Method for concentrating water-soluble protein and method for recovering water-soluble protein

Abstract

Provided are a method for concentrating a water-soluble protein and a method for recovering a water-soluble protein using the same, whereby it is possible to increase the concentration ratio of the water-soluble protein while maintaining the recovery rate of the water-soluble protein. The present invention relates to a method for concentrating a water-soluble protein, which is a method for separating and concentrating a water-soluble protein that is soluble in a salt solution having an ionic strength of 0.1 mol / L or less, the method comprising: supplying a supply solution containing the water-soluble protein to an NF membrane; a concentration step for separating the supply liquid into a permeate and a concentrated liquid such that the ion strength (mol / L) of the concentrated liquid is 1.0-2.0 times the ion strength (mol / L) of the supply liquid; also disclosed is a method for recovering a water-soluble protein, which comprises a desalination step for separating a salt from the concentrated solution obtained by an ion exchange resin method and / or an electrodialysis method after the concentration method has been performed.

Description

Technical Field

[0001] The present invention relates to a method for concentrating water-soluble proteins for separating and concentrating water-soluble proteins soluble in a salt solution having an ionic strength of 0.1 mol / L or less, and a method for recovering and treating the water-soluble proteins using the method. Background Art

[0002] The production of processed fish foods made from cod and other fish includes a washing (water-cleaning) step for cleaning the fish surimi. During this washing process, water-soluble proteins are eluted from the fish, and the resulting wastewater containing these proteins is discarded. Furthermore, the amount of water-soluble protein in this wastewater is estimated to be 40,000 to 50,000 tons annually. Therefore, in recent years, research has been underway to recover protein from wastewater, driven by the efficient use of natural resources and the efficiency of wastewater treatment.

[0003] For example, methods have been studied in which the wastewater is made acidic to insolubilize the protein and the insolubilized protein is recovered by centrifugation or the like; a method in which a coagulant is added to the insolubilized protein and solid-liquid separation is performed by pressurized dissolved air flotation, etc.

[0004] However, the recovery method using centrifugal separation or the like has low cohesion and requires a large amount of chemicals for pH adjustment. In addition, the method using a coagulant addition also has problems such as low recovery rate and high water content in the recovered product.

[0005] Therefore, methods for separating and concentrating water-soluble proteins using separation membranes have been proposed. For example, Patent Document 1 proposes a method for concentrating fish juice. In this method, the fish juice is first separated into an ultrafiltration membrane (UF membrane) concentrate and an UF membrane permeate using an ultrafiltration device. The UF membrane permeate is then separated into a reverse osmosis membrane (RO membrane) concentrate and a reverse osmosis membrane permeate using a reverse osmosis membrane. Finally, these two concentrates are concentrated using a high-order concentration method. Patent Document 1 also points out that the recovery rate of fish juice is low when concentration is performed using only an ultrafiltration device.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Publication No. 62-46148 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] However, the concentration method of Patent Document 1, when concentrating proteins using an RO membrane, also concentrates the salts contained in the feed solution. This increases the osmotic pressure and prevents the concentration ratio from being increased (preferably to be less than 6 times). Furthermore, during the concentration process using an RO membrane, protein accumulation reduces water permeability, necessitating cleaning of the RO membrane, which can easily shorten the membrane lifespan.

[0011] Therefore, an object of the present invention is to provide a method for concentrating water-soluble proteins that can increase the concentration ratio of water-soluble proteins while maintaining the recovery rate of water-soluble proteins, and a method for recovering water-soluble proteins using the method.

[0012] Means used to solve problems

[0013] The present inventors have conducted intensive research to address the above-mentioned issues and have discovered that, when using a NF membrane to separate a feed liquid into a permeate and a concentrate, the concentration ratio of water-soluble proteins can be increased by setting the ionic strength of the concentrate to 1.0 to 2.0 times that of the feed liquid. This has led to the completion of the present invention. Specifically, the present invention encompasses the following aspects.

[0014] [1] A method for concentrating a water-soluble protein, the method for concentrating a water-soluble protein being a method for separating and concentrating a water-soluble protein soluble in a salt solution having an ionic strength of 0.1 mol / L or less, wherein the method comprises the following concentration step: a concentration step, wherein a feed liquid containing the water-soluble protein is fed to a NF membrane, and the feed liquid is separated into a permeate and a concentrate in such a manner that the ionic strength (mol / L) of the concentrate becomes 1.0 to 2.0 times that of the feed liquid.

[0015] The method for concentrating water-soluble proteins of the present invention uses a NF membrane to separate the feed solution into a permeate and a concentrate so that the ionic strength of the concentrate is 1.0 to 2.0 times that of the feed solution. This prevents the concentration of salts on the surface of the NF membrane, which would otherwise increase the osmotic pressure, thereby increasing the concentration ratio of the water-soluble proteins. Furthermore, the use of the NF membrane can suppress the permeation of water-soluble proteins, thereby maintaining the recovery rate.

[0016] [2] The method for concentrating a water-soluble protein according to [1], wherein, in the concentration step, the concentration ratio of the concentrated liquid relative to the feed liquid is 3 times or more, or the concentration ratio of the final concentrated liquid relative to the feed liquid initially supplied to the NF membrane is 3 times or more.

[0017] By setting the concentration ratio to 3 times or more, the volume of the liquid to be treated is reduced during desalination, drying, storage, etc. in the post-treatment process, thereby achieving energy saving and simplification.

[0018] [3] The method for concentrating a water-soluble protein according to [1] or [2], wherein, in the concentration step, the concentration ratio of the concentrated liquid relative to the feed liquid is 6 times or more.

