Method for deamidating and modifying peanut protein by using protein glutaminase

Abstract

The invention discloses a method for deamidating and modifying peanut protein by using protein glutaminase, which comprises the following specific steps of: adding acetic acid / boric acid / NaOH buffer solution into peanut protein serving as a raw material while stirring to form protein dispersion liquid with certain substrate concentration; adding food-grade protein glutaminase into the peanut protein dispersion liquid for modification and termination; and carrying out vacuum freeze drying on the modified peanut protein dispersion liquid to obtain the deamidated modified peanut protein. Compared with unmodified peanut protein, the modified peanut protein obtained by the method disclosed by the invention has the advantages that the deamidation degree is obviously improved, the hydrolysis degree is not changed, and the functional properties such as solubility and foamability are all improved. The method for deamidating and modifying the peanut protein is simple in process and high in safety, can be used for large-scale industrial production and application, does not generate side reactions such as hydrolysis and crosslinking, and is beneficial to expanding the application scene of the peanut protein.

Description

Technical Field

[0001] The present invention belongs to the technical field of peanut protein processing, and particularly relates to a method and application for deamidating and modifying peanut protein by using protein glutaminase to improve the properties of peanut protein. Background Art

[0002] In China, peanut protein is a high-quality plant protein with a huge output, second only to wheat protein and soybean protein. This protein contains 10% water-soluble albumin and 90% globulin, and the globulin is further divided into two types: arachin and conarachin. Moreover, peanut protein is a complete protein, rich in essential nutrients for the human body, easy to digest and absorb, with a low content of anti-nutritional factors, and a protein utilization rate as high as 98%. It is a natural nutritional product with low sugar and low fat, suitable for people with special needs such as obesity, hyperlipidemia, and vegetarians. However, due to the differences in its molecular structure, the important food functional properties of peanut protein, such as solubility, foaming property, and emulsifying property, are all poor, resulting in great limitations in its application in the food industry and rarely being used in human food. Therefore, how to modify it to improve its food functionality is an urgent problem to be solved currently.

[0003] Protein-glutaminase (PG) is a food additive that has received much attention in recent years. It can catalyze the glutamine residues in the side chains of proteins or polypeptides to assist in deamidation, generating glutamic acid, thereby changing the structure of the protein to improve its functional properties. At the same time, the action of PG will not cause covalent cross-linking between proteins, nor will it cause excessive hydrolysis. From the perspectives of food protein safety, taste, and health, PG is an excellent enzyme preparation and can be widely used in the food industry.

[0004] The modification methods for improving the functional properties of peanut protein mainly include physical methods, chemical methods, enzymatic methods, etc. Physical methods often use heat treatment, ultrasonic treatment, etc. to modify proteins, but this method usually requires a large amount of energy consumption and is not easy to control. Moreover, its additional effects may even cause protein denaturation, resulting in a decrease in protein solubility and food quality. When using chemical methods to treat food proteins, a certain amount of foreign chemical substances need to be added, with low safety, which will cause consumers to worry about the edibility of the modified products, and its production process will also bring certain pressure to the environment. Enzymatic methods have attracted much attention from researchers due to their mild reaction conditions, rapid and controllable reactions, and strong specificity. Currently, the enzymes used for protein modification mainly include: proteases, transglutaminase, peptidylglutaminase, etc. However, due to problems such as substrate limitations and poor product taste, there are certain defects in their applications. Summary of the Invention

[0005] The object of the present invention is to overcome the defects and deficiencies of the prior art, and to provide a method for modifying peanut protein with protein glutaminase to improve the food functional properties of peanut protein. The present invention provides a method for modifying peanut protein with protein glutaminase to improve the performance of peanut protein. By using protein glutaminase to modify peanut protein, peanut protein with better food functional properties can be obtained, and its application scope in the food field can be broadened.

[0006] The present invention provides a method for deamidating and modifying peanut protein with protein glutaminase to improve the performance of peanut protein, comprising the following steps:

[0007] The first step: preparing a peanut protein dispersion solution

[0008] While stirring, peanut protein is added to a pH-adjusting buffer solution to form a peanut protein dispersion solution with a certain substrate concentration;

[0009] The second step: deamidation modification

[0010] To the peanut protein dispersion solution obtained in the first step, protein glutaminase is added for deamidation modification; the protein glutaminase is food-grade;

[0011] The third step: terminating the modification

[0012] After the modification is completed, the peanut protein dispersion solution is placed in an 80°C water bath to inactivate the protein glutaminase and terminate the modification;

[0013] The fourth step: freeze-drying

[0014] The modified peanut protein dispersion solution is subjected to vacuum freeze-drying to obtain deamidated and modified peanut protein.

