Method for preparing functional peptide from protein in organic wastewater produced by minced freshwater fish

Abstract

The invention discloses a method for preparing functional peptide from protein in organic wastewater produced by freshwater fish paste, which comprises the following steps: introducing carbon dioxide into the organic wastewater without large particulate matters, and adding acetic acid to obtain blended organic wastewater; adding a ferric chloride solution into the blended organic wastewater, stirring for a period of time, then adding a chitosan solution, and continuously stirring for a period of time to obtain a mixed solution; centrifuging the mixed solution, collecting a supernatant, carrying out ultrafiltration and nanofiltration on the supernatant, and collecting a cut-off liquid; pressurizing and heating the cut-off liquid, preserving heat for a period of time, releasing pressure, cooling to room temperature, and adding protease into the cut-off liquid for enzymolysis treatment; and then carrying out nanofiltration by adopting a 400Da nanofiltration membrane, and desalting to obtain the functional peptide. According to the method, the dosage of a flocculating agent can be reduced by 40-50%, the dosage of enzyme can be reduced by 30-50%, and the service life of the membrane can be prolonged to more than 5 years; peptide products with specific functions can be directionally prepared; the wastewater treatment efficiency is improved, and the COD value is reduced by more than 90%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional peptide processing, and particularly relates to a method for preparing functional peptides from proteins in organic wastewater produced by freshwater surimi. BACKGROUND

[0002] The organic wastewater produced in the process of freshwater surimi production has high pollution and contains a large amount of soluble protein resources. According to the latest research, the pH value of freshwater surimi wastewater is usually 7.33±0.12, which is weakly alkaline, which is significantly different from that of seawater surimi wastewater. The wastewater contains a large amount of suspended solids and high concentrations of bicarbonate and carbonate, resulting in the formation of insoluble minerals of calcium and magnesium ions, and sodium ions as the main cations. The COD value is usually in the range of 800-1500 mg / L, the BOD5 value is as high as 290-580 mg / L, and a large amount of soluble proteins (about 15% of the total amount) are contained. However, there are many problems in the existing technology in treating this kind of wastewater:

[0003] 1. Traditional flocculation and sedimentation method: mainly uses inorganic flocculants (such as ferric chloride, polyaluminum chloride) or organic flocculants (such as polyacrylamide) for protein recovery. Studies have shown that when the addition amount of ferric chloride is 0.13 g / L, the flocculation temperature is 18.44℃, the time is 5h, and the pH is 5.44, the protein recovery rate can reach 86.94%. However, this method has the following limitations: metal ion residue problem, affecting the quality of recovered protein; large amount of flocculant, high cost; pH adjustment depends on strong acid, there is a risk of equipment corrosion; protein recovery rate still has room for improvement.

[0004] 2. Natural flocculant method: edible-grade biological materials such as chitosan and alginate are used as flocculants, which have the characteristics of environmental protection, safety and high efficiency. Studies have shown that chitosan has the best flocculation effect on freshwater wastewater protein at pH 7.0, and alginate and chitosan can form high-efficiency polyelectrolyte complexes, especially at pH 7. This method has the advantage of not introducing toxic and harmful ingredients, and the recovered protein can be safely used in food and feed. However, the use of natural flocculants alone also has some disadvantages, such as limited flocculation efficiency for high calcium and magnesium ion wastewater, and high cost.

[0005] 3. Membrane separation technology: by controlling the molecular weight distribution through ultrafiltration, nanofiltration and other methods, precise recovery is achieved. Studies have shown that membrane separation technology can recover 84% of the protein, but there are the following problems: large equipment investment, high energy consumption; membrane pollution is serious, flux decay is fast; pretreatment is needed to remove oil and suspended solids; membrane material is easily affected by metal ions.

[0006] 4. Electric field assisted recovery technology: In 2024, research showed that the protein aggregation recovery effect in surimi rinse wastewater under the action of low-voltage direct current electric field was significant, and the best parameters were electric field treatment time 34 min, voltage 55 V, initial temperature 22℃, and salt content 0.06%. At this time, the protein recovery rate was 92.23%, and the COD removal rate was 89.54%. The advantage of this technology is that the recovery rate is higher than that of the traditional heat flocculation method, the COD removal efficiency is high, and no chemical flocculant needs to be added. However, the limitation of this technology is that it requires high equipment and is difficult to be applied on a large scale.