[0019] In the case of the conventional concentration method using an RO membrane, the concentration ratio of water-soluble proteins is less than 6 times (see Patent Document 1). However, by increasing the concentration ratio to 6 times or more as described above, energy saving and simplification can be achieved by reducing the volume during desalination, drying, storage, and other post-processing steps.

[0020] [4] The method for concentrating a water-soluble protein according to any one of [1] to [3], wherein the NF membrane comprises a separation functional layer having an anionic group.

[0021] Water-soluble proteins contain negatively charged proteins. Therefore, a NF membrane with a separation functional layer containing anionic groups can inhibit adsorption of water-soluble proteins through electrostatic repulsion, thereby improving protein retention and cleaning recovery by suppressing the accumulation of water-soluble proteins.

[0022] [5] The method for concentrating a water-soluble protein according to any one of [1] to [4], wherein the separation functional layer contains a polysulfone resin having a sulfonic acid group.

[0023] In particular, the presence of sulfonic acid groups, which are strong acid groups, further enhances the adsorption barrier effect, allowing for a further reduction in the frequency of membrane cleaning. Furthermore, polysulfone resins containing sulfonic acid groups exhibit enhanced durability against alkaline and chlorine-containing cleaning solutions.

[0024] [6] The method for concentrating a water-soluble protein according to any one of [1] to [5], wherein the method for concentrating a water-soluble protein comprises the following pre-concentration step: in the pre-concentration step, a treated liquid containing the water-soluble protein is supplied to at least a UF membrane to separate the treated liquid into a permeate and a concentrated liquid, and the permeate is supplied as a feed liquid to the concentration step while recovering the separated concentrated liquid.

[0025] By performing such a pre-concentration step, water-soluble proteins can be concentrated and recovered using low operating energy in the pre-concentration step, and the volume of the feed liquid supplied to the concentration step and the concentration of water-soluble proteins can be reduced, thereby improving operating efficiency.

[0026] [7] A method for recovering and treating water-soluble proteins, wherein the method for recovering and treating water-soluble proteins comprises the following desalting step: a desalting step, wherein, after implementing the method for concentrating water-soluble proteins described in any one of [1] to [6], salt is separated from the obtained concentrated solution by an ion exchange resin method and / or an electrodialysis method.

[0027] According to this recovery treatment method, the recovery rate of water-soluble protein can be maintained through the concentration step as described above, while the concentration ratio of water-soluble protein can be increased. Therefore, the volume can be reduced during the desalting step, thereby achieving energy saving and simplification.

[0028] [8] The method for recovering a water-soluble protein according to [7], wherein the method comprises a drying step of removing water from the concentrated liquid after the desalting step.

[0029] By including the drying step, a water-soluble protein in a dry state or with a reduced moisture content can be obtained, and the handling properties during storage and commercialization can be improved.

[0030] [9] The method for recovering and treating water-soluble proteins according to [7] or [8], wherein a food raw material or a fertilizer raw material is obtained through the drying step.

[0031] Since water-soluble proteins that were previously discarded can be recovered at high concentrations and high recovery rates and used as food or fertilizer raw materials, the present invention is a useful technology from the perspective of effective utilization of natural resources and efficiency of wastewater treatment.

[0032] Effects of the Invention

[0033] According to the present invention, there can be provided a method for concentrating water-soluble proteins capable of increasing the concentration ratio of water-soluble proteins while maintaining the recovery rate of water-soluble proteins, and a method for recovering water-soluble proteins using the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram showing an example of a method for concentrating water-soluble proteins.

[0035] Figure 2 This is a schematic diagram showing another example of a method for concentrating water-soluble proteins.

[0036] Figure 3 This is a partially cutaway perspective view showing an example of a spiral membrane element used in a method for concentrating water-soluble proteins. DETAILED DESCRIPTION

[0037] Hereinafter, embodiments of the present invention will be described.

[0038] [Method for concentrating water-soluble protein]

[0039] The method for concentrating water-soluble proteins of the present invention is a method for separating and concentrating water-soluble proteins that are soluble in a salt solution with an ionic strength of 0.1 mol / L or less. The method for concentrating water-soluble proteins includes a concentration step using an NF membrane (nanofiltration membrane), and may also include a pre-concentration step using at least a UF membrane (ultrafiltration membrane). In the pre-concentration step, an MF membrane (precision filtration membrane) or the like may be used to remove inclusions or recover solid proteins. As other pre-treatment steps, it may also include a step of precipitating the protein by pH adjustment and temperature adjustment and recovering it by centrifugation, a step of adding a coagulant and recovering it by pressurized dissolved air flotation after coagulation.

[0040] The method for concentrating water-soluble proteins of the present invention can be performed using, for example, Figure 1 or Figure 2 The membrane separation device shown is used for implementation.

[0041] For example, Figure 1 The membrane separation device shown includes a membrane module M1 having a separation membrane 1 as a NF membrane, a supply portion for a feed liquid 7, a discharge portion for a permeate liquid 8, and a discharge portion for a concentrated liquid 9. Figure 2 The membrane separation apparatus shown includes a membrane module M2 having a separation membrane 21 as a UF membrane, a supply section for a treated liquid 27, a discharge section for a permeate 28, and a discharge section for a concentrated liquid 29; and a membrane module M1 having a separation membrane 1 as a NF membrane, a supply section for supplying permeate 28 as a feed liquid 7 to the separation membrane 1, a discharge section for a permeate 8, and a discharge section for a concentrated liquid 9. These membrane separation apparatuses may also be provided with a circulation line for circulating a portion of the concentrated liquid 9 or the concentrated liquid 29 to the feed liquid side.

