Method for preparing high-protein solution by using hydrophobin

Abstract

The invention discloses a method for preparing a high-protein solution from hydrophobin through membrane treatment and ultrasonic assistance, and belongs to the technical field of food protein modification and membrane separation. The preparation method comprises the following steps: dispersing hydrophobic protein in an alkaline solution, adding maltodextrin into the alkaline solution, carrying out multiple times of concentration and dilution operation through membrane treatment to remove salt ions and macromolecular aggregates, and then adjusting the pH value of a solution system to be neutral by adopting an acidic solution; the preparation method comprises the following steps: firstly, preparing a solution, then treating the solution under the ultrasonic action to form a micro-nano particle structure with good colloidal stability, and finally, concentrating and drying to obtain powdery protein with high solubility. The soluble protein powder obtained by the invention can be widely applied to vegetable protein drinks, nutritional formula foods and functional foods.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of food processing and functional protein development, in particular to a method for preparing a high-protein solution using hydrophobic proteins. BACKGROUND

[0002] Under the background of the full name weight loss plan, people's demand for high-nutrition protein is growing rapidly, and the current available protein raw materials are mostly milk and soy milk. Milk is an animal-derived protein, which has serious carbon emissions and is not suitable for vegetarians; soy milk has serious genetic modification problems. At the same time, both proteins have hidden dangers of allergies. "Based on food security, expand food sources to farmland, forest, grassland, ocean, etc., and build a three-dimensional supply system for the coordinated development of plants, animals and microorganisms", microorganism protein represented by yeast protein and cereal protein represented by rice protein are an important part of the future protein source in food.

[0003] However, whether it is yeast protein or rice protein, it contains a large amount of hydrophobic amino acids, which leads to low solubility and is difficult to realize productization. Enzymatic technology can greatly improve the solubility of proteins by cutting off specific protein chains and reducing molecular weight, but it will cause nutrient loss, taste decline, and also greatly affect the functionality of proteins. Therefore, developing advanced protein modification technology to overcome the problem of protein hydrophobic aggregation is the top priority to build a new protein raw material system and solve the shortage of future protein resources.

[0004] At present, membrane separation technology as a high-efficiency protein grading and purification means has been widely used in protein preparation process. Membrane treatment can remove small molecular impurities and salt ions to some extent, and improve the purification degree of protein system. However, there are two problems in existing membrane treatment technology: first, during the membrane filtration process, proteins are prone to partial conformation unfolding and aggregation under high pH conditions, and if not regulated subsequently, turbidity or precipitation often occurs after resolubilization, indicating that the solubility and dispersion stability are poor; second, simply relying on membrane separation cannot effectively improve the interaction state between protein molecules, resulting in low structural compatibility between protein molecules in the system, which affects the functional properties and uniformity of the final product. SUMMARY

[0005] [TECHNICAL PROBLEM] The technical problem to be solved by the present application is how to effectively improve the water solubility of hydrophobic plant / microorganism proteins represented by yeast protein and rice protein without damaging the nutritional value and functional properties of proteins, so as to realize their wide application in high-nutrition food.

[0006] To solve the above problems, the present application realizes the local recombination of protein hydrophobic structure through the synergistic modification of membrane treatment, malt dextrin mediation and ultrasonic effect, so as to obtain a nano protein particle with good colloidal stability. The obtained product maintains the natural nutrition and functional characteristics, and has good solubility and emulsion stability, thereby overcoming the solubility bottleneck of hydrophobic proteins in application, and expanding the application prospect of new protein raw materials such as yeast protein in functional food and high-protein nutritional products.

[0007] [Technical scheme] The first object of the present application is to provide a method for preparing a high-protein solution using hydrophobic proteins, comprising the following steps: S1, dispersing the hydrophobic proteins in an alkaline solution to make the concentration 1-4%, then adding 0.02-0.1% malt dextrin thereto, and stirring uniformly to obtain a mixed solution; S2, concentrating the mixed solution obtained in step S1 by using an ultrafiltration membrane for 2-4 times, and adjusting the pH to 6.5-7.5 after the treatment; S3, treating the solution after the treatment in step S2 by using an ultrasonic power of 150-250W for 5-15min; S4, concentrating the protein solution after the ultrasonic treatment in step S3 to obtain a high-protein solution.

