Preparation method of edible light-color rapeseed protein

Abstract

The invention discloses a preparation method of edible light-colored rapeseed protein, which comprises the following steps: leaching rapeseed dregs by adopting a weakly acidic combined buffer salt solution cooled at low temperature under the action of a magnetic field, centrifuging an extracting solution, taking supernate, adjusting the pH value of the supernate to precipitate the rapeseed protein, and finally performing vacuum freeze drying to obtain the edible light-colored rapeseed protein. According to the preparation method, the problems of deep white, bitter taste and poor solubility of rapeseed eggs prepared by a traditional process can be solved, the light rapeseed protein with high purity is obtained, the preparation condition is mild, the non-denatured and low-toxicity rapeseed protein can be prepared, the edible standard specified by European Union is met, and the rapeseed protein can be used as a high-quality edible protein resource and has a very good application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of plant protein extraction, in particular to a method for preparing edible light-colored rapeseed protein. Background Art

[0002] As an important source that accounts for more than 80% of the world's total protein production, plant protein has played a vital role in the research and development of products such as plant milk and plant meat.

[0003] Rapeseed is the largest oil crop planted in my country, and also the largest source of edible vegetable oil and feed protein in my country. Rapeseed meal, as the main byproduct of rapeseed oil processing, is rich in protein (about 35-45%) and has a balanced amino acid composition. It is a potential high-quality plant protein resource. However, rapeseed meal contains a large amount of anti-nutritional factors such as phytic acid, glucosinolates and polyphenol compounds. For a long time, it has been mainly used as feed protein or fertilizer, resulting in extremely low economic benefits. Internationally, in recent years, related rapeseed protein products of Burcon and DSM have been approved by the U.S. Food and Drug Administration (FDA) and the European Food Safety Authority (EFSA) as new food resource raw materials that are generally recognized as safe (GRAS certified). Rapeseed protein is gradually shifting from the animal to the human nutrition market, with huge development potential, but currently such products are still relatively scarce.

[0004] The development of rapeseed protein for food production faces many challenges. The first is poor color and taste. Compared with other oil crops, rapeseed contains a higher content of polyphenol compounds. The interaction between rapeseed and protein, as well as high-temperature pressing and processing, cause rapeseed protein, rapeseed peptide and other processed products to be severely denatured, dark in color, bitter in taste, and poor in palatability. The second is insufficient functional properties. Phytic acid in rapeseed easily reacts with Ca 2+ Mg 2+ The metal ions such as tannins form insoluble chelates, reducing their bioavailability, and also combine with proteins to form complexes, reducing protein solubility, biological efficacy and digestibility, affecting their functions; tannins, as complex polyphenol compounds, combine with proteins to change their properties, reduce digestibility, interfere with animal pancreatic enzymes and α-amylase catalysis, and affect animal growth. Third, processing technology is limited. Existing rapeseed anti-nutritional factor detoxification technologies have their own limitations. For example, fermentation neutralization method is prone to produce bad flavor substances when removing mustard glycosides, affecting taste and quality; alkaline detoxification has strict requirements on alkali amount and reaction conditions, otherwise it is easy to cause excessive denaturation of protein and cause loss of nutrients; solvent leaching method has the risk of solvent residue. At the same time, the extraction method also has shortcomings. Traditional extraction methods such as alkali extraction and acid precipitation have high extraction rates, but they will cause serious denaturation of protein, decrease the soluble nitrogen solubility index (NSI), and consume a lot of acid and alkali, polluting the environment. New extraction technologies such as enzyme method and ultrasonic assisted extraction have improved extraction efficiency and protein quality, but they are costly and complex, making them difficult to promote on a large scale.

[0005] At present, the patent application with application number 202411895776.4 discloses "a cooling cage and a spiral cold press". This patented equipment realizes cold and low-temperature pressing in the true sense. The pressing temperature of the pressing chamber is less than 65°C throughout the whole process, which is lower than the denaturation temperature of rapeseed protein, thus ensuring the non-denaturation characteristics of rapeseed meal raw materials from the root. Therefore, exploring a method for preparing rapeseed protein with good sensory properties, low toxicity and non-denaturation is a key issue to be solved in the current development process of high-quality rapeseed protein for food. Summary of the invention

[0006] The invention provides a method for preparing edible light-colored rapeseed protein, which solves the defects of poor protein quality and low soluble nitrogen solubility index caused by the extraction method in the prior art, so as to meet the demand for rapeseed protein for high-quality food.