[0042] Furthermore, by providing a feed liquid tank to store the feed liquid 7 and circulating the entire amount of the concentrate 9 within the feed liquid tank, the concentration ratio can be increased by extending the filtration time, similar to dead-end filtration. Furthermore, the concentration ratio can be increased by configuring the concentration process in multiple stages. In this case, the concentration ratio of water-soluble proteins can be further increased by using NF membranes and separating the permeate and concentrate so that the ionic strength of the concentrate is 1.0 to 2.0 times that of the feed liquid.

[0043] Such a membrane separation apparatus is equipped with other equipment such as a pump, a sensor, a tank, a control valve, and a control device as needed, and is configured to be able to operate under desired conditions.

[0044] (Water-soluble protein)

[0045] In this specification, "water-soluble protein" refers to a protein soluble in a saline solution having an ionic strength of 0.1 (mol / L) or less, as measured below. Water-soluble proteins targeted for concentration are not limited to fish proteins but also include proteins derived from animals or plants. However, from the perspective of effective utilization of natural resources and efficient wastewater treatment, fish-derived proteins are preferably targeted for concentration.

[0046] For example, fish proteins are classified based on their solubility in neutral salt solutions into water-soluble proteins that are soluble in salt solutions with an ionic strength of 0.1 (mol / L) or less, salt-soluble proteins that are soluble in salt solutions with an ionic strength of 0.5 (mol / L), and insoluble proteins that are insoluble in these salt solutions. Examples of water-soluble proteins include saccharomyces cerevisiae, parvalbumin, myoglobin, and creatine kinase.

[0047] As the salt solution for confirming solubility, an aqueous solution obtained by dissolving NaCl or KCl in water so as to have an ionic strength of 0.1 (mol / L) can be used.

[0048] (ionic strength)

[0049] The ionic strength of a salt solution used to confirm the solubility of a water-soluble protein can be measured as follows. Ionic strength (mol / L) is the value obtained by summing the product of the molar concentration (mol / L) of the ion and the square of the valence of each ion in the liquid and further dividing this value by 2. Therefore, the ionic strength (mol / L) can be measured by measuring the molar concentration (mol / L) of various coexisting ions in the salt solution and calculating the measured values ​​using the following formula (I).

[0050]

[0051] I: ionic strength

[0052] ci: molar concentration of ionic species i

[0053] Zi: valence of ionic species i

[0054] The molar concentration (mol / L) of ions can be measured, for example, using an ion chromatograph (Shimadzu Corporation, Prominence HIP-SP). Alternatively, the ionic strength (mol / L) can be calculated using formula (I) based on the salt content when preparing the salt solution.

[0055] The ionic strength (mol / L) during the concentration process can be measured by sampling the feed solution or the concentrated solution as a sample. The molar concentration (mol / L) of the ions in the sample can be measured, for example, using an ion chromatograph (Shimadzu Corporation, Prominence HIP-SP). The ionic strength can be calculated using formula (I) based on the type and molar concentration (mol / L) of the ions.

[0056] [Concentration process]

[0057] The concentration step is a step of supplying the feed liquid containing the water-soluble protein to the NF membrane and separating the feed liquid into a permeate and a concentrate in such a manner that the ionic strength of the concentrate becomes 1.0 to 2.0 times that of the feed liquid. The treated liquid to be concentrated can be used as the feed liquid (see Figure 1 ), you can also use the permeate after the pre-concentration process (refer to Figure 2 ).

[0058] The concentration of water-soluble protein in the liquid to be treated, which is the subject of the concentration treatment, is, for example, 0.5 g / L to 50 g / L, preferably 0.8 g / L to 20 g / L. When using the permeate after the pre-concentration step, the concentration of water-soluble protein in the feed liquid is, for example, 0.1 g / L to 20 g / L, preferably 1 g / L to 10 g / L.

[0059] Furthermore, the ionic strength of the feed liquid during the concentration treatment is the same as or substantially the same as the ionic strength of the liquid to be treated, for example, 0.01 mol / L to 0.1 mol / L, preferably 0.02 mol / L to 0.08 mol / L. In the present invention, even when the ionic strength of the feed liquid is high, the concentration ratio of the water-soluble protein can be maintained high by maintaining the ionic strength of the concentrate at 1.0 to 2.0 times that of the feed liquid.

[0060] (Concentrate)

[0061] The ratio of the ionic strength of the concentrate to the ionic strength of the feed solution (concentrate / feed solution) is 1.0 to 2.0 times, preferably 1.01 to 1.9 times, and more preferably 1.05 to 1.2 times. A lower ionic strength ratio more effectively prevents salt concentration on the NF membrane surface, which increases osmotic pressure, thereby further increasing the concentration rate of water-soluble proteins. On the other hand, under conditions where ion retention is poor, the recovery rate of water-soluble proteins tends to decrease. Therefore, the ionic strength ratio is preferably greater than 1.0.

[0062] When these ionic strength ratio conditions are met, the concentration ratio of the water-soluble protein in the concentrate can be adjusted to 3 times or more, preferably 6 times or more, as the concentration ratio of the concentrate relative to the feed liquid supplied to the NF membrane, or the concentration ratio of the final concentrate relative to the feed liquid initially supplied to the NF membrane. Therefore, the concentration ratio of the concentrate relative to the feed liquid supplied to the NF membrane, or the concentration ratio of the final concentrate relative to the feed liquid initially supplied to the NF membrane, is, for example, 3 times or more, preferably 6 times or more, and more preferably 10 times or more. However, from the perspective of membrane performance recovery, it is preferably 50 times or less, and more preferably 30 times or less.

