Method for recovering protein in surimi washing water by combining a cationic hydrogel with an electric field

Abstract

The present invention provides a method for recovering proteins in surimi washing water by combining a cationic hydrogel with an electric field. While applying a low-voltage electric field to the surimi washing water, tannic acid-dextran copolymer is added. After obtaining protein flocs, a cationic hydrogel is added to in-situ gel on the surface of the protein flocs, which is beneficial to increasing the volume of the protein flocs, promoting protein sedimentation and solid-liquid separation, and finally realizing the recycling of proteins in surimi washing water.

Description

Technical Field

[0001] The present invention belongs to the technical field of protein recovery, and specifically relates to a method for recovering proteins in surimi washing water by combining a cationic hydrogel with an electric field. Background Art

[0002] Rinsing is an essential processing technology in the production of frozen surimi. Through rinsing, fishy smell, residual fish debris, fat, pigments and other substances in fish meat can be effectively removed, and the gel properties of surimi and surimi products can be improved. However, a large amount of organic water containing water-soluble proteins will be generated during the rinsing process. It is estimated that about 25 - 40t of water is required to produce 1t of surimi, and the protein concentration in the discharged surimi washing water is as high as 5 - 30mg / mL. How to recycle this part of protein has also become one of the research hotspots for scientists.

[0003] Regarding the methods for recycling proteins in surimi washing water, those reported currently include isoelectric point precipitation method, ohmic heating method, flocculation method, membrane separation method, etc., but these methods have their own advantages and disadvantages. The patent with the application number CN202410451379.1 discloses a method for recovering proteins in surimi washing water by combining low-voltage electric field with thermal flocculation. After research, it is found that the protein recovery effect of treating surimi washing water with low-voltage electric field is equivalent to the combination of chitosan flocculation method and isoelectric point precipitation method, but there is still a large room for improvement. Therefore, how to more efficiently recover proteins in surimi washing water and improve the utilization rate of water resources and the recovered proteins has become an urgent problem to be solved. Summary of the Invention

[0004] Technical Problem to be Solved: Aiming at the above problems, the purpose of the present invention is to provide a method for recovering proteins in surimi washing water by combining a cationic hydrogel with an electric field. While treating with a low-voltage electric field, tannic acid-dextran copolymer is added, and after obtaining protein flocs, a cationic hydrogel is added to in-situ gel on the surface of the protein flocs, which is beneficial to increasing the volume of the protein flocs, promoting protein sedimentation and solid-liquid separation. Through the combined treatment of a low-voltage electric field and a cationic hydrogel, the recovery and utilization of proteins in surimi washing water are realized.

[0005] Technical Solution: A method for recovering proteins in surimi washing water by combining a cationic hydrogel with an electric field includes the following steps:

[0006] S1. Collect surimi washing water;

[0007] S2. Place the surimi washing water in a low-voltage electric field protein recovery tank, and perform electric field treatment at 25 - 30 °C and 30 - 40 V. At the same time, add tannic acid-dextran copolymer to the recovery tank, mix evenly, react for 30 - 60 min, then add cationic hydrogel, mix evenly, react for 15 - 30 min, collect the lower protein sediment layer, and obtain protein solids and supernatant. Adjust the pH of the protein solids to 4 and then recover the protein.

[0008] Further, in step S1, the surimi washing water is obtained by washing fish meat and water at a mass ratio of 1:4, and the protein concentration in the surimi washing water is 4.8 - 20.5 mg / mL.

[0009] Further, 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 plate spacing between adjacent electrode plates is 3 - 6 cm.

[0010] Further, in step S2, the mass-volume ratio of tannic acid-dextran copolymer, cationic hydrogel and surimi washing water is (1.5 - 2):(1 - 1.5):3.

[0011] Further, the preparation method of the tannic acid-dextran copolymer in step S2 is as follows:

[0012] Step 1: Dissolve dextran in an acetic acid buffer solution with pH 4 - 5, and stir at 50 - 60 °C for 10 - 20 min to prepare a dextran solution with a concentration of 2 - 5%.

[0013] Step 2: Add tannic acid, stir evenly, then add laccase, and stir at 30 - 40 °C for 10 - 15 h to obtain a tannic acid-dextran copolymer solution.