[0007] 5. Enzymatic hydrolysis technology: Existing enzymatic hydrolysis technology relies on high enzyme dosage (such as 2-5% enzyme substrate for neutral protease), and does not combine small molecule peptides released by pretreatment, resulting in high cost and low yield.

[0008] In summary, the existing technology has problems such as low protein recovery rate, high energy consumption, serious membrane pollution, and large enzyme dosage in the treatment of organic wastewater from freshwater surimi production, and an innovative process with high efficiency, low energy consumption, and resource recovery is urgently needed. SUMMARY

[0009] The purpose of the present application is to provide a method for preparing functional peptides from proteins in organic wastewater from freshwater surimi production. This method effectively removes large particle suspensions through grating and sedimentation, reducing the damage to machinery in subsequent processing. It removes impurities through gas-assisted pH adjustment and natural flocculation synergy technology, reduces the amount of flocculant by 40-50%, and reduces the amount of enzyme by 30-50%. It uses ultrasonic cavitation effect to destroy collagen deposition on the membrane surface, prolonging the service life of the membrane to more than 5 years. Different types of proteases are used for enzymatic hydrolysis to produce specific functional peptide products. The wastewater treatment efficiency is improved, the COD value is reduced by more than 90%, the subsequent processing burden is reduced, and the total cost of wastewater treatment is reduced by more than 30%.

[0010] In order to achieve the above-mentioned purpose of the present application, the following technical solutions are adopted:

[0011] The first aspect of the present application provides a method for preparing functional peptides from proteins in organic wastewater from freshwater surimi production, comprising the following steps:

[0012] (a) Grating and filtering the organic wastewater from freshwater surimi production, and then settling to obtain organic wastewater with large particle substances removed;

[0013] (b) Under stirring conditions, carbon dioxide is introduced into the organic wastewater with large particle substances removed, and acetic acid is added until the pH value is 4.5-5.0, to obtain a prepared organic wastewater;

[0014] (c) adding ferric chloride solution into the prepared organic wastewater and stirring for a period of time, then adjusting the stirring speed, adding chitosan solution and stirring for a period of time to obtain a mixed solution;

[0015] (d) centrifuging the mixed solution, collecting the supernatant, ultrafiltrating the supernatant, nanofiltrating the ultrafiltrated solution, collecting the nanofiltrated solution, and periodically performing ultrasonic backwashing;

[0016] (e) pressurizing and heating the nanofiltrated solution, maintaining the temperature for a period of time, then depressurizing and cooling to room temperature, and adding protease into the nanofiltrated solution to perform enzymatic hydrolysis;

[0017] The protease is pepsin and flavor protease; or the protease is complex protease and neutral protease; or the protease is alkaline protease and papain;

[0018] (f) after the enzymatic hydrolysis is completed, performing enzyme inactivation, nanofiltrating using a 400 Da nanofiltration membrane, and desalting to obtain the functional peptide

[0019] Preferably, in the step (b), the flux of carbon dioxide is 0.5-2 L / min.

[0020] Preferably, in the step (c), the concentration of ferric chloride solution is 8%-12%; the final concentration of ferric chloride added is 500-550 mg / L; and the stirring speed after adding the ferric chloride solution is 100-150 rpm, and the stirring time is 1-2 min.

[0021] Preferably, in the step (c), the concentration of chitosan solution is 1%-2%; the final concentration of chitosan added is 100-200 mg / L; and the stirring speed after adding the chitosan solution is 30-50 rpm, and the stirring time is 10-20 min.

[0022] Preferably, in the step (d), the ultrafiltration membrane used in the ultrafiltration has a molecular weight cut-off of 10-30 kDa; and the nanofiltration membrane used in the nanofiltration has a molecular weight cut-off of 400-500 Da.

[0023] Preferably, in the step (d), ultrasonic treatment is performed during the ultrafiltration and nanofiltration, the ultrasonic frequency is 20-40 kHz, and the power density is 100-400 W / m 3 .