[0063] Here, the concentration ratio of the water-soluble protein is a value calculated by the following formula (II): The concentration of the water-soluble protein can be determined by measuring absorbance using a spectrophotometer or the like and a calibration curve.

[0064] Concentration ratio of water-soluble protein (-) = concentration of water-soluble protein in the concentrate (g / L) ÷ concentration of water-soluble protein in the feed solution (g / L) (II)

[0065] When the retention rate of water-soluble protein is close to 100%, the concentration ratio of water-soluble protein is equivalent to the apparent concentration ratio described below. The apparent concentration ratio can be calculated using the feed liquid volume and the concentrate volume using the following calculation formula (III).

[0066] Apparent concentration ratio (-) = supply volume (mL) ÷ concentrate volume (mL) (III)

[0067] When the pre-concentration step is performed, the total concentration ratio of the water-soluble proteins in the liquid to be treated in the pre-concentration step is preferably 10 times or more, more preferably 30 times or more.

[0068] Here, the total concentration ratio of water-soluble protein is a value calculated by the following formula (IV).

[0069] Total concentration ratio (-) = concentration of water-soluble protein in the concentrate (g / L) ÷ concentration of water-soluble protein in the treated liquid (g / L) (IV)

[0070] Examples of methods for adjusting the ratio of the ionic strength of the concentrate include adjusting the salt rejection rate of the NF membrane used, adjusting the pressure of the NF membrane, adjusting the ionic strength of the feed liquid, adjusting the flow rate of the feed liquid, and diafiltration by adding water to reduce the concentration. However, from the perspective of easily stabilizing the ratio of the ionic strength of the concentrate and not requiring additives, the method of adjusting the salt rejection rate of the nanofiltration membrane used is preferred.

[0071] (NF membrane)

[0072] In this specification, "NF membrane" refers to a separation membrane that has a NaCl rejection of 5% or more and less than 93% when filtering a 500 mg / L NaCl aqueous solution at an operating pressure of 0.5 MPa and 25°C. It should be noted that an RO membrane refers to a separation membrane that has a NaCl rejection of 93% or more when filtering a 500 mg / L NaCl aqueous solution at an operating pressure of 0.5 MPa and 25°C.

[0073] The NaCl retention rate can be measured, for example, by the following method in accordance with JIS K3805 (1990): For the measurement of the NaCl retention rate, a NaCl aqueous solution at 25° C., pH 6.5 to 7, and a concentration of 500 mg / L is used.

[0074] A NaCl aqueous solution is passed through a separation membrane of specified dimensions at an operating pressure of 0.5 MPa. After a 30-minute preparatory phase, the conductivity of the permeate and feed liquid is measured using a conductivity meter. The NaCl retention rate can be calculated using the following formula based on the results and a calibration curve (concentration-conductivity). Concentration measurement can also be performed using ion chromatography instead of conductivity measurement.

[0075] NaCl retention rate (%) = (1-(NaCl concentration of permeate / NaCl concentration of feed liquid)) × 100

[0076] As NF membrane (nanofiltration membrane), any membrane having a NaCl rejection rate lower than that of RO membrane (reverse osmosis membrane) can be used. As the salt rejection rate of the NF membrane, the rejection rate of NaCl is preferably 80% or less, more preferably 60% or less, and further preferably 30% or less. The lower the salt rejection rate, the easier it is to maintain the ionic strength so that the ionic strength of the concentrated solution becomes less than 2.0 times that of the supply solution. However, the lower the salt rejection rate, the more the recovery rate of water-soluble proteins tends to decrease. Therefore, as the salt rejection rate of the nanofiltration membrane, for example, the rejection rate of NaCl is preferably 5% or more, more preferably 9% or more.

[0077] Therefore, from the viewpoint of increasing the concentration ratio of water-soluble proteins while maintaining the recovery rate of water-soluble proteins, the molecular weight cutoff of the NF membrane is preferably 200 to 10,000 Daltons, more preferably 700 to 4,500 Daltons, and even more preferably 900 to 4,000 Daltons.

[0078] Here, the molecular weight cut-off of the NF membrane is determined as follows. First, a plurality of polyethylene glycols having different average molecular weights and monodisperse molecular weight distributions are prepared. An aqueous solution containing one of the plurality of polyethylene glycols at a concentration of 5000 ppm is stirred at a temperature of 25°C and a pressure of 4 kg / cm 2 The polyethylene glycol is supplied to the NF membrane surface under the following conditions. This allows the polyethylene glycol retention rate to be determined. The retention rates of other polyethylene glycols are determined using the same method. A classification curve is created to show the relationship between the retention rate obtained and the average molecular weight of the polyethylene glycol. Based on the classification curve, the average molecular weight of the polyethylene glycol that achieves a 90% retention rate is determined. This average molecular weight can be considered the molecular weight cutoff of the NF membrane.

[0079] The NF membrane may be, for example, a composite semipermeable membrane comprising a porous support membrane and a separation functional layer, wherein the separation functional layer is supported by the porous support membrane. The material and structure of the porous support membrane are not particularly limited. As the porous support membrane, for example, an ultrafiltration membrane is used in which a microporous layer having an average pore size of 0.01 μm to 0.4 μm is formed on a non-woven fabric. Examples of materials forming the microporous layer include polysulfone, polyethersulfone, and other polyarylethersulfones, polyimide, polyvinylidene fluoride, and polytetrafluoroethylene.

