CN111393685B - Method for preparing antioxidant soybean protein cold gel by tannic acid crosslinking - Google Patents
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Abstract
The invention discloses a method for preparing antioxidant soybean protein cold gel by tannic acid crosslinking, and relates to a preparation method of modified soybean protein gel. The invention aims to solve the technical problem that the existing soybean protein cold gel has insufficient functional characteristics. The method comprises the following steps: preparing a soybean protein isolate water solution, adjusting the pH value to 9-11, adding a tannic acid water solution with the pH value equal to that of the soybean protein isolate water solution according to the proportion of adding 88-146 mu mol of tannic acid into each gram of soybean protein isolate, stirring and reacting under the condition of keeping the mixed solution in contact with oxygen, then carrying out centrifugal treatment to remove gas to obtain a gel pre-solution, and storing the gel pre-solution in a refrigerator at the temperature of 0-4 ℃ to obtain the antioxidant soybean protein cold gel. The covalent binding rate of the protein and the tannic acid is as high as 65.47% -95.06%, the cold-induced gel has excellent performance, can carry heat-sensitive nutrients or functional active substances, and is used in the fields of food and medical treatment.
Description
Technical Field
The invention relates to a preparation method of modified soy protein gel.
Background
The soybean protein is a high-quality vegetable protein, has wide source, low price and high nutritive value, and simultaneously has excellent performances of degradability, biocompatibility, thermal stability, no pollution, environmental protection and the like. The soybean protein has good gel property, and is often used for improving the structure of related food. The denaturation of soybean protein is the basis for forming gel, and protein gel formed by heating or adding coagulants (mainly including acids, metal salts, coagulants and the like) has high elasticity, viscosity and plasticity, can be used as a carrier of a solvent, can also be used as a carrier of a flavor substance, a carbohydrate and other active ingredients, and is widely applied to the food industry.
Currently, the study of thermal gelation is the most extensive, for example, the fourth part of the study on the microstructure and characteristics of soy protein-based colloids in the university of south china university of china university of china "is to add soy protein isolate into water, fully hydrate, mix with tannic acid solution, adjust to acidity, heat to 85 ℃ in water bath with stirring and shearing in a high-speed dispersion machine, cool, and spray-dry to obtain protein-based gel particles. But their intense processing results in partially limited application of protein gels. The conventional preparation method of soybean protein cold gel is generally to heat soybean protein to denature the soybean protein to form aggregates, cool the aggregates and add salt (Ca) 2+ ,Mg 2+ ) Or formation of cold gels under the induction of acid (GDL). For example, chinese patent No. 201611031553.9 discloses a method for preparing a soybean protein isolate cold gel, which comprises ball milling soybean protein isolate, adding water, heating in a water bath at 90-100 ℃ for 10-30 minutes, cooling to 10-30 ℃, adding gluconolactone, stirring uniformly, keeping the temperature at 20-30 ℃ for 0.5-2 hours to form a gel, and keeping the temperature at 1-5 ℃ for 10-15 hours to fully ripen the gel, thereby completing the preparation of the cold gel. The method enhances the gelling property of the isolated soy protein by mixing and ball milling, so that the isolated soy protein can carry out gelling reaction under the condition of low temperature. Although the treatment of the condensed gel makes up the application defects of the thermal gel on heat-sensitive substances and active substances to a certain extent, the condensed gel only changes the food system in the aspect of sensory morphology and does not endow the food with new activity.
Disclosure of Invention
The invention provides a method for preparing antioxidant soybean protein cold-induced gel by tannin crosslinking, aiming at solving the technical problem that the existing soybean protein cold-induced gel has insufficient functional characteristics.
The method for preparing the antioxidant soybean protein cold gel by tannic acid crosslinking comprises the following steps:
1. adding the soybean protein isolate into water, stirring for at least 2 hours by using a magnetic stirrer, and storing in a refrigerator at the temperature of 0-4 ℃ to obtain a soybean protein isolate water solution;
2. regulating the pH value of the soybean protein isolate water solution to 9-11 by using NaOH solution;
3. preparing a tannic acid aqueous solution according to the proportion of adding 88-146 mu mol of tannic acid into each gram of soybean protein isolate, adjusting the pH value of the tannic acid aqueous solution to be equal to the pH value of the soybean protein isolate aqueous solution, mixing the soybean protein isolate aqueous solution and the tannic acid aqueous solution, stirring and reacting for 9-10 h at the temperature of 22-26 ℃, and keeping the mixed solution in contact with oxygen during the stirring and reacting; after the reaction is finished, carrying out centrifugal treatment to remove gas to obtain a gel pre-solution;
4. and (3) placing the gel pre-solution in a refrigerator with the temperature of 0-4 ℃ for storage and solidification to obtain the antioxidant soybean protein cold gel.