[0008] In an embodiment of the present application, the high-protein solution is further dried to obtain a protein powder. In the present application, the protein powder can be subsequently re-dissolved in water to obtain a high-protein solution.

[0009] In the present application, the protein solution is prepared by unfolding the protein chains, concentrating by membrane treatment, and finally locally recombining under the mediation of malt dextrin after ultrasonic treatment.

[0010] In an embodiment of the present application, the hydrophobic proteins are one or more of yeast proteins and rice proteins.

[0011] In an embodiment of the present application, in step S1, the alkaline solution is a sodium hydroxide solution with a concentration of 1-4mol / L.

[0012] In an embodiment of the present application, in step S2, the pH adjustment is performed by using one of a hydrochloric acid solution or a citric acid solution.

[0013] In an embodiment of the present application, the concentration is evaporation concentration of the protein solution.

[0014] In an embodiment of the present application, the drying is spray drying of the protein solution after evaporation concentration.

[0015] In one embodiment of the present application, the mass fraction of the protein in the high-protein solution is 5% to 15%.

[0016] A second object of the present application is to provide a high-protein solution prepared by the method.

[0017] A third object of the present application is to provide an application of the high-protein solution in a functional food or a high-protein nutritional health product.

[0018] In one embodiment of the present application, the functional food or the high-protein nutritional health product is a beverage, a dairy product or a nutritional supplement.

[0019] [Advantages] (1) The method of the present application is simple and efficient, but can significantly improve the solubility of hydrophobic proteins. By membrane treatment combined with ultrasonic treatment, the aggregation caused by hydrophobic amino acids in yeast proteins and rice proteins is effectively eliminated, so that the obtained powdered proteins can be completely dissolved in water at a concentration of 5% to 10%, overcoming the technical bottleneck that traditional hydrophobic proteins are difficult to apply.

[0020] (2) The present application does not use enzymatic method, which will not cause the breakage of amino acids and the loss of small molecule nutrients, and can improve the physicochemical properties of proteins while maintaining their natural nutritional ingredients.

[0021] (3) The micro / nanoparticles formed under the mediation of maltodextrin have good colloidal stability, can impart good emulsifying and dispersing properties to the protein solution, and at the same time avoid the bitter polypeptides produced by enzymatic hydrolysis, thereby maintaining the flavor quality of the product.

[0022] (4) The present application introduces ultrasonic treatment after membrane treatment, which helps to modify the hydrophobic proteins. The sample treated by ultrasonic treatment can break the protein aggregates, expose the hydrophobic regions, improve the solubility of the proteins in water, make the protein particles more uniform, form a micro / nano stable dispersion system, and improve the storage stability. Compared with other methods, ultrasonic treatment does not damage the protein backbone structure, avoids the loss of nutrients and the decrease of flavor, and can better maintain the functional properties of the protein.

[0023] (5) The yeast proteins and rice proteins used in the present application belong to microbial proteins and cereal proteins respectively, and have the advantages of being green, low-carbon and low allergic risk, which conforms to the development direction of "diversified protein sources" and has important application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 AFM image of the high-protein solution in Example 1 of the present application; Figure 2 C-SEM image of the high-protein solution in Example 1 of the present application; Figure 3Photo of protein powder reconstitution in Example 1 of the present application; Figure 4 Photo of protein solution after storage at 4℃ for 24h in Example 1 of the present application; Figure 5 PDI change graph of high protein solution at different stages in Example 2 of the present application; Figure 6 ZETA potential graph of high protein solution at different stages in Example 2 of the present application; Figure 7 AFM graph of protein solution without ultrasonic treatment in Comparative Example 1 of the present application; Figure 8 30s flux broken line graph of protein solution using membrane with pore size of 5nm and 15nm in Comparative Example 2 of the present application; Figure 9 AFM graph of protein solution without membrane treatment in Comparative Example 3 of the present application; Figure 10 Photo of solution after sample spray drying reconstitution and storage at 4℃ for 24h in Comparative Example 4 of the present application; Figure 11 Photo of sample after concentration and storage at 4℃ for 24h in Comparative Example 5 of the present application; Figure 12 C-SEM graph of sample after different times of membrane treatment in Example 5 of the present application. DETAILED DESCRIPTION

