Composite soybean protein gel capable of improving gel performance by using TG enzyme and preparation method of composite soybean protein gel

Abstract

The preparation method of the composite soybean protein gel comprises the following steps: adjusting the pH value of an egg white protein solution, carrying out heat preservation, adding protein glutaminase to carry out hydrolysis reaction, centrifuging, collecting supernate, and freeze-drying to obtain deamidated egg white protein; adding TG enzyme into the soybean protein isolate and deamidated egg white protein solution for enzymatic cross-linking reaction, centrifuging after enzyme deactivation, collecting supernate, and freeze-drying to obtain compound protein powder; dissolving the composite protein powder in water, stirring, and heating to form composite soybean protein gel; according to the preparation method disclosed by the invention, glutamine in the egg white protein is hydrolyzed by using the protein glutaminase, so that only the site of lysine is reserved, and then TG enzyme treatment is performed, so that the crosslinking of the egg white protein is avoided, and the content of disulfide bonds in the soybean protein is increased, thereby remarkably improving the gel strength and compression resistance of the composite soybean protein thermal gel.

Description

Technical Field

[0001] The invention relates to a composite soybean protein gel utilizing TG enzyme to improve gel performance and a preparation method thereof, belonging to the technical field of food material processing. Background Art

[0002] Soy protein contains various amino acids required by the human body and has high nutritional value. It is the plant protein with the greatest development potential. Although it has better gel properties than other plant proteins, it still has a large gap compared with egg white protein. Further improving the gel properties of soy protein is an urgent need for the application of soy protein food processing products. At present, the modification methods for improving the gel properties of soy protein include physical modification (heat treatment, high pressure, ultrasound, etc.), chemical modification (glutaraldehyde or oxidant, etc.) and enzyme modification (glutamine aminotransferase, laccase, etc.), among which enzyme modification is particularly concerned. Enzyme modification can significantly improve the gel strength, elasticity and stability of protein, while reducing the production of undesirable by-products, and has high environmental friendliness and application potential. The main action sites of glutamine aminotransferase (TG) are glutamine residues and lysine residues in proteins, which promotes cross-linking of glutamine residues with amino groups on lysine (Lys) residues to form ε~(γ~glutamyl)lysine covalent bonds. This cross-linking reaction forms a stable covalent network between protein molecules, improving the structural stability and gel properties of proteins.

[0003] However, the method of using TG enzyme to cross-link soy protein has some limitations in actual production applications. For example, this method is often used to improve the texture, water retention and structural stability of meat products. Soy protein is injected or added to meat products, and TG enzyme is added to promote the cross-linking of soy protein itself or with meat protein. However, this process usually requires about 1 hour at around 50°C to form a stable gel, which complicates the operation and may increase the risk of microbial reproduction at this temperature. In contrast, thermal gel formed by directly heating soy protein has better practicality.

[0004] The forces that generally form protein gels include hydrogen bonds, disulfide bonds, ionic bonds, covalent bonds formed by enzyme cross-linking, and hydrophobic interactions. Among them, disulfide bonds are also covalent bonds and are relatively stable. Egg white protein has more disulfide bonds, so compared with other proteins, egg white protein has better gel strength. Soy protein can increase the disulfide bond content of the prepared gel by pre-cross-linking egg white protein with TG enzyme, and at the same time, cross-linking forms more covalent bonds under the action of TG enzyme, thereby improving the gel strength of soy protein hot gel. However, soy protein and egg white protein both contain glutamine and lysine. Under the action of TG enzyme, soy protein self-crosslinking, egg white protein self-crosslinking, and soy protein and egg white protein crosslinking will occur simultaneously. The cross-linking of egg white protein itself is not helpful for improving the strength of soy protein gel. Summary of the invention

[0005]

Technical issues

[0006] The existing method of using TG enzyme to cross-link soy protein to improve the strength of soy protein gel has the problem of complex operation and the risk of microbial reproduction. The increase of disulfide bonds is conducive to improving the strength of soy protein gel. Using TG enzyme to cross-link with egg white protein is conducive to increasing the disulfide bond content of soy protein gel, but it is easy to cause egg white protein to cross-link itself, which is not conducive to improving the strength of soy protein gel.

