Extraction process of plant protein with low oxalic acid content

Abstract

The invention relates to the field of protein extraction, in particular to an extraction process of plant protein with low oxalic acid content, which comprises the following steps: S1, mixing a plant raw material with an extracting agent, extracting at 20-70 DEG C, and filtering to obtain an extracting solution; s2, performing chromatography on the extracting solution to obtain a chromatographic solution; s3, concentrating, precipitating and filtering the chromatographic solution to obtain a protein solid; and S4, drying the protein solid to obtain the plant protein with low oxalic acid content. According to the method, oxalic acid and protein in the plant raw materials are dissolved through the extracting agent, then oxalic acid is adsorbed through chromatography, separation of oxalic acid and protein is achieved, finally, the plant protein is obtained through concentration, precipitation, filtration and drying, and the residual amount of oxalic acid in the plant protein is effectively reduced.

Description

Technical Field

[0001] The present application relates to the field of protein extraction, and in particular to a process for extracting plant protein with low oxalic acid content. Background Art

[0002] Plants like spinach and beets contain high levels of oxalic acid, bound to cell walls in the form of calcium salts or free in the juice. The presence of oxalic acid can disrupt the charge balance and structural stability of plant proteins, leading to precipitation or deformation, which can interfere with their extraction. Therefore, removing oxalic acid is a challenge in plant protein extraction.

[0003] Existing methods for removing oxalic acid include adding calcium ions that combine with oxalic acid to form insoluble calcium oxalate precipitates, or adding enzymes to lyse plant cell walls, releasing oxalic acid while reducing its binding to proteins. However, these methods still contain significant amounts of residual oxalic acid in the plant protein, impacting its yield and quality. Therefore, there is an urgent need for a method to extract plant protein with a low oxalic acid content to minimize the residual oxalic acid content in plant protein. Summary of the Invention

[0004] In order to reduce the oxalic acid content in plant protein, the present application provides an extraction process for low oxalic acid content plant protein.

[0005] The present application provides a process for extracting low-oxalic-acid-content plant protein, which adopts the following technical solution: A process for extracting low-oxalic-acid-content plant protein comprises the following steps: S1: Mix the plant material and the extractant at 20-70°C for extraction, and filter to obtain the extract; S2: subjecting the extract to chromatography to obtain a chromatographic solution; S3: Concentrating, precipitating and filtering the chromatographic solution to obtain protein solids; S4: Drying the protein solids to obtain low oxalic acid content vegetable protein.

[0006] By adopting the above technical solution, in the process of extracting low-oxalic-acid-content plant protein, first, oxalic acid, protein and other substances in the plant raw materials are extracted using an extractant at 20-70°C, and then oxalic acid is adsorbed by chromatography to separate oxalic acid and protein. The protein concentration in the chromatography liquid is then increased by concentration, and the protein is precipitated and filtered to obtain protein solids. Finally, stable low-oxalic-acid-content plant protein is obtained by drying.

[0007] The present application extracts oxalic acid and protein from plant raw materials through an extract, separates the oxalic acid and protein in the extract through chromatography, adsorbs the oxalic acid in the extract as much as possible through chromatography, and finally obtains plant protein with low oxalic acid content through concentration, precipitation, and filtration, thereby effectively adsorbing oxalic acid in plants and reducing the impact of the presence of oxalic acid on the quality and yield of plant protein.

[0008] Preferably, the extractant is at least one of water, ethylene glycol, and glycerol.

[0009] By adopting the above technical solution, under the conditions of 20-70°C, the presence of water can provide a polar environment, and through hydrogen bonding and electrostatic interactions with oxalic acid molecules, oxalic acid molecules can be dispersed and dissolved in water. In addition, the polarity of water molecules can stabilize the ions produced by the ionization of oxalic acid, promoting the dissolution of oxalic acid and the shift of the ionization equilibrium to the right. At the same time, the surface of plant protein molecules usually also contains many polar groups. Water molecules can form hydrogen bonds and electrostatic interactions with these polar groups, thereby surrounding the protein molecules to form a hydration layer. The formation of the hydration layer enables the protein molecules to disperse in water and dissolve. In addition, water can also maintain the natural conformation of the protein by interacting with some polar regions inside the protein molecules, which helps it dissolve and stably exist in water.