[0015] Specifically, in the first step, a peanut protein dispersion solution with a certain substrate concentration is formed, that is, the concentration of the peanut protein dispersion solution is 1-5% (w / v); preferably, the concentration of the peanut protein dispersion solution is 1% (w / v). In a specific embodiment, the selection of the pH buffer solution includes, but is not limited to, any buffer solution that can be adjusted to the required pH, such as acetic acid / boric acid / NaOH buffer solution.

[0016] Specifically, in the second step, the ratio of the enzyme activity of the protein glutaminase to the mass of peanut protein (E / S) is 0-40 U / g; preferably, it is 20-40 U / g; more preferably, it is 30 U / g.

[0017] Specifically, in the second step, the reaction temperature for the deamidation modification is 30-60°C; preferably, it is 45°C.

[0018] Specifically, in the second step, the pH for deamidation modification of the enzymatic hydrolysis is 4.0 - 9.0; preferably, it is 4.5.

[0019] In the present invention, in the second step, the deamidation modification is carried out on a shaker, and the reaction time for deamidation modification is 0 - 6 h; preferably, the reaction time for deamidation modification is 3 h.

[0020] In the present invention, in the third step, the time for the water bath is 10 min.

[0021] In the present invention, in the fourth step, the conditions for vacuum freeze - drying are as follows: pre - freeze to - 50 °C within 30 minutes, at - 50 °C, the vacuum degree is 10 Pa, and the drying time is 35 h to obtain vacuum freeze - dried powder. In the present invention, by adopting the vacuum freeze - drying technology, compared with spray drying, etc., the quality of the PG - modified protein can be better guaranteed and is not damaged by high temperature, etc.

[0022] The method of the present invention further includes a detection step, that is, detecting the degree of deamidation, degree of hydrolysis, etc. of the peanut protein sample after the termination of deamidation modification.

[0023] The method of the present invention further includes a solubility detection step: detecting the solubility of the modified peanut protein powder obtained in the fourth step, that is, taking the peanut protein solution sample after the termination of deamidation modification for solubility detection. The specific steps are as follows: dissolve the deamidation - modified peanut protein in an acetic acid / boric acid / NaOH buffer solution with a pH of 7.0 to make the final concentration of the peanut protein solution 1 mg / mL, and conduct solubility detection.

[0024] Preferably, for the solubility detection, the obtained sample is centrifuged at 9000 rpm for 2 min, and the supernatant soluble part is used to detect the protein concentration in the solution by the BCA method. The calculation formula is as follows:

[0025] Solubility (%) = supernatant protein concentration ÷ total protein amount × 100.

[0026] The method of the present invention further includes a foaming property and stability detection step: detecting the foaming property and its stability of the modified peanut protein powder obtained in the fourth step, that is, taking the freeze - dried peanut protein sample for foaming property and foaming stability detection. Preferably, for the foaming property and foaming stability detection, a 0.5% w / v peanut protein solution is prepared, and the protein solution is homogenized at 20000 rpm for 1 min with a homogenizer. Record the volume of the solution before homogenization and the volume of the foam after homogenization. After standing for 10 min, record the volume of the foam again, and calculate the foaming property (FC) and foaming stability (FS) of the protein solution.

[0027] The calculation formulas are as follows:

[0028] FC(%) = volume of foam after homogenization ÷ volume of peanut protein solution × 100; FS(%) = volume of foam after standing for 10 min ÷ volume of foam after homogenization × 100.

[0029] In the method of the present invention, the deamidation degree of the protein glutaminase-modified peanut protein obtained is 0 - 52%; the hydrolysis degree is 11 - 15%; the solubility is 17.5 - 43.0%; the foaming property is 57.4 - 67.3%; the foam stability is 11 - 100%.

[0030] The present invention also provides the protein glutaminase-modified peanut protein modified by the above method. Specifically, the deamidation degree of the protein glutaminase-modified peanut protein is 0 - 52%, the hydrolysis degree is 11 - 15%, the solubility is 17.5 - 43%, the foaming property is 57.4 - 67.3%, and the foam stability is 11 - 100%. The protein glutaminase-modified peanut protein obtained by the method of the present invention improves the food functional properties of peanut protein, broadens the application scenarios of peanut protein, and effectively solves problems such as bitterness, off-flavor, flocculation, and precipitation caused by modifying peanut protein by other methods.

