Protein gel as well as preparation method and application thereof

Abstract

The invention discloses protein gel as well as a preparation method and application thereof. The protein gel comprises food protein with positive charges, food protein with negative charges and edible inorganic salt, the food protein with positive charges is at least one of lysozyme and gelatin, and the food protein with negative charges is at least one of soybean protein and whey protein. The preparation method of the protein gel comprises the following steps: 1) respectively preparing two kinds of protein dispersion liquid; and 2) mixing the two protein dispersion liquids, stirring until liquid-liquid phase separation occurs, centrifuging, taking a lower-layer product, and heating and cross-linking. The protein gel has the advantages of being excellent in mechanical property, good in structural stability, green, safe, degradable and the like, can be used for preparing food, toys for children and the like, and is simple in preparation method, green and environment-friendly in process, wide in raw material source, low in production cost, low in energy consumption and suitable for large-scale industrial production and application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of food processing, in particular to a protein gel and a preparation method and application thereof. BACKGROUND

[0002] Traditional protein gels usually exist in the form of hydrogel with high water content, and have loose network structure and generally weak mechanical properties, and the compression stress is usually in the order of kPa. Studies have shown that the mechanical properties of protein gels can be enhanced to some extent by increasing the content of proteins in the solution, but since there is an upper limit to the solubility of proteins, the improvement of the mechanical properties of protein gels by this method is very limited.

[0003] At present, the mechanical properties of protein gels (the compression stress can be increased to 1.8MPa-20MPa) are mainly improved by cross-linking, solvent replacement, and construction of a double network, for example: CN 118919310 A discloses a phytic acid-mediated degradable protein gel electrolyte and a preparation method and application thereof, and discloses a method for improving the compression stress of gelatin-based protein gels to 1.8MPa by phytic acid-mediated cross-linking; Zhou et al. discloses a method for improving the compression stress of gelatin gels to 10MPa by solvent replacement induced toughening (Journal of Materials Chemistry B, 2018, 6, 45,7366-7372); Tang et al. discloses a method for improving the compression stress of bovine serum protein gels to 20MPa by introducing polyvinyl alcohol and tannic acid to construct a double network (ACS Applied Materials & Interfaces, 2018, 10, 9,7593-7601). However, the above methods all need to rely on exogenous chemical additives, which may weaken the biological safety and degradability of protein gels, and thus are difficult to meet the requirements of application scenarios with strict safety requirements.

[0004] Therefore, it is of great significance to develop a protein gel with excellent mechanical properties, good structural stability, and green, safe and degradable. SUMMARY

[0005] One of the purposes of the present application is to overcome the problems of poor mechanical properties and reliance on exogenous chemical additives of existing protein gels, and to provide a protein gel with excellent mechanical properties, good structural stability, and green, safe and degradable.

[0006] The second purpose of the present application is to provide a protein gel preparation method which is simple to operate, green and environmentally friendly in process, has a wide source of raw materials, low production cost and low energy consumption.

[0007] The third object of the present application is to provide an application of the protein gel in the preparation of food or children's toys.

[0008] The technical solution adopted by the present application is: A protein gel, which comprises positively charged food protein, negatively charged food protein and edible inorganic salt, the positively charged food protein is at least one of lysozyme and gelatin, and the negatively charged food protein is at least one of soybean protein and whey protein.

[0009] Preferably, the positively charged food protein is lysozyme from chicken egg white.

[0010] Preferably, the mass percentage of the positively charged food protein in the protein gel is 6% to 40%.

[0011] Preferably, the negatively charged food protein is beta-lactoglobulin.

[0012] Preferably, the mass percentage of the negatively charged food protein in the protein gel is 6% to 40%.

[0013] Preferably, the mass ratio of the positively charged food protein to the negatively charged food protein is 1:0.25 to 4.

[0014] Preferably, the total mass of the positively charged food protein and the negatively charged food protein accounts for 6% to 40% of the mass of the protein gel.

[0015] Preferably, the edible inorganic salt is at least one of sodium chloride and potassium chloride.

[0016] Preferably, the mass percentage of the edible inorganic salt in the protein gel is 0.1% to 0.3%.