[0014] Step 3: Inactivate the enzyme, dialyze, and dry the tannic acid-dextran copolymer solution to obtain the tannic acid-dextran copolymer.

[0015] Further, in step 2, the mass ratio of tannic acid to dextran is 1:(2 - 4); the laccase concentration is 0.3 - 0.5 U / mL.

[0016] Further, in step S2, the cationic hydrogel is a bacterial cellulose cross-linked polyglutamic acid / Ca 2+ hydrogel, and the preparation steps are as follows:

[0017] Step 1: Dissolve polyglutamic acid in deionized water, adjust the pH to 7 - 8, and prepare a polyglutamic acid solution with a concentration of 1 - 3%.

[0018] Step 2: Immerse the bacterial cellulose in the polyglutamic acid solution, let it stand at room temperature for 12 - 24 h, and then wash it to obtain the bacterial cellulose - polyglutamic acid composite;

[0019] Step 3: Immerse the bacterial cellulose - polyglutamic acid composite in a 0.1 - 0.5 M CaCl2 solution, soak it at room temperature for 2 - 5 h, filter and wash it to obtain the bacterial cellulose cross - linked polyglutamic acid / Ca 2+ hydrogel.

[0020] Furthermore, in Step 2, the mass - to - volume ratio of the bacterial cellulose to the polyglutamic acid solution is 1:(2 - 3).

[0021] Furthermore, in Step 3, the mass - to - volume ratio of the bacterial cellulose - polyglutamic acid composite to the CaCl2 solution is 1:(1 - 2). Beneficial effects

[0022] While the present invention treats the protein flocculation in the surimi washing water under a low - voltage electric field, tannic acid - dextran copolymer is added to the washing water. After obtaining the protein flocculant, a cationic hydrogel is added, and in - situ gelation occurs on the surface of the protein flocculant, which is beneficial to increasing the volume of the protein flocculant, promoting protein sedimentation and solid - liquid separation, and realizing the recycling of proteins in the surimi washing water;

[0023] In the present invention, tannic acid - dextran copolymer is selected for protein flocculation. As a linear polysaccharide, dextran mainly promotes flocculation through steric hindrance and weak hydrogen - bond interactions. However, due to its strong hydrophilicity and lack of functional groups, the binding force with proteins is limited. Therefore, laccase is used to catalyze the oxidation of the phenolic hydroxyl groups of tannic acid to generate free - radical intermediates, and then covalent cross - linking with the hydroxyl groups of dextran forms the tannic acid - dextran copolymer to overcome this problem. After being put into the surimi washing water, the dextran chain segments in the copolymer act as long - chain skeletons, adsorb protein particles in the water through physical or chemical actions, form a "bridging" effect, and connect the dispersed protein particles into larger flocs. Tannic acid can further enhance the binding force with proteins through hydrogen bonds, hydrophobic interactions or electrostatic attraction. Therefore, this copolymer realizes further flocculation of proteins in the surimi washing water;

[0024] After the tannic acid - dextran copolymer is added to form the protein flocculant in the present invention, the bacterial cellulose cross - linked polyglutamic acid / Ca 2+ hydrogel is continuously added. Both polyglutamic acid and bacterial cellulose have the ability to promote protein flocculation. Polyglutamic acid contains a large number of carboxyl groups, which can combine with the hydroxyl groups of bacterial cellulose through chemical bonds. The carboxyl groups on the side chains of polyglutamic acid can also chelate with Ca 2+ to achieve further grafting; Therefore, after the cationic hydrogel is added, Ca 2+By binding to the negatively charged groups on the protein surface through electrostatic interactions, the cationic hydrogel tightly coats the surface of the protein floccules, achieving in-situ gelation to obtain protein solids, increasing the volume of the protein solids, promoting their sedimentation and solid-liquid separation. Then, the pH is adjusted below the isoelectric point of the protein, causing the protein to carry a positive charge and generating electrostatic repulsion with the hydrogel, enabling the protein to be desorbed from the hydrogel, and ultimately realizing the recycling of the protein in surimi washing water. Detailed implementation mode

[0025] The present invention will be further described below in conjunction with embodiments. The following embodiments are explanations of the present invention and the present invention is not limited to the following embodiments: Embodiment 1

[0026] A method for recycling protein in surimi washing water by combining a cationic hydrogel with an electric field includes the following steps:

[0027] S1. Preparation of tannic acid-dextran copolymer: Dissolve dextran in pH 5 acetate buffer solution, stir at 60 °C for 10 min to make a 3% dextran solution; add tannic acid, and 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 tannic acid-dextran copolymer solution; inactivate the enzyme, dialyze, and dry the tannic acid-dextran copolymer solution to obtain tannic acid-dextran copolymer;

[0028] S2. Preparation of bacterial cellulose crosslinked polyglutamic acid / Ca 2+ Hydrogel: Dissolve polyglutamic acid in deionized water, adjust the pH to 7, and prepare a 2% polyglutamic acid solution; immerse bacterial cellulose in the polyglutamic acid solution with a mass-to-volume ratio of 1:2, let it stand at room temperature for 20 h, and wash to obtain bacterial cellulose-polyglutamic acid complex; immerse the bacterial cellulose-polyglutamic acid complex in 0.3 M CaCl2 solution with a mass-to-volume ratio of 1:2, soak at room temperature for 3 h, filter, and wash to obtain bacterial cellulose crosslinked polyglutamic acid / Ca 2+ Hydrogel;

[0029] S3. Collect surimi washing water with a protein concentration of 10.5 mg / mL;

[0030] S4. Place the surimi washing water in a low-voltage electric field protein recovery tank, perform electric field treatment at 25 °C and 35 V, and simultaneously add tannic acid-dextran copolymer, mix evenly, after reacting for 60 min, then add bacterial cellulose crosslinked polyglutamic acid / Ca 2+For the hydrogel, the mass-volume ratio of tannic acid-dextran copolymer, cationic hydrogel and surimi washing water is 2:1:3. Mix them evenly. After reacting for 30 min, 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. Example 2

[0031] A method for recovering proteins from surimi washing water by combining a cationic hydrogel with an electric field, comprising the following steps:

[0032] S1. Preparation of tannic acid-dextran copolymer: Dissolve dextran in an acetic acid buffer solution with pH 5, stir at 60 °C for 10 min to prepare a 3% dextran solution; add tannic acid, and the mass ratio of tannic acid to dextran is 1:3. Stir evenly, then add laccase with a concentration of 0.5 U / mL, and stir at 40 °C for 10 h to obtain a tannic acid-dextran copolymer solution; inactivate the enzyme, dialyze and dry the tannic acid-dextran copolymer solution to obtain tannic acid-dextran copolymer;

[0033] S2. Preparation of bacterial cellulose cross-linked polyglutamic acid / Ca 2+ hydrogel: Dissolve polyglutamic acid in deionized water, adjust the pH to 7, and prepare a 2% polyglutamic acid solution; immerse bacterial cellulose in the polyglutamic acid solution with a mass-volume ratio of 1:2, let it stand at room temperature for 20 h, and wash to obtain a bacterial cellulose-polyglutamic acid complex; immerse the bacterial cellulose-polyglutamic acid complex in a 0.3 M CaCl2 solution with a mass-volume ratio of 1:2, soak at room temperature for 3 h, filter and wash to obtain bacterial cellulose cross-linked polyglutamic acid / Ca 2+ hydrogel;

[0034] S3. Collect surimi washing water with a protein concentration of 10.5 mg / mL;

[0035] S4. Place the surimi washing water in a low-voltage electric field protein recovery tank, perform electric field treatment at 25 °C and 35 V, and at the same time add tannic acid-dextran copolymer, mix evenly. After reacting for 60 min, add bacterial cellulose cross-linked polyglutamic acid / Ca 2+ hydrogel. The mass-volume ratio of tannic acid-dextran copolymer, cationic hydrogel and surimi washing water is 2:1:3. Mix them evenly. After reacting for 30 min, 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. Example 3

[0036] A method for recovering proteins from surimi washing water by combining a cationic hydrogel with an electric field, comprising the following steps:

[0037] S1. Preparation of tannic acid-dextran copolymer: Dissolve dextran in pH 5 acetate buffer solution, stir at 60 °C for 10 min to prepare a 3% dextran solution; add tannic acid, and 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 tannic acid-dextran copolymer solution; inactivate the enzyme, dialyze and dry the tannic acid-dextran copolymer solution to obtain tannic acid-dextran copolymer;