[0024] Preferably, in the step (e), when the protease is pepsin and flavour protease, the enzymatic treatment comprises: adjusting the pH value of the cut-off liquid to 1.5-2.5, adding pepsin for the first enzymatic treatment at 25-35℃ for 1.5-3h, and the addition amount of pepsin is 0.2%-0.4% of the mass of the cut-off liquid; then, adjusting the pH value to 6.2-6.8, adding flavour protease for the second enzymatic treatment at 45-55℃ for 0.8-1.5h, and the addition amount of flavour protease is 0.1%-0.3% of the mass of the cut-off liquid.

[0025] Preferably, in the step (e), when the protease is complex protease and neutral protease, the enzymatic treatment comprises: adjusting the pH value of the cut-off liquid to 6.8-7.2, adding complex protease for the first enzymatic treatment at 40-50℃ for 2-4h, and the addition amount of complex protease is 0.3%-0.5% of the mass of the cut-off liquid; then, keeping the pH value at 6.8-7.2, adding neutral protease for the second enzymatic treatment at 50-60℃ for 0.8-1.5h, and the addition amount of neutral protease is 0.2%-0.4% of the mass of the cut-off liquid.

[0026] Preferably, in the step (e), when the protease is alkaline protease and papain, the enzymatic treatment comprises: adjusting the pH value of the cut-off liquid to 8.5-9.5, adding alkaline protease for the first enzymatic treatment at 40-50℃ for 0.8-1.5h, and the addition amount of alkaline protease is 0.3%-0.4% of the mass of the cut-off liquid; then, adjusting the pH value to 5.5-6.5, adding papain for the second enzymatic treatment at 50-60℃ for 0.3-0.8h, and the addition amount of papain is 0.2%-0.3% of the mass of the cut-off liquid.

[0027] Preferably, in the step (e), the pressure of the pressurized heating is 0.8-1MPa, the heating temperature is 105-115℃, and the holding time is 4-6min.

[0028] Preferably, the step (e) further comprises: active carbon adsorption, ultrasonic treatment, and embedding treatment of the polypeptide by using sodium alginate and / or chitosan as wall material.

[0029] Compared with the prior art, the present application has at least the following beneficial effects:

[0030] This invention achieves efficient and green treatment, resource utilization, and target recovery of organic wastewater generated in freshwater surimi production through a combination of key technical units, including pretreatment in a grid sedimentation tank, gas-assisted pH adjustment and natural flocculation, ultrasonic-enhanced membrane separation, pressurized and heated steam explosion treatment, and targeted preparation of functional peptides. The combined process reduces flocculant usage by 40%-50%, enzyme usage by 30%-50%, extends membrane lifespan by more than 5 years, improves wastewater treatment efficiency, reduces COD value by more than 90%, reduces the burden of subsequent treatment, and lowers the total cost of wastewater treatment by more than 30%. Detailed Implementation

[0031] The embodiments of the technical solution of the present invention will be described in detail below with reference to the examples. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, and are therefore only examples, and should not be used to limit the scope of protection of the present invention.

[0032] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0033] An embodiment of the present invention provides a method for preparing functional peptides from proteins in organic wastewater produced from freshwater fish paste, comprising the following steps:

[0034] (a) The organic wastewater from freshwater fish paste production is filtered through a screen and settled to obtain organic wastewater with large particulate matter removed;

[0035] (b) Under stirring conditions, carbon dioxide is introduced into the organic wastewater from which large particulate matter has been removed and acetic acid is added until the pH value reaches 4.5~5.0, thus obtaining formulated organic wastewater;

[0036] (c) Add ferric chloride solution to the prepared organic wastewater and stir for a period of time. Then, adjust the stirring speed and add chitosan solution and continue stirring for a period of time to obtain a mixture.

[0037] (d) Centrifuge the mixture, collect the supernatant, then ultrafilter the supernatant, then nanofilter the ultrafiltrate and collect the threshing liquid and backwash it with ultrasonication periodically;

[0038] (e) Pressurize and heat the intercepted liquid and keep it at that temperature for a period of time, then depressurize and cool it to room temperature. Then, add protease to the intercepted liquid for enzymatic hydrolysis.

[0039] The protease is pepsin and flavor protease; or the protease is a complex protease and neutral protease; or the protease is alkaline protease and papain.

[0040] (f) After enzymatic hydrolysis, the enzyme is inactivated, and then nanofiltration and desalting are performed using a 400 Da nanofiltration membrane to obtain the functional peptide.