[0007]

Technical solution

[0008] To solve the above problems, the present invention first hydrolyzes glutamine in egg white protein with protein glutaminase, so that only lysine sites are retained. When TG enzyme is added to the mixed system of soy protein and deamidated egg white protein, the cross-linking reaction can only occur in soy protein itself or between soy protein and egg white protein, avoiding the cross-linking of egg white protein itself. This enables soy protein to be cross-linked with more egg white protein, increases the disulfide bond content in soy protein, thereby significantly improving the strength and stability of soy protein gel. The thermal gel preparation method has the advantages of simple operation, low microbial risk and high production efficiency. The present invention uses homemade soy protein as raw material, and performs thermal gel reaction after enzyme modification treatment, aiming to significantly improve the gel performance of soy protein, so as to be better applied to meat products, improve its texture and functionality.

[0009] The first object of the present invention is to provide a method for preparing a composite soybean protein gel, comprising the steps of:

[0010] (1) Deamidation of hen egg white protein (EWP): EWP was dissolved in water, the pH of the EWP solution was adjusted and kept warm, protein glutaminase was added for hydrolysis, the supernatant was collected after centrifugation and freeze-dried to obtain deamidated hen egg white protein (DEWP);

[0011] (2) Protein mixing and cross-linking: Soy protein isolate (SPI) and DEWP are dissolved in water and stirred to obtain a composite protein solution, TG enzyme is added to carry out an enzymatic cross-linking reaction, the enzyme is inactivated and the solution is centrifuged, the supernatant is collected and freeze-dried to obtain a composite protein powder;

[0012] (3) Preparation of composite soybean protein gel: dissolving composite protein powder in water, stirring, and heating to form composite soybean protein gel.

[0013] In one embodiment of the present invention, the extraction method of SPI is: dispersing soybean meal in water, adjusting the pH of the soybean meal dispersion and stirring, centrifuging to obtain the supernatant; adjusting the pH of the supernatant, collecting the precipitate after centrifugation; dispersing the precipitate in water, adjusting the pH of the precipitate dispersion, and freeze-drying to obtain SPI.

[0014] The commercially available SPI adopts spray drying, and the degree of protein denaturation is relatively high. The extraction method of SPI of the present invention adopts freeze drying, which reduces the degree of protein denaturation.

[0015] In one embodiment of the present invention, in the SPI extraction method, the mass ratio of soybean meal to water in the soybean meal dispersion is 1:10 to 1:20.

[0016] In one embodiment of the present invention, in the SPI extraction method, the pH of the soybean meal dispersion is adjusted to 7-9; the pH of the supernatant is adjusted to 3.5-5.5; and the pH of the precipitated dispersion is adjusted to 6-8.

[0017] In one embodiment of the present invention, in the SPI extraction method, the pH of the soybean meal dispersion is adjusted with a 1.5-2.5M NaOH solution; the pH of the supernatant is adjusted with a 1.5-2.5M HCl solution; and the pH of the precipitate dispersion is adjusted with a 1.5-2.5M NaOH solution.

[0018] In one embodiment of the present invention, in the SPI extraction method, the stirring temperature of the soybean meal dispersion is 20-30° C., and the stirring time is 2-3 h.

[0019] In one embodiment of the present invention, in the SPI extraction method, the centrifugal temperature of the soybean meal dispersion is 0-8°C, the centrifugal speed is 8000-12000g, and the centrifugal time is 10-30min.

[0020] In one embodiment of the present invention, in the SPI extraction method, the centrifugation temperature of the supernatant is 0-8°C, the centrifugation speed is 3000-3600g, and the centrifugation time is 5-15min.

[0021] In one embodiment of the present invention, in the SPI extraction method, the mass ratio of precipitate to water in the precipitate dispersion is 1:3 to 1:7.

[0022] In one embodiment of the present invention, in the SPI extraction method, the freezing temperature of freeze-drying is -40 to -20°C, the drying temperature is -30 to -5°C, the pressure is 0.8 to 0.85 MPa, and the drying time is 36 to 48 hours.

[0023] In one embodiment of the present invention, in step (1), the concentration of the EWP solution is 3 to 10 g / mL.