[0025] The present application will be further described below in conjunction with specific examples. These examples are only used to illustrate the present application and not intended to limit the scope of the present application. Furthermore, after reading the content taught in the present application, those skilled in the art can make various modifications or changes to the present application, and these equivalent forms also fall within the scope of the appended claims of the present application.

[0026] Raw material source Yeast protein powder: purchased from Angel Yeast Co., Ltd. Yeast protein F80.

[0027] Rice protein powder: extracted by alkali dissolution and acid precipitation method: after grinding and crushing the rice, pass through 80 mesh sieve, with 1:15 solid-liquid ratio, stir in water with pH 12.0 at room temperature for 4h. After completion, centrifuge at 12,000xg, 4℃ for 20min, collect supernatant and adjust pH to 4.5 with 1mol / L HCl, stand for precipitation for 1h, then centrifuge at 4,000xg, 4℃ for 20min, wash the precipitate with 20 times volume of deionized water for 3 times, then collect the precipitate as rice protein.

[0028] Maltodextrin: purchased from Sigma Co.

[0029] Detection method The technical solutions of the present application are described in detail below in combination with specific examples. In the following examples, the reagents, materials and equipment used, unless otherwise specified, can be purchased commercially, or prepared by conventional methods, or commonly used in the industry.

[0030] Example 1: Preparation of a hydrophobic protein solution with high concentration Specifically comprising the following steps: (1) Preparation of a protein solution: Take 0.5 g of yeast protein powder and disperse it in ultrapure water at a solid-liquid ratio of 1:50 (g / mL). Adjust the pH to 12.0 with a 2 mol / L sodium hydroxide solution, and fully stir (speed: 200 rpm, stirring time: 30 min) to expand the protein chains. Then add 1:2000 (g / mL) of maltodextrin to the solution, and continue to fully stir (speed: 200 rpm, stirring time: 30 min).

[0031] Concentrate the obtained solution by ultrafiltration membrane with a pore size of 5 nm, and add the same volume of water to the filtrate. Repeat this process three times. Adjust the pH to 7.0 with a 2 mol / L HCl solution to obtain a yeast protein solution.

[0032] (2) Ultrasonic treatment: Put the solution obtained in step (1) into an ultrasonic device and ultrasonic at 200 W for 10 min to make the protein hydrophobic region locally recombine under the mediation of maltodextrin, forming micro-nano particles with colloidal stability.

[0033] (3) Concentration and drying: Evaporative concentration is used to obtain a final protein concentration of 8%, and spray drying is used to obtain a powdery protein. The obtained powdery protein is dissolved in water at a mass fraction of 10% to form a uniform and stable high-protein solution.

[0034] The high-protein solution is detected by C-SEM as shown in Figure 1 The image shows that the particles on the surface of the sample are uniformly distributed, and the overall structure is small and independent, with almost no obvious sheet aggregation or large agglomeration. This indicates that the internal network of the treated hydrophobic protein system is relatively stable, forming a uniform spherical protein structure.

[0035] The high-protein solution is detected by AFM as shown in Figure 2As shown, the AFM image shows that the sample surface topography is flat, the bright spot distribution is relatively uniform, the particle size is consistent, and there is no obvious agglomeration or striped uneven area. This shows that the protein system has good dispersion and stability at the nanoscale, and the protein forms a fine and uniform structure under the action of ultrasonic waves.