[0038] S2. Preparation of bacterial cellulose cross-linked polyglutamic acid / Ca 2+ hydrogel: Dissolve polyglutamic acid in deionized water, adjust the pH to 7 to prepare a 2% polyglutamic acid solution; immerse bacterial cellulose in the polyglutamic acid solution with a mass-to-volume ratio of 1:2, let it stand at room temperature for 20 h, wash to obtain bacterial cellulose-polyglutamic acid complex; immerse the bacterial cellulose-polyglutamic acid complex in 0.3 M CaCl2 solution with a mass-to-volume ratio of 1:2, soak at room temperature for 3 h, filter and wash to obtain bacterial cellulose cross-linked polyglutamic acid / Ca 2+ hydrogel;

[0039] S3. Collect the surimi washing water with a protein concentration of 10.5 mg / mL;

[0040] S4. Place the surimi washing water in a low-voltage electric field protein recovery tank, perform electric field treatment at 25 °C and 35 V, and at the same time add tannic acid-dextran copolymer, stir evenly, after reacting for 60 min, then add bacterial cellulose cross-linked polyglutamic acid / Ca 2+ hydrogel, and the mass-to-volume ratio of tannic acid-dextran copolymer, cationic hydrogel and surimi washing water is 2:1:3, stir evenly, after reacting for 30 min, collect the lower protein sediment layer to obtain protein solids and supernatant, adjust the pH of the protein solids to 4 and then recover the protein. Example 4

[0041] A method for recovering proteins from surimi washing water by combining a cationic hydrogel with an electric field, comprising the following steps:

[0042] S1. Preparation of tannic acid-dextran copolymer: Dissolve dextran in pH 5 acetate buffer solution, stir at 60 °C for 10 min to prepare a 3% dextran solution; add tannic acid, and 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 tannic acid-dextran copolymer solution; inactivate the enzyme, dialyze and dry the tannic acid-dextran copolymer solution to obtain tannic acid-dextran copolymer;

[0043] S2. Preparation of Bacterial Cellulose Crosslinked Polyglutamic Acid / Ca 2+ Preparation of hydrogel: Dissolve polyglutamic acid in deionized water, adjust the pH to 7, and prepare a 2% polyglutamic acid solution; Immerse bacterial cellulose in the polyglutamic acid solution with a mass-to-volume ratio of 1:2, let it stand at room temperature for 20 h, wash it, and obtain the bacterial cellulose-polyglutamic acid complex; Immerse the bacterial cellulose-polyglutamic acid complex in 0.3 M CaCl2 solution with a mass-to-volume ratio of 1:2, soak it at room temperature for 3 h, filter and wash it to obtain bacterial cellulose crosslinked polyglutamic acid / Ca 2+ hydrogel;

[0044] S3. Collect surimi washing water with a protein concentration of 10.5 mg / mL;

[0045] S4. Place the surimi washing water in a low-voltage electric field protein recovery tank, perform electric field treatment at 25 °C and 35 V, and simultaneously add tannic acid-dextran copolymer, mix evenly, after reacting for 60 min, then add bacterial cellulose crosslinked polyglutamic acid / Ca 2+ hydrogel, the mass-to-volume ratio of tannic acid-dextran copolymer, cationic hydrogel and surimi washing water is 1.5:1:3, mix evenly, after reacting for 30 min, collect the lower protein sedimentation layer, obtain protein solids and supernatant, and adjust the pH of the protein solids to 4 and then recover the protein. Example 5

[0046] A method for recovering protein from surimi washing water by combining a cationic hydrogel with an electric field, comprising the following steps:

[0047] S1. Preparation of tannic acid-dextran copolymer: Dissolve dextran in pH 5 acetate buffer solution, stir at 60 °C for 10 min to prepare a 3% dextran solution; 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 tannic acid-dextran copolymer solution; Inactivate the enzyme, dialyze and dry the tannic acid-dextran copolymer solution to obtain tannic acid-dextran copolymer;

[0048] S2. Bacterial cellulose crosslinked polyglutamic acid / Ca 2+ Preparation of hydrogel: Dissolve polyglutamic acid in deionized water, adjust the pH to 7, and prepare a 2% polyglutamic acid solution; Immerse bacterial cellulose in the polyglutamic acid solution with a mass-to-volume ratio of 1:2, let it stand at room temperature for 20 h, wash it, and obtain the bacterial cellulose-polyglutamic acid complex; Immerse the bacterial cellulose-polyglutamic acid complex in 0.3 M CaCl2 solution with a mass-to-volume ratio of 1:2, soak it at room temperature for 3 h, filter and wash it to obtain bacterial cellulose crosslinked polyglutamic acid / Ca2+ Hydrogel;

