A composite soybean protein gel with enhanced gelation properties using TG enzyme and its preparation method

Abstract

A method for preparing a composite soybean protein gel includes the following steps: adjusting the pH of an egg white protein solution and maintaining the temperature; adding protein glutaminase for hydrolysis; collecting the supernatant after centrifugation and freeze-drying to obtain deamidated egg white protein; adding TG enzyme to a solution of soybean protein isolate and deamidated egg white protein for enzymatic cross-linking; centrifuging after enzyme inactivation; collecting the supernatant and freeze-drying to obtain composite protein powder; dissolving the composite protein powder in water and stirring; and heating to form a composite soybean protein gel. This invention, by first hydrolyzing the glutamine in egg white protein with protein glutaminase to retain only lysine sites, and then treating it with TG enzyme, avoids the cross-linking of the egg white protein itself, increases the disulfide bond content in soybean protein, and thus significantly improves the gel strength and compressive strength of the composite soybean protein thermal gel.

Description

TECHNICAL FIELD

[0001] The present application relates to a composite soybean protein gel with improved gel properties using TGase and a preparation method thereof, and belongs to the technical field of food material processing. BACKGROUND

[0002] Soybean protein contains various amino acids required by the human body and has high nutritional value, and is the most potential plant protein. Although soybean protein has better gel properties compared to other plant proteins, there is still a large gap compared to egg white protein. Further improving the gel properties of soybean protein is an urgent need for the application of soybean protein food processing products. The current modification methods for improving the gel properties of soybean protein include physical modification (heat treatment, high pressure, ultrasonic wave, etc.), chemical modification (glutaraldehyde or oxidizing agent, etc.), and enzymatic modification (glutamine transaminase, laccase, etc.), among which enzymatic modification is particularly concerned. Enzymatic modification can significantly improve the gel strength, elasticity and stability of proteins, while reducing the production of undesirable by-products, and has high environmental friendliness and application potential. The main action site of transglutaminase (TG) is the glutamine residue and lysine residue in the protein, which promotes the cross-linking of the amino group on the glutamine residue and lysine (Lys) residue to form an epsilon-(gamma-glutamyl) lysine covalent bond. 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 TGase to cross-link soybean protein has some limitations in actual production applications. For example, this method is often used to improve the texture, water holding capacity and structural stability of meat products, and soybean protein is injected or added to meat products, and TGase is added to promote the cross-linking of soybean protein itself or with meat protein. However, this process usually requires maintaining at about 50°C for about 1 hour to form a stable gel, which leads to complex operation and may increase the risk of microbial reproduction at this temperature. In contrast, heat-induced gel formed by directly heating soybean protein has better practicality.

[0004] The forces generally forming protein gel include hydrogen bond, disulfide bond, ionic bond, covalent bond formed by enzyme cross-linking, and hydrophobic interaction, etc. The disulfide bond is also a covalent bond and is relatively stable. Egg white protein has more disulfide bonds, so compared with other proteins, the gel strength of egg white protein is better. The pre-cross-linking of soybean protein by TGase to egg white protein can increase the disulfide bond content of the prepared gel, and more covalent bonds are formed under the action of TGase, so as to improve the gel strength of the soybean protein heat gel. However, both soybean protein and egg white protein contain glutamine and lysine, and under the action of TGase, cross-linking of soybean protein itself, cross-linking of egg white protein itself, and cross-linking of soybean protein and egg white protein will occur at the same time. The cross-linking of egg white protein itself is not helpful to improve the gel strength of soybean protein. SUMMARY

[0005] TECHNICAL PROBLEM

[0006] The existing method of using TGase to cross-link soybean protein to improve the gel strength of soybean protein has the problem of complex operation and the risk of microbial reproduction. The increase of disulfide bond is beneficial to improve the gel strength of soybean protein. Cross-linking of TGase and egg white protein is beneficial to increase the disulfide bond content of soybean protein gel, but it is easy to cause cross-linking of egg white protein itself, which is not conducive to improving the gel strength of soybean protein.

[0007] TECHNICAL SCHEME

[0008] To solve the above problems, the glutamine in the egg white protein is first hydrolyzed by protein glutamine enzyme to make it only retain the site of lysine. Then, when TGase is added to the mixed system of soybean protein and deamidated egg white protein, the cross-linking reaction can only occur in the soybean protein itself or between the soybean protein and the egg white protein, avoiding the cross-linking of the egg white protein itself. This makes the soybean protein be able to cross-link with more egg white protein, increases the disulfide bond content in the soybean protein, and thus significantly improves the strength and stability of the soybean protein gel. The preparation method of heat gel has the advantages of simple operation, low microbial risk and high production efficiency. The self-made soybean protein is used as raw material in the present application, and the heat gel reaction is carried out after enzyme modification treatment, aiming to significantly improve the gel performance of soybean protein, so as to better apply it to meat products and improve the texture and functionality thereof.

