Method for preparing low-purine soybean product and prepared soybean protein product

Abstract

The invention provides a method for preparing a low-purine soybean product and a prepared soybean protein product, and relates to the technical field of food. The method provided by the invention comprises the following steps: mixing chitosan-polyvinyl alcohol porous microspheres with soybean milk, adsorbing, and carrying out solid-liquid separation to obtain a liquid which is a low-purine soybean product. The chitosan-polyvinyl alcohol porous microspheres are prepared by a reverse emulsion method. The chitosan-polyvinyl alcohol porous microspheres internally have a cross-linked network structure, so that chitosan can fully react with purine, the absorption rate of purine in soybean meal is remarkably improved, and a soybean product is prepared. The chitosan-polyvinyl alcohol porous microspheres prepared by the method can be repeatedly used after ultrasonic treatment and washing, so that the cost is reduced.

Description

Technical Field

[0001] The invention relates to the field of food technology, and in particular to a method for preparing a low-purine soybean product and the prepared soybean protein product. Background Art

[0002] Hyperuricemia (HuA) and gout (Gout) are common diseases caused by abnormal uric acid production due to purine metabolism disorders. Traditional anti-gout drug treatment has a certain therapeutic effect, but is often accompanied by side effects such as rash, fever, gastrointestinal bleeding, and kidney damage. Adjusting the diet, reducing purine intake, limiting alcohol intake, and using certain drugs with caution are particularly important for the treatment of gout. If gout patients can be provided with a low-purine and high-protein food, it can ensure dietary safety while increasing nutritional intake.

[0003] Soybean meal is the product left after soybean oil is extracted. Compared with fresh soybeans, soybean meal still contains about 45-52% protein, 10-15% oligosaccharides, 20-25% polysaccharides and cellulose. It is rich in 8 essential amino acids for the human body, and its amino acid pattern is close to that of animal protein. Therefore, soybean meal is a by-product with extremely high nutritional value. It can not only be used as feed to feed animals, but also as a base material for high-protein food, and has a high development and utilization value.

[0004] However, there are still many defects in the use of soybean meal in the preparation of high-protein foods, including: soy foods made from soybean meal have a high purine content. After being metabolized by the human body, the uric acid formed is easily deposited in the human body, causing gout and its complications. It is not suitable for consumption by the elderly and people with high uric acid.

[0005] Therefore, improving the existing soybean meal processing technology in order to obtain soybean protein food with low purine content, good protein stability, good taste, easy absorption, low fat content and inactivated anti-nutritional factors is the research focus of researchers in this field.

[0006] A Chinese patent (publication number CN 107960478 A, publication date April 27, 2018) discloses a method for preparing low-purine soybean protein food and the prepared soybean protein food. The preparation includes: soaking soybean meal in 30-35°C water, adding a hydrolase for hydrolysis, and separating the soybean meal and the hydrolyzate after the hydrolysis reaction. The hydrolase includes soybean peptide hydrolase, neutral protease or cellulase or any combination thereof; the separated soybean meal is further pulped, separated and slag removed, and the separated supernatant is mixed with the aforementioned hydrolyzate to obtain a mixed solution; the mixed solution is mixed with an adsorbent, stirred evenly, and after adsorption for 1-3h, the solid-liquid separation is performed, and the obtained liquid is a soybean protein food; the adsorbent is a zeolite modified with graphene oxide. However, its adsorption rate for purine is only 50.7% at most, which needs to be improved.

[0007] Chinese Patent (Publication No. CN 102726539 A, published on October 17, 2012) discloses a method for producing low-purine defatted soybean powder, which comprises the following steps: 1. crushing defatted soybean meal having a protein content of 46-51%, a total sugar content of 34.4-38%, a fat content of 4-5%, and a purine content of 253-275 mg / 100 g and passing the mixture through a 120-mesh sieve, and then subjecting the defatted soybean meal powder to ultrasonic treatment after being mixed with water in a mass ratio of 1:12-1:16; 2. adding chitosan to the defatted soybean meal aqueous solution after ultrasonic treatment to adsorb nucleic acids; 3. centrifuging at 3000 r / min for 5 min, filtering off the chitosan adsorbed with nucleic acids, and obtaining low-purine defatted soybean milk; and 4. finally spray-drying the low-purine defatted soybean milk under the conditions of an inlet air temperature of 80-90° C. and an outlet air temperature of 175-185° C. to obtain low-purine defatted soybean powder. The purine content in the prepared soybean powder is less than 150 mg / 100 g, and the purine removal rate is 41-45%, which needs to be improved.