[0049] S3. Collect surimi washing water with a protein concentration of 10.5 mg / mL;

[0050] S4. Place the surimi washing water in a low-voltage electric field protein recovery tank, perform electric field treatment at 25 °C and 35 V, and simultaneously add tannic acid-dextran copolymer, mix evenly. After reacting for 60 min, then add bacterial cellulose cross-linked polyglutamic acid / Ca 2+ For the hydrogel, the mass-volume ratio of tannic acid-dextran copolymer, cationic hydrogel and surimi washing water is 1.5:1.5:3 (i.e., 1:1:2). Mix evenly. After reacting for 30 min, collect the lower protein sediment layer, that is, obtain protein solids and supernatant. Adjust the pH of the protein solids to 4 and then recover the protein. Example 6

[0051] A method for recovering proteins from surimi washing water by combining a cationic hydrogel with an electric field, comprising the following steps:

[0052] S1. Preparation of tannic acid-dextran copolymer: Dissolve dextran in a pH 5 acetate buffer solution, stir at 60 °C for 10 min to prepare a 3% dextran solution; add tannic acid, and 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, dialyze and dry the tannic acid-dextran copolymer solution to obtain tannic acid-dextran copolymer;

[0053] S2. Preparation of bacterial cellulose cross-linked polyglutamic acid / Ca 2+ Hydrogel: Dissolve polyglutamic acid in deionized water, adjust the pH to 7 to prepare a 2% polyglutamic acid solution; immerse bacterial cellulose in the polyglutamic acid solution with a mass-volume ratio of 1:2, let it stand at room temperature for 20 h, wash to obtain a bacterial cellulose-polyglutamic acid complex; immerse the bacterial cellulose-polyglutamic acid complex in a 0.3 M CaCl2 solution with a mass-volume ratio of 1:2, soak at room temperature for 3 h, filter and wash to obtain bacterial cellulose cross-linked polyglutamic acid / Ca 2+ Hydrogel;

[0054] S3. Collect surimi washing water with a protein concentration of 10.5 mg / mL;

[0055] S4. Place the surimi washing water in a low-voltage electric field protein recovery tank, perform electric field treatment at 25 °C and 35 V, and simultaneously add tannic acid-dextran copolymer, mix evenly. After reacting for 60 min, then add bacterial cellulose cross-linked polyglutamic acid / Ca 2+For the hydrogel, the mass - volume ratio of tannic acid - dextran copolymer, cationic hydrogel and surimi washing water is 2:1.5:3. Mix them evenly. After reacting for 30 min, collect the lower - layer protein sedimentation layer to obtain protein solids and supernatant. Adjust the pH of the protein solids to 4 and then recover the protein. Use the supernatant for the first rinsing of surimi or for washing raw fish. Comparative Example 1

[0056] The difference between this comparative example and Example 2 is that dextran without grafted tannic acid is used, specifically as follows:

[0057] A method for recovering protein from surimi washing water by combining a cationic hydrogel with an electric field, comprising the following steps:

[0058] S1. Preparation of bacterial cellulose cross - linked polyglutamic acid / Ca 2+ Preparation of the hydrogel: Dissolve polyglutamic acid in deionized water, adjust the pH to 7, and prepare a polyglutamic acid solution with a concentration of 2%. Immerse bacterial cellulose in the polyglutamic acid solution with a mass - volume ratio of 1:2, let it stand at room temperature for 20 h, wash it to obtain a bacterial cellulose - polyglutamic acid complex. Immerse the bacterial cellulose - polyglutamic acid complex in a 0.3M CaCl2 solution with a mass - volume ratio of 1:2, soak it at room temperature for 3 h, filter and wash it to obtain bacterial cellulose cross - linked polyglutamic acid / Ca 2+ hydrogel;

[0059] S2. Collect surimi washing water with a protein concentration of 10.5 mg / mL;