[0007] In view of this, the scheme of the present invention is:

[0008] A method for preparing edible light-colored rapeseed protein, comprising the steps of:

[0009] S1. The rapeseed meal is crushed and sieved to remove crude fiber to obtain rapeseed meal powder; the rapeseed meal is derived from rapeseed meal that has been cold pressed and defatted at low temperature;

[0010] S2. taking rapeseed meal powder and adding it to a low-temperature buffered salt solution, extracting it for 20 to 45 minutes under the action of a magnetic field with an intensity of 0.1 to 0.5 T to obtain an extract; the buffered salt solution is a potassium salt and / or sodium salt solution containing monovalent, divalent and trivalent anions, and the pH is weakly acidic;

[0011] S3. At low temperature, centrifuge the extract to obtain the supernatant, adjust the pH value to allow the protein to fully precipitate, and collect the precipitate;

[0012] S4. The precipitate is freeze-dried in vacuum to obtain edible light-colored rapeseed protein.

[0013] Furthermore, in step S1, the rapeseed meal is sieved through a 30-60 mesh sieve after being crushed.

[0014] Furthermore, in step S1, the cold low-temperature pressing is pressing at 65°C, and the residual oil rate is less than 7%.

[0015] Furthermore, in step S2, the buffered saline solution is a solution containing chloride, sulfate, dihydrogen phosphate and monohydrogen phosphate.

[0016] Preferably, in step S2, the total concentration of the buffered saline solution is 50-200 mmol / L, and the concentrations of the dihydrogen phosphate and monohydrogen phosphate are 20-100 mmol / L.

[0017] Furthermore, in step S2, the buffered saline solution has a temperature of 2 to 8°C; and / or a pH of 5.5 to 6.8.

[0018] Furthermore, in step S2, the volume ratio of the mass of the rapeseed meal to the buffered saline solution is 1:(10-30).

[0019] Furthermore, in step S3, the low temperature condition is below 10°C.

[0020] Furthermore, in step S3, the pH value of the protein precipitation process is adjusted to 4-4.5.

[0021] Furthermore, in step S3, the extract is centrifuged at 3000-5000 r / min for 10-20 min.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The preparation method of the present invention adopts a low-temperature weakly acidic combined buffer salt solution, comprising a potassium salt or sodium salt solution composed of at least one monovalent, divalent and trivalent anions, to extract rapeseed protein under a magnetic field environment. This method has multiple advantages: first, the weakly acidic condition of the combined salt can effectively reduce the complexation of polyphenolic compounds with proteins, thereby obtaining light-colored rapeseed protein, and the low temperature environment and the use of no organic solvents are conducive to preventing protein denaturation; second, the ions in the soluble salt are combined with anti-nutritional factors to generate insoluble precipitates, thereby reducing the content of anti-nutritional factors. Third, with the help of the effect of the magnetic induction electric field, the charged particles such as ions and protein molecules in the solution are caused to be acted upon by the Lorentz force, and the protein molecules are arranged in a directional manner, further reducing the non-specific binding of protein with polyphenolic compounds. The rapeseed protein obtained by the method not only significantly improves the purity and NSI value of the protein, but also meets the requirements of the light color of the rapeseed protein, and finally successfully obtains non-denatured, low-toxic and light-colored edible rapeseed protein. The rapeseed protein can be used as an alternative resource for high-quality plant protein and has a very broad application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the tannin standard curve of the embodiment of the present invention.

[0025] Figure 2 Sodium phytate standard curve of the present invention

[0026] Figure 3 The standard curve of potassium sinigrin in the embodiment of the present invention. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below in conjunction with the preferred embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The rapeseed meal provided in the following examples is rapeseed meal that has been defatted by cold low-temperature pressing, the pressing process is pressing at 65°C, and the residual oil rate is less than 7%. If the manufacturer of the reagents or instruments is not specified in the examples, conventional products can be purchased from the market. If no specific conditions are specified, conventional conditions or conditions recommended by the manufacturer can be used.

[0029] Example 1

[0030] This embodiment provides a method for preparing edible light-colored rapeseed protein, which comprises the following steps:

[0031] 1. Use a crusher to crush the rapeseed meal that has been cold-pressed and defatted, and pass it through a 30-mesh sieve to remove crude fiber to obtain rapeseed meal powder.