[0080] NF membranes come in either charged or uncharged types, depending on whether or not their surfaces are charged. Both types can be used in the present invention. However, since some water-soluble proteins are negatively charged, negatively charged NF membranes are preferred from the perspective of inhibiting adsorption through electrostatic repulsion with water-soluble proteins and reducing the frequency of membrane cleaning steps.

[0081] Examples of negatively charged NF membranes include separation functional layers having anionic groups. Examples of anionic groups include sulfonic acid groups and carboxylic acid groups, with sulfonic acid groups being preferred as strong acid groups.

[0082] In addition, examples of the resin constituting the separation functional layer include polysulfone resins, polyamide, cellulose acetate, and polyvinyl alcohol. Polysulfone resins are particularly preferred from the perspectives of chemical, mechanical, and thermal stability. Examples of the polysulfone resin include polysulfone, polyethersulfone, and polyphenylsulfone.

[0083] Specifically, a preferred separation functional layer of the NF membrane includes a polysulfone resin having sulfonic acid groups. NF membranes having such a separation functional layer have increased durability against alkaline cleaning solutions and chlorine-containing cleaning solutions.

[0084] As the NF membrane comprising sulfonated polyethersulfone in which the separation functional layer has a negative fixed charge, the NF membranes described in Japanese Patent Application Laid-Open Nos. 61-4505 and 61-4506 are particularly preferred.

[0085] Examples of the polysulfone-based resin having a sulfonic acid group include resins having the following repeating units (A) or (B).

[0086]

[0087]

[0088] The membrane module M1 using NF membranes can be composed of a single or multiple membrane elements. Typically, the membrane elements are spiral membrane elements using NF membranes. The membrane module M1 can also be composed of a pressure vessel and a single or multiple spiral membrane elements disposed within the pressure vessel. However, the structure of the membrane element containing the NF membrane is not limited to the spiral type and can also be other types such as hollow fiber, tubular, and frame plate.

[0089] (Spiral membrane element)

[0090] Spiral membrane elements such as Figure 3 As shown, there is a central tube 5 having a hole and a wound body R wound around the central tube 5 and including the separation membrane 1. Figure 3 In the example shown, the spiral membrane element comprises: a plurality of membrane sheets L with permeate-side flow path material 3 sandwiched between opposing separation membranes 1; a feed-side flow path material 2 interposed between the membrane sheets L; a perforated center tube 5 formed by winding the membrane sheets L and the feed-side flow path material 2; and a seal 12 to prevent mixing of the feed-side flow path and the permeate-side flow path. In this case, the permeate-side flow path within the membrane sheet L can be formed by the permeate-side flow path material 3 (also referred to as a permeate-side spacer).

[0091] exist Figure 3 In the figure, an example is shown in which the sealing portion includes two end sealing portions and an outer peripheral side sealing portion 12. The two end sealing portions in the sealing portion are formed by sealing the two end portions on both sides of the axial direction A1 of the membrane L with an adhesive. The outer peripheral side sealing portion 12 is formed by sealing the end portion of the outer peripheral front end of the membrane L with an adhesive. The following structure is formed: the area surrounded by the relative separation membrane 1, the two end sealing portions and the outer peripheral side sealing portion 12 becomes the permeate side flow path, which is connected to the opening 5a of the central tube 5. A first end member 10 having a function such as a sealing carrier can also be provided on the upstream side of the wound body R of the membrane element, and a second end member 20 having a function such as an anti-telescoping material can also be provided on the downstream side.

[0092] When the membrane element is in use, it is housed in a pressure vessel (container), and a feed liquid 7 is supplied from one end face of the membrane element. The supplied feed liquid 7 flows along the feed-side flow path material 2 in a direction parallel to the axial direction A1 of the central tube 5, and is discharged from the other end face of the membrane element as a concentrated liquid 9. Furthermore, the permeate 8 that permeates the separation membrane 1 while the feed liquid 7 flows along the feed-side flow path material 2 flows along the permeate-side flow path material 3, flows through the openings 5a into the central tube 5, and is discharged from the end face of the central tube 5.

[0093] [Pre-concentration process]

[0094] The pre-concentration step involves feeding the treated liquid containing the water-soluble protein to at least a UF membrane to separate it into a permeate and a concentrate. The permeate is then fed as the feed liquid to the concentration step, and the separated concentrate is recovered. The recovered concentrate may be directly mixed with the concentrate from the concentration step, or the two may be recovered separately.

[0095] When performing a pre-concentration step, it is preferable to set the concentration ratio in the pre-concentration step so that the concentration of water-soluble protein in the feed liquid in the concentration step falls within the above-mentioned range. Such a concentration ratio can be adjusted according to the fractionation performance of the UF membrane and various conditions during filtration.

[0096] Alternatively, in the pre-concentration process, an MF membrane can be used as the front-end, with the permeate fed to a UF membrane for separation into the permeate and concentrate. Here, a UF membrane has an average pore size of approximately 0.001 to 0.01 μm. An MF membrane has an average pore size of approximately 0.01 to 10 μm.

[0097] The material of the UF membrane or MF membrane is not particularly limited. For example, cellulose ester polymers such as cellulose acetate, polyethylene, polypropylene, polysulfone, polyvinylidene fluoride, polyethersulfone, etc. can be used. From the perspective of durability and cleanability, polyvinylidene fluoride and polyethersulfone are preferred.

[0098] The shape of the UF membrane or MF membrane is not particularly limited, and it can be selected from flat membranes, hollow fiber membranes, pleated membranes, tubular membranes, and the like.

[0099] [Recovery and treatment method of water-soluble protein]

[0100] The soluble protein recovery method of the present invention comprises a desalting step of separating salts from the concentrated solution obtained by ion exchange resin and / or electrodialysis after carrying out the above-described method for concentrating the water-soluble protein.