[0036] The high-protein solution was stored at 4°C for 24 h. Before storage, as shown in Figure 3 After storage, as shown in Figure 4 The results show that the high-protein solution prepared in Example 1 has good reconstitution after spray drying, and the properties remain stable after storage at 4°C for 24 h, maintaining high dispersion.

[0037] Example 2: Preparation of a high-concentration hydrophobic protein solution Specifically, the following steps are included: (1) Preparation of a protein solution: Take 0.5 g of rice protein powder and disperse it in ultrapure water at a solid-liquid ratio of 1:50 (g / mL). Adjust the pH to 12.0 with a 2 mol / L sodium hydroxide solution, and fully stir (speed: 200 rpm, stirring time: 30 min) to expand the protein chains. Then, add maltodextrin to the solution at a solid-liquid ratio of 1:2000 (g / mL), and continue to fully stir (speed: 200 rpm, stirring time: 30 min).

[0038] Concentrate the obtained solution one-fold using an ultrafiltration membrane with a pore size of 5 nm, and add an equal volume of water to the filtrate. Repeat this process 8 times until the pH is reduced to 7.0, obtaining a rice protein solution.

[0039] (2) Ultrasonic treatment: Put the solution obtained in step (1) into an ultrasonic device and ultrasonic at 200 W for 10 min, so that the hydrophobic regions of the protein locally recombine under the mediation of maltodextrin, forming micro-nano particles with colloidal stability.

[0040] (3) Concentration and drying: Evaporative concentration is used to obtain a final protein concentration of 8%, and spray drying is used to obtain a powdery protein. The obtained powdery protein is dissolved in water at a mass fraction of 10%, and a uniform and stable high-protein solution can be formed.

[0041] Sample the protein solution after each filtration (A1-A8), and then detect the PDI value and Zeta potential of the solution at each stage as shown in Figure 5 , Figure 6The results show that the PDI of the protein system gradually decreases with the increase of the number of membrane filtration, indicating that the particle distribution develops from uneven to uniform, the electrostatic shielding effect between protein molecules gradually weakens, which promotes the rearrangement and stable complexation between protein molecules, so that the particles tend to be uniform, and the PDI decreases. At the same time, the absolute value of the Zeta potential of the protein system also shows a downward trend, the surface system structure is stable, the distribution is uniform, and the whole still maintains good colloidal stability.

[0042] Example 3: Preparation of a high-concentration hydrophobic protein solution (1) Preparation of a protein solution: Take 0.5 g of yeast protein powder and disperse it in ultrapure water at a solid-liquid ratio of 1:25 (g / mL). Adjust the pH to 12.0 with a 2 mol / L sodium hydroxide solution, and fully stir (speed: 200 rpm, stirring time: 30 min) to expand the protein chains. Then add maltodextrin to the solution at a solid-liquid ratio of 1:2000 (g / mL), and continue to fully stir (speed: 200 rpm, stirring time: 30 min).

[0043] Concentrate the obtained solution by 1-fold using an ultrafiltration membrane with a pore size of 5 nm, add an equal volume of water to the filtrate, and concentrate it by 1-fold again using an ultrafiltration membrane. Repeat this process 3 times. Adjust the pH of the treated solution to 7.0 using a 2 mol / L HCl solution to obtain a yeast protein solution.

[0044] (2) Ultrasonic treatment: Put the solution obtained in step (1) into an ultrasonic device and ultrasonicate it at a power of 200 W for 10 min to make the protein hydrophobic regions locally recombine under the mediation of maltodextrin, forming micro-nano particles with colloidal stability.

[0045] (3) Concentration and drying: Evaporative concentration is used to make the final protein concentration reach 8%, and spray drying is used to obtain a powdery protein. Dissolving the obtained powdery protein in water at a mass fraction of 10% can form a uniform and stable high-protein solution.