[0032] 2. Mix the rapeseed meal with a combined buffer salt solution (20 mmol / L potassium chloride, 30 mmol / L sodium sulfate and 80 mmol / L sodium dihydrogen phosphate) with a total concentration of 130 mmol / L and cooled to 8°C at a liquid-to-solid ratio of 25:1 (v / w) and a pH of 6.5. Then place the mixture in a magnetic field environment with a magnetic induction intensity of 0.2 T and an extraction time of 35 min to obtain an extract.

[0033] 3. The extract was centrifuged at 4°C and 4500 r / min for 15 min to obtain a supernatant. The pH of the supernatant was adjusted to 4.0 to fully precipitate the protein in the solution, and then centrifuged at 4°C and 4500 r / min for 15 min to obtain a precipitate.

[0034] S4: collecting the precipitate, and freeze-drying it in vacuum to obtain edible light-colored rapeseed protein.

[0035] Example 2

[0036] This embodiment provides a method for preparing edible light-colored rapeseed protein, which comprises the following steps:

[0037] 1. Use a crusher to crush the rapeseed meal that has been cold-pressed and defatted, and pass it through a 50-mesh sieve to remove crude fiber to obtain rapeseed meal powder.

[0038] 2. The rapeseed meal powder was mixed with a combined buffered salt solution (50 mmol / L potassium chloride, 60 mmol / L potassium sulfate and 70 mmol / L sodium dihydrogen phosphate) with a total concentration of 180 mmol / L and cooled to 5°C at a liquid-to-solid ratio of 20:1 (v / w), pH 6.0, and then the mixture was placed in a magnetic field environment with a magnetic induction intensity of 0.3 T and an extraction time of 25 min to obtain an extract.

[0039] 3. The extract was centrifuged at 4°C and 4500 r / min for 15 min to obtain a supernatant. The pH of the supernatant was adjusted to 4.0 to fully precipitate the protein in the solution, and then centrifuged at 4°C and 4500 r / min for 15 min to obtain a precipitate.

[0040] 4. Collect the precipitate and freeze-dry it in vacuum to obtain edible light-colored rapeseed protein.

[0041] Example 3

[0042] This embodiment provides a method for preparing edible light-colored rapeseed protein, which comprises the following steps:

[0043] 1. Use a crusher to crush the rapeseed meal that has been cold-pressed and defatted, and pass it through a 60-mesh sieve to remove crude fiber to obtain rapeseed meal powder.

[0044] 2. The rapeseed meal powder was mixed with a combined buffered salt solution (20 mmol / L sodium chloride, 10 mmol / L potassium sulfate and 30 mmol / L sodium dihydrogen phosphate) with a total concentration of 60 mmol / L and cooled to 2°C at a liquid-to-solid ratio of 15:1 (v / w), pH 5.8, and then the mixture was placed in a magnetic field environment with a magnetic induction intensity of 0.5 T for 20 min to obtain an extract.

[0045] 3. The extract was centrifuged at 4°C and 4500 r / min for 15 min to obtain a supernatant. The pH of the supernatant was adjusted to 4.0 to fully precipitate the protein in the solution, and then centrifuged at 4°C and 4500 r / min for 15 min to obtain a precipitate.

[0046] S4: collecting the precipitate, and freeze-drying it in vacuum to obtain edible light-colored rapeseed protein.

[0047] Example 4

[0048] This embodiment provides a method for preparing edible light-colored rapeseed protein, which comprises the following steps:

[0049] 1. Use a crusher to crush the rapeseed meal that has been cold-pressed and defatted, and pass it through a 30-mesh sieve to remove crude fiber to obtain rapeseed meal powder.

[0050] 2. The rapeseed meal powder was mixed with a combined buffered salt solution (20 mmol / L potassium chloride, 30 mmol / L sodium sulfate and 80 mmol / L sodium dihydrogen phosphate) with a total concentration of 130 mmol / L and cooled to 4°C at a liquid-to-solid ratio of 30:1 (v / w), pH 6.5, and then the mixture was placed in a magnetic field environment with a magnetic induction intensity of 0.1 T for 45 min to obtain an extract.

[0051] 3. The extract was centrifuged at 4°C and 4500 r / min for 15 min to obtain a supernatant. The pH of the supernatant was adjusted to 4.0 to fully precipitate the protein in the solution, and then centrifuged at 4°C and 4500 r / min for 15 min to obtain a precipitate.

