to 4 and then recover the protein.

[0006] Furthermore, in step S1, the surimi rinsing water is obtained by rinsing fish meat and water in a mass ratio of 1:4, and the protein concentration in the surimi rinsing water is 4.8-20.5 mg / mL.

[0007] Furthermore, in step S2, the anode plate of the low-voltage electric field protein recovery tank is a ruthenium-iridium-titanium plate, the cathode plate is a pure titanium plate, and the spacing between adjacent electrode plates is 3-6 cm.

[0008] Furthermore, in step S2, the mass volume ratio of tannic acid-dextran copolymer, cationic hydrogel and fish paste rinsing water is (1.5-2): (1-1.5):3.

[0009] Furthermore, the preparation method of the tannic acid-dextran copolymer in step S2 is as follows: Step 1: dissolve dextran in a pH 4-5 acetate buffer solution, stir at 50-60°C for 10-20 minutes to prepare a dextran solution with a concentration of 2-5%; Step 2: Add tannic acid, stir evenly, then add laccase, stir at 30-40°C for 10-15h to obtain a tannic acid-dextran copolymer solution; Step 3: inactivate the enzyme in the tannic acid-dextran copolymer solution, dialyze, and dry to obtain the tannic acid-dextran copolymer.

[0010] Furthermore, in step 2, the mass ratio of tannic acid to dextran is 1:(2-4); and the concentration of laccase is 0.3-0.5 U / mL.

[0011] Furthermore, the cationic hydrogel in step S2 is bacterial cellulose cross-linked polyglutamic acid / Ca 2+ The hydrogel was prepared as follows: Step 1: dissolving polyglutamic acid in deionized water, adjusting the pH to 7-8, and preparing a polyglutamic acid solution with a concentration of 1-3%; Step 2: immersing bacterial cellulose in a polyglutamic acid solution, leaving it to stand at room temperature for 12-24 hours, and washing it to obtain a bacterial cellulose-polyglutamic acid complex; Step 3: Soak the BC-PGM complex in 0.1-0.5 M CaCl 2The solution was soaked at room temperature for 2-5 hours, filtered and washed to obtain bacterial cellulose cross-linked polyglutamic acid / Ca 2+ Hydrogel.

[0012] Furthermore, in step 2, the mass volume ratio of bacterial cellulose to polyglutamic acid solution is 1:(2-3).

[0013] Furthermore, in step 3, the bacterial cellulose-polyglutamic acid complex and CaCl 2 The mass volume ratio of the solution is 1:(1-2). Beneficial Effects

[0014] The present invention treats protein flocculation in fish paste rinsing water in a low-voltage electric field, and at the same time, adds tannic acid-dextran copolymer to the rinsing water, obtains protein floccules, and then adds cationic hydrogel to gel in situ on the surface of the protein floccules, which is beneficial to increase the volume of the protein floccules, promotes protein sedimentation and solid-liquid separation, and realizes the recovery and utilization of protein in fish paste rinsing water; In the present invention, tannic acid-dextran copolymer is selected for protein flocculation. Dextran, as a linear polysaccharide, mainly promotes flocculation through steric hindrance and weak hydrogen bonding. However, it has strong hydrophilicity and lacks functional groups, resulting in limited binding force with proteins. Therefore, laccase is used to catalyze the oxidation of phenolic hydroxyl groups of tannic acid to generate free radical intermediates, which are then covalently cross-linked with hydroxyl groups of dextran to form tannic acid-dextran copolymer to overcome this problem. After being put into fish paste rinsing water, the dextran chain segments in the copolymer serve as long-chain skeletons to adsorb protein particles in the water through physical or chemical effects to form a "bridging" effect, connecting the dispersed protein particles into larger flocs, and tannic acid can further enhance the binding force with proteins through hydrogen bonds, hydrophobic effects or electrostatic attraction. Therefore, the copolymer realizes further flocculation of proteins in fish paste rinsing water. In the present invention, after adding tannic acid-dextran copolymer to form protein floccules, bacterial cellulose cross-linked polyglutamic acid / Ca is continuously added. 2+ Hydrogel, polyglutamic acid and bacterial cellulose have the ability to promote protein flocculation. Polyglutamic acid contains a large number of carboxyl groups, which can be combined with the hydroxyl groups of bacterial cellulose through chemical bonds. The carboxyl groups on the side chains of polyglutamic acid can also be combined with Ca 2+ Chelation occurs to achieve further grafting; therefore, after the addition of cationic hydrogel, Ca 2+The negatively charged groups on the protein surface are combined through electrostatic interactions, so that the cationic hydrogel is tightly coated on the surface of the protein flocculants, achieving in situ gelation to obtain protein solids, increase the volume of the protein solids, promote their sedimentation and solid-liquid separation, and then adjust the pH to be lower than the isoelectric point of the protein, so that the protein is positively charged and produces electrostatic repulsion with the hydrogel, allowing the protein to be desorbed from the hydrogel, ultimately achieving the recovery and utilization of protein in the fish paste rinsing water. DETAILED DESCRIPTION