[0017] Preferably, the pore size of the gel network in the protein gel is 1 μm to 15 μm.

[0018] Preferably, the compression stress of the protein gel is 2 MPa to 10 MPa.

[0019] A preparation method of the protein gel as described above comprises the following steps: 1) separately dispersing the positively charged food protein and the negatively charged food protein in water, adding edible inorganic salt and adjusting the pH value to 6 to 7 to obtain a dispersion of the positively charged food protein and a dispersion of the negatively charged food protein; 2) mixing the dispersion of the positively charged food protein and the dispersion of the negatively charged food protein under stirring until liquid-liquid phase separation occurs, centrifuging, taking the lower layer product and heating cross-linking to obtain a protein gel.

[0020] Preferably, the dispersion in step 1) is by mechanical stirring.

[0021] Preferably, the mechanical stirring is at a stirring rate of 200 rpm to 300 rpm, at a temperature of 10 °C to 40 °C, and for a stirring time of 1 h to 3 h.

[0022] Preferably, the mass percentage of the positively charged food protein in the dispersion of the positively charged food protein in step 1) is 0.1% to 2.0%.

[0023] Preferably, the mass percentage of the edible inorganic salt in the dispersion of the positively charged food protein in step 1) is 0.1% to 0.3%.

[0024] Preferably, the mass percentage of the negatively charged food protein in the dispersion of the negatively charged food protein in step 1) is 0.1% to 2.0%.

[0025] Preferably, the mass percentage of the edible inorganic salt in the dispersion of the negatively charged food protein in step 1) is 0.1% to 0.3%.

[0026] Preferably, the mass ratio of the dispersion of the positively charged food protein to the dispersion of the negatively charged food protein in step 2) is 1:0.25 to 4.

[0027] Preferably, the stirring in step 2) is at a stirring rate of 100 rpm to 200 rpm, at a temperature of 10 °C to 40 °C, and for a stirring time of 1 min to 5 min.

[0028] Preferably, the centrifuging in step 2) is at a centrifuging rate of 3000 rpm to 5000 rpm, at a temperature of 10 °C to 40 °C, and for a centrifuging time of 10 min to 20 min.

[0029] Preferably, the heating cross-linking in step 2) is at a temperature of 70 °C to 90 °C, and for a heating cross-linking time of 20 min to 30 min.

[0030] Use of a protein gel as described above in the preparation of a food product or a children's toy.

[0031] The protein gel has the advantages of excellent mechanical properties, good structural stability, green safety and degradability, and can be used for the preparation of food, children's toys and the like.

[0032] Specifically, 1) The protein gel has high cross-linking density, compact gel structure and excellent self-supporting property, the pore size of the gel network is 1-15 pm, the pore size size distribution is concentrated, and the compressive stress and tensile stress at break reach the MPa level (the compressive stress is much higher than the kPa level of traditional protein gel, and the mechanical properties are more excellent), which breaks through the upper limit of the mechanical properties of ordinary food-derived protein gel; 2) The protein gel has excellent fatigue resistance in the cyclic compression test, and can maintain the complete structure and stable performance after deformation for many times; 3) The protein gel has a rigid network structure, which can well resist the swelling stress caused by water penetration, and is stable in quality and not easy to swell or break in water environment (after being stored in water environment at 4℃ for 12 days, the mass, morphology and mechanical properties of the protein gel remain basically unchanged, and no obvious swelling, shrinkage or delamination phenomenon occurs); 4) The positively charged food protein in the protein gel is at least one of lysozyme and gelatin, and the two food proteins are the main components of egg white and whey, which are egg processing by-products and cheese processing by-products, respectively, and have the characteristics of wide source and stable supply, and also have natural antibacterial and other biological activities, which is beneficial to improve the functionality of the protein gel; 5) The negatively charged food protein in the protein gel is at least one of soy protein and whey protein, and the two food proteins are the main components of soy protein and whey protein, which are soy oil processing by-products and cheese processing by-products, respectively, and have the characteristics of rich resources and low cost, which reduces the production cost of the protein gel; 6) The protein gel only uses water as a solvent in preparation, which is green, non-toxic and environmentally friendly, and the preparation process is simple, energy-saving, and does not require large equipment, which is suitable for large-scale industrial production and application. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The SEM image of the protein gel of Example 1.