[0052] 4. Collect the precipitate and freeze-dry it in vacuum to obtain edible light-colored rapeseed protein.

[0053] Comparative Example 1 Preparation of rapeseed protein by traditional alkali extraction and acid precipitation method

[0054] The rapeseed meal defatted by cold low-temperature pressing was crushed by a pulverizer, and the crude fiber was removed through a 30-mesh sieve to obtain rapeseed meal powder. The rapeseed meal powder was added to deionized water with a liquid-to-solid ratio of 30:1 (v / w), and the pH of the mixed solution was adjusted to 10.0 with 1 mol / L NaOH solution, and the mixture was stirred and extracted in a 50°C water bath for 40 minutes, and the supernatant was taken by centrifugation (4°C, 4000r / min, 15min), and the pH was adjusted to 4.0 with 1 mol / L HCl to fully precipitate the protein in the solution, and the precipitate was collected by centrifugation (4°C, 4000r / min, 15min) and freeze-dried to obtain rapeseed protein.

[0055] Comparative Example 2 Preparation method without magnetic field

[0056] The preparation method of this comparative example is basically the same as that of Example 1, except that there is no magnetic field effect during the leaching process.

[0057] Comparative Example 3 Preparation method under high-intensity magnetic field

[0058] The preparation method of this comparative example is basically the same as that of Example 1, except that the magnetic field intensity during the leaching process is 1T.

[0059] Comparative Example 4 Preparation method under the action of normal temperature buffered saline solution

[0060] The preparation method of this comparative example is basically the same as that of Example 1, except that the buffered saline solution used in the leaching process is not cooled but at room temperature of 25°C.

[0061] Comparative Example 5: Preparation method of changing the composition of the combined salt solution

[0062] The preparation method of this comparative example is basically the same as that of Example 1, except that the total concentration of the buffered saline solution is 130 mmol / L, and the combined buffered saline solution (20 mmol / L magnesium sulfate, 30 mmol / L sodium sulfate and 80 mmol / L potassium dihydrogen phosphate) cooled to 4°C with a pH of 6.5.

[0063] Test Case

[0064] The color, purity, soluble nitrogen solubility index (NSI), and anti-nutritional factor (tannin, phytic acid, glucosinolate) content of the rapeseed protein obtained in each example and comparative example were measured below to identify the quality of the obtained rapeseed protein.

[0065] Color: Use HunterLab colorimeter to measure the color difference of the sample, calibrate the instrument with a black and white plate, set the reflection mode to specular reflection, take an appropriate amount of sample and add it to the cuvette, and record the L*, a*, and b* values ​​of the sample.

[0066] Protein purity: The protein content in rapeseed protein extract was determined by Kjeldahl method.

[0067] Soluble nitrogen solubility index (NSI): Take 5g sample, add 200mL deionized water, stir at 25℃ for 2h, transfer the mixture to a 250mL volumetric flask, and add water to make up to volume. After mixing, take 30mL and transfer it to a centrifuge tube. After centrifugation at 4000r / min for 10min, filter the supernatant with filter paper into a beaker, and determine the protein content of the filtrate by Kjeldahl method. Soluble nitrogen solubility index (NSI) = water-soluble nitrogen content / total nitrogen content of sample × 100%.

[0068] Determination of tannin content: refer to GB / T 27985~2011 Folin-Denis colorimetric method. The standard curve of the determination process is as follows: Figure 1 shown.

[0069] Determination of phytic acid content: The phytic acid content in protein was quantitatively determined by the ammonium ferric sulfate-bipyridine colorimetric method. Weigh 25 mg of protein into a 10 mL test tube, add 2.5 mL of 3% TCA and 5 mL of 0.02% ammonium ferric sulfate solution in sequence, cool in a boiling water bath for 30 minutes, centrifuge, take 2 mL of the supernatant and add 3 mL of bipyridine solution to shake well, measure the absorbance at 519 nm within 10 minutes, and use 2 mL of distilled water plus 3 mL of bipyridine solution as a control. The standard curve of the phytic acid content determination process is as follows: Figure 2 shown.

[0070] Determination of glucosinolate content: palladium chloride method is used to determine glucosinolates in protein. Take 100 mg of sample and add it to a 10 mL stoppered test tube. Dry steam it in a boiling water bath for 10 min. Add 10 mL of 9°C hot water and boil it again for 30 min. Stir it twice in the middle. After cooling, dilute it to 10 mL with water and shake it well. Centrifuge and take the supernatant. Add 2 mL of 0.1% sodium carboxymethyl cellulose solution and then add 1 mL of palladium chloride colorimetric solution. After shaking well, place it in a 24°C water bath for 3 hours. Measure the absorbance at 540 nm. Use palladium chloride and sodium carboxymethyl cellulose blank solutions as control solutions. The standard curve of the determination process is as follows: Figure 3 shown.