[0101] In the desalination step, at least one of an ion exchange resin method and an electrodialysis method is performed. From the viewpoint of further reducing the salt concentration, at least the ion exchange resin method is preferably performed, and both the ion exchange resin method and the electrodialysis method are more preferably performed.

[0102] The salt concentration in the concentrate after desalting is preferably 3000 mg / L or less, and more preferably 1000 mg / L or less, from the viewpoint of using the water-soluble protein as a food raw material or the like.

[0103] (Ion exchange resin method)

[0104] In the ion exchange resin method, salts are separated from the concentrated solution using an ion exchange resin. While at least one of a cation exchange resin and an anion exchange resin can be used as the ion exchange resin, it is preferred to use both a cation exchange resin and an anion exchange resin to further reduce the salt concentration. The use of a cation exchange resin and a strongly basic anion exchange resin is particularly preferred.

[0105] When desalination is performed by attaching the concentrated solution to a cation exchange resin and a strong base anion exchange resin, the concentrated solution can be attached to an electrodialysis device in advance to remove some of the salts. That is, the desalination treatment can be performed as follows.

[0106] Method (1): A method in which the concentrate is passed through a cation exchange resin and then attached to a strongly basic anion exchange resin to obtain a desalted water-soluble protein concentrate. In this method, approximately 90% of the salts contained in the concentrate can be removed by the ion exchange resin.

[0107] Method (2): A method combining the pre-desalination means of an electrodialysis device with method (1). Specifically, the concentrate is first applied to the electrodialysis device to remove a portion of the salts, and then further desalts the concentrate by passing it through a cation exchange resin and a strongly basic anion exchange resin, thereby obtaining a desalted concentrate of water-soluble proteins. In this method, 20% to 70% of the salts contained are first removed in the electrodialysis device, and then 90% to 98% of the salts are removed by treatment with the ion exchange resin.

[0108] Of these methods, considering power consumption, ease of cleaning the membrane surface and resin of the electrodialysis device, and costs for resin regeneration, method (2) using an electrodialysis device and an ion exchange resin in combination is preferred.

[0109] The resin column filled with the ion exchange resin may be used in a multi-bed configuration in which the cation exchange resin and the anion exchange resin are separately filled, or in a mixed-bed configuration in which both are filled in one resin column.

[0110] Regarding the cation exchange resin among the ion exchange resins, both strongly acidic ion exchange resins and weakly acidic ion exchange resins can be used. Examples thereof include Amberlite IR-120B, Amberlite IRC-50, Duolite D20HC, Duolite C-464, Duolite C-225, Diaion SK1B, Diaion PK208, Dowex ECR-S, and Dowex CCR-2.

[0111] On the other hand, examples of the strongly basic anion exchange resin include Duolite A-116, Amberlite IRA-416, Amberlite IRA-410, Diaion PA418, and Dyex11.

[0112] When using an ion exchange resin, it is appropriate to conduct the concentration under the flow conditions of flow rate SV = 2 to 7, concentration (fixation rate) 5% to 40%, and temperature 5°C to 50°C. However, any flow rate conditions may be used as long as the target desalination rate (80% to 98%) is achieved. In addition, any concentration and temperature conditions may be used as long as the dissolved components are not precipitated.

[0113] (Electrodialysis)

[0114] Electrodialysis is preferably performed using an electrodialysis device utilizing a separation membrane such as an ion exchange membrane or a molecular sieve membrane. Examples of the electrodialysis device include a device in which a plurality of anion exchange membranes and cation exchange membranes are alternately arranged between an anode and a cathode, and the device comprises a desalting chamber and an ion recovery chamber, wherein, when viewed from the anode, in the desalting chamber, the treated liquid flows between the membranes arranged in the order of the anion exchange membrane and the cation exchange membrane, and in the ion recovery chamber, the cations and anions in the treated liquid accumulate between the membranes arranged in the order of the cation exchange membrane and the anion exchange membrane.

[0115] In the anode chamber and cathode chamber, for example, the electrode solution is circulated through the electrode solution flow path by a pump, and in the desalination chamber, the treated solution is circulated through the treated solution flow path by a pump. In addition, in the ion recovery chamber, the recovery solution is circulated through the recovery solution flow path by a pump.

[0116] When a voltage is applied between the anode and cathode, cations in the extract pass through the cation exchange membrane and accumulate in the recovery chamber, while anions in the extract pass through the anion exchange membrane and accumulate in the recovery chamber. This removes inorganic salts and other substances from the extract, resulting in a desalinated, concentrated solution from the desalination chamber.

[0117] As the ion exchange membrane, in order to prevent the permeation of water-soluble proteins themselves and selectively allow salts to permeate, an ion exchange membrane or molecular sieve membrane with a molecular weight cutoff of preferably 5000 or less, more preferably 300 to 1000, is used. It should be noted that various inorganic salt solutions can be used as the ion recovery liquid, with a salt solution being preferred, and its concentration preferably being approximately 0.1% to 1.0% by mass.

[0118] (Drying process)

[0119] The drying step is a step for removing water from the concentrated solution that has undergone the desalting step. This drying step can produce a water-soluble protein with a reduced moisture content. The moisture content after drying is preferably 15% by mass or less, and more preferably 3% to 7% by mass, from the perspectives of operability and production efficiency for commercialization.

[0120] As the drying method, various methods can be used, such as spray drying, drum drying, freeze drying, evaporation, etc. In the present invention, the concentration ratio of the water-soluble protein is high, so that energy saving can be achieved in the drying process in particular.