[0010] Ethylene glycol is a polar organic solvent with two hydroxyl groups. Its hydroxyl groups can form hydrogen bonds with the carboxyl groups of oxalic acid. This hydrogen bonding creates an attraction between the oxalic acid and ethylene glycol molecules, resulting in a certain solubility of oxalic acid in ethylene glycol. Furthermore, the polarity of ethylene glycol facilitates electrostatic interactions with oxalic acid molecules, further promoting oxalic acid's dissolution. Furthermore, the polarity of ethylene glycol can interact with polar groups on the surface of protein molecules, thereby enhancing the solubility of proteins in ethylene glycol.

[0011] Glycerol contains three hydroxyl groups, which have strong polarity and the ability to form hydrogen bonds. Its hydroxyl groups can form multiple hydrogen bonds with the carboxyl groups of oxalic acid. This multi-hydrogen bond interaction allows oxalic acid to dissolve in glycerol. In addition, the polar environment of glycerol also helps stabilize the oxalic acid molecules, keeping them dissolved in glycerol. At the same time, the hydroxyl groups of glycerol can also form hydrogen bonds with the polar groups on the main chain and side faces of protein molecules. These hydrogen bonds can stabilize the secondary and tertiary structures of proteins and reduce the probability of aggregation and precipitation of protein molecules. In addition, glycerol can also form a protective film on the surface of protein molecules to prevent other adverse factors from affecting the protein, thereby contributing to the stable existence and dissolution of proteins in solution.

[0012] Preferably, the solid-liquid ratio of the plant raw material to the extractant is 1:10-20.

[0013] By adopting the above technical solution, the cell wall and protein matrix of the plant raw material have a stronger inclusion effect on oxalic acid and protein. When the solid-liquid ratio of the plant raw material to the extractant is 1:10-20, the concentration gradient at the solid-liquid interface can be significantly reduced, ensuring sufficient swelling of the plant raw material, prompting the intracellular components to diffuse rapidly into the solvent, allowing oxalic acid to be fully dissolved, and reducing protein aggregation or denaturation.

[0014] When the amount of extractant added is too small, the extractant cannot fully penetrate the plant material, resulting in insufficient space for oxalic acid and protein to dissolve. This prevents the oxalic acid and protein in the raw material from being fully released into the extractant, resulting in a decrease in the extraction rate and a reduction in the final yield of low-oxalic acid plant protein. Furthermore, insufficient extractant addition leads to excessively high protein concentrations, which enhances interactions between protein molecules and easily forms aggregates or precipitates. Furthermore, excessive oxalic acid concentrations may exceed the dynamic adsorption capacity of the adsorbent, leading to premature saturation of the adsorbent and an increase in the residual amount of oxalic acid in the chromatographic fluid.

[0015] When too much extractant is added, the large volume of the extractant will dilute the solution, destroying the hydrogen bond between oxalic acid and the extractant, resulting in a decrease in the solubility of oxalic acid. In addition, if the concentration of oxalic acid in the extract is too low, the subsequent adsorbent's adsorption driving force for oxalic acid will be weakened, the adsorption rate will decrease, and the residual amount of oxalic acid in the chromatography fluid will increase. In addition, during the concentration process, low-concentration protein solutions require more energy to remove the solvent, and prolonged heating may cause protein denaturation. Preferably, the extractant is a mixture of water, ethylene glycol and glycerol.

