Method for preparing protein concentrate from high-denaturation oilseed meal

Abstract

The invention discloses a method for preparing protein concentrate from high-denaturation oilseed meal, and belongs to the technical field of edible protein processing. The method comprises the following steps: crushing and screening to obtain meal powder with different protein contents by utilizing the distribution rule of proteins and structural carbohydrates in the microstructure of the high-denaturation oilseed meal and the physical property characteristics of components, and carrying out graded processing treatment according to the property difference of the meal powder; an air-electric field separation device is used for treating large-particle oilseed meal, high-fiber components which are difficult to remove in a traditional process are separated out, and high-protein components with solubility (NSI) similar to that of low-denaturation soybean meal and high gel property are obtained; proper concentration or alcoholase treatment is selected according to the protein content, denaturation degree and structural characteristics of the screening component, and a concentrated protein product meeting specific protein content requirements and / or functional characteristics can be obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of edible protein processing, and particularly relates to a method for preparing concentrated protein from highly denatured oilseed meal. Background Art

[0002] The by-product oilseed meal of vegetable oil processing is a raw material for processing vegetable protein. It can be directly used as a feed raw material or made into concentrated protein or isolated protein for food or feed processing. The functional and nutritional properties of proteins jointly determine the uses of concentrated protein or isolated protein, and the functional properties include solubility, water-holding capacity, oil-holding capacity, emulsifying property, and gelling property, etc.

[0003] Taking soy protein concentrate as an example, the existing mainstream process is the alcohol washing method, that is, using low-denatured defatted soybean meal as the raw material, dissolving small molecule impurities in the meal with 65%-70% ethanol, and the insoluble protein components are made into soy protein concentrate through processes such as desolventization, drying, and pulverization. The protein content of commercial products is above 65% (dry basis). If functional modification is required, soy protein concentrate can be mixed with water in a certain proportion and the pH value is adjusted to alkaline, and then through micro-fineization, sterilization, and drying to obtain functional soy protein concentrate. Compared with the alkali dissolution and acid precipitation process of isolated protein, the alcohol process of concentrated protein has less environmental impact.

[0004] Based on the differences in soybean oil processing technology, soybean meal can be divided into low-temperature defatted soybean meal (white soybean flakes) and highly denatured soybean meal (high-temperature meal). Low-temperature defatted soybean meal is the soybean meal obtained after oil extraction processing and low-temperature or flash desolventization. Its protein denaturation is small and it is suitable for the production of soy protein. Highly denatured soybean meal has undergone conditioning, puffing, pulverization, and high-temperature desolventization treatment, and the protein denaturation is serious. If it is used to produce concentrated protein (alcohol washing process), the efficiency is low, the protein content of the product is low, the solubility is low (NSI<10), the functional properties are poor, and it is not feasible. At present, there are no commercial products for producing soy protein concentrate and isolated protein from highly denatured soybean meal.

[0005] Therefore, how to efficiently utilize highly denatured oilseed meal to prepare concentrated protein has become a technical problem urgently to be solved in this field. Summary of the Invention

[0006] To solve the above technical problems, the present invention proposes a method for preparing concentrated protein from highly denatured oilseed meal.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing concentrated protein from highly denatured oilseed meal, comprising the following steps:

[0009] (1) Crush and screen the highly denatured oilseed meal to obtain large particle oilseed meal, medium particle oilseed meal and small particle oilseed meal respectively;

[0010] (2) Perform air-electric field separation treatment on the large particle oilseed meal obtained in step (1) to obtain a high protein component and a high fiber component respectively;

[0011] Perform first concentration on the high protein component obtained in step (2) and the small particle oilseed meal obtained in step (1) respectively to obtain concentrated protein;

[0012] Perform alcohol-enzymatic treatment and second concentration on the medium particle oilseed meal obtained in step (1) to obtain functional concentrated protein.

[0013] Technical principle: Utilize the distribution law of proteins and structural carbohydrates and the physical properties of components in the microstructure of oilseed meal. First, obtain meal powders with different protein contents through crushing and screening, and perform hierarchical processing according to their property differences; use an air-electric field separation device to treat large particle oilseed meal, separate the high fiber component that is difficult to remove in traditional processes, and obtain a high protein component with a solubility (NSI) similar to that of low denatured soybean meal and with high gel properties; select suitable concentration or alcohol-enzymatic treatment according to the protein content, denaturation degree and structural characteristics of the screened components to obtain concentrated protein products that meet specific protein content requirements and / or functional characteristics.