[0015] The present invention will be further described below in conjunction with embodiments, which are explanations of the present invention and are not limited to the following embodiments: Example 1

[0016] A method for recovering protein in surimi rinsing water by using cationic hydrogel combined with electric field, comprising the following steps: S1. Preparation of tannic acid-dextran copolymer: dissolve dextran in pH 5 acetic acid buffer solution, stir at 60°C for 10 min to prepare a dextran solution with a concentration of 3%; add tannic acid, the mass ratio of tannic acid to dextran is 1:2, stir evenly, then add laccase with a concentration of 0.5 U / mL, stir at 40°C for 10 h to obtain a tannic acid-dextran copolymer solution; inactivate the enzyme in the tannic acid-dextran copolymer solution, dialyze, and dry to obtain a tannic acid-dextran copolymer; S2. BC cross-linked polyglutamic acid / Ca 2+ Preparation of hydrogel: polyglutamic acid was dissolved in deionized water, and the pH was adjusted to 7 to prepare a polyglutamic acid solution with a concentration of 2%. Bacterial cellulose was immersed in the polyglutamic acid solution with a mass volume ratio of 1:2, and allowed to stand at room temperature for 20 h, and then washed to obtain a bacterial cellulose-polyglutamic acid complex. The bacterial cellulose-polyglutamic acid complex was immersed in 0.3 M CaCl 2 The solution was prepared with a mass volume ratio of 1:2, and then immersed at room temperature for 3 h, filtered, and washed to obtain bacterial cellulose cross-linked polyglutamic acid / Ca 2+ Hydrogel; S3. Collecting the surimi rinse water with a protein concentration of 10.5 mg / mL; S4. Place the surimi rinse water in a low-voltage electric field protein recovery tank and perform electric field treatment at 25°C and 35V. Add tannic acid-dextran copolymer and mix well. After reacting for 60 minutes, add bacterial cellulose cross-linked polyglutamic acid / Ca 2+ The mass volume ratio of hydrogel, tannic acid-dextran copolymer, cationic hydrogel and fish paste rinsing water is 2:1:3, mixed evenly, reacted for 30 minutes, and the lower protein sedimentation layer was collected to obtain protein solids and supernatant. The protein solids were adjusted to pH 4 and then the protein was recovered. Example 2