[0024] In one embodiment of the present invention, in step (1), the pH of the EWP solution is adjusted to 6-8.

[0025] In one embodiment of the present invention, in step (1), the pH of the EWP solution is adjusted using a 0.5-1.5 M NaOH solution.

[0026] In one embodiment of the present invention, in step (1), the insulation temperature is 34 to 42° C., and the insulation time is 10 to 30 minutes.

[0027] In one embodiment of the present invention, in step (1), the amount of protein glutaminase added relative to the mass of EWP is 5 to 10 U / g.

[0028] In one embodiment of the present invention, in step (1), the temperature of the hydrolysis reaction is 34-42° C., and the time of the hydrolysis reaction is 120-180 min.

[0029] In one embodiment of the present invention, in step (1), the centrifugation temperature is 0-8°C, the centrifugation speed is 8000-12000g, and the centrifugation time is 5-15min.

[0030] In one embodiment of the present invention, in step (1), the freezing temperature of freeze-drying is -40 to -20°C, the drying temperature is -30 to -5°C, the pressure is 0.8 to 0.85 MPa, and the drying time is 36 to 48 hours.

[0031] In one embodiment of the present invention, in step (2), the SPI concentration of the composite protein solution is 2.25-4.0 g / 100 mL, the DEWP concentration is 0.75-1.33 g / 100 mL, and the mass ratio of SPI to DEWP is 2.5-3.5:1.

[0032] In one embodiment of the present invention, in step (2), the stirring temperature is 40 to 60° C., and the stirring time is 10 to 30 min.

[0033] In one embodiment of the present invention, in step (2), the amount of TG enzyme added relative to the total mass of SPI and DEWP is 10 U / g to 80 U / g.

[0034] In one embodiment of the present invention, in step (2), the temperature for the enzymatic cross-linking reaction is 45 to 55° C. and the time is 1 to 2 hours.

[0035] In one embodiment of the present invention, in step (2), the enzyme inactivation temperature is 70-80° C. and the enzyme inactivation time is 5-15 min.

[0036] In one embodiment of the present invention, in step (2), the centrifugation temperature is 4-20° C., the centrifugation speed is 8000-10000 g, and the centrifugation time is 10-15 min.

[0037] In one embodiment of the present invention, in step (2), the freezing temperature of freeze drying is -40 to -20°C, the drying temperature is -30 to -5°C, the pressure is 0.8 to 0.85 MPa, and the drying time is 36 to 48 hours.

[0038] In one embodiment of the present invention, in step (3), the concentration of the composite protein powder solution is 8 to 16 wt %.

[0039] In one embodiment of the present invention, in step (3), the stirring speed is 200 to 600 rpm, and the stirring time is 20 to 40 min.

[0040] In one embodiment of the present invention, in step (3), the heating temperature is 85 to 105° C., and the heating time is 30 to 90 minutes.

[0041] The second object of the present invention is to provide the composite soybean protein gel prepared by the above preparation method.

[0042] The third object of the present invention is to provide application of the above-mentioned composite soybean protein gel in the field of food.

[0043] Beneficial effects:

[0044] Compared with the prior art, the outstanding advantages of the present invention are:

[0045] 1. The present invention first hydrolyzes glutamine in egg white protein with protein glutaminase to retain only the site of lysine. When TG enzyme is added to the mixed system of soy protein and deamidated egg white protein, the cross-linking reaction can only occur in the soy protein itself or between the soy protein and the egg white protein, avoiding the reduction of the solubility of the composite protein and the gel performance caused by the cross-linking of the egg white protein itself.

[0046] 2. The present invention pre-crosslinks the egg white protein to the soy protein by TG enzyme, thereby increasing the disulfide bond content in the soy protein and promoting the formation of more covalent bonds between the soy proteins. This crosslinking reaction strengthens the molecular network and covalent bond structure of the soy protein, significantly improving the gel strength and compressive resistance of its thermal gel. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a photo of the composite soybean protein gel of Example 1.

[0048] Figure 2 These are photos of the composite soybean protein gels of Examples 2-3.

[0049] Figure 3 These are photos of protein gels of Comparative Examples 2 to 4. DETAILED DESCRIPTION

[0050] The protein glutaminase used in the examples and comparative examples was purchased from Japan's Amano Enzyme Preparation Co., Ltd., and the TG enzyme was purchased from Taixing Dongsheng Biotechnology Co., Ltd.