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

[0010] (1) Deamidation of egg white protein (EWP): dissolve EWP in water, adjust the pH of EWP solution and incubate, add protein glutamine enzyme for hydrolysis reaction, centrifuge and collect the supernatant and freeze-dry to obtain deamidated egg white protein (DEWP);

[0011] (2) Protein mixed cross-linking: soybean protein isolate (SPI) and DEWP are dissolved in water and stirred to prepare a composite protein solution, TG enzyme is added for enzymatic cross-linking reaction, and after enzyme inactivation, centrifugation is performed, the supernatant is collected and freeze-dried to obtain a composite protein powder;

[0012] (3) Preparation of composite soybean protein gel: the composite protein powder is dissolved in water and stirred, and heated to form a composite soybean protein gel.

[0013] In an embodiment of the present application, the extraction method of SPI is as follows: soybean meal is dispersed in water, the pH of the soybean meal dispersion is adjusted and stirring is performed, and the supernatant is collected by centrifugation; the pH of the supernatant is adjusted, and the precipitate is collected after centrifugation; the precipitate is dispersed in water, the pH of the precipitate dispersion is adjusted, and SPI is obtained by freeze-drying.

[0014] Commercially available SPI is prepared by spray drying, and the denaturation degree of protein is high. The extraction method of SPI in the present application uses freeze-drying, thereby reducing the denaturation degree of protein.

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

[0016] In an embodiment of the present application, in the extraction method of SPI, 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 precipitate dispersion is adjusted to 6-8.

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

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

[0019] In an embodiment of the present application, in the extraction method of SPI, the centrifugation temperature of the soybean meal dispersion is 0-8℃, the centrifugation speed is 8000-12000g, and the centrifugation time is 10-30min.

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

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

[0022] In one embodiment of the present application, the freezing temperature of the freeze-drying is -40 to -20℃, the drying temperature is -30 to -5℃, the pressure is 0.8 to 0.85 Mpa, and the drying time is 36 to 48 h in the extraction method of SPI.

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

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

[0025] In one embodiment of the present application, the pH of the EWP solution is adjusted with 0.5 to 1.5 M NaOH solution in step (1).

[0026] In one embodiment of the present application, the temperature of the incubation is 34 to 42℃, and the incubation time is 10 to 30 min in step (1).

[0027] In one embodiment of the present application, the amount of the protein glutamine enzyme added is 5 to 10 U / g with respect to the mass of the EWP in step (1).

[0028] In one embodiment of the present application, the temperature of the hydrolysis reaction is 34 to 42℃, and the hydrolysis reaction time is 120 to 180 min in step (1).

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

[0030] In one embodiment of the present application, the freezing temperature of the freeze-drying is -40 to -20℃, the drying temperature is -30 to -5℃, the pressure is 0.8 to 0.85 Mpa, and the drying time is 36 to 48 h in step (1).

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

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

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

[0034] In one embodiment of the present application, in step (2), the enzymatic cross-linking reaction is carried out at a temperature of 45-55℃ for 1-2h.

[0035] In one embodiment of the present application, in step (2), the enzyme inactivation is carried out at a temperature of 70-80℃ for 5-15min.

[0036] In one embodiment of the present application, in step (2), the centrifugation is carried out at a temperature of 4-20℃ at a speed of 8000-10000g for 10-15min.

[0037] In one embodiment of the present application, in step (2), the freeze-drying is carried out at a freezing temperature of -40--20℃, a drying temperature of -30--5℃, a pressure of 0.8-0.85Mpa, and a drying time of 36-48h.

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

[0039] In one embodiment of the present application, in step (3), the stirring is carried out at a speed of 200-600rpm for 20-40min.

[0040] In one embodiment of the present application, in step (3), the heating is carried out at a temperature of 85-105℃ for 30-90min.

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

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

[0043] Advantages:

[0044] Compared with the prior art, the present application has the following outstanding advantages:

[0045] 1. The present application first hydrolyzes the glutamine in egg white protein by using protein glutamine enzyme, so that only the lysine site is reserved. When TG enzyme is added to the mixed system of soybean protein and deamidated egg white protein, the cross-linking reaction can only occur between the soybean protein itself or the soybean protein and the egg white protein, avoiding the cross-linking of the egg white protein itself, which leads to the decrease of the solubility of the compound protein and the decline of the gel performance.