[0046] Example 4: Preparation of a high-concentration hydrophobic protein solution (1) Preparation of a protein solution: Take 0.5 g of yeast protein powder and disperse it in ultrapure water at a solid-liquid ratio of 1:50 (g / mL). Adjust the pH to 12.0 with a 2 mol / L sodium hydroxide solution, and fully stir (speed: 200 rpm, stirring time: 30 min) to expand the protein chains. Then add maltodextrin to the solution at a solid-liquid ratio of 1:2000 (g / mL), and continue to fully stir (speed: 200 rpm, stirring time: 30 min).

[0047] The obtained solution was concentrated once by using an ultrafiltration membrane with a pore size of 10 nm, an equal volume of water was added to the filtrate, and the solution was concentrated again by using an ultrafiltration membrane. This process was repeated three times. The treated solution was adjusted to pH 7.0 using a 2 mol / L citric acid solution to obtain a yeast protein solution.

[0048] (2) Ultrasonic treatment: The solution obtained in step (1) was placed in an ultrasonic device and ultrasonically treated at a power of 200 W for 10 min, so that the hydrophobic regions of the protein were locally reorganized under the mediation of the maltodextrin to form micro-nano particles with colloidal stability.

[0049] (3) Concentration and drying: Evaporative concentration was used to obtain a final protein concentration of 8%, and spray drying was used to obtain a powdery protein. The powdery protein obtained was dissolved in water at a mass fraction of 10% to form a uniform and stable high-protein solution.

[0050] Comparative Example 1 The steps were basically the same as in Example 1, but no ultrasonic treatment was performed. The specific steps are as follows: (1) Preparation of a protein solution: 0.5 g of yeast protein powder was dispersed in ultrapure water at a solid-liquid ratio of 1:50 (g / mL), and the pH value was adjusted to 12.0 using a 2 mol / L sodium hydroxide solution. The solution was thoroughly stirred (speed: 200 rpm, stirring time: 30 min) to expand the protein chains, and then 1:2000 (g / mL) maltodextrin was added to the solution. The solution was further stirred thoroughly (speed: 200 rpm, stirring time: 30 min).

[0051] The obtained solution was concentrated once by using an ultrafiltration membrane with a pore size of 5 nm, an equal volume of water was added to the filtrate, and the solution was concentrated again by using an ultrafiltration membrane. This process was repeated three times. The treated solution was adjusted to pH 7.0 using a 2 mol / L HCl solution to obtain a yeast protein solution.

[0052] (2) Concentration and drying: Evaporative concentration was used to obtain a final protein concentration of 8%, and spray drying was used to obtain a powdery protein. The powdery protein obtained was dissolved in water at a mass fraction of 10%. It was found that the protein solubility was poor and the protein solution had a high turbidity, which was not conducive to the formation of a high-stability structure. As shown in FIG. 1, the surface of the sample without ultrasonic treatment showed obvious irregular aggregate structures, and the particle size distribution was uneven, indicating that there was still strong hydrophobic aggregation structure between the protein molecules, resulting in poor dispersion of the sample system and easy precipitation. Figure 7

[0053] Comparative Example 2​ The procedure is basically the same as that of Example 1, except that the filter membrane used is an ultrafiltration membrane with a pore size of 15 nm, and the specific steps are as follows: (1) Preparation of protein solution: Take 0.5 g of yeast protein powder and disperse it in ultrapure water at a solid-liquid ratio of 1:50 (g / mL). Adjust the pH to 12.0 with a 2 mol / L sodium hydroxide solution, and thoroughly stir (speed: 200 rpm, stirring time: 30 min) to expand the protein chains. Then, add 1:2000 (g / mL) of maltodextrin to the solution, and continue to thoroughly stir (speed: 200 rpm, stirring time: 30 min).

[0054] Concentrate the obtained solution by 1-fold using an ultrafiltration membrane with a pore size of 15 nm, and add an equal volume of water to the filtrate. Repeat this process 3 times. Adjust the pH to 7.0 using a 2 mol / L HC1 solution to obtain a yeast protein solution.