[0017] A method for recovering protein in surimi rinsing water by using cationic hydrogel combined with electric field, comprising the following steps: S1. Preparation of tannic acid-dextran copolymer: dissolve dextran in pH 5 acetic acid buffer solution, stir at 60°C for 10 min to prepare a dextran solution with a concentration of 3%; add tannic acid, the mass ratio of tannic acid to dextran is 1:3, stir evenly, then add laccase with a concentration of 0.5 U / mL, stir at 40°C for 10 h to obtain a tannic acid-dextran copolymer solution; inactivate the enzyme in the tannic acid-dextran copolymer solution, dialyze, and dry to obtain a tannic acid-dextran copolymer; S2. BC cross-linked polyglutamic acid / Ca 2+ Preparation of hydrogel: polyglutamic acid was dissolved in deionized water, and the pH was adjusted to 7 to prepare a polyglutamic acid solution with a concentration of 2%. Bacterial cellulose was immersed in the polyglutamic acid solution with a mass volume ratio of 1:2, and allowed to stand at room temperature for 20 h, and then washed to obtain a bacterial cellulose-polyglutamic acid complex. The bacterial cellulose-polyglutamic acid complex was immersed in 0.3 M CaCl 2 The solution was prepared with a mass volume ratio of 1:2, and then immersed at room temperature for 3 h, filtered, and washed to obtain bacterial cellulose cross-linked polyglutamic acid / Ca 2+ Hydrogel; S3. Collecting the surimi rinse water with a protein concentration of 10.5 mg / mL; S4. Place the surimi rinse water in a low-voltage electric field protein recovery tank and perform electric field treatment at 25°C and 35V. Add tannic acid-dextran copolymer and mix well. After reacting for 60 minutes, add bacterial cellulose cross-linked polyglutamic acid / Ca 2+ The mass volume ratio of hydrogel, tannic acid-dextran copolymer, cationic hydrogel and fish paste rinsing water is 2:1:3, mixed evenly, reacted for 30 minutes, and the lower protein sedimentation layer was collected to obtain protein solids and supernatant. The protein solids were adjusted to pH 4 and then the protein was recovered. Example 3

[0018] A method for recovering protein in surimi rinsing water by using cationic hydrogel combined with electric field, comprising the following steps: S1. Preparation of tannic acid-dextran copolymer: dissolve dextran in pH 5 acetic acid buffer solution, stir at 60°C for 10 min to prepare a dextran solution with a concentration of 3%; add tannic acid, the mass ratio of tannic acid to dextran is 1:4, stir evenly, then add laccase with a concentration of 0.5 U / mL, stir at 40°C for 10 h to obtain a tannic acid-dextran copolymer solution; inactivate the enzyme in the tannic acid-dextran copolymer solution, dialyze, and dry to obtain a tannic acid-dextran copolymer; S2. BC cross-linked polyglutamic acid / Ca 2+ Preparation of hydrogel: polyglutamic acid was dissolved in deionized water, and the pH was adjusted to 7 to prepare a polyglutamic acid solution with a concentration of 2%. Bacterial cellulose was immersed in the polyglutamic acid solution with a mass volume ratio of 1:2, and allowed to stand at room temperature for 20 h, and then washed to obtain a bacterial cellulose-polyglutamic acid complex. The bacterial cellulose-polyglutamic acid complex was immersed in 0.3 M CaCl 2 The solution was prepared with a mass volume ratio of 1:2, and then immersed at room temperature for 3 h, filtered, and washed to obtain bacterial cellulose cross-linked polyglutamic acid / Ca 2+ Hydrogel; S3. Collecting the surimi rinse water with a protein concentration of 10.5 mg / mL; S4. Place the surimi rinse water in a low-voltage electric field protein recovery tank and perform electric field treatment at 25°C and 35V. Add tannic acid-dextran copolymer and mix well. After reacting for 60 minutes, add bacterial cellulose cross-linked polyglutamic acid / Ca 2+ The mass volume ratio of hydrogel, tannic acid-dextran copolymer, cationic hydrogel and fish paste rinsing water is 2:1:3, mixed evenly, reacted for 30 minutes, and the lower protein sedimentation layer was collected to obtain protein solids and supernatant. The protein solids were adjusted to pH 4 and then the protein was recovered. Example 4