[0121] The dried water-soluble protein can be used in various products such as food raw materials such as nutritional supplements, food additives, and beverage additives, fertilizer raw materials, container raw materials, and film raw materials. Among them, from the perspective of effective utilization of protein, it is preferably used as a food raw material or a fertilizer raw material.

[0122] Example

[0123] The present invention is described below with reference to the following examples, but the present invention is not limited to these examples. It should be noted that in the examples, physical properties are measured or evaluated by the following methods. Specifically, the physical property values ​​in the present invention are values ​​measured by the following methods.

[0124] (1) Ionic strength

[0125] The feed liquid, permeate, or concentrate was sampled to obtain a sample for measurement. The conductivity of the feed liquid, permeate, or concentrate was measured using a conductivity measuring device. The molar concentration (mol / L) was calculated from the results and a calibration curve (concentration - conductivity). The ionic strength was calculated using the following formula (I) based on the ion type and molar concentration (mol / L). The molar concentration of the concentrate during the pressurized measurement was calculated using a mass balance (NaCl content in the feed liquid = NaCl content in the permeate + NaCl content in the concentrate) based on the molar concentrations of the permeate and feed liquids and the solution volumes.

[0126]

[0127] I: ionic strength

[0128] ci: molar concentration of ionic species i

[0129] Zi: valence of ionic species i

[0130] (2) Concentration ratio

[0131] When the molecular weight cutoff of the NF membrane and the molecular weight of the water-soluble protein are taken into consideration, the water-soluble protein does not permeate and is concentrated. Therefore, the apparent concentration ratio can be used to determine the concentration ratio of the water-soluble protein. The apparent concentration ratio is calculated using the feed liquid volume and the concentrate volume using the following formula (III).

[0132] Apparent concentration ratio (-) = supply volume (mL) ÷ concentrate volume (mL) (III)

[0133] (3) NaCl retention rate

[0134] The NaCl retention rate was determined using the following method in accordance with JIS K3805 (1990). A NaCl aqueous solution at 25°C, pH 6.5-7, and a concentration of 500 mg / L to 2000 mg / L was used. The NaCl aqueous solution was passed through a separation membrane of specified dimensions at an operating pressure of 0.34 MPa to 1.13 MPa. After a 30-minute preparatory phase, the conductivity of the permeate, concentrate, and feed solution was measured using a conductivity measuring device. The NaCl retention rate was calculated using the following formula based on the results and a calibration curve (concentration-conductivity).

[0135] NaCl retention rate (%) = (1-(NaCl concentration of permeate / (NaCl concentration of feed solution + NaCl concentration of concentrate) / 2)) × 100

[0136] (4) Molecular weight cut-off of NF membrane

[0137] First, a plurality of polyethylene glycols having different average molecular weights and monodisperse molecular weight distributions were prepared. An aqueous solution containing one of the plurality of polyethylene glycols at a concentration of 5000 ppm was stirred at a temperature of 25°C and a pressure of 4 kg / cm 2 The polyethylene glycol is supplied to the membrane surface under the following conditions. This allows the polyethylene glycol retention rate to be measured. The retention rates of other polyethylene glycols are measured using the same method. A classification curve is created to show the relationship between the retention rate obtained and the average molecular weight of the polyethylene glycol. Based on the classification curve, the average molecular weight of the polyethylene glycol that achieves a 90% retention rate is determined. The determined average molecular weight is considered the molecular weight cutoff of the NF membrane.

[0138] (Example 1)

[0139] To confirm the control state of the ionic strength of the NF membrane, an experiment was conducted using a model treatment liquid. As the model treatment liquid, an aqueous solution containing a water-soluble protein and an inorganic salt was used, having the following composition.

[0140] <Composition of the Model Processing Liquid>

[0141] An aqueous solution containing bovine serum-derived albumin (BSA) at a concentration of 0.5% by mass as a water-soluble protein and sodium chloride at a concentration of 0.47% by mass as an inorganic salt.

[0142] As the NF membrane, a nanofiltration membrane (manufactured by Nitto Denko Corporation, HYDRACoRe10, NaCl rejection 10%, molecular weight cut-off 3000 Daltons) was used, in which a separation functional layer comprising a polysulfone resin having sulfonic acid groups was formed on the surface of a porous polysulfone membrane. The NF membrane was cut into a predetermined shape and size and installed in a dead-end filtration system unit (effective membrane surface area: 32 cm) for flat membrane evaluation. 2 Then, the water-soluble protein was further concentrated in the model treatment liquid, which was the feed liquid of the NF membrane, at a pressure of 2.0 bar to 4.0 bar, a temperature of 25° C., and a pH of 8.

[0143] At this time, the ionic strength of the supply liquid was 0.080 mol / L, and the ionic strength of the concentrated liquid after 54 minutes was 0.080 mol / L (1.0 times). In addition, the ionic strength of the concentrated liquid after 92 minutes was 0.080 mol / L (1.0 times). Thereafter, until 128 minutes, the ionic strength ratio remained at 1.0 times.

[0144] The concentration ratio reached 2.0 times after 92 minutes, and 3.0 times after 128 minutes. Specifically, by using the aforementioned NF membrane and adjusting the ionic strength of the concentrate to 1.0 to 2.0 times that of the feed solution, a high concentration ratio can be achieved. This is presumably because the concentration of salt on the NF membrane surface, which would increase osmotic pressure, can be suppressed. This improves the concentration ratio of water-soluble proteins, not only in dead-end filtration but also in cross-flow filtration.