Furthermore, in the step one, the mass percentage concentration of the soy protein isolate in the soy protein isolate water solution is 12-13%.
Furthermore, in the step one, the time for storing in the refrigerator is 8-12 h.
Furthermore, in the second step, the concentration of the NaOH solution is 1-1.2 mol/L.
Furthermore, the rotation speed during the centrifugal treatment in the third step is 4000-5000 rpm/min, and the centrifugal treatment time is 15-20 min.
Further, in the fourth step, the mixture is stored in a refrigerator for 8 to 12 hours to be solidified.
In the invention, the soybean protein, a high molecular material, contains a plurality of active side groups, such as amino, carboxyl, hydroxyl and sulfydryl, and can chemically react with a plurality of substances. Tannic acid is a natural water-soluble polyphenol compound, and is a secondary metabolite derived from plants. The protein can be crosslinked with tannic acid under alkaline conditions. After the covalent reaction under alkaline environment occurs, the structure of the protein is changed, and whether the protein structure is unfolded or not directly influences the gel ability of the protein. The gel with antioxidant activity can be prepared while changing the sensory properties of food by crosslinking tannic acid and soy protein isolate. The invention creatively utilizes the covalent reaction of polyphenol protein in an alkaline environment to prepare the protein cold gel, selects the proper concentration of tannic acid, and ensures that the covalent bonding rate of the protein and the tannic acid is as high as 65.47% -95.06%, the cold gel has excellent performance, and the soybean protein with higher antioxidant activity is obviously improved. The cold gel can carry heat-sensitive nutrients or functional active substances, and the application of the protein gel is widened.
The preparation method is simple in preparation process, is carried out at room temperature, is not added with organic reagents, is mild and safe in means, is green and environment-friendly, and can be applied to the fields of food, medical treatment and the like.
Drawings
FIG. 1 is a graph showing the results of the tryptophan content test for 15 kinds of soybean protein tannin complexes prepared in examples 1 to 3;
FIG. 2 is a graph showing the results of measuring the covalent binding rate of 15 kinds of soybean protein tannin complexes prepared in examples 1 to 3;
FIG. 3 is a photograph showing the electrophoretic identification of the soybean protein tannin complexes prepared in examples 1 to 3;
FIG. 4 is a Fourier infrared spectrum of 15 soybean protein tannin complexes prepared in examples 1 to 3;
FIG. 5 is a Fourier infrared spectrum of 15 soybean protein tannin complexes prepared in examples 1 to 3;
FIG. 6 is a graph of DPPH radical scavenging profiles of 15 soy protein tannin complexes prepared in examples 1-3;
FIG. 7 is a graph showing the ABTS radical scavenging ability of 15 soybean protein tannin complexes prepared in examples 1 to 3;
FIG. 8 is a graph showing the iron ion reduction ability of 15 soybean protein tannin complexes prepared in examples 1 to 3;
FIG. 9 is a comparison chart of water binding capacity of 15 antioxidant soy protein cryogels prepared in examples 1-3;
FIG. 10 is a graph showing hardness comparison of 15 kinds of antioxidant soybean protein cryogels prepared in examples 1 to 3;
FIG. 11 is the SEM pictures of 5 antioxidant soy protein cryogels prepared at pH11 and different tannin concentrations in example 1.