[0019] A method for recovering protein in surimi rinsing water by using cationic hydrogel combined with electric field, comprising the following steps: S1. Preparation of tannic acid-dextran copolymer: dissolve dextran in pH 5 acetic acid buffer solution, stir at 60°C for 10 min to prepare a dextran solution with a concentration of 3%; add tannic acid, the mass ratio of tannic acid to dextran is 1:3, stir evenly, then add laccase with a concentration of 0.5 U / mL, stir at 40°C for 10 h to obtain a tannic acid-dextran copolymer solution; inactivate the enzyme in the tannic acid-dextran copolymer solution, dialyze, and dry to obtain a tannic acid-dextran copolymer; S2. BC cross-linked polyglutamic acid / Ca 2+Preparation of hydrogel: polyglutamic acid was dissolved in deionized water, and the pH was adjusted to 7 to prepare a polyglutamic acid solution with a concentration of 2%. Bacterial cellulose was immersed in the polyglutamic acid solution with a mass volume ratio of 1:2, and allowed to stand at room temperature for 20 h, and then washed to obtain a bacterial cellulose-polyglutamic acid complex. The bacterial cellulose-polyglutamic acid complex was immersed in 0.3 M CaCl 2 The solution was prepared with a mass volume ratio of 1:2, and then immersed at room temperature for 3 h, filtered, and washed to obtain bacterial cellulose cross-linked polyglutamic acid / Ca 2+ Hydrogel; S3. Collecting the surimi rinse water with a protein concentration of 10.5 mg / mL; S4. Place the surimi rinse water in a low-voltage electric field protein recovery tank and perform electric field treatment at 25°C and 35V. Add tannic acid-dextran copolymer and mix well. After reacting for 60 minutes, add bacterial cellulose cross-linked polyglutamic acid / Ca 2+ The mass volume ratio of hydrogel, tannic acid-dextran copolymer, cationic hydrogel and fish paste rinsing water is 1.5:1:3, mixed evenly, reacted for 30 minutes, and the lower protein sedimentation layer was collected to obtain protein solids and supernatant. The protein solids were adjusted to pH 4 and then the protein was recovered. Example 5

[0020] A method for recovering protein in surimi rinsing water by using cationic hydrogel combined with electric field, comprising the following steps: S1. Preparation of tannic acid-dextran copolymer: dissolve dextran in pH 5 acetic acid buffer solution, stir at 60°C for 10 min to prepare a dextran solution with a concentration of 3%; add tannic acid, the mass ratio of tannic acid to dextran is 1:3, stir evenly, then add laccase with a concentration of 0.5 U / mL, stir at 40°C for 10 h to obtain a tannic acid-dextran copolymer solution; inactivate the enzyme in the tannic acid-dextran copolymer solution, dialyze, and dry to obtain a tannic acid-dextran copolymer; S2. BC cross-linked polyglutamic acid / Ca 2+ Preparation of hydrogel: polyglutamic acid was dissolved in deionized water, and the pH was adjusted to 7 to prepare a polyglutamic acid solution with a concentration of 2%. Bacterial cellulose was immersed in the polyglutamic acid solution with a mass volume ratio of 1:2, and allowed to stand at room temperature for 20 h, and then washed to obtain a bacterial cellulose-polyglutamic acid complex. The bacterial cellulose-polyglutamic acid complex was immersed in 0.3 M CaCl 2 The solution was prepared with a mass volume ratio of 1:2, and then immersed at room temperature for 3 h, filtered, and washed to obtain bacterial cellulose cross-linked polyglutamic acid / Ca 2+ Hydrogel; S3. Collecting the surimi rinse water with a protein concentration of 10.5 mg / mL; S4. Place the surimi rinse water in a low-voltage electric field protein recovery tank and perform electric field treatment at 25°C and 35V. Add tannic acid-dextran copolymer and mix well. After reacting for 60 minutes, add bacterial cellulose cross-linked polyglutamic acid / Ca 2+ The mass volume ratio of hydrogel, tannic acid-dextran copolymer, cationic hydrogel and fish paste rinsing water is 1.5:1.5:3 (i.e. 1:1:2), mixed evenly, and after reacting for 30 minutes, the lower protein sedimentation layer was collected to obtain protein solids and supernatant, and the protein solids were adjusted to pH 4 to recover the protein. Example 6