[0041] In one embodiment, in step (b), the carbon dioxide flux is 0.5~2 L / min.

[0042] In one embodiment, in step (c), the concentration of the ferric chloride solution is 8%~12%; the final concentration of ferric chloride added is 500~550 mg / L; the stirring speed after adding the ferric chloride solution is 100~150 rpm, and the stirring time is 1~2 min.

[0043] In one embodiment, in step (c), the chitosan solution concentration is 1%~2%; the final concentration of chitosan added is 100~200 mg / L; after adding the chitosan solution, the stirring speed is 30~50 rpm and the stirring time is 10~20 min.

[0044] In one embodiment, in step (d), the ultrafiltration membrane used for ultrafiltration has a molecular weight cutoff of 10~30kDa; the nanofiltration membrane used for nanofiltration has a molecular weight cutoff of 400~500Da.

[0045] In one embodiment, in step (d), ultrasonic treatment is performed during ultrafiltration and nanofiltration, with an ultrasonic frequency of 20-40 kHz and a power density of 100-400 W / m³. 3 .

[0046] In one embodiment, when the protease in step (e) is pepsin and flavor protease, the enzymatic hydrolysis treatment includes: adjusting the pH of the effluent to 1.5-2.5 and adding pepsin for a first enzymatic hydrolysis treatment at 25-35°C for 1.5-3 hours, wherein the amount of pepsin added is 0.2%-0.4% of the mass of the effluent; subsequently, adjusting the pH to 6.2-6.8 and adding flavor protease for a second enzymatic hydrolysis treatment at 45-55°C for 0.8-1.5 hours, wherein the amount of flavor protease added is 0.1%-0.3% of the mass of the effluent.

[0047] In one embodiment, when the protease in step (e) is a complex protease and a neutral protease, the enzymatic hydrolysis treatment includes: adjusting the pH of the intercepted liquid to 6.8-7.2 and adding the complex protease for a first enzymatic hydrolysis treatment at 40-50°C for 2-4 hours, wherein the amount of complex protease added is 0.3%-0.5% of the mass of the intercepted liquid; subsequently, maintaining the pH at 6.8-7.2 and adding the neutral protease for a second enzymatic hydrolysis treatment at 50-60°C for 0.8-1.5 hours, wherein the amount of neutral protease added is 0.2%-0.4% of the mass of the intercepted liquid.

[0048] In one embodiment, when the protease in step (e) is an alkaline protease and papain, the enzymatic hydrolysis treatment includes: adjusting the pH of the intercepted liquid to 8.5-9.5 and adding alkaline protease for a first enzymatic hydrolysis treatment at 40-50°C for 0.8-1.5 h, wherein the amount of alkaline protease added is 0.3%-0.4% of the mass of the intercepted liquid; subsequently, adjusting the pH to 5.5-6.5 and adding papain for a second enzymatic hydrolysis treatment at 50-60°C for 0.3-0.8 h, wherein the amount of papain added is 0.2%-0.3% of the mass of the intercepted liquid.

[0049] In one embodiment, in step (e), the pressure for pressurization heating is 0.8~1MPa, the heating temperature is 105~115℃, and the holding time is 4~6min.

[0050] In one embodiment, step (e) further includes: activated carbon adsorption, ultrasonic treatment, and encapsulation of the polypeptide using sodium alginate and / or chitosan as a wall material.

[0051] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0052] Example 1

[0053] This embodiment describes a method for preparing functional peptides from proteins in organic wastewater produced using freshwater fish paste, comprising the following steps:

[0054] (a) The organic wastewater from freshwater surimi production is passed through a curved screen at a speed of 2 m / min. The screen rake tooth spacing is 5 mm, the inclination angle is 75°, and the maximum flow rate is controlled at 80 m³ / h to remove large particulate suspended solids from the wastewater. At the same time, mechanical or manual cleaning is carried out regularly. Then, the organic wastewater from freshwater surimi production enters a vertical flow sedimentation tank with an upward flow velocity controlled at 1.5 m / h, a surface loading of 0.60 m³ / (m²·h), and a sedimentation time of 60 minutes to obtain organic wastewater with large particulate matter removed.