[0051] Test method:

[0052] Texture test:

[0053] The hardness and elasticity of the gel were tested using a TA-XT2i texture analyzer with a P / 35 probe. The program parameters were set as follows: pre-test rate 1 mm / s, test rate 1 mm / s, post-test rate 2 mm / s, compression percentage 50%, trigger force 5 g, and compression interval 3 s. The samples were tested three times and the mean ± standard deviation was calculated.

[0054] The maximum compressive stress of the gel was tested using a TA-XT2i texture analyzer with a P / 35 probe and program parameters set as follows: pre-test rate 1 mm / s, test rate 1 mm / s, post-test rate 2 mm / s, compression percentage 100%, trigger force 5 g. The strain of the gel was calculated by the change in sample length relative to the initial length, and the stress of the gel was calculated by dividing the force by the initial cross-sectional area of ​​the gel. The sample was measured three times and the average ± standard deviation was calculated.

[0055] Water holding capacity test:

[0056] Weigh the gel and place it in a 50 mL centrifuge tube. Centrifuge at 10,000 g for 15 min and absorb the water stain with filter paper. Calculate the water holding rate (%) based on the mass ratio of the gel before and after centrifugation. Repeat the measurement for three times and calculate the average value ± standard deviation.

[0057] Example 1

[0058] A method for preparing a composite soybean protein gel, comprising the following steps:

[0059] (1) Extraction of soy protein isolate (SPI): 100 g of soybean meal was dispersed in 1000 mL of deionized water, and the pH of the soybean meal dispersion was adjusted to 8 with 2 M NaOH solution. The mixture was stirred at 500 rpm for 2 h at room temperature, centrifuged at 4 °C and 10,000 g for 20 min, and the supernatant was collected. The pH of the supernatant was adjusted to 4.5 with 2 M HCl solution, and the precipitate was collected after centrifugation at 4 °C and 3,300 g for 10 min. The precipitate was dispersed in deionized water with a mass ratio of precipitate to deionized water of 1:5, and the pH of the precipitate dispersion was adjusted to 7 with 2 M NaOH solution. The SPI was obtained by freeze drying at a freezing temperature of -40 °C, a drying temperature of -25 °C, a pressure of 0.8 MPa, and a drying time of 48 h.

[0060] (2) Deamidation of hen egg white protein (EWP): EWP was dissolved in deionized water with an EWP concentration of 3 g / 100 mL. The pH of the EWP solution was adjusted to 7.0 with 1 M NaOH solution, and the mixture was stirred and kept warm at 37°C at 300 rpm for 20 min. Then, protein glutaminase with a mass of 5 U / g of EWP was added, and the mixture was hydrolyzed at 37°C and 300 rpm for 120 min. The mixture was centrifuged at 10,000 g for 10 min at 4°C, and the supernatant was collected and freeze-dried at a freezing temperature of -40°C, a drying temperature of -25°C, a pressure of 0.8 MPa, and a drying time of 48 h to obtain DEWP.

[0061] (3) Protein mixing and cross-linking: SPI and DEWP were dissolved in deionized water with a SPI concentration of 2.25 g / 100 mL and a DEWP concentration of 0.75 g / 100 mL. The mixture was stirred under magnetic stirring at 50°C and 300 rpm for 20 min to obtain a composite protein solution. TGase with a total mass of SPI and DEWP of 40 U / g was added, and the enzymatic cross-linking reaction was carried out at 50°C and 300 rpm for 2 h. The solution was heated at 75°C for 10 min to inactivate the enzyme. The solution was centrifuged at 10,000 g at 4°C for 10 min, and the supernatant was collected. The solution was freeze-dried at a freezing temperature of -40°C, a drying temperature of -25°C, a pressure of 0.8 MPa, and a drying time of 48 h to obtain a composite protein powder.

[0062] (4) Preparation of composite soybean protein gel: The composite protein powder was dissolved in deionized water with a concentration of 12 g / 100 mL, stirred at 300 rpm for 30 min, and then heated at 95° C. for 60 min to form a composite soybean protein gel.