Detailed Description
The following examples are used to demonstrate the beneficial effects of the present invention:
example 1: the method for preparing the antioxidant soybean protein cold gel by tannic acid crosslinking comprises the following steps:
1. adding the soybean protein isolate into water according to the mass percentage concentration of the soybean protein isolate of 12%, stirring for 2 hours by using a magnetic stirrer, and then storing for 8 hours in a refrigerator at the temperature of 4 ℃ to ensure complete dissolution to obtain a soybean protein isolate aqueous solution;
2. adjusting the pH value of the soybean protein isolate water solution to 11 by using a NaOH solution to obtain a soybean protein isolate water solution;
3. preparing tannin aqueous solution by taking 5 parts of soybean protein isolate aqueous solution and adding 29 mu mol, 58 mu mol, 88 mu mol, 117 mu mol and 146 mu mol of tannin into each gram of soybean protein isolate in the soybean protein isolate aqueous solution respectively to obtain 5 groups of soybean protein isolate aqueous solutions and tannin aqueous solutions corresponding to the soybean protein isolate aqueous solutions; regulating the pH values of the five parts of tannic acid aqueous solution to 11, mixing the soybean protein isolate aqueous solution and the tannic acid aqueous solution in each group, stirring and reacting the mixed solution at the temperature of 25 ℃ for 9 hours, and keeping the mixed solution in contact with oxygen during the stirring and reacting; after the reaction is finished, carrying out centrifugal treatment for 15min at the rotating speed of 4000rpm/min to remove gas, and obtaining 5 gel pre-solutions; taking a part of each gel pre-solution, placing the gel pre-solution in deionized water for dialysis for 48 hours, and freeze-drying to obtain five soybean protein-tannin complexes for characterization of protein properties;
4. and placing the gel pre-solutions in a refrigerator at the temperature of 4 ℃ for 8h for solidification to obtain five antioxidant soybean protein cold gels.
In the present example, the soybean protein cold gel prepared by adding tannic acid in an amount of 29. Mu. Mol and 58. Mu. Mol per gram of isolated soybean protein in step III was used for comparison.
Example 2: the method for preparing the antioxidant soybean protein cold gel by tannic acid crosslinking comprises the following steps:
1. adding the soybean protein isolate into water according to the mass percentage concentration of the soybean protein isolate being 12%, stirring for 2 hours by using a magnetic stirrer, and then storing for 8 hours in a refrigerator with the temperature of 4 ℃ to ensure complete dissolution so as to obtain a soybean protein isolate aqueous solution;
2. regulating the pH value of the soybean protein isolate aqueous solution to 10 by using NaOH solution to obtain a soybean protein isolate aqueous solution;
3. taking 5 parts of soybean protein isolate water solution, and adding 29 mu mol, 58 mu mol, 88 mu mol, 117 mu mol and 146 mu mol tannic acid into each gram of soybean protein isolate to prepare five kinds of tannic acid water solution so as to obtain 5 groups of soybean protein isolate water solution and tannic acid water solution corresponding to the soybean protein isolate water solution; adjusting the pH values of the five parts of tannic acid aqueous solution to 10, mixing the soybean protein isolate aqueous solution and the tannic acid aqueous solution in each group, stirring and reacting the mixed solution at the temperature of 25 ℃ for 9 hours, and keeping the mixed solution in contact with oxygen during the stirring and reacting; after the reaction is finished, carrying out centrifugal treatment for 15min at the rotating speed of 4000rpm/min to remove gas, and obtaining 5 gel pre-solutions; taking a part of each gel pre-solution, placing the gel pre-solution in deionized water for dialysis for 48 hours, and freeze-drying to obtain five soybean protein-tannin complexes for characterization of protein properties;
4. and placing the gel pre-solutions in a refrigerator at the temperature of 4 ℃ for storing for 8h to obtain five antioxidant soybean protein cold gels.
In the present example, the soybean protein cold gel prepared by adding tannic acid in an amount of 29. Mu. Mol and 58. Mu. Mol per gram of isolated soybean protein in step III was used for comparison.
Example 3: the method for preparing the antioxidant soybean protein cold gel by tannin crosslinking comprises the following steps of:
1. adding the soybean protein isolate into water according to the mass percentage concentration of the soybean protein isolate of 12%, stirring for 2 hours by using a magnetic stirrer, and then storing for 8 hours in a refrigerator at the temperature of 4 ℃ to ensure complete dissolution to obtain a soybean protein isolate aqueous solution;
2. regulating the pH value of the soybean protein isolate aqueous solution to 9 by using NaOH solution to obtain the soybean protein isolate aqueous solution;
3. taking 5 parts of soybean protein isolate water solution, and adding 29 mu mol, 58 mu mol, 88 mu mol, 117 mu mol and 146 mu mol tannic acid into each gram of soybean protein isolate to prepare five kinds of tannic acid water solution so as to obtain 5 groups of soybean protein isolate water solution and tannic acid water solution corresponding to the soybean protein isolate water solution; regulating the pH values of the five parts of tannic acid aqueous solution to 9, mixing the soybean protein isolate aqueous solution and the tannic acid aqueous solution in each group, stirring and reacting the mixed solution at the temperature of 25 ℃ for 9 hours, and keeping the mixed solution in contact with oxygen during the stirring and reacting; after the reaction is finished, carrying out centrifugal treatment for 15min at the rotating speed of 4000rpm/min to remove gas, and obtaining 5 gel pre-solutions; taking a part of each gel pre-solution, placing the gel pre-solution in deionized water for dialysis for 48 hours, and freeze-drying to obtain five soybean protein-tannin complexes for characterization of protein properties;
4. and placing the gel pre-solutions in a refrigerator at the temperature of 4 ℃ for storing for 8h to obtain five antioxidant soybean protein cold gels.