[0016] By adopting the above technical solution, water, as a polar solvent, can promote the dissolution of oxalic acid through hydrogen bonds and electrostatic interactions, while maintaining the ionic strength of the solution, so that oxalic acid is mainly in an ionic state, making it easier to be adsorbed by the adsorbent. The addition of ethylene glycol and mixing with water form a solvent system with a moderate dielectric constant. It can not only stabilize the ions produced by the ionization of oxalic acid through the strong polarity of water, but also enhance the dispersion ability of oxalic acid molecules through the moderate polarity of ethylene glycol. The high polarity and polyhydroxy structure of glycerol can adjust the dielectric constant of the mixed solvent and maintain the stability of oxalate ions. At the same time, since the presence of ethylene glycol may cause protein deformation, the addition of glycerol can also play a protective role for the protein. The hydroxyl groups of glycerol can form multiple hydrogen bonds with polar groups on the main chain or side chain of the protein, strengthening the secondary structure of the protein. At the same time, it forms a "protective film" on the surface of the protein, reducing the destructive effect of ethylene glycol on the protein hydration layer.

[0017] Preferably, the mixing ratio of water, ethylene glycol and glycerin is 5-7:2-4:1.

[0018] By adopting the above technical solution, a large proportion of water can serve as the main polar solvent, providing a strong polar environment, and dissolving oxalic acid and plant protein through hydrogen bonds and electrostatic effects. When the proportion of water is too high, the hydrogen bond strengthening effect of ethylene glycol and the structural protection effect of glycerol are insufficient, resulting in easy aggregation or denaturation of protein, affecting the final yield of plant protein.

[0019] When the proportion of water is too low and the proportion of ethylene glycol or glycerol is too high, the viscosity of the system will increase significantly, the mass transfer resistance during extraction will increase, and the dissolution efficiency of oxalic acid and protein in the raw materials will decrease. At the same time, too much ethylene glycol will destroy the hydration layer on the surface of the protein, causing some protein hydrophobic groups to be exposed, aggregated and precipitated, resulting in a decrease in the yield of the resulting plant protein.

[0020] Preferably, in S2, oxalic acid is adsorbed by an adsorbent, and the adsorbent is at least one of a strongly basic anion exchange resin, alumina, and activated carbon.

[0021] Preferably, the adsorbent is a strongly basic anion exchange resin.

[0022] By adopting the above technical solution, Al in alumina 3+ The electrons of hydroxyl oxygen are strongly attracted, which increases the polarity of OH bond and makes hydrogen protons easily dissociate. In the undissociated hydroxyl group, the hydrogen atom reveals a partial positive charge because the electron cloud is biased towards oxygen. In addition, the surface of Al2O3 is not completely covered by hydroxyl groups. 3+ It will directly exist as a positive charge site to adsorb oxalate. At the same time, oxalic acid, as a bidentate ligand, can also bind to Al through two carboxyl groups. 3+ Forming coordination bonds further enhances the adsorption effect.

[0023] Activated carbon utilizes physical adsorption of its porous structure to adsorb oxalic acid molecules through van der Waals forces and pore interception, while removing impurities such as pigments and odors to purify the extract.

[0024] The active groups of strong basic anion exchange resins are positively charged, allowing them to specifically adsorb oxalate ions produced by the dissociation of oxalic acid through ion exchange. Furthermore, the ion exchange of strong basic anion exchange resins is highly selective for oxalate adsorption, enabling efficient adsorption even at low concentrations. Furthermore, the high functional group density of strong basic anion exchange resins allows for maximum oxalate dissociation through pH adjustment, thereby improving adsorption efficiency.

[0025] The alcohol molecules of ethylene glycol in the extractant can penetrate the cross-linked network of the strongly basic anion exchange resin, increasing its swelling and enlarging its pore size. Furthermore, the presence of ethylene glycol reduces the surface tension of the solution on the strongly basic anion exchange resin, resulting in a more uniform dispersion of the strongly basic anion exchange resin particles in the mixed solvent. Furthermore, the addition of ethylene glycol reduces the dielectric constant of the solvent, weakening the solvation of oxalate ions and enhancing their electrostatic interaction with the strongly basic anion exchange resin, further promoting oxalate adsorption and forming an "adsorption-swelling" positive feedback loop, resulting in more oxalate adsorption.