[0014] Preferably, in step (1), the particle size of the large particle oilseed meal is >500 μm, the particle size of the medium particle oilseed meal is 100 - 500 μm, and the particle size of the small particle oilseed meal is <100 μm.

[0015] Preferably, in step (2), the inter-plate voltage of the air-electric field separation treatment is 0.5 - 25 kV / cm, and the air flow rate is 1 - 30 L / min.

[0016] Preferably, the first concentration and the second concentration are both carried out by countercurrent gradient alcohol extraction.

[0017] Preferably, the ethanol concentration for the countercurrent gradient alcohol extraction is increased from 10 - 65% to 50 - 80%, and the solid-liquid ratio is 1:(8 - 20).

[0018] Preferably, the solid-liquid ratio for the alcohol-enzymatic treatment is 1:(4 - 20), and the mass ratio of the enzyme to the medium particle oilseed meal is 1:(50 - 500).

[0019] Preferably, the temperature for the alcohol-enzymatic treatment is 20 - 60 °C, and the treatment time is 0.5 - 5 h.

[0020] Preferably, the enzyme used for the alcohol-enzymatic treatment includes glycosidase or protease.

[0021] Preferably, after the first concentration to obtain concentrated protein, an enzymatic modification step is further included to obtain functional concentrated protein.

[0022] Preferably, after the first concentration or the second concentration, a post-treatment step is further included; the post-treatment includes modification, ultrasonic treatment, sterilization, and drying.

[0023] Preferably, the modification method is to adjust the pH to neutral; and / or,

[0024] The power density of the ultrasonic treatment is 0.5 - 1 W / cm 2 , and the time is 5 - 30 min.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] The present invention uses crushing, screening, electrostatic adsorption, air classification, and enzymatic hydrolysis treatments, and uses different pre-treatment schemes for different classified components to simultaneously achieve the purpose of improving the content of concentrated protein and regulating functional characteristics.

[0027] The method provided by the present invention makes full use of high-temperature meal resources, and can share some equipment with the low-temperature meal alcohol method for concentrated protein, and also has the advantage of customizable product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0029] Figure 1 is the process flow chart of the method for preparing concentrated protein from highly denatured oilseed meal in Example 5 of the present invention;

[0030] Figure 2 is the schematic diagram of the equipment used in the method for preparing concentrated protein from highly denatured oilseed meal provided by the present invention;

[0031] Among them, 1 - crusher, 2 - sieve, 3 - lifting platform, 4 - gas cylinder, 5 - air - electric field separation device, 6 - conveyor, 7 - sample inlet, 8 - extractor, 9 - solution storage tank, 10 - wet meal conveyor, 11 - high-temperature short-time sterilizer, 12 - homogenizer, 13 - spray drying tower;

[0032] Figure 3 is the front view of the air - electric field separation device;

[0033] Figure 4 is the northeast isometric view of the air - electric field separation device;

[0034] Among them, 1 - gas cylinder, 2 - gas-solid mixing chamber, 3 - spiral tube, 4 - separation chamber, 5 - electrode plate, 6 - collection bag, 7 - bag filter. Specific embodiments

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0036] To make the above objects, features, and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] The embodiments of the present invention provide a method for preparing concentrated protein from highly denatured oilseed meal, including the following steps:

[0038] (1) Crush and screen the highly denatured oilseed meal to obtain large particle oilseed meal, medium particle oilseed meal, and small particle oilseed meal respectively;

[0039] (2) Perform air - electric field separation treatment on the large particle oilseed meal obtained in step (1) to obtain a high - protein component and a high - fiber component respectively;

[0040] Perform first concentration on the high - protein component obtained in step (2) and the small particle oilseed meal obtained in step (1) respectively to obtain concentrated protein;

[0041] Perform alcohol - enzyme treatment and second concentration on the medium particle oilseed meal obtained in step (1) to obtain functional concentrated protein.

[0042] In a preferred embodiment, in step (1), the crude protein content of the highly denatured oilseed meal is 41 - 44%.

[0043] In a preferred embodiment, in step (1), the crushing method is grinding; the grinding speed is 20000 - 35000 rpm, and the time is 30 - 60 s. The present invention crushes the highly denatured oilseed meal by short - time high - speed grinding, which not only achieves the purpose of crushing the highly denatured oilseed meal but also avoids the aggravation of protein denaturation due to too long grinding time.