[0008] In summary, developing a method for preparing a low-purine defatted soybean product to further reduce the purine content in the soybean product is an urgent problem to be solved by researchers in this field. Summary of the invention

[0009] In view of the above problems, the present invention provides a method for preparing a low-purine soybean product and a soybean protein product made therefrom. The low-purine defatted soybean product is prepared by preparing chitosan-polyvinyl alcohol porous microspheres and mixing them with soybean milk, thereby significantly reducing the purine content of the soybean product. The preparation method is simple and easy to operate, and is suitable for large-scale promotion.

[0010] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0011] On the one hand, the present invention provides a method for preparing a low-purine soybean product, comprising the following steps: mixing chitosan-polyvinyl alcohol porous microspheres with soybean milk, adsorption, solid-liquid separation, and the liquid is a low-purine soybean product.

[0012] Preferably, the chitosan-polyvinyl alcohol porous microspheres are prepared by an inverse emulsion method.

[0013] Preferably, the method for preparing the chitosan-polyvinyl alcohol porous microspheres comprises the following specific steps:

[0014] S1: edible oil and emulsifier are mixed to obtain mixed solution 1;

[0015] S2: Mixed solution 1 is mixed with an aqueous solution containing ascorbic acid and chitosan to obtain mixed solution 2;

[0016] S3: Mixing the mixed solution 2 with the aqueous solution containing salicylaldehyde and polyvinyl alcohol, demulsifying, separating and drying.

[0017] Preferably, in S1, the edible oil is selected from at least one of soybean oil, peanut oil and sunflower oil; further preferably, in S1, the edible oil is soybean oil.

[0018] Preferably, in S1, the emulsifier is selected from at least one of Span 60, Tween 80, Span 80, Span 45 and Span 85; further preferably, in S1, the emulsifier is Span 60.

[0019] Preferably, in S1, the volume ratio of the edible oil to the emulsifier is 3-5:1; further preferably, in S1, the volume ratio of the edible oil to the emulsifier is 4:1.

[0020] Preferably, in S1, the mixing is stirring.

[0021] Preferably, the stirring rate is 1000-1500 r / min, and the time is 1-20 min; further preferably, the stirring rate is 1200 r / min, and the time is 3-8 min.

[0022] Preferably, in S2, the concentration of ascorbic acid is 0.05-0.3 mol / L, further preferably, in S2, the concentration of ascorbic acid is 0.1-0.2 mol / L; more preferably, in S2, the concentration of ascorbic acid is 0.12 mol / L.

[0023] Preferably, in S2, the mass fraction of chitosan is 1-6%; further preferably, in S2, the mass fraction of chitosan is 2-5%; more preferably, in S2, the mass fraction of chitosan is 3%.

[0024] Preferably, in S2, the mixing is stirring.

[0025] Preferably, the stirring rate is 1000-1500 r / min, and the time is 3-5 min; further preferably, the stirring rate is 1800 r / min, and the time is 2 min.

[0026] Preferably, in S3, the concentration of salicylaldehyde is 0.2-0.8 mol / L; further preferably, in S3, the concentration of salicylaldehyde is 0.3-0.6 mol / L; more preferably, in S3, the concentration of salicylaldehyde is 0.5 mol / L.

[0027] Preferably, in S3, the mass fraction of the polyvinyl alcohol is 3-12%; further preferably, in S3, the mass fraction of the polyvinyl alcohol is 5-12%; more preferably, in S3, the mass fraction of the polyvinyl alcohol is 10%.

[0028] Preferably, in S3, the mixing is stirring.

[0029] The stirring rate is 1000-1500 r / min, and the time is 1-5 min; more preferably, the stirring rate is 1200 r / min, and the time is 2 min.

[0030] Preferably, in S3, the demulsification operation is: adding water, stirring at a rate of 1600-2000 r / min for 8-15 min; further preferably, the demulsification operation is: adding water, stirring at a rate of 1800 r / min for 10 min.

[0031] Preferably, the S3 further comprises washing.

[0032] Preferably, the chitosan-polyvinyl alcohol porous microspheres can be reused after being sonicated and washed.

[0033] Preferably, the soy milk is a solution obtained by grinding soybean meal.