[0026] Preferably, during the precipitation process of S3, acid precipitation is performed by adding an acid reagent, wherein the pH of the acid reagent is 2-5.

[0027] By adopting the above technical solution, plant proteins are precipitated through acid precipitation. Compared with enzyme precipitation and salting-out methods, acid precipitation is a simpler process. By adjusting the pH to the isoelectric point of the protein, the surface charge is directly neutralized and the protein aggregation is induced, without the need for additional substances or post-processing. At the same time, by adsorbing the negatively charged oxalate ions on the strong alkaline anion exchange resin in S2, acid precipitation can directly and selectively enrich the remaining plant proteins.

[0028] Moreover, due to the presence of ethylene glycol and glycerol, ethylene glycol and glycerol can act as protein stabilizers, occupying the hydrophobic areas on the protein surface, reducing the irreversible aggregation caused by hydrophobic exposure under acidic conditions, and helping to weaken the electrostatic repulsion between protein molecules, promoting milder aggregation of proteins.

[0029] Preferably, the plant raw material is selected from wild plants and / or artificially cultivated plants containing oxalic acid.

[0030] Preferably, the plant raw material is selected from one of the following plants: spinach, celery, broccoli, lettuce, bell pepper, ginger, apple, pineapple, kiwi, black strawberry and leaf beet.

[0031] In summary, this application includes at least one of the following beneficial technical effects: 1. This application extracts oxalic acid and protein from plant raw materials using an extract, then separates the oxalic acid and protein in the extract by chromatography, absorbs the oxalic acid in the extract as much as possible through chromatography, and finally obtains a plant protein with a low oxalic acid content through concentration, precipitation, and filtration. This effectively absorbs the oxalic acid in the plant and reduces the impact of the presence of oxalic acid on the quality and yield of the plant protein. 2. This application uses a mixture of water, ethylene glycol, and glycerol as the extraction agent. The combination of water and ethylene glycol allows the strong polarity of water to stabilize the ions produced by oxalic acid ionization, while the moderate polarity of ethylene glycol enhances the dispersion of oxalic acid molecules. The addition of glycerol maintains the stability of oxalate ions. The presence of glycerol also forms multiple hydrogen bonds with polar groups on the protein backbone or side chains, strengthening the protein's secondary structure and reducing the destructive effect of ethylene glycol on the protein's hydration layer. 3. This application uses a strong basic anion exchange resin as an adsorbent to adsorb oxalic acid. The strong basic anion exchange resin can specifically adsorb oxalate ions produced by the dissociation of oxalic acid through ion exchange. The strong basic anion exchange resin has high selectivity for oxalate and can still efficiently adsorb at low concentrations. At the same time, the ethylene glycol in the extractant can further promote the adsorption effect of the strong basic anion exchange resin on oxalate ions. DETAILED DESCRIPTION

[0032] The raw materials in this application include the following parts: Strong basic anion exchange resin: Strong basic anion exchange resin with purity ≥96% from Bengbu Sanyi Technology Co., Ltd.; Strong basic anion exchange resin with CAS number 9050-97-9 and purity ≥99% from Shanghai Kaiping Resin Co., Ltd.

[0033] The present application is further described in detail below with reference to the following examples and comparative examples.

[0034] Example 1 A process for extracting low-oxalic-acid-content plant protein comprises the following steps: S1: 200 g of spinach was mixed with 3 L of extractant and extracted at 20-70°C, and the extract was filtered to obtain the extract; S2: subjecting the extract to chromatography to obtain a chromatographic solution; S3: Concentrate the chromatographic solution to a solid content of 20-40%, then add 1M hydrochloric acid at a pH of 2-5 for acid precipitation, and finally filter to obtain a protein solid; S4: Drying the protein solid under the conditions of vacuum degree ≥ 0.07 MPa and temperature of 70-85° C. to obtain low oxalic acid content plant protein.