[0044] In a preferred embodiment, in step (1), the particle size of the large particle oilseed meal is >500 μm, the particle size of the medium particle oilseed meal is 100 - 500 μm, and the particle size of the small particle oilseed meal is <100 μm. The present invention utilizes the microstructural characteristics of oilseed meal, and through moderate pulverization and screening, classifies the highly denatured oilseed meal into soybean meals with different particle sizes and protein contents. The method of classification by pulverization and screening has the advantages of low power consumption and environmental protection.

[0045] In a preferred embodiment, in step (2), the inter-plate voltage of the air-electric field separation treatment is 0.5 - 25 kV / cm, the air flow rate is 1 - 30 L / min, and the treatment time is determined according to the treatment volume. The present invention utilizes the distribution law of proteins and structural carbohydrates in the microstructure of oilseed meal and the physical properties of the components, and through air-electric field separation treatment of large particle oilseed meal, separates the high-fiber components that are difficult to remove in the traditional process, and obtains a high-protein component with an NSI similar to that of low-denatured soybean meal and having high gelation properties. Both the inter-plate voltage and the air flow rate of the air-electric field separation treatment will affect the separation effect of the high-protein component and the high-fiber component. The high-protein component has more negative charges after friction and moves towards the negative electrode in the electric field; the high-fiber component is closer to the positive electrode region; by controlling the charge-mass ratio, the separation efficiency can be improved; if the air flow rate is too high, it will carry away some high-protein components and reduce the protein recovery rate, while if the air flow rate is too low, it cannot effectively separate the high-protein component and the high-fiber component, affecting the separation effect.

[0046] In a preferred embodiment, the first concentration and the second concentration are both carried out by countercurrent gradient ethanol extraction. The present invention improves the protein content in the product by countercurrent gradient ethanol extraction.

[0047] In a preferred embodiment, the high-protein component and the small particle oilseed meal can be concentrated separately or can be concentrated after mixing.

[0048] In a preferred embodiment, during the first concentration process, the ethanol concentration is increased from 10 - 60% to 50 - 75%, the solid-liquid ratio is 1:(8 - 20), and the temperature is 50 - 60 °C. In the preferred embodiment of the present invention, countercurrent gradient ethanol extraction can be carried out using general industrial equipment, and this equipment includes an ethanol recovery device, a material conveying device, and a drying device. The present invention achieves the purpose of concentration by adopting the method of countercurrent gradient ethanol extraction, and using ethanol with the above concentration is beneficial to obtaining high-purity concentrated protein.

[0049] In a preferred embodiment, the solid-liquid ratio of the alcohol-enzymatic treatment is 1:(4 - 20), and the mass ratio of the enzyme to the medium-sized granular oilseed meal is 1:(50 - 500); the alcohol used in the alcohol-enzymatic treatment is ethanol; the volume concentration of the ethanol is 20 - 65%. By subjecting the medium-sized granular oilseed meal to alcohol-enzymatic treatment, the present invention can obtain a high water-holding capacity concentrated protein with specific functional characteristics, and can also increase the protein content and digestibility of the product. The protein content of the concentrated protein products obtained by concentration after enzymatic hydrolysis at different ethanol concentrations is different, and the protein content of the concentrated protein products obtained by concentration after different enzymatic hydrolyses at the same ethanol concentration is also different.

[0050] In a preferred embodiment, the temperature of the alcohol-enzymatic treatment is 20 - 60°C, the treatment time is 0.5 - 5 h, and the pH is adjusted to the appropriate range of the enzyme. Conducting the alcohol-enzymatic treatment at the above temperature ensures the activity of the enzyme.

[0051] In a preferred embodiment, the enzyme used in the alcohol-enzymatic treatment includes glycosidase or protease.

[0052] In a preferred embodiment, during the second concentration process, the ethanol concentration is increased from 10 - 65% to 50 - 80%, the liquid-solid ratio is 1:(8 - 20), and the temperature is 50 - 60°C.

[0053] In a preferred embodiment, after the first concentration to obtain the concentrated protein, an enzyme modification step is further included to obtain a functional concentrated protein.

[0054] In a preferred embodiment, a post-treatment step is further included after the first concentration or the second concentration; the post-treatment includes modification, ultrasonic treatment, sterilization, and drying. The concentrated protein obtained after concentration has poor solubility, and the solubility can be improved by modification.