[0071] The various indicators of the rapeseed protein obtained from the products obtained in Examples 1 to 4 and Comparative Examples 1 to 5 were tested, and the test results are as follows:

[0072] Table 1: Comparison of rapeseed protein purity, NSI and anti-nutritional factor content

[0073]

[0074] Note: For the same index, different letters indicate significant difference, P<0.05.

[0075] As shown in Table 1, the purity and NSI value of the rapeseed protein obtained in Example 1 are the highest among all samples, and the content of anti-nutritional factors is low, which meets the EU edible protein standard. Compared with the traditional alkali extraction and acid precipitation method used in Comparative Example 1, the purity of the protein prepared by this method is increased by about 7%, and the NSI is increased by about 38%. This is because in an alkaline environment, the polyphenols in the rapeseed meal are easily oxidized and combined with the protein, and more impurities may be introduced at the same time, resulting in a decrease in protein purity. In addition, the use of strong acids and strong bases in the alkali extraction and acid precipitation process can partially denature the protein, thereby affecting its purity. The low-temperature cooling combined buffer salt is weakly acidic. Under such weakly acidic conditions, the binding effect of polyphenols and rapeseed protein is weakened, and the solubility of protein is reduced. At this time, adding an appropriate amount of sodium and potassium ion salts can produce a salt-dissolving effect, solve the problem of low solubility of protein in acidic solution, and can also effectively remove anti-nutritional factors such as phytic acid in the extract.

[0076] Low-temperature combined buffered salt solutions can effectively prevent protein denaturation and stabilize its conformation. Sodium ions, potassium ions, and phosphate ions produce a synergistic salt-dissolving effect. Sodium ions and potassium ions can destroy the interaction between protein molecules, making protein molecules more easily dispersed in the solution. Phosphate ions help to regulate the surface charge of proteins and enhance the interaction between proteins and water molecules, thereby improving the solubility of proteins, that is, improving the NSI value. In addition, the ions in the combined salt can preferably bind to impurity molecules (such as phytic acid, etc.), preventing the binding of phytic acid to proteins, making it easier to remove impurities in the subsequent separation process and improving protein purity.

[0077] Compared with Comparative Example 5, the potassium ions in Example 1 will interact with the tannin molecules, change their solubility, and form a complex that is easier to separate. The complex formed by magnesium ions and tannins in Comparative Example 5 is more stable and difficult to remove, which will cause more tannin residues. Although phosphate ions have the effect of destroying tannin-metal ion complexes, magnesium ions in Comparative Example 5 may form new relatively stable complexes. Therefore, the components of the buffered salt solution in Example 1 are more conducive to reducing the tannin content through the synergistic effect of potassium ions and phosphate ions.

[0078] In addition, a magnetic field is applied during the extraction process, and the charged particles (such as anions and cations, protein molecules) in the solution are subjected to the Lorentz force. Under suitable magnetic induction intensity, the charge distribution changes in the protein molecule and between molecules, prompting its directional arrangement, reducing the non-specific binding with other molecules (such as polyphenolic compounds, polysaccharides, etc.), facilitating the subsequent separation of protein and impurities by separation operations such as centrifugation, improving protein purity, and magnetic field treatment can promote the degradation of glucosinolates, reducing anti-nutritional factor content. However, compared with comparative example 3, it is found that too high magnetic induction intensity (such as 1T) may cause excessive aggregation of protein molecules or conformational changes. Although the combination with impurities can be reduced to a certain extent, excessive aggregation can change the solubility of protein in solution, causing the NSI value to decline, and making it difficult to disperse well in separation operations such as centrifugation, thereby affecting the promotion of protein purity.

[0079] Table 2 Comparison of rapeseed protein color

[0080]

[0081] As shown in Table 2, the L* values ​​of Examples 1 to 4 are relatively high, the a* values ​​are relatively low, and the samples are white or light yellow, while the L* value of Comparative Example 1 is the lowest, the a* value is the highest, and the sample is brown, and the L* and a* values ​​of the samples of Comparative Examples 2 and 5 are between the two, and are yellow or light brown. This may be because the combined buffered salt solution can effectively reduce the combination of protein and anti-nutritional factors (such as tannin) under low temperature and weak acid environment, reduce the content of anti-nutritional factors, reduce the oxidation and discoloration of protein during the extraction process, and thus maintain a relatively high L* value.