[0055] (2) Ultrasonic treatment: Put the solution obtained in step (1) into an ultrasonic device and ultrasonicate for 10 min at a power of 200 W to cause local reorganization of the protein hydrophobic region mediated by maltodextrin, forming micro-nanoparticles with colloidal stability.

[0056] (3) Concentration and drying: Concentrate by evaporation to obtain a final protein concentration of 8%, and then spray dry to obtain a powdery protein. Dissolve the obtained powdery protein in water at a mass fraction of 10%. The protein can form a stable and uniform high-protein solution, and remains relatively stable after 24 h of storage. However, as shown in the figure, when a membrane with a pore size of 15 nm is used, the filtrate flux is low and gradually tends to 0, indicating that when the pore size is too large, the protein aggregates cannot be effectively removed, but instead deposit on the membrane surface during the filtration process, causing serious membrane clogging. Figure 8

[0057] The inventors also tried using an ultrafiltration membrane with a pore size of 100 nm for treatment, but the membrane was clogged within 30 min, with no filtrate flowing out.

[0058] Comparative Example 3 The procedure is basically the same as that of Example 1, except that no membrane treatment is performed, and the specific steps are as follows: (1) Preparation of protein solution: ​Take yeast protein powder 0.5 g, with solid-liquid ratio 1:50 (g / mL) dispersed in ultrapure water, with 2 mol / L sodium hydroxide solution to pH value of 12.0, fully stirred (speed: 200 rpm, stirring time: 30 min), the protein chain is unfolded, then to the solution with solid-liquid ratio 1:2000 (g / mL) maltodextrin is weighed and added to the solution, continue to fully stir (speed: 200 rpm, stirring time: 30 min). The treated solution is adjusted to pH 7.0 using 2 mol / L HCl solution, and a yeast protein solution is obtained.

[0059] (2) ultrasonic treatment: The solution obtained in step (1) is placed in an ultrasonic device and ultrasonically treated at 200 W power for 10 min, so that the protein hydrophobic region is locally reorganized under the mediation of maltodextrin to form micro-nano particles with colloidal stability.

[0060] (3) concentration and drying: Evaporative concentration is used to obtain a final protein concentration of 8%, and spray drying is used to obtain a powdery protein. The powdery protein obtained is dissolved in water at a mass fraction of 10%. The results also show that the protein solubility is poor and the protein solution has high turbidity, which is not conducive to the formation of a high-stability structure. The AFM image of the protein solution is shown in Figure 9 The overall structure of the sample without membrane treatment is loose and the large particles are obvious, which further illustrates that membrane filtration has a significant improvement effect on particle dispersion and structural stability.

[0061] Comparative Example 4 It is basically the same as Example 1, except that the pH is not adjusted to 7.0 after membrane treatment. The specific steps are as follows: (1) Preparation of protein solution: Take yeast protein powder 0.5 g, with solid-liquid ratio 1:50 (g / mL) dispersed in ultrapure water, with 2 mol / L sodium hydroxide solution to pH value of 12.0, fully stirred (speed: 200 rpm, stirring time: 30 min), the protein chain is unfolded, then to the solution with solid-liquid ratio 1:2000 (g / mL) maltodextrin is weighed and added to the solution, continue to fully stir (speed: 200 rpm, stirring time: 30 min).

[0062] The obtained solution is concentrated one time using an ultrafiltration membrane with a pore size of 5 nm, and the same volume of water as the filtrate is added. The solution is concentrated one time again through the ultrafiltration membrane, and this process is repeated 3 times to obtain a yeast protein solution.

[0063] (2) ultrasonic treatment: The solution obtained in step (1) was placed in an ultrasonic device and sonicated at 200W power for 10 min, so that the hydrophobic region of the protein under the mediation of maltodextrin undergoes local reorganization to form micro-nano particles with colloidal stability.

[0064] (3) Concentration and drying: The final protein concentration reached 8% by evaporation and concentration, and powdered protein was obtained by spray drying.

[0065] The obtained powdered protein was dissolved in water at a concentration of 10%. The results showed that the protein exhibited poor solubility and increased turbidity. After storage at 4℃ for 24 hours, the following results were observed: Figure 10 Show.