[0055] (b) Under stirring at 40 rpm, carbon dioxide was introduced into the organic wastewater from which large particulate matter was removed at a flux of 1.2 L / min and acetic acid was added until the pH value reached 4.8, thus obtaining the formulated organic wastewater;

[0056] (c) Add ferric chloride solution (solution concentration 10%, final ferric chloride concentration 530 mg / L) to the prepared organic wastewater and stir at 120 rpm for 1 min. Then, adjust the stirring speed to 40 rpm, add chitosan solution (solution concentration 1.5%, final chitosan concentration 150 mg / L) and continue stirring for 15 min to obtain a mixture.

[0057] (d) Pour the mixture into a spiral centrifuge and centrifuge at 3800 rpm for 15 min. Collect the supernatant and then perform ultrafiltration on the supernatant (molecular weight cutoff 10 kDa, pressure 0.25 MPa). Then perform nanofiltration on the ultrafiltrate (molecular weight cutoff 400 Da, pressure 0.75 MPa) and collect the filtrate. Perform ultrasonic backwashing periodically. During ultrafiltration and nanofiltration, ultrasonic treatment (30 kHz, 300 W / m) is applied. 3 );

[0058] (e) The intercepted liquid was pressurized and heated (0.8 MPa, 110 °C) and kept at that temperature for 5 min. Then, the pressure was released and the liquid was cooled to room temperature. The pH of the intercepted liquid was then adjusted to 2, and pepsin was added for the first enzymatic hydrolysis treatment at 30 °C for 2 h. The amount of pepsin added was 0.3% of the mass of the intercepted liquid. Subsequently, the pH was adjusted to 6.5, and flavor protease was added for the second enzymatic hydrolysis treatment at 50 °C for 1 h. The amount of flavor protease added was 0.2% of the mass of the intercepted liquid.

[0059] (f) After the enzymatic hydrolysis is completed, the enzyme is inactivated, and then nanofiltration and desalting are performed using a 400Da nanofiltration membrane to obtain the functional peptide with antioxidant function.

[0060] Example 2

[0061] This embodiment describes a method for preparing functional peptides from proteins in organic wastewater produced using freshwater fish paste, comprising the following steps:

[0062] (a) The organic wastewater from freshwater surimi production is passed through a curved screen at a speed of 2 m / min. The screen rake tooth spacing is 5 mm, the inclination angle is 75°, and the maximum flow rate is controlled at 80 m³ / h to remove large particulate suspended solids from the wastewater. At the same time, mechanical or manual cleaning is carried out regularly. Then, the organic wastewater from freshwater surimi production enters a vertical flow sedimentation tank with an upward flow velocity controlled at 1.5 m / h, a surface loading of 0.60 m³ / (m²·h), and a sedimentation time of 60 minutes to obtain organic wastewater with large particulate matter removed.

[0063] (b) Under stirring at 35 rpm, carbon dioxide was introduced into the organic wastewater from which large particulate matter was removed at a flow rate of 1 L / min and acetic acid was added until the pH value reached 4.7, thus obtaining the formulated organic wastewater.

[0064] (c) Add ferric chloride solution (solution concentration 10%, final ferric chloride concentration 520 mg / L) to the prepared organic wastewater and stir at 100 rpm for 1 min. Then, adjust the stirring speed to 35 rpm, add chitosan solution (solution concentration 1.5%, final chitosan concentration 130 mg / L) and continue stirring for 15 min to obtain a mixture.

[0065] (d) Pour the mixture into a spiral centrifuge and centrifuge at 3800 rpm for 15 min. Collect the supernatant and then perform ultrafiltration on the supernatant (molecular weight cutoff 10 kDa, pressure 0.2 MPa). Then perform nanofiltration on the ultrafiltrate (molecular weight cutoff 400 Da, pressure 0.6 MPa) and collect the filtrate. Perform ultrasonic backwashing periodically. During ultrafiltration and nanofiltration, ultrasonic treatment (25 kHz, 250 W / m) is applied. 3 );

[0066] (e) The intercepted liquid was pressurized and heated (0.8 MPa, 110 °C) and held at that temperature for 5 min. Then, the pressure was released and the liquid was cooled to room temperature. Next, the pH of the intercepted liquid was adjusted to 7, and a compound protease was added for the first enzymatic hydrolysis treatment at 45 °C for 3 h. The amount of compound protease added was 0.4% of the mass of the intercepted liquid. Subsequently, the pH was maintained at 7, and a neutral protease was added for the second enzymatic hydrolysis treatment at 55 °C for 1 h. The amount of neutral protease added was 0.3% of the mass of the intercepted liquid.