[0021] A method for recovering protein in surimi rinsing water by using cationic hydrogel combined with electric field, comprising the following steps: S1. Preparation of tannic acid-dextran copolymer: dissolve dextran in pH 5 acetic acid buffer solution, stir at 60°C for 10 min to prepare a dextran solution with a concentration of 3%; add tannic acid, the mass ratio of tannic acid to dextran is 1:3, stir evenly, then add laccase with a concentration of 0.5 U / mL, stir at 40°C for 10 h to obtain a tannic acid-dextran copolymer solution; inactivate the enzyme in the tannic acid-dextran copolymer solution, dialyze, and dry to obtain a tannic acid-dextran copolymer; S2. BC cross-linked polyglutamic acid / Ca 2+ Preparation of hydrogel: polyglutamic acid was dissolved in deionized water, and the pH was adjusted to 7 to prepare a polyglutamic acid solution with a concentration of 2%. Bacterial cellulose was immersed in the polyglutamic acid solution with a mass volume ratio of 1:2, and allowed to stand at room temperature for 20 h, and then washed to obtain a bacterial cellulose-polyglutamic acid complex. The bacterial cellulose-polyglutamic acid complex was immersed in 0.3 M CaCl 2 The solution was prepared with a mass volume ratio of 1:2, and then immersed at room temperature for 3 h, filtered, and washed to obtain bacterial cellulose cross-linked polyglutamic acid / Ca 2+ Hydrogel; S3. Collecting the surimi rinse water with a protein concentration of 10.5 mg / mL; S4. Place the surimi rinse water in a low-voltage electric field protein recovery tank and perform electric field treatment at 25°C and 35V. Add tannic acid-dextran copolymer and mix well. After reacting for 60 minutes, add bacterial cellulose cross-linked polyglutamic acid / Ca 2+ The mass volume ratio of hydrogel, tannic acid-dextran copolymer, cationic hydrogel and fish paste rinsing water is 2:1.5:3, and they are mixed evenly. After reacting for 30 minutes, the lower protein sedimentation layer is collected to obtain protein solids and supernatant. The protein solids are adjusted to pH 4 to recover the protein, and the supernatant is used for the first rinsing of fish paste or for cleaning raw fish. Comparative Example 1

[0022] The difference between this comparative example and Example 2 is that dextran without grafted tannic acid is used, which is as follows: A method for recovering protein in surimi rinsing water by using cationic hydrogel combined with electric field, comprising the following steps: S1. BC cross-linked polyglutamic acid / Ca 2+ Preparation of hydrogel: polyglutamic acid was dissolved in deionized water, and the pH was adjusted to 7 to prepare a polyglutamic acid solution with a concentration of 2%. Bacterial cellulose was immersed in the polyglutamic acid solution with a mass volume ratio of 1:2, and allowed to stand at room temperature for 20 h, and then washed to obtain a bacterial cellulose-polyglutamic acid complex. The bacterial cellulose-polyglutamic acid complex was immersed in 0.3 M CaCl 2 The solution was prepared with a mass volume ratio of 1:2, and then immersed at room temperature for 3 h, filtered, and washed to obtain bacterial cellulose cross-linked polyglutamic acid / Ca 2+ Hydrogel; S2. Collecting the surimi rinse water with a protein concentration of 10.5 mg / mL; S3. Place the surimi rinse water in a low-voltage electric field protein recovery tank and perform electric field treatment at 25°C and 35V. Add dextran and react at 60°C for 60 minutes to mix evenly. Then add bacterial cellulose cross-linked polyglutamic acid / Ca 2+ The mass volume ratio of hydrogel, dextran, cationic hydrogel and surimi rinsing water is 2:1:3, mixed evenly, reacted for 30 minutes, and the lower protein sedimentation layer was collected to obtain protein solids and supernatant. The protein solids were adjusted to pH 4 and then the protein was recovered. Comparative Example 2

[0023] The difference between this comparative example and Example 2 is that no cationic hydrogel is added, specifically as follows: A method for recovering protein in surimi rinsing water comprises the following steps: S1. Preparation of tannic acid-dextran copolymer: dissolve dextran in pH 5 acetic acid buffer solution, stir at 60°C for 10 min to prepare a dextran solution with a concentration of 3%; add tannic acid, the mass ratio of tannic acid to dextran is 1:3, stir evenly, then add laccase with a concentration of 0.5 U / mL, stir at 40°C for 10 h to obtain a tannic acid-dextran copolymer solution; inactivate the enzyme in the tannic acid-dextran copolymer solution, dialyze, and dry to obtain a tannic acid-dextran copolymer; S2. Collecting the surimi rinse water with a protein concentration of 10.5 mg / mL; S3. Place the fish paste rinse water in a low-voltage electric field protein recovery tank and perform electric field treatment at 25°C and 35V. At the same time, add tannic acid-dextran copolymer and mix evenly. After reacting for 60 minutes, the mass volume ratio of tannic acid-dextran copolymer and fish paste rinse water is 2:3. Mix evenly and react for 30 minutes. Then collect the lower protein sedimentation layer to obtain protein solids and supernatant. Comparative Example 3