[0031] The present invention also provides the application of the protein glutaminase-modified peanut protein in improving the performance of peanut protein by enzymatic modification of peanut protein. The present invention provides a method for improving the performance of peanut protein by modifying it with protein glutaminase.

[0032] The beneficial effects of the present invention include: The method for modifying peanut protein with protein glutaminase proposed by the present invention uses peanut protein obtained by extracting peanut cake and meal remaining after peanut oil extraction as the raw material. It has a wide source and a low price, and is a complete protein that is rich in nutrition and easy to digest and absorb. The protein glutaminase used in the present invention is derived from Chryseobacterium proteolyticum, and has been approved by the US Food and Drug Administration, the Food Standards Australia New Zealand, and the National Health Commission of China, and can be safely applied to the food industry. This enzyme can catalyze the deamidation of glutamine in food proteins or polypeptides, and will not cause adverse reactions such as hydrolysis and cross-linking of the object of action, nor will it introduce additional chemical substances, ensuring the safety of food proteins. The modified peanut protein obtained by the present invention has an increased deamidation degree, an increased surface net charge, improved food functional properties such as solubility and foaming property, broadens the application scenarios of peanut protein, and effectively solves problems such as bitterness, off-flavor, flocculation, and precipitation caused by modifying peanut protein by other methods. The entire process is simple, rapid, easy to master, requires low equipment requirements, and is easy to industrialize. Description of the Drawings

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0034] Figure 1 The situation after modifying peanut protein with different peanut protein concentrations.

[0035] Figure 2 The situation after modifying peanut protein with different enzyme-to-substrate ratios.

[0036] Figure 3 The situation after modifying peanut protein at different temperatures.

[0037] Figure 4 The situation after modifying peanut protein for different times. Detailed implementation manners

[0038] The following specific embodiments illustrate the implementation manners of the present invention. Those familiar with this technology can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0039] In the present invention, each detection method includes:

[0040] 1. Determination of deamidation degree:

[0041] Determination of ammonia content in the experimental group: Take the peanut protein sample after deamidation modification, centrifuge at 8000 r / min for 2 min. After centrifugation, take 12 μL of the supernatant and use an ammonia detection kit (Sigma-Aldrich) to determine the ammonia content in the supernatant of the experimental group.

[0042] Determination of total ammonia content: Prepare a peanut protein dispersion solution with the same concentration as the experimental group, then add an equal volume of 2 M sulfuric acid solution, heat in a water bath at 100 °C for 4 h, and then use the same method as above to determine the ammonia content in the supernatant, which is the total ammonia content.

[0043] The formula for calculating the deamidation degree is: DD(%) = ammonia content in the experimental group ÷ total ammonia content × 100

[0044] 2. Determination of hydrolysis degree:

[0045] Determination of supernatant protein content: Take 1 mL of the modified peanut protein solution, add 1 mL of 0.2 M trichloroacetic acid solution and mix well. After precipitating the protein, centrifuge at 12,000 r / min for 5 min. Take an appropriate amount of the supernatant and detect the soluble protein content in the supernatant by the BCA protein concentration assay method.

[0046] Determination of total protein content: Prepare peanut protein dispersion solutions with equal concentrations, and determine the total protein content therein by the Kjeldahl method.

[0047] The calculation formula for the degree of hydrolysis is: DH(%) = supernatant protein content ÷ total protein content × 100

[0048] 3. Determination of solubility:

[0049] Determination of the solubility of peanut protein: Take a certain amount of freeze-dried peanut protein sample and disperse it in a 0.05 M acetic acid / boric acid / NaOH buffer solution with a pH of 7.0 to make the final concentration of the peanut protein solution 1 mg / mL. Place the above solution in a shaker at 25 °C and shake it at 220 r / min for 1 h. Then centrifuge it at 9,000 r / min for 2 min, take the supernatant to measure the protein concentration (BCA protein concentration assay method), and convert it to the protein content.

[0050] The calculation formula for solubility is: solubility (%) = soluble protein amount in the supernatant ÷ total protein × 100

[0051] 4. Determination of foaming property and foam stability:

[0052] Take the freeze-dried peanut protein sample and distilled water to prepare a 0.5% (W / V) peanut protein solution. Homogenize the protein solution at 20,000 rpm for 1 min with a homogenizer, record the volume of the solution before homogenization and the volume of the foam after homogenization. After standing for 10 min, record the volume of the foam again, and calculate the foaming property (FC) and foam stability (FS) of the protein solution.