[0034] Preferably, the adsorption time is 60-180 min, and more preferably, the adsorption time is 80 min.

[0035] Preferably, the mass of the chitosan-polyvinyl alcohol porous microspheres is 10-25% of the mass of the soy milk; further preferably, the mass of the chitosan-polyvinyl alcohol porous microspheres is 15-20% of the mass of the soy milk.

[0036] On the other hand, the present invention provides a low-purine soybean protein product prepared by the method described above.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The present invention has found in the research that the chitosan-polyvinyl alcohol porous microspheres have a cross-linked network structure inside, which can make chitosan fully react to purine, significantly improve the absorption rate of purine in soybean meal, and the prepared soybean product has a low purine content.

[0039] 2. The chitosan-polyvinyl alcohol porous microspheres prepared by the present invention can be reused after ultrasonication and washing, which reduces the production cost and is suitable for large-scale promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the SEM image of the chitosan-polyvinyl alcohol porous microspheres obtained in Example 1. DETAILED DESCRIPTION

[0041] In order to make the technical means, creative features, purpose and effect of the present invention easy to understand, the present invention is further explained below in conjunction with specific embodiments, but the following embodiments are only preferred embodiments of the present invention, not all. Based on the embodiments in the implementation mode, other embodiments obtained by those skilled in the art without making creative work all belong to the protection scope of the present invention. It is worth noting that the raw materials used in the present invention are all common commercial products, and their sources are not specifically limited. The technology and scientific terms used in the embodiments have the meanings commonly understood by those of ordinary skill in the art to which the present invention belongs.

[0042] Example 1

[0043] A method for preparing a low-purine soybean product:

[0044] 1) Preparation of chitosan-polyvinyl alcohol porous microspheres:

[0045] S1: Take 20 mL of soybean oil, add 1 mL of Span 60, and stir at 1200 r / min for 5 min;

[0046] S2: Slowly drip 10 mL of an aqueous solution containing ascorbic acid (0.12 mol / L) and chitosan (3 wt%), and continue stirring for 2 min after the addition is complete, at a stirring rate of 1800 r / min;

[0047] S3: Continue to slowly add an aqueous solution containing salicylaldehyde (0.5 mol / L) and polyvinyl alcohol (10 wt%), and continue stirring for 2 min after the addition is completed; then quickly add water to break the emulsion, continue stirring at a rate of 1800 r / min for 10 min, and then centrifuge, wash, and dry.

[0048] 2) The solution obtained by grinding soybean meal is soybean milk: the treated soybean meal is added with water at a weight ratio of soybean meal to water of 1:6-12, and hot water grinding is performed for 20-30 minutes at a water temperature of 85-100° C. The obtained slurry is filtered through a 80-100 mesh sieve and the slurry residue is separated to obtain soybean milk.

[0049] 3) Chitosan-polyvinyl alcohol porous microspheres are mixed with soybean milk, the mass of the chitosan-polyvinyl alcohol porous microspheres is 20% of the soybean milk, and stirred evenly. After adsorption for 80 minutes, the solid and liquid are separated, and the obtained liquid is soybean protein food.

[0050] Example 2

[0051] A method for preparing a low-purine soybean product:

[0052] Compared with Example 1, only the mass of the chitosan-polyvinyl alcohol porous microspheres was changed to 15% of the soy milk instead of 20%;

[0053] The remaining operations are the same as those in Example 1.

[0054] Example 3

[0055] A method for preparing a low-purine soybean product:

[0056] 1) Preparation of chitosan-polyvinyl alcohol porous microspheres:

[0057] S1: Take 20 mL of soybean oil, add 1 mL of Span 60, and stir at 1200 r / min for 5 min;

[0058] S2: Slowly drip 10 mL of an aqueous solution containing ascorbic acid (0.12 mol / L) and chitosan (5 wt%), and continue stirring for 2 min after the addition is completed, at a stirring rate of 1800 r / min;

[0059] S3: Continue to slowly add an aqueous solution containing salicylaldehyde (0.5 mol / L) and polyvinyl alcohol (10 wt%), and continue stirring for 2 min after the addition is completed; then quickly add water to break the emulsion, continue stirring at a rate of 1800 r / min for 10 min, and then centrifuge, wash, and dry.