[0067] (f) After the enzymatic hydrolysis is completed, the enzyme is inactivated, and then nanofiltration and desalting are performed using a 400 Da nanofiltration membrane to obtain the functional peptide with growth-promoting function.

[0068] Example 3

[0069] This embodiment describes a method for preparing functional peptides from proteins in organic wastewater produced using freshwater fish paste, comprising the following steps:

[0070] (a) The organic wastewater from freshwater surimi production is passed through a curved screen at a speed of 2 m / min. The screen rake tooth spacing is 5 mm, the inclination angle is 75°, and the maximum flow rate is controlled at 80 m³ / h to remove large particulate suspended solids from the wastewater. At the same time, mechanical or manual cleaning is carried out regularly. Then, the organic wastewater from freshwater surimi production enters a vertical flow sedimentation tank with an upward flow velocity controlled at 1.5 m / h, a surface loading of 0.60 m³ / (m²·h), and a sedimentation time of 60 minutes to obtain organic wastewater with large particulate matter removed.

[0071] (b) Under stirring at 45 rpm, carbon dioxide was introduced into the organic wastewater from which large particulate matter was removed at a flow rate of 1.5 L / min and acetic acid was added until the pH value reached 4.6, thus obtaining the formulated organic wastewater.

[0072] (c) Add ferric chloride solution (solution concentration 10%, final ferric chloride concentration 540 mg / L) to the prepared organic wastewater and stir at 130 rpm for 1 min. Then, adjust the stirring speed to 45 rpm, add chitosan solution (solution concentration 1.5%, final chitosan concentration 170 mg / L) and continue stirring for 15 min to obtain a mixture.

[0073] (d) Pour the mixture into a spiral centrifuge and centrifuge at 3800 rpm for 15 min. Collect the supernatant and then perform ultrafiltration on the supernatant (molecular weight cutoff 10 kDa, pressure 0.28 MPa). Then perform nanofiltration on the ultrafiltrate (molecular weight cutoff 400 Da, pressure 0.85 MPa) and collect the filtrate. Perform ultrasonic backwashing periodically. During ultrafiltration and nanofiltration, ultrasonic treatment (35 kHz, 350 W / m) is applied. 3 );

[0074] (e) The intercepted liquid was pressurized and heated (0.8 MPa, 110 °C) and kept at that temperature for 5 min. Then, the pressure was released and the liquid was cooled to room temperature. The pH of the intercepted liquid was then adjusted to 9 and alkaline protease was added for the first enzymatic hydrolysis treatment at 45 °C for 1 h. The amount of alkaline protease added was 0.35% of the mass of the intercepted liquid. Subsequently, the pH was adjusted to 6 and papain was added for the second enzymatic hydrolysis treatment at 55 °C for 0.5 h. The amount of papain added was 0.25% of the mass of the intercepted liquid.

[0075] (f) After the enzymatic hydrolysis is completed, the enzyme is inactivated, and then nanofiltration and desalting are performed using a 400Da nanofiltration membrane to obtain the functional peptide with immunomodulatory function.

[0076] Example 4

[0077] This embodiment describes a method for preparing functional peptides from proteins in organic wastewater produced using freshwater fish paste, comprising the following steps:

[0078] (a) The organic wastewater from freshwater surimi production is passed through a curved screen at a speed of 2 m / min. The screen rake tooth spacing is 5 mm, the inclination angle is 75°, and the maximum flow rate is controlled at 80 m³ / h to remove large particulate suspended solids from the wastewater. At the same time, mechanical or manual cleaning is carried out regularly. Then, the organic wastewater from freshwater surimi production enters a vertical flow sedimentation tank with an upward flow velocity controlled at 1.5 m / h, a surface loading of 0.60 m³ / (m²·h), and a sedimentation time of 60 minutes to obtain organic wastewater with large particulate matter removed.

[0079] (b) Under stirring at 45 rpm, carbon dioxide was introduced into the organic wastewater from which large particulate matter was removed at a flow rate of 1.5 L / min and acetic acid was added until the pH value reached 4.6, thus obtaining the formulated organic wastewater.