[0046] 2. The present application increases the disulfide bond content in the soy protein and promotes the formation of more covalent bonds between the soy proteins by cross-linking the egg white proteins to the soy proteins in advance by TGase. This cross-linking reaction strengthens the molecular network and covalent bond structure of the soy proteins, significantly improving the gel strength and compression resistance of the heat-induced gel. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 Photograph of the composite soy protein gel of Example 1.

[0048] Figure 2 Photograph of the composite soy protein gel of Examples 2-3.

[0049] Figure 3 Photograph of the protein gel of Comparative Examples 2-4. DETAILED DESCRIPTION

[0050] The proteins used in the examples and comparative examples were purchased from Tanoue Enzyme Preparation Co., Ltd., Japan, and the TGase was purchased from Dongsheng Biological Technology Co., Ltd., Taixing.

[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, and the program parameters were set as follows: pre-test speed 1 mm / s, test speed 1 mm / s, post-test speed 2 mm / s, compression percentage 50%, trigger force 5 g, and compression interval 3 s. The sample was measured three times in repetition, and the average value ± standard deviation was calculated.

[0054] The maximum compression stress of the gel was tested using a TA-XT2i texture analyzer with a P / 35 probe, and the program parameters were set as follows: pre-test speed 1 mm / s, test speed 1 mm / s, post-test speed 2 mm / s, compression percentage 100%, and trigger force 5 g. The strain of the gel was calculated by the change in the length of the sample 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 in repetition, and the average value ± standard deviation was calculated.

[0055] Water holding capacity test:

[0056] The gel was weighed and placed in a 50 mL centrifuge tube, centrifuged at 10,000 g for 15 min, and the water stain was absorbed with filter paper. The water holding capacity (%) was calculated based on the mass ratio of the gel before and after centrifugation. The sample was measured three times in repetition, and the average value ± standard deviation was calculated.

[0057] Example 1

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

[0059] (1) Extraction of soy protein isolate (SPI): 100 g of soybean meal was dispersed in 1000 mL of deionized water, the pH of the soybean meal dispersion was adjusted to 8 with 2M NaOH solution, stirred at 500 rpm at room temperature for 2 h, centrifuged at 10000 g at 4℃ for 20 min, and the supernatant was taken. The supernatant was adjusted to pH 4.5 with 2M HCl solution, and the precipitate was collected after centrifugation at 3300 g at 4℃ for 10 min. The precipitate was dispersed in deionized water at a mass ratio of 1:5, the pH of the precipitate dispersion was adjusted to 7 with 2M NaOH solution, and the precipitate was freeze-dried at a freezing temperature of -40℃, a drying temperature of -25℃, a pressure of 0.8 Mpa, and a drying time of 48 h to obtain SPI.

[0060] (2) Egg white protein (EWP) deamidation: EWP was dissolved in deionized water at a concentration of 3 g / 100 mL. The pH of the EWP solution was adjusted to 7.0 with 1M NaOH solution, and the solution was incubated at 37℃ with stirring at 300 rpm for 20 min. Then, 5 U / g of protein glutamine enzyme was added, and the solution was hydrolyzed at 37℃ with stirring at 300 rpm for 120 min. The solution was centrifuged at 10000 g at 4℃ for 10 min, and the supernatant was collected and freeze-dried at a freezing temperature of -40℃, a drying temperature of -25℃, 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 at concentrations of 2.25 g / 100 mL and 0.75 g / 100 mL, respectively, and the solution was stirred at 50℃ with a magnetic stirrer at 300 rpm for 20 min to prepare a composite protein solution. Then, 40 U / g of TG enzyme was added, and the solution was subjected to enzymatic cross-linking at 50℃ with stirring at 300 rpm for 2 h. The enzyme was inactivated by heating at 75℃ for 10 min, and the solution was centrifuged at 10000 g at 4℃ for 10 min. The supernatant was collected and freeze-dried at a freezing temperature of -40℃, a drying temperature of -25℃, a pressure of 0.8 Mpa, and a drying time of 48 h to obtain a composite protein powder.

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

[0063] Example 2

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

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

[0069] Comparative Example 1

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

[0071] Dissolve the EWP in deionized water, the EWP concentration is 12 g / 100 mL, stir at 300 rpm for 30 min, then heat at 95°C for 60 min to form a protein gel.