In the present example, the soybean protein cold gel prepared by adding tannic acid in an amount of 29. Mu. Mol and 58. Mu. Mol per gram of isolated soybean protein in step III was used for comparison.
The tryptophan content and the covalent bonding rate of the total 15 soybean protein-tannin complexes prepared in examples 1, 2 and 3 were measured as follows:
1. the method for measuring the tryptophan content comprises the following steps: mixing 1mL of 16M nitric acid with 0.9mL of the soy protein tannin complex sample, and adding water at 50 deg.CTaking out immediately after bathing for 15min, cooling in ice water bath, adding 4mL of 5mol/L NaOH solution and equal volume of anhydrous ethanol, mixing completely, and measuring the concentration of sample solution A by using ultraviolet spectrophotometer 360 And A 430 The absorbance of the sample was calculated by using the following formula.
C＝0.5357×A 430 -0.35714×A 360
Wherein C is the concentration of tryptophan residues, A430 is the absorbance at 430nm, and A360 is the absorbance at 360 nm.
2. The method for measuring the covalent binding rate comprises the following steps: the sample of the soy protein tannin complex before and after dialysis was redissolved in deionized water at a concentration of 1 mg/mL. 0.5mL of the sample solution was added with 2.5mL of Fulin phenol reagent, vortexed and mixed, reacted at room temperature in the dark for 5min, and then 10% Na was added 2 CO 3 After uniformly mixing, reacting for 2h in a dark place at room temperature, measuring a light absorption value at 760nm by using an ultraviolet spectrophotometer, and taking the aqueous solution after the same treatment as a blank control.
Preparing tannin standard substance solutions with different concentrations, and drawing a light absorption value-tannin concentration standard curve by the same detection method. The covalent binding rate of tannic acid to SPI was calculated using the following formula.
3. Sodium dodecyl sulfate-polypropylene gel electrophoresis test: the concentrations of the concentrated gel and the separating gel are respectively 5 percent and 12 percent, and a Marker with the molecular weight distribution of 25-100 kDa is selected for carrying out SDS-PAGE electrophoresis test.
4. Determination of antioxidant Activity: the antioxidant activity of the compound is measured by taking DPPH free radical scavenging capacity, ABTS free radical scavenging capacity and FARP iron ion reducing capacity as indexes, and the standard substance is selected to be Trolox.
5. The specific determination method of the soybean protein cold gel hardness comprises the following steps: a probe model TA10 (diameter: 12.7 mm) was used, and the test speed was 0.5mm/s19. The gel pre-solution formed a gel in a glass container having a height of 50mm and an internal diameter of 35 mm. The sample was tested without removing it from the container. The maximum penetration force, defined as the force required to break the gel, was measured and expressed as the gel stiffness.
The results of the tryptophan content test on the 15 kinds of soybean protein tannin complexes prepared in examples 1 to 3 are shown in fig. 1, and the results of the covalent bonding rate test are shown in fig. 2.
As can be seen from fig. 1, the tryptophan content of the soy protein tannin complex is significantly reduced compared to the soy protein isolate control. Quinone formed by the oxidation of the side chain of tannic acid can react with tryptophan in the soybean protein, so that the content of tryptophan is reduced. The content of tryptophan gradually decreases with the increase of the concentration of the tannic acid, and when the proportion of the tannic acid added to each gram of the soybean protein isolate is 88 to 146 mu mol selected by the invention, the content of the tryptophan is 7.5 to 15mg/mL, which indicates that the tannic acid and the soybean protein are covalently combined. When the amount of tannic acid added is less than 88. Mu. Mol per gram of soy protein isolate, the tryptophan content increases.
As can be seen from FIG. 2, when the ratio of tannic acid added to the soy protein isolate per gram is 88-146 μmol selected by the present invention, the covalent bonding rate is as high as 65.47% -95.06%. When 117 mu mol of tannic acid is added into each gram of soy protein isolate and the pH value is 11, the binding rate reaches the highest value of 95.06 percent; when the tannin addition ratio is lower than 88. Mu. Mol per gram of soy protein isolate, the binding rate is low.