[0082] Comparative Examples 1 to 4, Comparative Examples 2 and 3 show that a suitable magnetic induction intensity can orient protein molecules, reduce their non-specific binding with impurity molecules or pigment substances, and thus maintain a good color (high L* value). If there is no magnetic field or the magnetic field intensity is low, the separation of protein and anti-nutritional factors is not thorough, and the protein is more likely to bind with pigment substances during the extraction process, resulting in a darker color of rapeseed protein; while too high a magnetic induction intensity may change the protein structure, affect its interaction with other molecules, and make the color of rapeseed protein worse.

[0083] In summary, the present invention uses a low-temperature cooled combined buffered salt solution to extract rapeseed protein under a magnetic field environment. On the one hand, the combination of different valence anions in the combined salt makes it weakly acidic. Extraction under this condition can reduce the complexation of polyphenolic compounds with proteins and obtain light-colored rapeseed protein; on the other hand, anti-nutritional factors are combined with sodium and potassium ions in soluble salts to form insoluble precipitates to reduce the content of anti-nutritional factors. At the same time, with the help of the effect of magnetic induction electric field, the non-specific binding of protein with polyphenolic compounds is further reduced, and the degradation of glucosinolates is promoted, which not only effectively improves the protein purity and NSI value, but also meets the requirements of light color of rapeseed protein, thereby obtaining non-denatured, low-toxic and light-colored edible rapeseed protein. Compared with the rapeseed protein prepared by the traditional alkali dissolution and acid precipitation method, the rapeseed protein prepared by this method has a light color, and the content of anti-nutritional factors such as phytic acid, glucosinolates, and tannins is low, which meets the standards of edible rapeseed protein specified by the European Union. Therefore, the rapeseed protein can be used as an alternative resource for high-quality plant protein and has a very broad application prospect.

[0084] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing edible light-colored rapeseed protein, characterized in that the steps include: S1. The rapeseed meal is crushed and sieved to remove crude fiber to obtain rapeseed meal powder; the rapeseed meal is derived from rapeseed meal that has been cold pressed and defatted at low temperature; S2. taking rapeseed meal powder and adding it to a low-temperature buffered salt solution, extracting it for 20 to 45 minutes under the action of a magnetic field with an intensity of 0.1 to 0.5 T to obtain an extract; the buffered salt solution is a potassium salt and / or sodium salt solution containing monovalent, divalent and trivalent anions, and the pH is weakly acidic; S3. At low temperature, centrifuge the extract to obtain the supernatant, adjust the pH value to allow the protein to fully precipitate, and collect the precipitate; S4. The precipitate is freeze-dried in vacuum to obtain edible light-colored rapeseed protein.

2. The preparation method according to claim 1, characterized in that: In step S1, the rapeseed meal is crushed and then sieved through a 30-60 mesh sieve.

3. The preparation method according to claim 1, characterized in that: In step S1, the cold low-temperature pressing is pressing at 65°C, and the residual oil rate is less than 7%.

4. The preparation method according to claim 1, characterized in that: In step S2, the buffered saline solution is a solution containing chloride, sulfate, dihydrogen phosphate and monohydrogen phosphate.

5. The preparation method according to claim 4, characterized in that: In step S2, the total concentration of the buffered saline solution is 50-200 mmol / L, and the concentrations of the dihydrogen phosphate and monohydrogen phosphate are 20-100 mmol / L.

6. The preparation method according to claim 1, characterized in that: In step S2, the buffered saline solution has a temperature of 2 to 8°C; and / or a pH of 5.5 to 6.

8.

7. The preparation method according to claim 1, characterized in that: In step S2, the volume ratio of the mass of the rapeseed meal to the buffered saline solution is 1:(10-30).

8. The preparation method according to claim 1, characterized in that: In step S3, the low temperature condition is below 10°C.

9. The preparation method according to claim 1, characterized in that: In step S3, the pH value of the protein precipitation process is adjusted to 4-4.

5.

10. The preparation method according to claim 1, characterized in that: In step S3, the extract is centrifuged at 3000-5000 r / min for 10-20 min.

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