[0072] Comparative Example 2

[0073] A method for preparing a soy protein gel, comprising the steps of:

[0074] (1) Extract soy protein isolate (SPI): Disperse 100 g of soybean meal in 1000 mL of deionized water, adjust the pH of the soybean meal dispersion to 8 with 2M NaOH solution, stir at 500 rpm at room temperature for 2 h, centrifuge at 4°C and 10000 g for 20 min, and take the supernatant. Adjust the pH of the supernatant to 4.5 with 2M HCl solution, centrifuge at 4°C and 3300 g for 10 min to collect the precipitate. Disperse the precipitate in deionized water, the mass ratio of precipitate to deionized water is 1:5, adjust the pH of the precipitate dispersion to 7 with 2M NaOH solution, freeze-dry treatment, freeze temperature -40°C, dry temperature -25°C, pressure 0.8Mpa, dry time 48h, to obtain SPI.

[0075] (2) Prepare a soy protein gel: Dissolve the SPI in deionized water, the SPI concentration is 12 g / 100 mL, stir at 300 rpm for 30 min, then heat at 95°C for 60 min to form a soy protein gel.

[0076] Comparative Example 3

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

[0078] (1) Extraction of soy protein isolate (SPI): 100 g of soybean meal was dispersed in 1000 mL of deionized water, the pH of the soybean meal dispersion was adjusted to 8 with 2M NaOH solution, stirred at room temperature for 2 h at 500 rpm, centrifuged at 4°C for 20 min at 10000 g, and the supernatant was taken. The supernatant was adjusted to pH 4.5 with 2M HCl solution, and the precipitate was collected after centrifugation at 4°C for 10 min at 3300 g. The precipitate was dispersed in deionized water, the mass ratio of precipitate to deionized water was 1:5, the pH of the precipitate dispersion was adjusted to 7 with 2M NaOH solution, and the precipitate was freeze-dried at -25°C and 0.8Mpa for 48h to obtain SPI.

[0079] (2) Protein mixed cross-linking: SPI and EWP were dissolved in deionized water, the concentration of SPI was 2.25g / 100mL, the concentration of EWP was 0.75g / 100mL, and the composite protein solution was prepared by magnetic stirring at 50°C for 20 min at 300 rpm, 40U / g of TG enzyme was added based on the total mass of SPI and EWP, and the enzyme cross-linking reaction was carried out at 50°C for 2h at 300 rpm, and the enzyme was inactivated by heating at 75°C for 10 min, and the supernatant was collected by centrifugation at 4°C for 10 min at 10000 g, and freeze-dried to obtain a composite protein powder. The freezing temperature was -40°C, the drying temperature was -25°C, the pressure was 0.8Mpa, and the drying time was 48h.

[0080] (3) Preparation of composite soy protein gel: The composite protein powder was dissolved in deionized water, the concentration of composite protein powder was 12g / 100mL, and the composite soy protein gel was formed by stirring at 300 rpm for 30 min and then heating at 95°C for 60 min.

[0081] Comparative Example 4

[0082] A method for preparing a composite soy 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, the pH of the soybean meal dispersion was adjusted to 8 with 2M NaOH solution, stirred at room temperature for 2 h at 500 rpm, centrifuged at 4°C for 20 min at 10000 g, and the supernatant was taken. The supernatant was adjusted to pH 4.5 with 2M HCl solution, and the precipitate was collected after centrifugation at 4°C for 10 min at 3300 g. The precipitate was dispersed in deionized water, the mass ratio of precipitate to deionized water was 1:5, the pH of the precipitate dispersion was adjusted to 7 with 2M NaOH solution, and the precipitate was freeze-dried at -25°C and 0.8Mpa for 48h to obtain SPI.

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

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

[0086] (4) Preparation of composite soy protein gel: The mixed protein powder was dissolved in deionized water with a concentration of 12 g / 100 mL, and the solution was stirred at 300 rpm for 30 min and then heated 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 between Example 2 and Comparative Example 5 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 min of enzymatic cross-linking reaction in step (3), the protein gel was formed, which resulted in the failure of subsequent experiments. After freeze-drying, a large gel block was formed, which 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 gel prepared in Examples 1-3 and Comparative Examples 1-5 are shown in Table 1.

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

[0096] When the amount of TGase added was insufficient, the water holding capacity and the maximum compression stress were both reduced according to the comparison of Examples 1-3. This is because the cross-linking of the soybean protein with the deamidated egg white protein and the soybean protein itself was not complete, resulting in an insufficient number of covalent bonds formed in the system, which in turn affected the gel texture. When the amount of TGase added was excessive, in addition to the formation of more covalent bonds, the cross-linking of the soybean protein with the deamidated egg white protein and the soybean protein itself was excessive, resulting in insoluble aggregates and reducing the solubility of the complex protein, thereby reducing the gel performance.