[0055] In a preferred embodiment, the modification method is to adjust the pH to neutral.

[0056] In a preferred embodiment, the power density of the ultrasonic treatment is 0.5 - 1 W / cm 2 , and the time is 5 - 30 min.

[0057] In a preferred embodiment, the schematic diagram of the equipment used in the method for preparing concentrated protein from highly denatured oilseed meal provided by the present invention is shown in Figure 2 , and the equipment includes a crusher, a screening machine, a lifting platform, a gas cylinder, an air-electric field separation device, a conveyor, a sampling port, a leaching tank, a solution storage tank, a wet meal conveyor, an ultrasonic machine, and a spray drying tower.

[0058] In a preferred embodiment, the front view of the air-electric field separation device is shown in Figure 3 , and the northeast isometric view is shown in Figure 4, the device includes a gas cylinder, a gas-solid mixing chamber, a spiral tube, a separation chamber, electrode plates, a collection bag, and a bag filter; the separation chamber includes two electrode plates, one electrode plate is grounded (negative electrode), and one electrode plate is connected to a positive electrode. The negative electrode collects high-protein components, and the positive electrode collects high-fiber components; the material of the spiral tube includes nylon, aluminum, or stainless steel.

[0059] In the air-electric field separation treatment of the present invention, after screening the oilseed meal, the large particles that are difficult to pulverize and have a low protein content are subjected to air-electric field separation. The large particle components rub against each other in the spiral separation tube and also come into contact with the chamber wall. The particles rich in protein tend to lose electrons and carry a positive charge, while the particles rich in carbohydrates (such as fibers) tend to gain electrons and carry a negative charge. After being carried out by the air flow, under the combined action of the electric field and gravity, the particles with different compositions show different distribution laws. The heavier particles are on the near side of the electrode plate, and the lighter particles with high protein purity fall on the far side. There are 4 or more collection bags in the middle of the two electrode plates to divide the separation area, and the collection area can be divided according to the type and properties of the oilseed meal. The high-purity protein particles tend to be distributed at the far end of the separation field (away from the spiral tube mouth); the components with a high fiber content tend to be at the near end of the separation field (close to the spiral tube mouth). The separated materials can be separated again, or a magnetic field module can be added in the middle of the electrode plates to further improve the separation degree of protein and carbohydrates. The air flow rate, electric field strength, magnetic field strength, number of divided areas, and particle size of the material can be adjusted according to the separation efficiency and target.

[0060] In the embodiments of the present invention, room temperature refers to "25 ± 2 °C".

[0061] Unless otherwise specified, the raw materials in the embodiments of the present invention are all obtained through commercial channels.

[0062] Example 1

[0063] (1) Grind the high-temperature meal with a crude protein content of 41% at 30000 rpm for 30 s using a pulverizer, and screen it to obtain large particle oilseed meal M with a particle size of >500 μm 1 , medium particle oilseed meal M with a particle size of 100 - 500 μm 2 and small particle oilseed meal M with a particle size of <100 μm 3 ;

[0064] (2) Perform air-electric field separation treatment on the large particle oilseed meal M obtained in step (1) 1 under the conditions of a plate voltage of 10 V / cm and an air flow rate of 15 L / min. After 4 min, high-protein component ME 1 and high-fiber component ME 2 are obtained respectively.

[0065] The high-protein component ME obtained in Example 1 was measured by the Kjeldahl method 1 to have a protein content of 70%, meeting the commercial requirements, and a nitrogen solubility index higher than 65%.

[0066] Weigh 5.0 g of ME 1 dissolve it in 20 mL of water, stir for 2 h at room temperature to make it evenly dispersed, heat it in a 90 °C water bath for 30 min, then quickly cool it with running water, place it in a 4 °C refrigerator overnight, and use a texture analyzer to measure the gel strength. The trigger force is 5 g, and the measured gel strength > 400 g.

[0067] Example 2

[0068] (1) Grind the high-temperature meal with a crude protein content of 41% using a pulverizer at 30,000 rpm for 0.5 min, and sieve it to obtain large particle oilseed meal M with a particle size > 500 μm 1 , medium particle oilseed meal M with a particle size of 100 - 500 μm 2 and small particle oilseed meal M with a particle size < 100 μm 3 ;

[0069] (2) At 60 °C, subject the small particle oilseed meal M obtained in step (1) 3 to countercurrent gradient ethanol extraction, with the ethanol concentration increasing from 30% to 75% and the solid-to-liquid ratio of 1:20, to obtain concentrated protein PC 3 . Adjust the pH of PC 3 to neutral, then ultrasonically treat it for 15 min under the condition of a power density of 1 W / cm 2 , sterilize, dry, pulverize, and pack it to obtain the finished concentrated protein.