[0035] The extractant is a mixture of water, ethylene glycol, and glycerol, and the mixing ratio of water, ethylene glycol, and glycerol is 3:1:1. In S2, the extract is chromatographed using a strong basic anion exchange resin as an adsorbent, and the chromatography flow rate is 1 mL / min.

[0036] Examples 2-4 In Examples 2-4, based on the preparation method of Example 1, the components of the extractant were adjusted. The specific adjustments are shown in Table 1.

[0037] Performance testing The plant proteins of Examples 1-4 above were analyzed, and the specific detection method was as follows: 1. Protein extraction rate The total protein mass of the initial spinach sample and the final total protein mass of the spinach protein were detected by the Kjeldahl method to obtain the protein extraction rate. The protein extraction rate was calculated as follows: protein extraction rate = final total protein mass of spinach protein / initial total protein mass of spinach sample × 100%.

[0038] 2. Oxalic acid residual rate First, prepare standard solutions at concentrations of 0.1, 1, 10, 50, and 100 mg / L. HPLC conditions are set as a C18 reverse-phase column, a mobile phase consisting of 0.1 mol / L ammonium dihydrogen phosphate and phosphoric acid, a flow rate of 1.0 mL / min, and a column temperature of 40°C. Then, detect oxalic acid content under UV light at a wavelength of 210 nm. The standard solutions are injected and a calibration curve is plotted. The total oxalic acid content of spinach and the oxalic acid content in spinach protein are calculated using the calibration curve to determine the residual oxalic acid rate. The residual oxalic acid rate is calculated as follows: Residual oxalic acid = Oxalic acid content in spinach protein / Total oxalic acid content in spinach × 100%.

[0039] According to the above detection method, the performance test results of Examples 1-4 were obtained, and the test results are shown in Table 1.

[0040] Table 1 Extractant components and performance test table of Examples 1-4 project Example 1 Example 2 Example 3 Example 4 Extractant components Water, glycol, glycerin water Ethylene glycol glycerin Protein extraction rate / % 81.3 79.1 76.7 75.9 Oxalic acid residual rate / % 0.41 0.44 0.47 0.49 Referring to Table 1, it can be seen from the comparison of Examples 1-4 that the yield of plant protein obtained in Example 1 is the best and the residual amount of oxalic acid in the plant protein is the lowest. This may be because the coordination between water and ethylene glycol enables the mixed system to stabilize the ions generated by oxalic acid ionization through the strong polarity of water, and to enhance the dispersion ability of oxalic acid molecules through the medium polarity of ethylene glycol. The addition of glycerol maintains the stability of oxalate ions and promotes the electrostatic structure of oxalic acid and strong basic anion exchange resin. At the same time, the presence of glycerol can also protect the protein and reduce the destructive effect of ethylene glycol on the protein hydration layer. By increasing the solubility of oxalic acid and protein in the extractant and promoting the electrostatic bonding between oxalic acid and strong basic anion exchange resin, the protein and oxalic acid can be separated, thereby reducing the residual amount of oxalic acid in the obtained plant protein.

[0041] Examples 5-6 In Example 5-6, based on the preparation method of Example 1, the mixing ratio of water, ethylene glycol and glycerol was adjusted. The specific adjustments are shown in Table 2.

[0042] Comparative Example 1-2 Comparative Example 1-2 Based on the preparation method of Example 1, the mixing ratio of water, ethylene glycol and glycerol was adjusted. The specific adjustments are shown in Table 2.

[0043] The plant proteins of Examples 5-6 and Comparative Examples 1-2 were subjected to the above-mentioned performance tests, and the test results are shown in Table 2.