[0063] Example 2

[0064] A method for preparing a composite soybean protein gel, comprising the following steps:

[0065] The difference from Example 1 is that in step (3), the amount of TG enzyme added is 5 U / g of the total mass of SPI and DEWP.

[0066] Example 3

[0067] A method for preparing a composite soybean protein gel, comprising the following steps:

[0068] The difference from Example 1 is that in step (3), the amount of TG enzyme added is 100 U / g of the total mass of SPI and DEWP.

[0069] Comparative Example 1

[0070] A method for preparing EWP gel, comprising the following steps:

[0071] EWP was dissolved in deionized water with an EWP concentration of 12 g / 100 mL, stirred at 300 rpm for 30 min, and then heated at 95 °C for 60 min to form a protein gel.

[0072] Comparative Example 2

[0073] A method for preparing soybean protein gel, comprising the following steps:

[0074] (1) Extraction of soy protein isolate (SPI): 100 g of soybean meal was dispersed in 1000 mL of deionized water, and the pH of the soybean meal dispersion was adjusted to 8 with 2 M NaOH solution. The mixture was stirred at 500 rpm for 2 h at room temperature, centrifuged at 4 °C and 10,000 g for 20 min, and the supernatant was collected. The pH of the supernatant was adjusted to 4.5 with 2 M HCl solution, and the precipitate was collected after centrifugation at 4 °C and 3,300 g for 10 min. The precipitate was dispersed in deionized water with a mass ratio of precipitate to deionized water of 1:5, and the pH of the precipitate dispersion was adjusted to 7 with 2 M NaOH solution. The SPI was obtained by freeze drying at a freezing temperature of -40 °C, a drying temperature of -25 °C, a pressure of 0.8 MPa, and a drying time of 48 h.

[0075] (2) Preparation of soybean protein gel: SPI was dissolved in deionized water with a SPI concentration of 12 g / 100 mL, stirred at 300 rpm for 30 min, and then heated at 95° C. for 60 min to form soybean protein gel.

[0076] Comparative Example 3

[0077] A method for preparing a composite soybean protein gel, comprising the following steps:

[0078] (1) Extraction of soy protein isolate (SPI): 100 g of soybean meal was dispersed in 1000 mL of deionized water, and the pH of the soybean meal dispersion was adjusted to 8 with 2 M NaOH solution. The mixture was stirred at 500 rpm for 2 h at room temperature, centrifuged at 4 °C and 10,000 g for 20 min, and the supernatant was collected. The pH of the supernatant was adjusted to 4.5 with 2 M HCl solution, and the precipitate was collected after centrifugation at 4 °C and 3,300 g for 10 min. The precipitate was dispersed in deionized water with a mass ratio of precipitate to deionized water of 1:5, and the pH of the precipitate dispersion was adjusted to 7 with 2 M NaOH solution. The SPI was obtained by freeze drying at -25 °C and 0.8 MPa for 48 h.

[0079] (2) Protein mixing and cross-linking: SPI and EWP were dissolved in deionized water with a SPI concentration of 2.25 g / 100 mL and an EWP concentration of 0.75 g / 100 mL. The mixture was stirred under magnetic stirring at 50°C and 300 rpm for 20 min to obtain a composite protein solution. TGase with a total mass of SPI and EWP of 40 U / g was added, and the enzymatic cross-linking reaction was carried out at 50°C and 300 rpm for 2 h. The solution was heated at 75°C for 10 min to inactivate the enzyme. The solution was centrifuged at 10,000 g at 4°C for 10 min, and the supernatant was collected and freeze-dried at a freezing temperature of -40°C, a drying temperature of -25°C, a pressure of 0.8 MPa, and a drying time of 48 h to obtain a composite protein powder.

[0080] (3) Preparation of composite soybean protein gel: The composite protein powder was dissolved in deionized water with a concentration of 12 g / 100 mL, stirred at 300 rpm for 30 min, and then heated at 95° C. for 60 min to form a composite soybean protein gel.