[0024] The difference between this comparative example and Example 2 is that only the low-voltage electric field method is used to perform protein flocculation, as follows: A method for recovering protein in surimi rinsing water using a low-voltage electric field comprises the following steps: S1. Collect the surimi rinse water with a protein concentration of 10.5 mg / mL; S2. Place the surimi rinse water in a low-voltage electric field protein recovery tank, treat it with an electric field at 25°C and 35V for 25 minutes, centrifuge it at 8000r / min for 10 minutes, and collect the protein solids and supernatant. Performance measurement:

[0025] (1) Protein recovery rate The soluble protein content in the supernatant was determined by the Lowry method, and the protein recovery rate in the surimi rinse water was expressed as: Protein recovery rate (%) = (CC 1 ) / C×100% Where, C is the mass concentration of protein in the supernatant after treatment, mg / mL; C 1 is the mass concentration of protein in the original surimi rinse water, mg / mL.

[0026] Table 1 Protein recovery rates in Examples 1-6 and Comparative Examples 1-3

[0027] As shown in Table 1, the method for removing protein from surimi rinse water adopted by the present invention has a protein recovery rate of 95.86-97.33%. Comparative Example 1 uses dextran without tannic acid grafting, and the protein recovery rate is slightly reduced to 91.76%; Comparative Example 2 does not add cationic hydrogel, and the protein recovery rate is significantly reduced to 84.14%; and Comparative Example 3 only uses a low-voltage electric field to recover protein from surimi rinse water, and the recovery rate is only 78.37%. Therefore, it can be seen that adding tannic acid-dextran copolymer and cationic hydrogel to the rinse water on the basis of a low-voltage electric field can achieve a higher degree of protein recovery.

[0028] (2) Turbidity After determining the protein content in the supernatant of Examples 1-6 and Comparative Examples 1-3, the supernatant was diluted to the same mass concentration and the absorbance (A) was measured at a wavelength of 320 nm. 320nm ) to indicate turbidity.

[0029] Table 2 Turbidity of supernatant in Examples 1-6 and Comparative Examples 1-3

[0030] As can be seen from Table 2, the turbidity of the supernatant after treatment by the method of the present invention is 0.19-0.24, and low turbidity means successful removal of protein; while in Comparative Example 1, dextran without tannic acid grafting is used, and the turbidity is slightly increased; in Comparative Example 2, no cationic hydrogel is added, the protein removal effect is reduced, and the turbidity is increased; in Comparative Example 3, only a low-voltage electric field is used to recover the protein in the surimi rinsing water, and there is still a lot of protein that has not been removed, so the turbidity is significantly higher.

[0031] (3) Determination of chemical oxygen demand (COD) and COD removal rate Chemical oxygen demand (COD) is determined according to the national standard GB / T 15456-2019 "Determination of chemical oxygen demand (COD) in industrial circulating cooling water - Permanganate index method". The COD removal rate is calculated as follows: COD removal rate (%) = (X 0 -X 1 ) / X 0 ×100 Where, X 0 is the COD value of the original surimi rinse water, mg / L; X 1 COD value in the rinsing water of fish paste after treatment, mg / L.