[0080] (c) Add ferric chloride solution (solution concentration 10%, final ferric chloride concentration 540 mg / L) to the prepared organic wastewater and stir at 130 rpm for 1 min. Then, adjust the stirring speed to 45 rpm, add chitosan solution (solution concentration 1.5%, final chitosan concentration 170 mg / L) and continue stirring for 15 min to obtain a mixture.

[0081] (d) Pour the mixture into a spiral centrifuge and centrifuge at 3800 rpm for 15 min. Collect the supernatant and then perform ultrafiltration on the supernatant (molecular weight cutoff 10 kDa, pressure 0.28 MPa). Then perform nanofiltration on the ultrafiltrate (molecular weight cutoff 400 Da, pressure 0.85 MPa) and collect the filtrate. Perform ultrasonic backwashing periodically. Ultrasonic treatment (35 kHz, 350 W / m3) during ultrafiltration and nanofiltration.

[0082] (e) The intercepted liquid was pressurized and heated (0.8 MPa, 110 °C) and kept at that temperature for 5 min. Then, the pressure was released and the liquid was cooled to room temperature. The pH of the intercepted liquid was then adjusted to 9 and alkaline protease was added for the first enzymatic hydrolysis treatment at 45 °C for 1 h. The amount of alkaline protease added was 0.35% of the mass of the intercepted liquid. Subsequently, the pH was adjusted to 6 and papain was added for the second enzymatic hydrolysis treatment at 55 °C for 0.5 h. The amount of papain added was 0.25% of the mass of the intercepted liquid.

[0083] (f) After enzymatic hydrolysis, enzyme inactivation is performed, followed by nanofiltration and desalting using a 400 Da nanofiltration membrane. The desalted enzymatic hydrolysis product is then introduced into an adsorption tank, and pretreated activated carbon (activated with 0.1% acetic acid solution to improve adsorption efficiency) is added simultaneously. The ratio of activated carbon to enzymatic hydrolysis product is 0.5% (mass fraction). The pH is adjusted to 4.6, the stirring device is turned on, and the stirring speed is maintained at 130 rpm. The temperature is controlled at 30°C for 50 minutes. The activated carbon is then removed by centrifugation (4000 rpm, 15 minutes). The product adsorbed by the activated carbon is then introduced into an ultrasonic treatment tank, and the ultrasonic generator parameters are set to a frequency of 28 kHz. Hz, power 28W, turn on ultrasound, maintain for 15 minutes while controlling the temperature at 30℃. After treatment, centrifuge (4000rpm, 15 minutes) to remove possible flocculants. The ultrasonically treated solution is thoroughly mixed with the pre-prepared composite microencapsulated wall material (sodium alginate: chitosan 4:1) (mass ratio 4.35:1). Turn on the spray drying system with the inlet air temperature at 190℃ and the outlet air temperature at 85℃. After atomization, the droplets enter a 2% calcium chloride solution (crosslinking agent solution) to form microcapsules. Then collect the dried microencapsulated functional peptide powder, package and store it.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for producing functional peptides from proteins in organic wastewater using freshwater surimi, characterized by, The method comprises the following steps: (a) performing grid filtration and sedimentation on organic wastewater generated in the production of freshwater surimi to obtain organic wastewater from which large particulate matter is removed; (b) under stirring, introducing carbon dioxide into the organic wastewater from which large particulate matter is removed and adding acetic acid until the pH value is 4.5-5.0 to obtain adjusted organic wastewater; (c) adding a ferric chloride solution to the adjusted organic wastewater and stirring for a period of time, then adjusting the stirring speed, adding a chitosan solution and continuing to stir for a period of time to obtain a mixed solution; (d) performing centrifugation on the mixed solution, collecting the supernatant, performing ultrafiltration on the supernatant, then performing nanofiltration on the ultrafiltrate, collecting the nanofiltration liquid and performing regular ultrasonic backwashing; (e) performing pressurized heating on the nanofiltration liquid and maintaining the temperature for a period of time, then depressurizing and cooling to room temperature, then adding a protease to the nanofiltration liquid to perform enzymatic hydrolysis treatment; the protease is pepsin and flavour protease; or the protease is complex protease and neutral protease; or the protease is alkaline protease and papain; (f) after the enzymatic hydrolysis ends, performing enzyme inactivation, then performing nanofiltration and desalination on the nanofiltration liquid by using a 400 Da nanofiltration membrane to obtain the functional peptide.