[0066] Comparative Example 5 The procedure is basically the same as in Example 1, except that the ultrasonic treatment time is 5 minutes. The specific steps are as follows: (1) Preparation of protein solution: Take 0.5g of yeast protein powder and disperse it in ultrapure water at a material-to-liquid ratio of 1:50 (g / mL). Adjust the pH to 12.0 with 2mol / L sodium hydroxide solution and stir thoroughly (200rpm, 30min) to allow the protein chains to expand. Then, weigh maltodextrin into the solution at a material-to-liquid ratio of 1:2000 (g / mL) and continue stirring thoroughly (200rpm, 30min).

[0067] The obtained solution was concentrated by one-fold using an ultrafiltration membrane with a pore size of 5 nm. The same volume of water as the filtrate was added to it, and the solution was concentrated by one-fold again using an ultrafiltration membrane. This process was repeated 3 times to obtain a yeast protein solution.

[0068] (2) Ultrasonic treatment: The solution obtained in step (1) was placed in an ultrasonic device and sonicated for 5 minutes at a power of 200W, so that the hydrophobic region of the protein under the mediation of maltodextrin would undergo local reorganization to form micro-nano particles with colloidal stability.

[0069] (3) Concentration and drying: Evaporation concentration was used to achieve a final protein concentration of 8%. The concentrated sample was then stored at 4°C for 24 hours. The results are as follows: Figure 11 As shown, the sample exhibited stratification after being concentrated and stored at 4°C for 24 hours, indicating that the colloidal system was unstable and that flocculation or precipitation occurred between particles, resulting in poor stability.

[0070] Further spray drying was used to obtain powdered protein, which was then dispersed in water at a concentration of 10% for resolution, but the dissolution effect was poor.

[0071] Example 5 The preparation method and embodiment 1 are consistent, the only difference is that the number of membrane filtration is changed, specifically comprising the following steps: (1) Preparation of protein solution: Take 0.5 g of yeast protein powder, disperse it in ultrapure water at a solid-liquid ratio of 1:50 (g / mL), adjust the pH value to 12.0 with 2 mol / L sodium hydroxide solution, and stir thoroughly (speed: 200 rpm, stirring time: 30 min) to expand the protein chain. Then add 1:2000 (g / mL) of malt dextrin to the solution, and continue to stir thoroughly (speed: 200 rpm, stirring time: 30 min).

[0072] Concentrate the obtained solution by ultrafiltration membrane with a pore size of 5 nm, add the same volume of water as the filtrate, and concentrate it again by ultrafiltration membrane. Repeat this process 1 and 2 times respectively. Adjust the pH value of the treated solution to 7.0 with 2 mol / L HCl solution to obtain yeast protein solutions with 1 and 2 times of membrane filtration.

[0073] (2) Ultrasonic treatment: Put the solution obtained in step (1) into an ultrasonic device and ultrasonic for 10 min at a power of 200 W, so that the hydrophobic region of the protein is partially reorganized under the mediation of malt dextrin, forming micro-nanoparticles with colloidal stability.

[0074] (3) Concentration and drying: Evaporative concentration is used to obtain a final protein concentration of 8%, and spray drying is used to obtain a powdery protein. The obtained powdery protein is dissolved in water at a mass fraction of 10%.

[0075] The results show that with the increase of the number of membrane filtration, the large aggregates in the protein system are significantly reduced, and the system tends to be uniform and continuous, indicating that membrane treatment can effectively remove part of the macromolecular aggregates and improve the stability of the protein solution.

[0076] The zeta potential, PDI, average particle size and 600 nm transmittance of the solutions obtained in Example 1, Comparative Example 3 and Example 5 were detected respectively, and the results are shown in Table 1: Table 1 Colloidal stability characterization of mixed solutions with different numbers of membrane filtration

[0077] The results show that: (1) When the mixed solution is not treated by membrane, there are more salt ions, the zeta potential reaches -32.63 mV, the solution system is not uniform, the PDI value is 0.94, the average particle size is 1318.7 nm, and the transmittance is low.