[0060] 2) The solution obtained by grinding soybean meal is soybean milk: the treated soybean meal is added with water at a weight ratio of soybean meal to water of 1:6-12, and hot water grinding is performed for 20-30 minutes at a water temperature of 85-100° C. The obtained slurry is filtered through a 80-100 mesh sieve and the slurry residue is separated to obtain soybean milk.

[0061] 3) Chitosan-polyvinyl alcohol porous microspheres are mixed with soybean milk, the mass of the chitosan-polyvinyl alcohol porous microspheres is 20% of the soybean milk, and stirred evenly. After adsorption for 80 minutes, the solid and liquid are separated, and the obtained liquid is soybean protein food.

[0062] Comparative Example 1

[0063] A method for preparing a low-purine soybean product:

[0064] 1) Preparation of chitosan-polyvinyl alcohol porous microspheres:

[0065] S1: Take 20 mL of soybean oil, add 1 mL of Span 60, and stir at 1200 r / min for 5 min;

[0066] S2: Slowly drip 10 mL of an aqueous solution containing ascorbic acid (0.5 mol / L) and chitosan (8 wt%), and continue stirring for 2 min after the addition is completed at a stirring rate of 1800 r / min;

[0067] S3: Continue to slowly add an aqueous solution containing salicylaldehyde (0.1 mol / L) and polyvinyl alcohol (7 wt%), and continue stirring for 2 min after the addition is completed; then quickly add water to break the emulsion, continue stirring at a rate of 1800 r / min for 10 min, and then centrifuge, wash, and dry.

[0068] 2) The solution obtained by grinding soybean meal is soybean milk: the treated soybean meal is added with water at a weight ratio of soybean meal to water of 1:6-12, and hot water grinding is performed for 20-30 minutes at a water temperature of 85-100° C. The obtained slurry is filtered through a 80-100 mesh sieve and the slurry residue is separated to obtain soybean milk.

[0069] 3) Chitosan-polyvinyl alcohol porous microspheres are mixed with soybean milk, the mass of the chitosan-polyvinyl alcohol porous microspheres is 20% of the soybean milk, and stirred evenly. After adsorption for 80 minutes, the solid and liquid are separated, and the obtained liquid is soybean protein food.

[0070] Comparative Example 2

[0071] A method for preparing a low-purine soybean product:

[0072] 1) Preparation of chitosan-polyvinyl alcohol porous microspheres:

[0073] S1: Take 20 mL of soybean oil, add 1 mL of Span 60, and stir at 1200 r / min for 5 min;

[0074] S2: Slowly drip 10 mL of an aqueous solution containing ascorbic acid (0.5 mol / L) and chitosan (0.5 wt%), and continue stirring for 2 min after the addition is completed, at a stirring rate of 1800 r / min;

[0075] S3: Continue to slowly add an aqueous solution containing salicylaldehyde (1 mol / L) and polyvinyl alcohol (2 wt%), and continue stirring for 2 min after the addition is completed; then quickly add water to break the emulsion, continue stirring at a rate of 1800 r / min for 10 min, and then centrifuge, wash, and dry.

[0076] 2) The solution obtained by grinding soybean meal is soybean milk: the treated soybean meal is added with water at a weight ratio of soybean meal to water of 1:6-12, and hot water grinding is performed for 20-30 minutes at a water temperature of 85-100° C. The obtained slurry is filtered through a 80-100 mesh sieve and the slurry residue is separated to obtain soybean milk.

[0077] 3) Chitosan-polyvinyl alcohol porous microspheres are mixed with soybean milk, the mass of the chitosan-polyvinyl alcohol porous microspheres is 20% of the soybean milk, and stirred evenly. After adsorption for 80 minutes, the solid and liquid are separated, and the obtained liquid is soybean protein food.

[0078] Comparative Example 3

[0079] A method for preparing a low-purine soybean product:

[0080] Compared with Example 1, only the chitosan-polyvinyl alcohol porous microspheres were changed to graphene oxide-modified zeolite (refer to Chinese patent CN 107960478 A);

[0081] The remaining operations are the same as those in Example 1.

[0082] Comparative Example 4

[0083] A method for preparing a low-purine soybean product:

[0084] 1) Preparation of chitosan material:

[0085] S1: Prepare 20 mL of aqueous solution of glacial acetic acid (0.03 mol / L) and chitosan (3 wt%). After the addition, continue stirring for 15 min at a stirring rate of 300 r / min.