[0097] The protein concentration was also crucial in the cross-linking reaction. When the total protein concentration of the complex protein solution reached 6.66% (Comparative Example 5), the excessively high protein concentration led to excessive cross-linking sites, and the enzymatic reaction rapidly formed a gel, which could not be re-dissolved after freeze-drying, making it difficult to apply.

[0098] The protein gel formed by pure SPI (Comparative Example 2) was weak in strength, with a hardness of only 10% of Example 1 and a maximum compression stress of only 28%; when the egg white protein without deamidation was directly cross-linked with the soybean protein by TGase (Comparative Example 3), the cross-linking degree was too high due to the cross-linking of the egg white protein itself, resulting in insoluble aggregates and reducing the solubility of the complex protein, thereby reducing the gel performance. When the SPI was only mixed with the deamidated egg white protein without TGase cross-linking (Comparative Example 4), although the gel performance was improved compared to the pure SPI protein gel (Comparative Example 2) due to the increase in the content of disulfide bonds in the system, the lack of TGase-promoted cross-linking resulted in a lower content of covalent bonds in the system, leading to a much lower gel texture, water holding capacity, and maximum compression stress than Example 1.

[0099] The appearance of the protein gel prepared in Example 1 is shown in Figure 1 The appearance of the protein gel prepared in Examples 2-3 is shown in Figure 2 The appearance of the protein gel prepared in Comparative Examples 2-4 is shown in Figure 3 The color was greatly related to the amount of TGase added. When the amount of TGase added was high, the protein gel produced more aggregates. When there were more aggregates, there was a strong light scattering effect, and the color was more white. When there were fewer aggregates, the gel had higher transparency and relatively darker color. Figure 2 The gel color was darker than Figure 1 , indicating that the aggregates formed were insufficient. Figure 3 The color was whiter than Figure 1 . Figure 3 The gel in Example 3 had more bubbles and uneven distribution, which may have been caused by the high viscosity of the solution due to the large number of aggregates, resulting in more bubbles during the stirring process and making it difficult to remove the bubbles.

[0100] The above examples are not intended to limit the scope of the present application, nor are the described steps intended to limit the order in which they are performed. Modifications apparent to one skilled in the art in light of the above teachings are intended to fall within the scope of the claims.

Claims

1. A method for preparing a composite soy protein gel, characterized by, The method comprises the following steps: (1) deamidation of egg white protein: dissolving egg white protein in water, adjusting pH of the egg white protein solution and incubating, adding protein glutamine enzyme for hydrolysis reaction, collecting supernatant after centrifugation and freeze-drying to obtain deamidated egg white protein; adjusting pH of the egg white protein solution to 6-8; the amount of protein glutamine enzyme added is 5-10 U / g relative to the mass of egg white protein; the temperature of incubation is 34-42°C, and the time of incubation is 10-30 min; the temperature of hydrolysis reaction is 34-42°C, and the time of hydrolysis reaction is 120-180 min; (2) protein mixed cross-linking: dissolving soybean protein isolate and deamidated egg white protein in water and stirring to prepare a composite protein solution, adding TG enzyme for enzymatic cross-linking reaction, centrifuging after enzyme inactivation, collecting supernatant and freeze-drying to obtain composite protein powder; the concentration of soybean protein isolate in the composite protein solution is 2.25-4.0 g / 100 mL, the concentration of deamidated egg white protein is 0.75-1.33 g / 100 mL, and the mass ratio of soybean protein isolate to deamidated egg white protein is 2.5-3.5:1; the amount of TG enzyme added is 10 U / g-80 U / g relative to the total mass of soybean protein isolate and deamidated egg white protein; the temperature for enzymatic cross-linking reaction is 45-55°C, and the time is 1-2 h; the temperature for enzyme inactivation is 70-80°C, and the time for enzyme inactivation is 5-15 min; (3) preparing composite soy protein gel: dissolving the composite protein powder in water and stirring, and heating to form a composite soy protein gel.

2. The production method according to claim 1, characterized by, In step (1), the concentration of the egg white protein solution is 3-10 g / mL.

3. The production method according to claim 1, characterized by, In step (1), the pH of the egg white protein solution is adjusted by using a 0.5-1.5 M NaOH solution.

4. The method of claim 1, wherein, In step (2), the temperature for stirring is 40-60°C, and the time for stirring is 10-30 min.

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

6. The composite soy protein gel prepared by the method of any one of claims 1-5.

7. The use of the composite soy protein gel of claim 6 in the field of food.

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