2. The method for producing functional peptides from proteins in organic wastewater using freshwater surimi according to claim 1, characterized in that, In the step (b), the flux of the carbon dioxide is 0.5-2 L / min.

3. The method for producing functional peptides from proteins in organic wastewater using freshwater surimi according to claim 1, characterized in that, In the step (c), the concentration of the ferric chloride solution is 8%-12%; the final concentration of the ferric chloride added is 500-550 mg / L; after the ferric chloride solution is added, the stirring speed is 100-150 rpm and the stirring time is 1-2 min.

4. The method for producing functional peptides from proteins in organic wastewater using freshwater surimi according to claim 1, characterized in that, In the step (c), the concentration of the chitosan solution is 1%-2%; the final concentration of the chitosan added is 100-200 mg / L; after the chitosan solution is added, the stirring speed is 30-50 rpm and the stirring time is 10-20 min.

5. The method for producing functional peptides from proteins in organic wastewater using freshwater surimi according to claim 1, characterized in that, In the step (d), the ultrafiltration membrane used in the ultrafiltration has a molecular weight cut-off of 10-30 kDa; the nanofiltration membrane used in the nanofiltration has a molecular weight cut-off of 400-500 Da.

6. The method for producing functional peptides from proteins in organic wastewater using freshwater surimi according to claim 1, characterized in that, In step (d), the ultrasonic treatment is performed in the ultrafiltration and nanofiltration process, the ultrasonic frequency is 20-40 kHz, and the power density is 100-400 W / m 3 .

7. The method for producing functional peptides from proteins in organic wastewater using freshwater surimi according to claim 1, characterized in that, In the step (e), when the protease is pepsin and flavour protease, the enzymatic hydrolysis treatment comprises: adjusting the pH value of the nanofiltration liquid to 1.5-2.5, adding pepsin to perform first-time enzymatic hydrolysis treatment at 25-35 ℃ for 1.5-3 h, the amount of the pepsin added is 0.2%-0.4% of the mass of the nanofiltration liquid; then, adjusting the pH value to 6.2-6.8, adding flavour protease to perform second-time enzymatic hydrolysis treatment at 45-55 ℃ for 0.8-1.5 h, the amount of the flavour protease added is 0.1%-0.3% of the mass of the nanofiltration liquid.

8. The method for producing functional peptides from proteins in organic wastewater using freshwater surimi according to claim 1, characterized in that, In the step (e), when the protease is complex protease and neutral protease, the enzymatic hydrolysis treatment comprises: adjusting the pH value of the nanofiltration liquid to 6.8-7.2, adding complex protease to perform first-time enzymatic hydrolysis treatment at 40-50 ℃ for 2-4 h, the amount of the complex protease added is 0.3%-0.5% of the mass of the nanofiltration liquid; then, keeping the pH value at 6.8-7.2, adding neutral protease to perform second-time enzymatic hydrolysis treatment at 50-60 ℃ for 0.8-1.5 h, the amount of the neutral protease added is 0.2%-0.4% of the mass of the nanofiltration liquid.

9. The method for producing functional peptides from proteins in organic wastewater using freshwater surimi according to claim 1, characterized in that, In step (e), when the protease is alkaline protease and papain, the enzymatic treatment comprises: adjusting the pH value of the cut-off liquid to 8.5-9.5, adding alkaline protease, and performing first enzymatic treatment at 40-50°C for 0.8-1.5h, the addition amount of alkaline protease being 0.3%-0.4% of the mass of the cut-off liquid; then, adjusting the pH value to 5.5-6.5, adding papain, and performing second enzymatic treatment at 50-60°C for 0.3-0.8h, the addition amount of papain being 0.2%-0.3% of the mass of the cut-off liquid.

10. The method for producing functional peptides from proteins in organic wastewater using freshwater surimi according to claim 1, characterized in that, In step (e), the process further comprises: active carbon adsorption, ultrasonic treatment, and embedding treatment of the polypeptide by using sodium alginate and / or chitosan as wall material.