[0086] S2: Continue to slowly add the aqueous solution of agar oligosaccharide (0.2 wt%), and continue to stir for 45 min after the addition is completed; then freeze and thaw three times (freeze at -70°C for 6 h, then thaw at room temperature for 18 h; repeat three times) to obtain chitosan hydrogel;

[0087] S3: The chitosan hydrogel obtained in S2 is freeze-dried and then crushed, and passed through a 100-mesh sieve to obtain a porous chitosan powder material.

[0088] 2) The solution obtained by grinding soybean meal is soybean milk: the treated soybean meal is added with water at a weight ratio of soybean meal to water of 1:6-12, and hot water grinding is performed for 20-30 minutes at a water temperature of 85-100° C. The obtained slurry is filtered through a 80-100 mesh sieve and the slurry residue is separated to obtain soybean milk.

[0089] 3) The porous chitosan powder material is mixed with soybean milk, the mass of the porous chitosan powder material is 20% of the soybean milk, and the mixture is stirred evenly. After adsorption for 80 minutes, the solid and liquid are separated, and the obtained liquid is soybean protein food.

[0090] Comparative Example 5

[0091] A method for preparing a low-purine soybean product:

[0092] 1) Preparation of chitosan-polyvinyl alcohol porous microspheres:

[0093] S1: Take 20 mL of soybean oil, add 1 mL of Span 60, and stir at 1200 r / min for 5 min;

[0094] S2: Slowly drip 10 mL of an aqueous solution containing chitosan (3 wt%), and continue stirring for 2 min after the addition is completed, with a stirring rate of 1800 r / min;

[0095] S3: Continue to slowly add an aqueous solution containing salicylaldehyde (0.5 mol / L) and polyvinyl alcohol (10 wt%), and continue stirring for 2 min after the addition is completed; then quickly add water to break the emulsion, continue stirring at a rate of 1800 r / min for 10 min, and then centrifuge, wash, and dry. The difference between Comparative Example 5 and Example 1 is that ascorbic acid is not added.

[0096] 2) The solution obtained by grinding soybean meal is soybean milk: the treated soybean meal is added with water at a weight ratio of soybean meal to water of 1:6-12, and hot water grinding is performed for 20-30 minutes at a water temperature of 85-100° C. The obtained slurry is filtered through a 80-100 mesh sieve and the slurry residue is separated to obtain soybean milk.

[0097] 3) Chitosan-polyvinyl alcohol porous microspheres are mixed with soybean milk, the mass of the chitosan-polyvinyl alcohol porous microspheres is 20% of the soybean milk, and stirred evenly. After adsorption for 80 minutes, the solid and liquid are separated, and the obtained liquid is soybean protein food.

[0098] Test Case

[0099] The purine content in soybean milk was determined by high performance liquid chromatography; the chromatographic separation conditions were: Zorbax C18 reverse phase (4.6 mm × 250 mm, 5.0 μm) chromatographic column, determination at a wavelength of 254 nm, and KH2PO4 buffer as the mobile phase; accurately weighed 5 mg of each of adenine, guanine, xanthine and hypoxanthine standards, fixed to 5 mL, and prepared into a standard solution with a concentration of 1.0 g / L, which was stored in a refrigerator at 2-4°C for later use; the prepared standard solutions of the four purines were diluted with the mobile phase to a certain concentration gradient for standby use; the standard solutions of the four purines were filtered with a microporous filter membrane with a pore size of 0.22 μm and then tested; and standard curves of adenine, guanine, xanthine and hypoxanthine were drawn.

[0100] 10 mL of each sample of soybean milk, Examples 1-4 and Comparative Examples 1-5 was placed in a 50 mL flask, and the samples were tested on a machine. The contents of the four purines in the soybean milk were calculated based on the standard curve.

[0101] The change in the sum of the contents of the four purines before and after adsorption treatment is called the purine adsorption rate, and the adsorption rate is calculated as follows:

[0102] X / % = (C0-C0) / C0×100%;

[0103] Wherein, C0 is the concentration of purine in soy milk before treatment (mg / L); C is the concentration of purine in soy milk after treatment (mg / L).