[0053] The calculation formulas for foaming property and foaming stability are as follows: FC(%) = volume of foam after homogenization ÷ volume of peanut protein solution × 100; FS(%) = volume of foam after standing for 10 min ÷ volume of foam after homogenization × 100 (Reference: Hadidi M, Ibarz A, Pouramin S. Optimization of extraction and deamidation of edible protein from evening primrose (Oenothera biennis L.) oil processing by-products and its effect on structural and techno-functional properties. Food Chem. 2021 Jan 1; 334: 127613. doi: 10.1016 / j.foodchem.2020.127613. Epub 2020 Jul 19. PMID: 32711281.).

[0054] Example 1: Modification of peanut protein solutions with different concentrations by protein glutaminase

[0055] Weigh an appropriate amount of peanut protein, add it to a beaker containing an appropriate amount of distilled water while stirring and continue stirring for 10 min to prepare peanut protein dispersion solutions with final concentrations of 1%, 2%, 3%, 4%, and 5% respectively. Add an appropriate amount of food-grade protein glutaminase and stir to make the mass ratio of protein glutaminase activity to peanut protein E / S be 10 U / g. Place the above reaction system in a constant-temperature shaker and shake it at a temperature of 40 °C and a rotation speed of 220 rpm for 2 h or without reaction. After the reaction is completed, place the reaction system in a constant-temperature water bath at 80 °C for 10 min to terminate the reaction. After cooling, take a small amount of the sample for the detection of deamidation degree and hydrolysis degree, and place the remaining samples in a freeze dryer for vacuum freeze-drying. The vacuum freeze-drying conditions are: temperature -50 °C, vacuum degree 10 Pa, and time 35 h.

[0056] The experimental results are shown in Table 1 below and Figure 1 as follows.

[0057] Table 1

[0058]

[0059] Note: 1, 4, 7, 10, 13 are blank groups, 2, 5, 8, 11, 14 are control groups, and 3, 6, 9, 12, 15 are experimental groups.

[0060] In this example, the experimental results show that peanut proteins with different concentrations can be effectively deamidated. Moreover, as the concentration of peanut protein increases, the degree of deamidation gradually decreases. Meanwhile, the influence of the reaction system, that is, shaking at 40°C for 2 h on the degree of deamidation of peanut protein, is excluded, indicating that a peanut protein concentration of 1% is more conducive to modification by protein glutaminase. Its degree of hydrolysis does not show a trend of change with the increase in reaction time and the enzyme-to-substrate ratio. The degree of hydrolysis has been fluctuating within the range of 11.00 - 18.00%, indicating that protein glutaminase has almost no hydrolytic effect on peanut protein, which is beneficial to the improvement of the functional properties of peanut protein foods and will not cause side reactions such as excessive hydrolysis of proteins to produce bitter peptides.

[0061] As can be seen from Table 1, under the preferred conditions: when the enzyme-to-substrate ratio is 10 U / g, the reaction temperature is 40°C, and the reaction time is 2 h, the deamidation effect of 1% peanut protein is more ideal, and the degree of hydrolysis does not fluctuate significantly.

[0062] Example 2: Modification of peanut protein solution by protein glutaminase under different enzyme-to-substrate ratios

[0063] Weigh an appropriate amount of peanut protein, add it to a beaker containing an appropriate amount of distilled water while stirring and continue stirring for 10 min to prepare a peanut protein dispersion solution with a final concentration of 1%. Add an appropriate amount of food-grade protein glutaminase and stir to make the mass ratio of protein glutaminase activity to peanut protein E / S 0 - 40 U / g. Place the above reaction system in a constant-temperature shaker and shake at a temperature of 40°C and a rotation speed of 220 rpm for 2 h or without reaction. After the reaction, place the reaction system in a constant-temperature water bath at 80°C for 10 min to terminate the reaction. After cooling, take a small amount of the sample for detection of the degree of deamidation and the degree of hydrolysis, and place the remaining samples in a freeze dryer for vacuum freeze-drying. The vacuum freeze-drying conditions are the same as those in Example 1 of the present invention.

[0064] The experimental results are as shown in Table 2 below and Figure 2 as follows.