[0070] The protein content of PC 3 measured by the Kjeldahl method was > 65%, and the nitrogen solubility index (NSI) > 40%.

[0071] Example 3

[0072] (1) Grind the high-temperature meal with a crude protein content of 41% using a pulverizer at 30,000 rpm for 0.5 min, and sieve it to obtain large particle oilseed meal M with a particle size > 500 μm 1 , medium particle oilseed meal M with a particle size of 100 - 500 μm 2 and small particle oilseed meal M with a particle size < 100 μm 3 ;

[0073] (2) Mix the medium particle oilseed meal M obtained in step (1) 2 with glycosidase and ethanol for alcohol-enzymatic treatment. The glycosidase and the medium particle oilseed meal M 2The mass ratio is 1:100, the volume concentration of ethanol is 65%, the solid-liquid ratio is 1:5, the pH is adjusted to 5.0 ± 0.1, the temperature is controlled at 50 °C, and after 1 h, EM is obtained. 2 ; At 60 °C, the above EM 2 is subjected to countercurrent gradient ethanol extraction, the ethanol concentration is increased from 20% to 55%, and the material-liquid ratio is 1:20 to obtain the functional concentrated protein PCEM. 2 Adjust the pH of PCEM 2 to neutral, and then ultrasonically treat it for 15 min under the condition of a power density of 1 W / cm 2 . Sterilize, dry, pulverize, and pack to obtain the finished product of functional concentrated protein.

[0074] The protein content of PCEM 2 measured by the Kjeldahl method is > 70%.

[0075] Example 4

[0076] (1) Grind the high-temperature meal with a crude protein content of 41% with a pulverizer at 30,000 rpm for 30 s, and sieve to obtain large particle oilseed meal M with a particle size of > 500 μm 1 , medium particle oilseed meal M with a particle size of 100 - 500 μm 2 and small particle oilseed meal M with a particle size of < 100 μm 3 ;

[0077] (2) Mix the medium particle oilseed meal M 2 obtained in step (1) with protease and ethanol for alcohol-enzymatic treatment. The mass ratio of protease to medium particle oilseed meal M 2 is 1:50, the volume concentration of ethanol is 65%, the solid-liquid ratio is 1:5, the pH is adjusted to 8.0 ± 0.1, the temperature is controlled at 50 °C, and after 1 h, EM is obtained. 2 ; At 60 °C, the above EM 2 is subjected to countercurrent gradient ethanol extraction, the ethanol concentration is increased from 65% to 80%, and the material-liquid ratio is 1:20 to obtain the functional concentrated protein PCEM. 2 Sterilize, dry, pulverize, and pack PCEM 2 to obtain the finished product of functional concentrated protein.

[0078] The protein content of PCEM 2 measured by the Kjeldahl method is > 65%, and NSI > 25%; Using the method in Example 1, the gel strength of PCEM 2 is > 500 g.

[0079] Example 5

[0080] A method for preparing concentrated protein from highly denatured oilseed meal. The process flow is shown inFigure 1 , a schematic diagram of the equipment used is shown in Figure 2 , and the specific steps are as follows:

[0081] (1) Grind the high-temperature meal with a crude protein content of 41% using a pulverizer at 30,000 rpm for 30 s, and then screen it to obtain large particle oilseed meal M with a particle size of >500 μm 1 , medium particle oilseed meal M with a particle size of 100 - 500 μm 2 and small particle oilseed meal M with a particle size of <100 μm 3 ;

[0082] (2) Perform air - electric field separation treatment on the large particle oilseed meal M obtained in step (1) under the conditions of a plate - to - plate voltage of 10 kV / cm and an air flow rate of 15 L / min to obtain a high - protein component ME 1 and a high - fiber component ME 1 ; 2 ;

[0083] (3) At 60 °C, perform counter - current gradient ethanol extraction on the high - protein component ME 1 obtained in step (2) and the small particle oilseed meal M 3 obtained in step (1) respectively. The ethanol concentration is increased from 60% to 75% for both, and the solid - to - liquid ratio is 1:10 for both, to obtain concentrated protein PCME 1 and PC 3 ;