[0044] Table 2 Mixing ratio and performance test table of water, ethylene glycol and glycerin of Example 1, Examples 5-6 and Comparative Examples 1-2 Referring to Table 2, it can be seen from the comparison of Example 1, Examples 5-6 and Comparative Examples 1-2 that when the mixing ratio of water, ethylene glycol and glycerol is 5-7:2-4:1, especially when the mixing ratio of water, ethylene glycol and glycerol is 6:3:1, the yield of the obtained plant protein is higher and the residual rate of oxalic acid in the plant protein is lower. This may be because, when the proportion of water is too low, the viscosity of the extractant mixture system increases, which increases the mass transfer resistance during extraction and reduces the dissolution efficiency of oxalic acid and protein in the plant raw material. At the same time, excessive ethylene glycol will destroy the hydration layer on the surface of the protein, causing the hydrophobic groups of some proteins to be exposed and aggregated and precipitated, resulting in a decrease in the yield of plant protein; when the proportion of water is too high, the hydrogen bond strengthening effect of ethylene glycol and the structural protection effect of glycerol are insufficient, which makes the protein prone to aggregation or denaturation, affecting the final yield of plant protein.

[0045] Examples 7-8 In Examples 7-8, based on the preparation method of Example 1, the amount of the extractant added was adjusted. The specific adjustments are shown in Table 3.

[0046] Comparative Examples 3-4 Comparative Example 3-4 Based on the preparation method of Example 1, the amount of the extractant added was adjusted, and the specific adjustments are shown in Table 3.

[0047] The plant proteins of Examples 7-8 and Comparative Examples 3-4 were subjected to the above-mentioned performance tests, and the test results are shown in Table 3.

[0048] Table 3 Extractant addition amount and performance test table of Example 1, Examples 7-8 and Comparative Examples 3-4 Referring to Table 3, it can be seen from the comparison of Example 1, Examples 7-8 and Comparative Examples 3-4 that when the solid-liquid ratio of the plant raw material to the extractant is 1:10-20, especially when the solid-liquid ratio of the plant raw material to the extractant is 1:15, the obtained plant protein yield is the highest and the residual amount of oxalic acid in the plant protein is the lowest. This may be because when the amount of extractant added is too little, the extractant cannot fully infiltrate the plant raw material, and the dissolution space for oxalic acid and protein is insufficient. When the amount of extractant added is too much, the volume of the extractant is too large, which may cause the solution to be diluted, destroying the hydrogen bond between oxalic acid and the extractant, resulting in a decrease in the solubility of oxalic acid, making the oxalic acid concentration in the extract too low, resulting in a weakened adsorption driving force of the adsorbent for oxalic acid, a decrease in the adsorption effect, and an increase in the residual rate of oxalic acid in the obtained plant protein.

[0049] Examples 9-10 In Examples 9-10, based on the preparation method of Example 1, the type of adsorbent in S2 was adjusted, and the specific adjustments are shown in Table 4.

[0050] The plant proteins of Examples 9-10 were subjected to the above-mentioned performance tests, and the test results are shown in Table 4.

[0051] Table 4 Adsorbent types and performance test table of Example 1 and Examples 9-10 project Example 1 Example 9 Example 10 Adsorbent type Strong basic anion exchange resin Alumina activated carbon Protein extraction rate / % 81.3 80.2 79.7 Oxalic acid residual rate / % 0.41 0.49 0.46 Referring to Table 4, by comparing Example 1 with Examples 9-10, it can be seen that the yield of plant protein obtained in Example 1 is the highest and the residual amount of oxalic acid in the plant protein is low. This may be because the ion exchange of the strong basic anion exchange resin has high selectivity for the adsorption of oxalate, and can still efficiently adsorb at low oxalic acid concentrations. At the same time, the ethylene glycol in the extractant can increase the swelling degree of the strong basic anion exchange resin and expand the pore size of the strong basic anion exchange resin. In addition, ethylene glycol can reduce the dielectric constant of the solvent, and the solvation degree of oxalate ions is weakened, thereby enhancing the electrostatic interaction between oxalic acid and the strong basic anion exchange resin, further promoting the adsorption of oxalate, forming a positive feedback of "adsorption-swelling", so that more oxalate is adsorbed, and the residual rate of oxalic acid in the plant protein is significantly reduced.