[0065] Table 2

[0066]

[0067] Note: 1 is the blank group, and 2, 3, 4, 5, 6, 7 are the experimental groups.

[0068] In this example, the experimental results show that: within the range of the enzyme-to-substrate ratio from 0 to 40 U / g, as the enzyme-to-substrate ratio increases, the degree of deamidation gradually increases. When the enzyme-to-substrate ratio reaches 30 U / g, the degree of deamidation of peanut protein is the highest. Then, further increasing the enzyme-to-substrate ratio, the deamidation effect of peanut protein slightly decreases; however, the degree of hydrolysis of peanut protein does not show a trend change with the addition amount of protein glutaminase and remains at about 13.00%, indicating that there is a certain hydrolysis background in peanut protein itself and it has little to do with protein glutaminase. Therefore, through comprehensive analysis, it is preferred to use an enzyme-to-substrate ratio of 30 U / g for peanut protein modification, which has the best effect, and at the same time will not cause excessive waste of resources and can reduce costs.

[0069] Example 3: Modification of Peanut Protein Solution by Protein Glutaminase under Different Temperature Conditions

[0070] Weigh an appropriate amount of peanut protein, add it to a beaker containing an appropriate amount of distilled water while stirring and continue stirring for 10 min to prepare a peanut protein dispersion solution with a final concentration of 1%. Add an appropriate amount of food-grade protein glutaminase and stir to make the mass ratio of protein glutaminase activity to peanut protein E / S be 10 U / g. Place the above reaction system in a constant-temperature shaker and oscillate. The temperatures are set to 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, and 60°C respectively, the rotation speed is 220 rpm, and the reaction is carried out for 2 h or not. After the reaction is completed, place the reaction system in a constant-temperature water bath at 80°C for 10 min to terminate the reaction. After cooling, take a small amount of the sample for the detection of the degree of deamidation and the degree of hydrolysis, and place the remaining samples in a freeze dryer for vacuum freeze drying. The vacuum freeze drying conditions are the same as those in Example 1 of the present invention.

[0071] The experimental results are as shown in Table 3 below and Figure 3 as follows.

[0072] Table 3

[0073]

[0074]

[0075] Note: 1 is the blank group, 2, 4, 6, 8, 10, 12, 14 are the control groups, and 3, 5, 7, 9, 11, 13, 15 are the experimental groups.

[0076] In this example, the experimental results show that: within the range of reaction temperature from 30 to 60 °C, with the increase of reaction temperature, the deamidation degree of peanut protein increases slowly. Specifically, when the modification temperature is 30 - 40 °C, the deamidation effect of peanut protein is slightly poor. When the temperature rises to 45 - 60 °C, the deamidation degree of peanut protein is relatively high and there is no significant difference. The degree of hydrolysis of peanut protein does not change significantly with the change of reaction temperature, suggesting that PG may have no hydrolytic effect on peanut protein. Therefore, different degrees of deamidation modification of peanut protein can be achieved at 30 - 60 °C. Considering comprehensively, the preferred temperature for modifying peanut protein is 45 °C. This temperature can ensure a relatively high deamidation degree of peanut protein while saving electrical energy as much as possible.

[0077] Example 4: Modification of peanut protein solution by protein glutaminase at different times

[0078] Weigh an appropriate amount of peanut protein and add it to a beaker containing an appropriate amount of acetic acid / boric acid / NaOH buffer solution (pH 4.5) while stirring, and continue to stir for 10 minutes to prepare a peanut protein dispersion solution with a final concentration of 1%. Add an appropriate amount of food-grade protein glutaminase and stir to make the mass ratio of protein glutaminase activity to peanut protein E / S 30 U / g. Place the above reaction system in a constant temperature shaker and oscillate at a temperature of 45 °C and a rotation speed of 220 rpm for 0 min, 10 min, 30 min, and 180 min. After the reaction is completed, place the reaction system in a constant temperature water bath at 80 °C for 10 minutes to terminate the reaction. After cooling, take a small amount of the sample for the detection of deamidation degree and hydrolysis degree, and place the remaining samples in a freeze dryer for vacuum freeze drying. The vacuum freeze drying conditions are the same as those in Example 1 of the present invention. After drying is completed, take an appropriate amount of the modified peanut protein sample and measure its solubility, foaming property, and foaming stability.

[0079] The experimental results are as shown in Table 4 and Figure 4 shown below.