[0032] Table 3 COD values ​​and COD removal rates in Examples 1-6 and Comparative Examples 1-3

[0033] COD value is an important indicator for evaluating organic pollution in water bodies. As shown in Table 3, the COD value in the original surimi rinsing water is as high as 2810 mg / L. After being treated by the method of the present invention, the COD value in the rinsing water is significantly reduced, with a minimum value of 603 mg / L. The removal rate at this time is 78.54%. It can be seen that adding tannic acid-dextran copolymer and cationic hydrogel to the rinsing water on the basis of low-voltage electric field treatment can further remove organic matter (mainly protein) in the water body, thereby reducing the COD value; the COD removal rate of comparative example 1 has no obvious change, and the COD removal rates of comparative examples 2 and 3 have both decreased significantly. It can be seen that the methods of comparative examples 2 and 3 have limited extents in removing protein in water bodies.

[0034] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A method for recovering protein from surimi rinsing water by combining cationic hydrogel with electric field, characterized in that: The following steps are involved: S1. Collecting surimi rinse water; S2. placing the surimi rinse water in a low-voltage electric field protein recovery tank, performing electric field treatment at 25-30°C and 30-40V, adding tannic acid-dextran copolymer to the recovery tank, mixing evenly, reacting for 30-60min, then adding cationic hydrogel, mixing evenly, reacting for 15-30min, collecting the lower protein sedimentation layer, obtaining protein solids and supernatant, adjusting the protein solids pH to 4 and recovering the protein; The preparation method of the tannic acid-dextran copolymer in step S2 is as follows: Step 1: dissolve dextran in a pH 4-5 acetate buffer solution, stir at 50-60°C for 10-20 minutes to prepare a dextran solution with a concentration of 2-5%; Step 2: Add tannic acid, stir evenly, then add laccase, stir at 30-40°C for 10-15h to obtain a tannic acid-dextran copolymer solution; Step 3: inactivate the enzyme in the tannic acid-dextran copolymer solution, dialyze, and dry to obtain the tannic acid-dextran copolymer; The cationic hydrogel in step S2 is bacterial cellulose cross-linked polyglutamic acid / Ca 2+ The hydrogel was prepared as follows: Step 1: dissolving polyglutamic acid in deionized water, adjusting the pH to 7-8, and preparing a polyglutamic acid solution with a concentration of 1-3%; Step 2: immersing bacterial cellulose in a polyglutamic acid solution, leaving it to stand at room temperature for 12-24 hours, and washing it to obtain a bacterial cellulose-polyglutamic acid complex; Step 3: Immerse the bacterial cellulose-polyglutamic acid complex in a 0.1-0.5M CaCl2 solution for 2-5 hours at room temperature, filter, and wash to obtain bacterial cellulose cross-linked polyglutamic acid / Ca 2+ Hydrogel.

2. The method for recovering protein from surimi rinsing water by combining cationic hydrogel with electric field according to claim 1, characterized in that: In step S1, the surimi rinsing water is obtained by rinsing fish meat and water in a mass ratio of 1:4, and the protein concentration in the surimi rinsing water is 4.8-20.5 mg / mL.

3. The method for recovering protein from surimi rinsing water by combining cationic hydrogel with electric field according to claim 1, characterized in that: In the step S2, the anode plate of the low-voltage electric field protein recovery tank is a ruthenium-iridium-titanium plate, the cathode plate is a pure titanium plate, and the distance between adjacent electrode plates is 3-6 cm.

4. The method for recovering protein from surimi rinsing water by combining cationic hydrogel with electric field according to claim 1, characterized in that: In step S2, the mass volume ratio of tannic acid-dextran copolymer, cationic hydrogel and fish paste rinsing water is (1.5-2): (1-1.5):

3.

5. The method for recovering protein from surimi rinsing water by combining cationic hydrogel with electric field according to claim 1, characterized in that: In the step 2, the mass ratio of tannic acid to dextran is 1:(2-4); the concentration of laccase is 0.3-0.5 U / mL.

6. The method for recovering protein from surimi rinsing water by combining cationic hydrogel with electric field according to claim 1, characterized in that: In the step 2, the mass volume ratio of bacterial cellulose to polyglutamic acid solution is 1:(2-3).

7. The method for recovering protein from surimi rinsing water by combining cationic hydrogel with electric field according to claim 1, characterized in that: In step 3, the mass volume ratio of the bacterial cellulose-polyglutamic acid complex to the CaCl2 solution is 1:(1-2).

Images