[0145] (Example 2)

[0146] In Example 1, a NF membrane having a separation functional layer comprising a polysulfone resin having sulfonic acid groups formed on the surface of a porous membrane made of polysulfone (manufactured by Nitto Denko Corporation, HYDRACoRe50, NaCl rejection rate 50%, molecular weight cutoff 1000 Daltons) was used as the NF membrane, and the concentration conditions were set to a pressure of 3.0 bar to 6.0 bar. Otherwise, the concentration of water-soluble proteins was continued under the same conditions as in Example 1.

[0147] As a result, the ionic strength of the concentrated solution reached 0.085 mol / L (1.1 times) after 86 minutes, and 0.087 mol / L (1.1 times) after 136 minutes. The ionic strength ratio remained at 1.2 times until 183 minutes. Furthermore, the concentration ratio reached 2.0 times after 136 minutes, and 3.0 times after 183 minutes. Thus, by using the above-mentioned NF membrane and adjusting the ionic strength of the concentrated solution to a range of 1.0 to 2.0 times that of the feed solution, a high concentration ratio can be achieved.

[0148] (Example 3)

[0149] In Example 1, a NF membrane having a separation functional layer comprising a polysulfone resin having sulfonic acid groups formed on the surface of a porous membrane made of polysulfone (manufactured by Nitto Denko Corporation, HYDRACoRe70pHT, NaCl rejection rate 70%, molecular weight cutoff 700 Daltons) was used as the NF membrane, and the concentration conditions were set to a pressure of 5.0 bar to 9.0 bar. Otherwise, the concentration of water-soluble proteins was continued under the same conditions as in Example 1.

[0150] As a result, the ionic strength of the concentrate reached 0.096 mol / L (1.2 times) after 294 minutes, and 0.11 mol / L (1.4 times) after 421 minutes. The ionic strength ratio remained at 1.9 times until 540 minutes. Furthermore, the concentration ratio reached 2.0 times after 421 minutes, and 3.0 times after 540 minutes. Thus, by using the nanofiltration membrane and adjusting the ionic strength of the concentrate to a range of 1.0 to 2.0 times that of the feed solution, a high concentration ratio can be achieved.

[0151] (Comparative Example 1)

[0152] In Example 1, the concentration of water-soluble protein was continued under the same conditions as in Example 1 except that an RO membrane (manufactured by Nitto Denko Corporation, ESPA2-LD, NaCl rejection rate 99.6%) was used instead of the NF membrane and the concentration conditions were set to a pressure of 6.0 bar to 13 bar.

[0153] The results showed that after 221 minutes, the ionic strength of the concentrated solution exceeded 0.16 mol / L (twice that of the supply solution), and it was difficult to increase the concentration ratio to more than 2 times.

[0154] Industrial Applicability

[0155] According to the present invention, there can be provided a method for concentrating water-soluble proteins capable of increasing the concentration ratio of water-soluble proteins while maintaining the recovery rate of water-soluble proteins, and a method for recovering water-soluble proteins using the method.

[0156] In recent years, from the perspective of effective utilization of natural resources and efficiency of waste liquid treatment, methods for recovering water-soluble proteins contained in waste liquids have been studied. The present invention is particularly effective as a method for concentrating such water-soluble proteins and a method for recovering and treating water-soluble proteins using this method.

[0157] Description of labels

[0158] 1Separation membrane (NF membrane)

[0159] 7 Supply liquid

[0160] 8 permeate

[0161] 9 concentrates

[0162] M1 membrane module (for concentration process)

[0163] M2 membrane module (for pre-concentration process)

Claims

1. A method for concentrating water-soluble proteins, the method comprising separating and concentrating water-soluble proteins soluble in a salt solution having an ionic strength of 0.1 mol / L or less, wherein: The method for concentrating the water-soluble protein comprises the following concentration steps: The concentration step comprises supplying the feed liquid containing the water-soluble protein to a NF membrane and separating the feed liquid into a permeate and a concentrate so that the ionic strength (mol / L) of the concentrate becomes 1.0 to 2.0 times that of the feed liquid.

2. The method for concentrating water-soluble protein according to claim 1, wherein In the concentration step, the concentration ratio of the concentrated liquid relative to the feed liquid is 3 times or more, or the concentration ratio of the final concentrated liquid relative to the feed liquid initially supplied to the NF membrane is 3 times or more.

3. The method for concentrating water-soluble protein according to claim 1, wherein: In the concentration step, the concentration ratio of the concentrated liquid relative to the supply liquid is 6 times or more.

4. The method for concentrating water-soluble protein according to claim 1, wherein The NF membrane includes a separation functional layer having anionic groups.

5. The method for concentrating water-soluble protein according to claim 4, wherein: The separation functional layer includes a polysulfone-based resin having a sulfonic acid group.

6. The method for concentrating water-soluble protein according to claim 1, wherein: The method for concentrating the water-soluble protein comprises the following pre-concentration steps: The pre-concentration step comprises supplying the treated liquid containing the water-soluble protein to at least a UF membrane to separate the treated liquid into a permeate and a concentrate, and supplying the permeate as a feed liquid to the concentration step while recovering the separated concentrate.

7. A method for recovering and treating water-soluble proteins, wherein: The water-soluble protein recovery method comprises the following desalting process: A desalting step comprising separating salts from the concentrated solution obtained by an ion exchange resin method and / or an electrodialysis method after performing the method for concentrating a water-soluble protein according to any one of claims 1 to 6.

8. The method for recovering water-soluble protein according to claim 7, wherein: The method for recovering water-soluble protein includes a drying step of removing water from the concentrated liquid that has undergone the desalting step.

9. The method for recovering water-soluble protein according to claim 8, wherein: Through the drying step, a food material or a fertilizer material is obtained.

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