[0052] Example 11 Example 11 Based on the preparation method of Example 1, the acid precipitation method in S3 was replaced by adding 1 g of papain to the concentrated chromatographic liquid for enzyme precipitation, and then ultrafiltration of the obtained precipitate, while the other conditions remained unchanged.

[0053] Example 12 Example 12 Based on the preparation method of Example 1, the acid precipitation method in S3 is replaced by adding ammonium sulfate to the concentrated chromatographic liquid for salting out, and then the obtained precipitate is dialyzed and filtered through PBS buffer, and the other conditions remain unchanged.

[0054] The plant proteins of Examples 11-12 were subjected to the above-mentioned performance tests, and the test results are shown in Table 5.

[0055] Table 5 Performance test table of Example 1 and Examples 11-12 project Example 1 Example 11 Example 12 Protein extraction rate / % 81.3 79.5 80.1 Oxalic acid residual rate / % 0.41 0.48 0.45 Referring to Table 5, by comparing Example 1 and Examples 11-12, it can be seen that the protein yield obtained in Example 1 is the highest. This may be because the acid precipitation is carried out under acidic conditions, and the residual oxalic acid has a high solubility in the acidic ring and is not easily co-precipitated with the protein, which can effectively reduce the residual amount of oxalic acid in the plant protein.

[0056] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A process for extracting plant protein with low oxalic acid content, characterized in that: The following steps are involved: S1: Mix the plant material and the extractant at 20-70°C for extraction, and filter to obtain the extract; S2: subjecting the extract to chromatography to obtain a chromatographic solution; S3: Concentrating, precipitating and filtering the chromatographic solution to obtain protein solids; S4: Drying the protein solids to obtain low oxalic acid content vegetable protein.

2. The extraction process of a low oxalic acid content plant protein according to claim 1, characterized in that: The extractant is at least one of water, ethylene glycol and glycerol.

3. The process for extracting plant protein with low oxalic acid content according to claim 2, characterized in that: The solid-liquid ratio of the plant raw material to the extractant is 1:10-20.

4. The process for extracting plant protein with low oxalic acid content according to claim 2, characterized in that: The extractant is a mixture of water, ethylene glycol and glycerol.

5. The process for extracting plant protein with low oxalic acid content according to claim 4, characterized in that: The mixing ratio of the water, ethylene glycol and glycerin is 6-7:2-3:

1.

6. The process for extracting plant protein with low oxalic acid content according to claim 4, characterized in that: In S2, oxalic acid is adsorbed by an adsorbent, wherein the adsorbent is at least one of a strongly basic anion exchange resin, alumina, and activated carbon.

7. The process for extracting plant protein with low oxalic acid content according to claim 6, characterized in that: The adsorbent is a strongly basic anion exchange resin.

8. The process for extracting plant protein with low oxalic acid content according to claim 1, characterized in that: During the precipitation process of S3, acid precipitation is performed by adding an acid reagent, wherein the pH of the acid reagent is 2-5.

9. The process for extracting plant protein with low oxalic acid content according to claim 1, wherein the plant raw material is selected from wild plants and / or artificially cultivated plants containing oxalic acid.

10. The process for extracting plant protein with low oxalic acid content according to claim 9, characterized in that: The plant raw material is selected from one of the following plants: spinach, celery, broccoli, lettuce, bell pepper, ginger, apple, pineapple, kiwi fruit, black strawberry and leaf beet.

Images