The photographs of the electrophoretic identification of the soybean protein-tannin complexes prepared in examples 1 to 3 are shown in FIG. 3, wherein M is protein Marker, SPI is control soybean protein isolate, lanes 1, 2 and 3 are soybean protein-tannin complexes prepared at pH 9, 10 and 11 with tannin concentration of 58. Mu. Mol/g SPI, and lanes 4, 5 and 6 are soybean protein-tannin complexes prepared at pH 9, 10 and 11 with tannin concentration of 117. Mu. Mol/g SPI. As can be seen from FIG. 3, bands with molecular weight of more than 100kDa appear in lanes 1-6, and dark color accumulation appears at the comb well where the sample was loaded, which is probably due to polymerization of soybean protein isolate and tannic acid to form a macromolecular polymer, which is too large to pass through the gel network and thus accumulate at the comb well. A lighter band of subunits of the complex compared to subunits in the SPI control ( lanes 2 and 4, for example) indicates that the subunits are involved in the covalent reaction; the subunit bands become progressively lighter in lanes 4, 5, 6 at the same tannin concentration, indicating that the extent of covalent reaction increases with increasing pH.
Fourier infrared spectrum analysis is carried out on the 15 soybean protein tannin complexes prepared in examples 1-3, and Fourier infrared spectrum graphs are shown in figures 4 and 5, wherein in figure 4, a is SPI, and b-d are infrared spectra of the complexes prepared at pH values of 9, 10 and 11 and sequentially showing tannin concentration 117 mu mol/g SPI; FIG. 5, wherein a is tannic acid, b is SPI, and c-g are IR spectra of complexes prepared at tannic acid concentrations of 146, 117, 88, 58, 29 μmol/g SPI at pH11, respectively; as can be seen from FIGS. 4 and 5, the spectrum of Soybean Protein Isolate (SPI) mainly shows a main peak of 3272cm -1 (amide A band, representing N-H stretch and hydrogen bond) 1635cm -1 (amide I band, representing C-O stretch/hydrogen bond and COO-) and 1524cm -1 (amide II band, representing C-N telescopic and N-H bending modes). The peak of the soy protein tannin complex absorption near the amide A band was shifted compared to the control SPI, indicating the-NH of the protein 2 Participates in the reaction; tannic acid is 3300cm -1 The absorption peak (-OH stretching vibration) does not appear in the covalent complex, indicating that phenolic hydroxyl groups participate in the reaction of protein and polyphenol. 868cm of tannic acid -1 The absorption peak is out-of-plane bending vibration of the aromatic ring, and the compound is red-shifted to 979cm-1, and belongs to in-plane bending vibration. The peak intensity of the complex prepared at a tannin concentration of 58, 29. Mu. Mol/g SPI was low. The peak intensity of the compound prepared under the conditions that the concentration of the tannic acid is selected to be 146, 117 and 88 mu mol/g SPI is higher and the change is more obvious.
The antioxidant activity of the 15 kinds of soybean protein tannin complexes prepared in examples 1 to 3 was measured. The resultant DPPH radical scavenging ability is shown in FIG. 6, the ABTS radical scavenging ability is shown in FIG. 7, and the iron ion reducing ability is shown in FIG. 8. As can be seen from FIGS. 6, 7 and 8, the composite prepared at a tannic acid concentration of 146 μmol/g SPI exhibited the highest overall oxidation resistance.
For DPPH radical scavenging, the complexes prepared at tannin concentrations of 29 and 58. Mu. Mol/g SPI were compared to be inferior, while the complexes prepared at tannin concentrations of 88, 117 and 146. Mu. Mol/g SPI selected by the present invention had better DPPH radical scavenging, between 60 and 150. Mu. Mol Trolox/mL sample.
As for ABTS free radical scavenging capacity, only the comparative compound prepared under the condition that the concentration of tannic acid is 29 mu mol/g SPI is poor, and the ABTS free radical scavenging capacity difference of the compounds prepared under other conditions is not obvious, and reaches 160-185 mu mol Trolox/mL sample.
As for the iron ion reducing ability, the iron ion reducing ability of the complexes prepared under the conditions of tannic acid concentrations of 88, 117 and 146. Mu. Mol/g SPI selected in the present invention was good, and slightly worse, as compared to the complexes prepared under the conditions of tannic acid concentrations of 29 and 58. Mu. Mol/g SPI, was 80 to 200. Mu. Mol Fe 2+ between/L sample.