[0081] Comparative Example 4

[0082] A method for preparing a composite soybean protein gel, comprising the following steps:

[0083] (1) Extraction of soy protein isolate (SPI): 100 g of soybean meal was dispersed in 1000 mL of deionized water, and the pH of the soybean meal dispersion was adjusted to 8 with 2 M NaOH solution. The mixture was stirred at 500 rpm for 2 h at room temperature, centrifuged at 4 °C and 10,000 g for 20 min, and the supernatant was collected. The pH of the supernatant was adjusted to 4.5 with 2 M HCl solution, and the precipitate was collected after centrifugation at 4 °C and 3,300 g for 10 min. The precipitate was dispersed in deionized water with a mass ratio of precipitate to deionized water of 1:5, and the pH of the precipitate dispersion was adjusted to 7 with 2 M NaOH solution. The SPI was obtained by freeze drying at -25 °C and 0.8 MPa for 48 h.

[0084] (2) Deamidation of hen egg white protein (EWP): EWP was dissolved in deionized water with an EWP concentration of 3 g / 100 mL. The pH of the EWP solution was adjusted to 7.0 with 1 M NaOH solution, and the mixture was stirred at 300 rpm at 37°C for 20 min. Then, protein glutaminase with a mass of 5 U / g of EWP was added, and the mixture was hydrolyzed at 37°C and 300 rpm for 120 min. The mixture was centrifuged at 10,000 g at 4°C for 10 min, and the supernatant was collected and freeze-dried at -25°C and 0.8 MPa for 48 h to obtain DEWP.

[0085] (3) Protein mixing and cross-linking: SPI and DEWP were dissolved in deionized water with a SPI concentration of 2.25 g / 100 mL and a DEWP concentration of 0.75 g / 100 mL. The mixture was stirred under magnetic stirring at 50°C and 300 rpm for 20 min to obtain a mixed protein solution. The mixed protein solution was freeze-dried at -25°C and 0.8 MPa for 48 h to obtain a mixed protein powder.

[0086] (4) Preparation of composite soy protein gel: Dissolve the mixed protein powder in deionized water to a concentration of 12 g / 100 mL, stir at 300 rpm for 30 min, and then heat at 95° C. for 60 min to form a composite protein gel.

[0087] Comparative Example 5

[0088] A method for preparing a protein gel, comprising the following steps:

[0089] The difference from Example 2 is that in step (3), the concentration of SPI is 5 g / 100 mL and the concentration of DEWP is 1.66 g / 100 mL.

[0090] After 10 minutes of enzymatic cross-linking reaction in step (3), the protein gelled, making it impossible to carry out subsequent experiments. After freeze-drying, large gel blocks were formed and could not be redissolved.

[0091] Table 1 Texture, water holding capacity and maximum compressive stress of protein gel

[0092]

[0093]

[0094] The texture, water holding capacity and maximum compressive stress of the protein gels prepared in Examples 1 to 3 and Comparative Examples 1 to 5 are shown in Table 1.

[0095] The protein gels prepared in Example 1 and Comparative Example 1 are comparable in hardness, elasticity, and water holding capacity, and Example 1 has a higher maximum compressive stress, indicating that the composite soybean protein gel is superior to egg white protein in mechanical properties and has a wider application potential.

[0096] According to the comparison of Examples 1 to 3, when the amount of TG enzyme added is insufficient, the water holding rate and the maximum compressive stress are both reduced. This is because the cross-linking of soy protein with deamidated egg white protein and soy protein itself is incomplete, resulting in an insufficient number of covalent bonds formed in the system, thereby affecting the gel texture. When the amount of TG enzyme added is too much, in addition to forming more covalent bonds, it will also cause excessive cross-linking of soy protein with deamidated egg white protein and soy protein itself, produce insoluble aggregates, reduce the solubility of the composite protein, and thus reduce the gel performance.

[0097] Protein concentration is also crucial in the cross-linking reaction. When the total protein concentration of the composite protein solution reaches 6.66% (Comparative Example 5), the high protein concentration leads to too many cross-linking sites, and the enzymatic reaction quickly forms a gel. After freeze-drying, the composite protein cannot be dissolved again and is difficult to use.