[0060] S3. Place the surimi washing water in a low - voltage electric - field protein recovery tank, perform electric - field treatment at 25 °C and 35 V, and at the same time add dextran, react and mix evenly at 60 °C for 60 min, then add bacterial cellulose cross - linked polyglutamic acid / Ca 2+ hydrogel. The mass - volume ratio of dextran, cationic hydrogel and surimi washing water is 2:1:3. Mix them evenly. After reacting for 30 min, collect the lower - layer protein sedimentation layer to obtain protein solids and supernatant. Adjust the pH of the protein solids to 4 and then recover the protein. Comparative Example 2

[0061] The difference between this comparative example and Example 2 is that no cationic hydrogel is added, specifically as follows:

[0062] A method for recovering protein from surimi washing water, comprising the following steps:

[0063] S1. Preparation of tannic acid-dextran copolymer: Dissolve dextran in acetic acid buffer solution with pH 5, stir at 60 °C for 10 min to prepare a dextran solution with a concentration of 3%; add tannic acid, and 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 tannic acid-dextran copolymer solution; inactivate the enzyme, dialyze and dry the tannic acid-dextran copolymer solution to obtain tannic acid-dextran copolymer;

[0064] S2. Collect fish mince rinsing water with a protein concentration of 10.5 mg / mL;

[0065] S3. Place the fish mince rinsing water in a low-voltage electric field protein recovery tank, perform electric field treatment at 25 °C and 35 V, and at the same time add tannic acid-dextran copolymer, stir evenly, after reacting for 60 min, the mass-volume ratio of tannic acid-dextran copolymer to fish mince rinsing water is 2:3, stir evenly, after reacting for 30 min, collect the lower protein sediment layer to obtain protein solids and supernatant. Comparative Example 3

[0066] The difference between this comparative example and Example 2 is that only the low-voltage electric field method is used for protein flocculation, specifically as follows:

[0067] A method for recovering protein from fish mince rinsing water by low-voltage electric field includes the following steps:

[0068] S1. Collect fish mince rinsing water with a protein concentration of 10.5 mg / mL;

[0069] S2. Place the fish mince rinsing water in a low-voltage electric field protein recovery tank, perform electric field treatment at 25 °C and 35 V for 25 min, centrifuge at 8000 r / min for 10 min, and collect protein solids and supernatant.

[0070] Performance determination:

[0071] (1) Protein recovery rate

[0072] Use the lowry method to measure the content of soluble protein in the supernatant, and the protein recovery rate in fish mince rinsing water is expressed as:

[0073] Protein recovery rate (%) = (C - C1) / C × 100%

[0074] In the formula, C is the mass concentration of protein in the treated supernatant, mg / mL; C1 is the mass concentration of protein in the original fish mince rinsing water, mg / mL.

[0075] Table 1 Protein recovery rates in Examples 1 - 6 and Comparative Examples 1 - 3

[0076]

[0077] As can be seen from Table 1, for the method of removing proteins from surimi washing water adopted in the present invention, the protein recovery rate is 95.86 - 97.33%. In Comparative Example 1, dextran without grafted tannic acid was used, and the protein recovery rate decreased slightly to 91.76%. In Comparative Example 2, no cationic hydrogel was added, and the protein recovery rate decreased significantly to 84.14%. In Comparative Example 3, only a low-voltage electric field was used to recover proteins from surimi washing water, and the recovery rate was only 78.37%. Therefore, it can be seen that on the basis of a low-voltage electric field, adding tannic acid-dextran copolymer and cationic hydrogel to the washing water can achieve a higher degree of protein recovery.

[0078] (2)Turbidity

[0079] After measuring 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 320nm )was measured at a wavelength of 320 nm to represent turbidity.

[0080] Table 2 Turbidity of the supernatant in Examples 1 - 6 and Comparative Examples 1 - 3

[0081]

[0082] As can be seen from Table 2, the turbidity of the supernatant after being treated by the method of the present invention is 0.19 - 0.24. A low turbidity means the successful removal of proteins. In Comparative Example 1, dextran without grafted tannic acid was used, and the turbidity increased slightly. In Comparative Example 2, no cationic hydrogel was added, the protein removal effect decreased, and the turbidity increased. In Comparative Example 3, only a low-voltage electric field was used to recover proteins from surimi washing water, and there were still many proteins not removed, so the turbidity was significantly higher.