The phenolic substances of tannins can be oxidized into respective quinones in an alkaline solution or in the presence of polyphenol oxidase, and the quinones can react with free amino groups of proteins to make the compound have antioxidant activity.
The 15 antioxidant soy protein cryogels prepared in examples 1-3 were subjected to water binding assays. The obtained water binding capacity comparison chart is shown in fig. 9, and it can be seen from fig. 9 that the water binding capacities of the 15 antioxidant soybean protein cold gels are all more than 95%.
The 15 antioxidant soy protein cryogels prepared in examples 1-3 were subjected to hardness measurements. The hardness comparison graph is shown in FIG. 10, and it can be seen from FIG. 10 that the antioxidant soy protein-cold gel prepared under the conditions of the tannic acid concentration of 117. Mu. Mol/g SPI and the pH value of 11 has the highest hardness. On the premise of consistent concentration of tannic acid, the hardness of the antioxidant soybean protein cold gel prepared under the condition of pH value of 11 is higher than that of the antioxidant soybean protein cold gel prepared under the condition of pH value of 9 or 10.
In example 1, scanning electron micrographs of 5 antioxidant soy protein cryogels prepared at pH11 and different tannin concentrations are shown in FIG. 11, where A-E are 50 μm images of antioxidant soy protein cryogels with tannin concentrations of 29, 58, 88, 117, 146 μmol/g SPI, and F is a 50 μm image of SPI at pH11 compared to the same concentration; a-F are 20 μm images corresponding to A-F. As can be seen from FIG. 11, the 3 antioxidant soybean protein cold gels prepared under the conditions of pH11 and tannin concentrations of 88, 117 and 146 μmol/g SPI have uniform and dense texture and ordered arrangement; after covalent crosslinking, the gel presents an oval or round network structure, and the pore wall of the gel is smooth. The porosity of 2 antioxidant soybean protein cold gels prepared under the conditions of pH value of 11 and tannin concentration of 29 and 58 mu mol/g SPI is slightly larger, but is also smaller than that of the soybean protein used as a control, which is consistent with the change trend of gel hardness. The change of the microstructure indicates that the protein polyphenol has changed chemical bonds due to covalent reaction, so that the microstructure is changed.
Claims (6)
1. A method for preparing antioxidant soybean protein cold gel by tannic acid crosslinking is characterized by comprising the following steps:
1. adding the isolated soy protein into water, stirring at least 2h by using a magnetic stirrer, and storing in a refrigerator at the temperature of 0~4 ℃ to obtain an isolated soy protein aqueous solution;
2. adjusting the pH value of the soybean protein isolate water solution to 11 by using NaOH solution;
3. preparing a tannic acid aqueous solution according to the proportion that 117 mu mol of tannic acid is added into each gram of soy protein isolate, adjusting the pH value of the tannic acid aqueous solution to be equal to the pH value of the soy protein isolate aqueous solution, mixing the soy protein isolate aqueous solution and the tannic acid aqueous solution, stirring and reacting for 9-10 h at the temperature of 22-26 ℃, and keeping the mixed solution in contact with oxygen during stirring and reacting; after the reaction is finished, carrying out centrifugal treatment to remove gas to obtain a gel pre-solution;
4. and (3) placing the gel pre-solution in a refrigerator with the temperature of 0~4 ℃ for storage and solidification to obtain the antioxidant soybean protein cold gel.
2. The method for preparing the antioxidant soybean protein cold gel through tannin crosslinking as claimed in claim 1, wherein in the first step, the mass percentage concentration of the soybean protein isolate in the soybean protein isolate water solution is 12% -13%.
3. The method for preparing the antioxidant soybean protein cold gel through tannic acid crosslinking as claimed in claim 1 or 2, wherein in the first step, the storage time in a refrigerator is 8 to 12 hours.
4. The method for preparing antioxidant soybean protein cold gel through tannic acid crosslinking as claimed in claim 1 or 2, wherein in the second step, the concentration of NaOH solution is 1-1.2 mol/L.
5. The method for preparing the antioxidant soybean protein cold gel through tannic acid crosslinking according to claim 1 or 2, wherein the rotation speed during the centrifugal treatment in the third step is 4000 to 5000rpm/min, and the centrifugal treatment time is 15 to 20min.
6. The method for preparing the antioxidant soybean protein cold-condensed gel by tannin crosslinking according to claim 1 or 2, characterized in that the solidification is achieved by storing in a refrigerator for 8 to 12h in the fourth step.
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