[0084] (4) Mix the medium particle oilseed meal M 2 obtained in step (1) with protease and ethanol for alcohol - enzyme treatment. The mass ratio of protease to medium particle oilseed meal M 2 is 1:50, the volume concentration of ethanol is 65%, the solid - to - liquid ratio is 1:10, adjust the pH to 9.0 ± 0.1, control the temperature at 60 °C, and after 1 h, obtain EM 2 ; At 60 °C, perform counter - current gradient ethanol extraction on the above - mentioned EM 2 , with the ethanol concentration increased from 60% to 75% and the solid - to - liquid ratio of 1:20, to obtain functional concentrated protein PCEM 2 ;

[0085] (5) Adjust the pH of the concentrated protein PCME 1 and PC 3 obtained in step (3) and the functional concentrated protein PCEM 2 obtained in step (4) to neutral respectively, and then perform ultrasonic treatment for 15 min under the condition of a power density of 1 W / cm 2 , sterilize, dry, pulverize, and pack them respectively to obtain finished product PC 3 , finished product PCME 1and the finished PCEM 2 。

[0086] The protein content of the finished PC measured by the Kjeldahl method 3 is > 65%, and NSI > 25%; the protein content of the finished PCME 1 is > 70%, and NSI > 25%; the protein content of the finished PCEM 2 is > 65%, and NSI > 25%.

[0087] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for preparing concentrated protein from highly denatured oilseed meal, characterized in that: The following steps are involved: (1) crushing and screening the highly denatured oilseed meal to obtain large-particle oilseed meal, medium-particle oilseed meal and small-particle oilseed meal respectively; (2) subjecting the large-particle oilseed meal obtained in step (1) to air-electric field separation to obtain a high-protein component and a high-fiber component, respectively; The high-protein component obtained in step (2) and the small-particle oilseed meal obtained in step (1) are respectively subjected to a first concentration to obtain concentrated protein; The medium-grained oilseed meal obtained in step (1) is subjected to alcohol enzyme treatment and a second concentration to obtain a functional concentrated protein.

2. The method for preparing concentrated protein from highly denatured oilseed meal according to claim 1, characterized in that: In step (1), the particle size of the large-particle oilseed meal is greater than 500 μm, the particle size of the medium-particle oilseed meal is between 100 and 500 μm, and the particle size of the small-particle oilseed meal is less than 100 μm.

3. The method for preparing concentrated protein from highly denatured oilseed meal according to claim 1, characterized in that: In step (2), the inter-plate voltage of the air-electric field separation treatment is 0.5 to 25 kV / cm, and the air flow rate is 1 to 30 L / min.

4. The method for preparing concentrated protein from highly denatured oilseed meal according to claim 1, characterized in that: The first concentration and the second concentration are both performed by countercurrent gradient alcohol extraction.

5. The method for preparing concentrated protein from highly denatured oilseed meal according to claim 4, characterized in that: The ethanol concentration of the countercurrent gradient alcohol extraction is increased from 10-65% to 50-80%, and the solid-liquid ratio is 1:(8-20).

6. The method for preparing concentrated protein from highly denatured oilseed meal according to claim 1, characterized in that: The solid-liquid ratio of the alcohol-enzyme treatment is 1:(4-20), and the mass ratio of the enzyme to the medium-grained oilseed meal is 1:(50-500).

7. The method for preparing concentrated protein from highly denatured oilseed meal according to claim 1, characterized in that: The temperature of the alcohol enzyme treatment is 20-60° C., and the treatment time is 0.5-5 h.

8. The method for preparing concentrated protein from highly denatured oilseed meal according to claim 1 or 6, characterized in that: The enzyme used in the alcohol enzyme treatment includes glycosidase or protease.

9. The method for preparing concentrated protein from highly denatured oilseed meal according to claim 1, characterized in that: After the first concentration to obtain concentrated protein, an enzyme modification step is also included to obtain functional concentrated protein.

10. The method for preparing concentrated protein from highly denatured oilseed meal according to claim 1, characterized in that: The first concentration or the second concentration further includes a post-processing step; the post-processing includes modification, ultrasound, sterilization and drying; The modification method is to adjust the pH to neutral; and / or, The power density of the ultrasound is 0.5-1 W / cm 2 , time is 5 to 30 minutes.

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