[0104] The purine adsorption rates of Examples 1-3 and Comparative Examples 1-5 are shown in Table 1 below:

[0105] Table 1:

[0106] Group Purine adsorption rate Example 1 63.74％ Example 2 53.56％ Example 3 61.45％ Comparative Example 1 48.82％ Comparative Example 2 30.21％ Comparative Example 3 15.85％ Comparative Example 4 18.74％ Comparative Example 5 44.26％

[0107] The purine adsorption rate of Example 1 is 63.74%, that of Example 2 is 53.56%, that of Example 3 is 61.45%, that of Comparative Example 1 is 48.82%, that of Comparative Example 2 is 30.21%, that of Comparative Example 3 is 15.85%, that of Comparative Example 4 is 18.74%, and that of Comparative Example 5 is 44.26%.

[0108] From the adsorption rates of Examples 1-3 and Comparative Examples 1-5, it can be seen that the chitosan-polyvinyl alcohol porous microspheres of the present invention have a cross-linked network structure (such as Figure 1As shown), chitosan can fully react with purine, significantly improve the adsorption rate of purine in soybean meal extract, and prepare a soybean protein product with low purine content. However, when the chitosan content is too high (Comparative Example 1), its cross-linking degree and porosity are reduced (closer to the morphology of round microspheres), and the specific surface area is smaller, so the adsorption effect of purine is not as good as that of Examples 1-3. When the chitosan content is too low (Comparative Example 2), not only the amount of adsorbed purine is reduced, but the mechanical properties and continuity of the microspheres themselves are also destroyed. Comparative Example 4 does not use the chitosan-polyvinyl alcohol porous microspheres provided by the present invention, but prepares a porous chitosan powder material. By comparing the effects of Examples 1-4 and Comparative Example 4, it can be seen that the purine adsorption effect of the porous chitosan powder material prepared by the freeze-thaw method is far less than that shown in Examples 1-3. The role of ascorbic acid is mainly a pore-forming agent and a surfactant. For the chitosan-polyvinyl alcohol porous microspheres in Comparative Example 5 without a pore-forming agent, the specific surface area is reduced, which affects the effect of adsorbing purine.

[0109] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a low-purine soybean product, characterized in that: The method comprises the following steps: mixing chitosan-polyvinyl alcohol porous microspheres with soybean milk, adsorption, solid-liquid separation, and the liquid is a low-purine soybean product.

2. The method according to claim 1, characterized in that: The chitosan-polyvinyl alcohol porous microspheres are prepared by a reverse emulsion method.

3. The method according to claim 1, characterized in that The preparation method of chitosan-polyvinyl alcohol porous microspheres comprises the following specific steps: S1: edible oil and emulsifier are mixed to obtain mixed solution 1; S2: Mixed solution 1 is mixed with an aqueous solution containing ascorbic acid and chitosan to obtain mixed solution 2; S3: Mixing the mixed solution 2 with the aqueous solution containing salicylaldehyde and polyvinyl alcohol, demulsifying, separating and drying.

4. The method according to claim 3, characterized in that Meet at least one of the following conditions: In S1, the emulsifier is at least one selected from Span 60, Tween 80, Span 80, Span 45 and Span 85; In S1, the volume ratio of the edible oil to the emulsifier is 3-5:1; In S1, the mixing is stirring; the stirring rate is 1000-1500 r / min, and the time is 1-20 min.

5. The method according to claim 3, characterized in that: Meet at least one of the following conditions: In S2, the concentration of ascorbic acid is 0.05-0.3 mol / L; In S2, the mass fraction of chitosan is 1-6%; In S2, the mixing is stirring; the stirring rate is 1000-1500 r / min, and the time is 3-5 min.

6. The method according to claim 3, characterized in that Meet at least one of the following conditions: In S3, the concentration of salicylaldehyde is 0.2-0.8 mol / L; In S3, the mass fraction of the polyvinyl alcohol is 3-12%; In S3, the mixing is stirring; the stirring rate is 1000-1500r / min, and the time is 3-5min; In S3, the demulsification operation is: adding water and stirring at a rate of 1600-2000 r / min for 8-15 min; The S3 further comprises washing.

7. The method according to claim 1, characterized in that The soy milk is a solution obtained by grinding soybean meal.

8. The method according to claim 1, characterized in that The adsorption time is 60-180 minutes.

9. The method according to claim 1, characterized in that: The mass of the chitosan-polyvinyl alcohol porous microspheres is 10-25% of the mass of soybean milk.

10. The low-purine soybean protein product prepared by the method according to any one of claims 1 to 9.

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