[0098] The protein gel formed by pure SPI (Comparative Example 2) is weak in strength, with a hardness of only 10% of that in Example 1, and a maximum compressive stress of only 28%; when the undeamidated egg white protein is directly cross-linked with the soy protein by TG enzyme (Comparative Example 3), the egg white protein itself will also undergo cross-linking, resulting in excessive cross-linking, forming insoluble aggregates, reducing the solubility of the composite protein, thereby reducing the gel performance. When SPI is only mixed with deamidated egg white protein without TG enzyme cross-linking (Comparative Example 4), although the gel performance is improved compared to the pure SPI protein gel (Comparative Example 2) due to the increase in the disulfide bond content in the system, the covalent bond content in the system is less due to the lack of TG enzymatic cross-linking, resulting in the texture, water holding rate and maximum compressive stress of the gel being much lower than that in Example 1.

[0099] The appearance of the protein gel prepared in Example 1 is as follows Figure 1 As shown, the appearance of the protein gel prepared in Examples 2 to 3 is as follows Figure 2 As shown, the appearance of the protein gel prepared in Comparative Examples 2 to 4 is as follows Figure 3 As shown. The color is closely related to the amount of TG enzyme added. When the amount of TG enzyme added is high, the protein gel produces more aggregates. When there are more aggregates, a stronger light scattering effect will be produced, and the color will be more white. When there are fewer aggregates, the gel transparency is higher and the color is relatively darker. Figure 2 Relative to Figure 1 The gel color was dark, indicating that insufficient aggregates were formed. Figure 3 Relative to Figure 1 The color is whiter. Figure 3 The gel contained many bubbles and their distribution was uneven, which might be due to the fact that more aggregates resulted in a higher viscosity of the solution, which resulted in more bubbles during the stirring process and was difficult to defoam.

[0100] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a composite soybean protein gel, characterized in that: Includes steps: (1) Deamidation of egg white protein: dissolving egg white protein in water, adjusting the pH of the egg white protein solution and keeping it warm, adding protein glutaminase to perform a hydrolysis reaction, collecting the supernatant after centrifugation and freeze-drying to obtain deamidated egg white protein; (2) Protein mixing and cross-linking: soy protein isolate and deamidated chicken egg white protein are dissolved in water and stirred to obtain a composite protein solution, TG enzyme is added to carry out an enzymatic cross-linking reaction, the enzyme is inactivated and then centrifuged, the supernatant is collected and freeze-dried to obtain a composite protein powder; (3) Preparation of composite soybean protein gel: dissolving composite protein powder in water, stirring, and heating to form composite soybean protein gel.

2. The preparation method according to claim 1, characterized in that: In step (1), the concentration of the egg white protein solution is 3 to 10 g / mL.

3. The preparation method according to claim 1, characterized in that: In step (1), the pH of the egg white protein solution is adjusted to 6-8; the amount of protein glutaminase added relative to the egg white protein mass is 5-10 U / g.

4. The preparation method according to claim 1, characterized in that: In step (1), the pH of the egg white protein solution is adjusted with a 0.5-1.5 M NaOH solution.

5. The preparation method according to claim 1, characterized in that: In step (1), the insulation temperature is 34-42° C., and the insulation time is 10-30 min; the hydrolysis reaction temperature is 34-42° C., and the hydrolysis reaction time is 120-180 min.

6. The preparation method according to claim 1, characterized in that: In step (2), the SPI concentration of the composite protein solution is 2.25-4.0 g / 100 mL, the deamidated chicken egg white protein concentration is 0.75-1.33 g / 100 mL, and the mass ratio of soy protein isolate to deamidated chicken egg white protein is 2.5-3.5:1; the stirring temperature is 40-60° C., and the stirring time is 10-30 min.

7. The preparation method according to claim 1, characterized in that: In step (2), the amount of TG enzyme added relative to the total mass of soy protein isolate and deamidated chicken egg white protein is 10U / g to 80U / g; the temperature for the enzymatic cross-linking reaction is 45 to 55°C, and the time is 1 to 2h; the temperature for inactivating the enzyme is 70 to 80°C, and the time for inactivating the enzyme is 5 to 15min.

8. The preparation method according to claim 1, characterized in that: In step (3), the dissolved concentration of the composite protein powder is 8 to 16 wt %; the heating temperature is 85 to 105° C., and the heating time is 30 to 90 min.

9. The composite soybean protein gel prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the composite soybean protein gel according to claim 9 in the food field.

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