[0080] Table 4

[0081]

[0082] In this example, the experimental results show that: within the range of 0 - 180 min of deamidation modification, with the increase of reaction time, the deamidation degree of peanut protein gradually increases; however, the degree of hydrolysis does not show a trend change and only fluctuates slightly within the range of 13.50 - 15.00%. For the modified peanut protein, its solubility, foaming property, and foaming stability are all significantly improved with the increase of deamidation degree, indicating that the food functional properties of peanut protein after deamidation modification have been improved, broadening the application scenarios and properties of peanut protein.

[0083] As can be seen from Table 4, under the preferred conditions: when the peanut protein concentration is 1%, the enzyme-to-substrate ratio is 30 U / g, the reaction temperature is 45 °C, and the pH is 4.5, the effect is more ideal after 180 minutes of modification, that is, 3 hours.

[0084] The protection scope of the present invention is not limited to the above embodiments. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be conceived by those skilled in the art are included in the present invention, and the appended claims are used as the protection scope.

Claims

1. A method for deamidating and modifying peanut protein using protein glutaminase, characterized in that, The method includes the following steps: First step: Add peanut protein into the pH-adjusting buffer while stirring to form a peanut protein dispersion solution with a certain substrate concentration; Second step: Add protein glutaminase to the peanut protein dispersion solution obtained in the first step for deamidation modification; Third step: After the modification is completed, place the peanut protein dispersion in an 80°C water bath to inactivate the protein glutaminase and terminate the modification; Fourth step: Subject the modified peanut protein dispersion solution to vacuum freeze-drying to obtain deamidated modified peanut protein.

2. The method according to claim 1, characterized in that, In the first step, the peanut protein is dispersed in the pH-adjusting buffer to obtain a peanut protein dispersion solution with a concentration of 1-5% w / v; the pH-adjusting buffer includes acetic acid / boric acid / NaOH buffer.

3. The method according to claim 1, characterized in that, In the second step, the ratio E / S of the enzyme activity of the protein glutaminase to the mass of the peanut protein is 0-40 U / g; and / or, the reaction temperature for the deamidation modification is 30-60°C; and / or, the pH for the deamidation modification is 4.0-9.0; and / or, the reaction time for the deamidation modification is 0-6 h.

4. The method according to claim 1, characterized in that, In the third step, the water bath time for terminating the modification is 10 min.

5. The method according to claim 1, characterized in that, In the fourth step, the conditions for vacuum freeze-drying the modified peanut protein dispersion solution are: pre-freezing to -50°C within 30 minutes, at -50°C, with a vacuum degree of 10 Pa, and a drying time of 35 h to obtain deamidated modified peanut protein powder.

6. The method according to claim 1, characterized in that, The method further includes a solubility detection step: Take the deamidated modified peanut protein obtained in the fourth step, dissolve it in acetic acid / boric acid / NaOH buffer with a pH of 7.0 to make the final concentration of the peanut protein solution 1 mg / mL, and conduct solubility detection; The solubility detection is to centrifuge the obtained sample at 9000 rpm for 2 min, take the supernatant soluble part, and detect the protein concentration in the solution by the BCA method, The calculation formula is as follows: Solubility (%) = supernatant protein concentration ÷ total protein amount × 100.

7. The method according to claim 1, characterized in that, The method further includes a foaming property and stability detection step: Take the deamidated modified peanut protein obtained in the fourth step, dissolve it in water, and conduct foaming property and foaming stability detection; For the detection of the foaming property and foaming stability, prepare a 0.5% w / v peanut protein solution, homogenize the protein solution with a homogenizer at 20000 rpm for 1 min, record the solution volume before homogenization and the foam volume after homogenization, after standing for 10 min, record the foam volume again, and calculate the foaming property FC and foaming stability FS of the protein solution, The calculation formula is as follows: FC (%) = foam volume after homogenization ÷ peanut protein solution volume × 100; FS (%) = foam volume after standing for 10 min ÷ foam volume after homogenization × 100.

8. The method according to claim 1, characterized in that, The deamidation degree of the protein glutaminase-modified peanut protein obtained by the method is 0-52%; the hydrolysis degree is 11-15%; the solubility is 17.5-43.0%; the foaming property is 57.4-67.3%; the foaming stability is 11-100%.

9. Protein glutaminase-modified peanut protein prepared by the method according to any one of claims 1-8.

10. Application of the method according to any one of claims 1-8, or the protein glutaminase-modified peanut protein according to claim 9, in improving the performance of peanut protein by enzymatic modification of peanut protein.

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