[0078] (2) When the mixed solution is treated by the membrane once, the salt ions are more, the zeta potential reaches -27.78 mV, the solution system is not uniform, the PDI value is 0.859, the average particle size is 630.6 nm, and the light transmittance is improved.

[0079] (3) When the mixed solution is treated by the membrane twice, the salt ions are reduced, the zeta potential is -26.57 mV, the solution system is uniform, the PDI value is 0.692, the average particle size is 591.5 nm, and the light transmittance is improved.

[0080] (4) When the mixed solution is treated by the membrane three times, the salt ions are less, the zeta potential is -20.17 mV, the solution system is more uniform, the PDI value is 0.48, the average particle size is 499.9 nm, and the light transmittance is improved.

[0081] (5) As can be seen from Table 1, when the membrane filtration times of the mixed solution are 1, 2 and 3 respectively, the PDI values of the particles in the mixed system are 0.859, 0.692 and 0.48 respectively, the particle distribution is gradually uniformized, and the polydispersity of the system is effectively improved; the light transmittance also increases with the increase of the filtration times, and the turbidity of the system is reduced. The zeta potential of the overall solution system remains in the negative potential interval, and has a certain electrostatic stability.

[0082] Therefore, by multiple membrane filtration, not only the salt ions can be effectively removed, but also the distribution uniformity and optical performance of the colloidal system can be improved, so as to improve the physical stability of the solution. The results have application value for food protein beverages, functional protein formula solutions and protein solutions that need to be stored for a long time.

[0083] Figure 12 The freeze scanning electron microscope images of the mixed solutions in Example 1 and Example 5 with the change of the membrane filtration times are shown in the following figure. Figure 12 As shown in the figure, from left to right, the mixed solution systems are filtered 1-3 times. It can be seen that with the increase of the filtration times, the large particles in the mixed protein system are gradually removed, the particles tend to be uniformized and refined, which is beneficial to the improvement of the light transmittance of the system and the stability in subsequent application in food.

[0084] The examples provided above are not intended to limit the scope covered by the present application, and the described steps are not intended to limit the execution order. Those skilled in the art can make obvious improvements to the present application in combination with the existing common knowledge, which also falls within the protection scope defined by the claims of the present application.

Claims

1. A method for preparing a high protein solution using hydrophobin, characterized by, The method comprises the following steps: S1, dispersing hydrophobic protein in an alkali solution to make the concentration of the hydrophobic protein 1-4%, and then adding 0.02-0.1% malt dextrin to the alkali solution and stirring to obtain a mixed solution; S2, concentrating the mixed solution obtained in the step S1 by using an ultrafiltration membrane for 2-4 times, and adjusting the pH of the solution to 6.5-7.5 after the treatment; S3, treating the solution obtained in the step S2 by using an ultrasonic power of 150-250 W for 5-15 min; S4, concentrating the protein solution obtained in the step S3 to obtain a high-protein solution.

2. The method of claim 1, wherein, The method further comprises drying the high-protein solution to obtain a protein powder.

3. The method according to claim 1 or 2, characterized in that, The hydrophobic protein is one or more of yeast protein and rice protein.

4. The method of claim 1, wherein, In the step S1, the alkali solution is a sodium hydroxide solution with a concentration of 1-4 mol / L.

5. The method of claim 1, wherein, In the step S2, the pH is adjusted by using one of hydrochloric acid solution and citric acid solution.

6. The method of claim 1, wherein, The concentration is evaporation concentration of the protein solution.

7. The method of claim 1, wherein, The drying is spray drying of the protein solution after evaporation concentration.

8. The method of claim 1, wherein, The mass fraction of the protein in the high-protein solution is 5-15%.

9. A high-protein solution prepared by the method according to any one of claims 1-8.

10. Application of the high-protein solution according to claim 9 to a functional food or a high-protein health-care product.

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