[0083] (3)Determination of chemical oxygen demand (COD) and COD clearance rate

[0084] The chemical oxygen demand (COD) was determined according to the national standard GB / T 15456 - 2019 "Determination of Chemical Oxygen Demand (COD) in Industrial Recirculating Cooling Water - Permanganate Index Method". The calculation formula for the COD clearance rate is as follows:

[0085] COD clearance rate (%) = (X0 - X1) / X0 × 100

[0086] In the formula, X0 is the COD value in the original surimi washing water, mg / L; X1 is the COD value in the treated surimi washing water, mg / L.

[0087] Table 3 COD values and COD clearance rates in Examples 1 - 6 and Comparative Examples 1 - 3

[0088]

[0089] The COD value is an important indicator for evaluating the organic pollution of water bodies. As can be seen from 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, and the minimum value is 603 mg / L. At this time, the removal rate reaches 78.54%. It can be seen that on the basis of low-voltage electric field treatment, adding tannic acid-dextran copolymer and cationic hydrogel to the rinsing water can further remove the organic matter (mainly protein) in the water body, thereby reducing the COD value; there is no obvious change in the COD removal rate of Comparative Example 1, and the COD removal rates of Comparative Example 2 and Comparative Example 3 both decrease significantly. It can be seen that the methods of Comparative Example 2 and Comparative Example 3 have limited ability to remove protein in the water body.

[0090] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and technical solution of the present invention, or modify it into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for recovering proteins in surimi washing water by using a cationic hydrogel combined with an electric field, characterized in that, It includes the following steps: S1. Collect surimi washing water; S2. Place the surimi washing water in a low-voltage electric field protein recovery tank, and perform electric field treatment at 25 - 30 °C and 30 - 40 V. At the same time, add tannic acid-dextran copolymer to the recovery tank, mix evenly, react for 30 - 60 min, then add cationic hydrogel, mix evenly, react for 15 - 30 min, collect the lower protein sedimentation layer, and obtain protein solids and supernatant. Adjust the pH of the protein solids to 4 and then recover the protein; in step S2, the mass-volume ratio of tannic acid-dextran copolymer, cationic hydrogel, and surimi washing water is (1.5 - 2):(1 - 1.5):3; The preparation method of the tannic acid-dextran copolymer in step S2 is as follows: Step 1: Dissolve dextran in an acetic acid buffer solution with a pH of 4 - 5, and stir at 50 - 60 °C for 10 - 20 min to prepare a dextran solution with a concentration of 2 - 5%; Step 2: Add tannic acid, stir evenly, then add laccase, and stir at 30 - 40 °C for 10 - 15 h to obtain a tannic acid-dextran copolymer solution; Step 3: Inactivate the enzyme, dialyze, and dry the tannic acid-dextran copolymer solution to obtain the tannic acid-dextran copolymer; In the step S2, the cationic hydrogel is a bacterial cellulose cross-linked polyglutamic acid / Ca 2+ hydrogel, and the preparation steps are as follows: Step 1: Dissolve polyglutamic acid in deionized water, adjust the pH to 7 - 8, and prepare a polyglutamic acid solution with a concentration of 1 - 3%; Step 2: Immerse bacterial cellulose in the polyglutamic acid solution, let it stand at room temperature for 12 - 24 h, and wash to obtain a bacterial cellulose-polyglutamic acid composite; Step 3: Immerse the bacterial cellulose-polyglutamic acid complex in a 0.1-0.5 M CaCl2 solution, soak at room temperature for 2-5 h, filter, and wash to obtain bacterial cellulose crosslinked polyglutamic acid / Ca 2+ hydrogel.

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

3. A method for recovering proteins in surimi washing water by combining a cationic hydrogel with an electric field according to claim 1, characterized in that: 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 plate spacing between adjacent electrode plates is 3 - 6 cm.

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

5. A method for recovering proteins in surimi washing water by combining a cationic hydrogel with an electric field according to claim 1, characterized in that, In step 2, the mass-volume ratio of bacterial cellulose to the polyglutamic acid solution is 1:(2 - 3).

6. A method for recovering proteins in surimi washing water by combining a cationic hydrogel with an electric field according to claim 1, characterized in that In step 3, the mass-volume ratio of the bacterial cellulose-polyglutamic acid composite to the CaCl2 solution is 1:(1 - 2).

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