[0034] Figure 2 The CT image of the protein gel of Example 1.

[0035] Figure 3A photograph of a child toy made of the protein gel of Examples 1 to 3 and the β-lactoglobulin gel of Comparative Examples 2 and 3.

[0036] Figure 4 A graph of the compression and tensile test results of the protein gel of Examples 1 to 3 and the β-lactoglobulin gel of Comparative Examples 2 and 3.

[0037] Figure 5 A graph of the cyclic compression test results of the protein gel of Examples 1 to 3 and the β-lactoglobulin gel of Comparative Examples 2 and 3.

[0038] Figure 6 A graph of the long-term mass stability test results of the protein gel of Examples 1 to 3 and the β-lactoglobulin gel of Comparative Examples 2 and 3 in a water environment.

[0039] Figure 7 A graph of the cytotoxicity test results of the protein gel of Examples 1 to 3, the food protein mixed dispersion of Comparative Example 1, and the β-lactoglobulin gel of Comparative Examples 2 and 3. DETAILED DESCRIPTION

[0040] The present application will be further explained and described with reference to specific examples.

[0041] Example 1 A protein gel was prepared as follows: 1) Egg white lysozyme was added to distilled water at a mass ratio of 0.1:99.9, 0.1 wt% NaCl was further added, and then the mixture was stirred at a stirring rate of 200 rpm and a temperature of 10°C for 1 h, and then the pH value was adjusted to 6 to obtain an egg white lysozyme dispersion; β-lactoglobulin was added to distilled water at a mass ratio of 0.1:99.9, 0.1 wt% NaCl was further added, and then the mixture was stirred at a stirring rate of 200 rpm and a temperature of 10°C for 1 h, and then the pH value was adjusted to 6 to obtain a β-lactoglobulin dispersion; 2) The egg white lysozyme dispersion and the β-lactoglobulin dispersion were mixed at a mass ratio of 1:0.25, and then the mixture was stirred at a stirring rate of 100 rpm and a temperature of 10°C for 1 min until liquid-liquid phase separation occurred, and then the mixture was centrifuged at a centrifugal rate of 3000 rpm and a temperature of 10°C for 10 min, and then the lower layer product was placed in a water bath at 80°C and heated for crosslinking for 30 min to obtain a protein gel.

[0042] The scanning electron microscope (SEM) image of the protein gel of this example is shown in Figure 1 (a and b represent SEM images at different magnifications), and the X-ray computed tomography (CT) image is shown inFigure 2 (Blue represents water) as shown.

[0043] Depend on Figure 1 and Figure 2 It can be seen that the pore size of the gel network in protein gel is small and relatively uniform, with pore diameter ranging from 1μm to 15μm.

[0044] Example 2: A protein gel, the preparation method of which is as follows: 1) Add egg white-derived lysozyme to distilled water at a mass ratio of 2:98, then add 0.3wt% NaCl, and stir for 3 hours at a stirring speed of 300 rpm and a temperature of 30℃. Then adjust the pH value to 7 to obtain a dispersion containing egg white-derived lysozyme. 2) Add β-lactoglobulin to distilled water at a mass ratio of 2:98, then add 0.3wt% NaCl, and stir for 3 hours at a stirring speed of 300 rpm and a temperature of 30℃. Then adjust the pH value to 7 to obtain a β-lactoglobulin dispersion. 2) Mix the egg white lysozyme dispersion and the β-lactoglobulin dispersion at a mass ratio of 1:4, and then stir for 5 minutes at a stirring speed of 200 rpm and a temperature of 30°C until liquid-liquid phase separation occurs. Then centrifuge for 20 minutes at a centrifugation speed of 5000 rpm and a temperature of 25°C. Then take the lower layer product and heat it in a water bath at 70°C for 20 minutes to crosslink, thus obtaining a protein gel.

[0045] Example 3: A protein gel, the preparation method of which is as follows: 1) Add egg white-derived lysozyme to distilled water at a mass ratio of 1:99, then add 0.2wt% NaCl, and stir for 2 hours at a stirring speed of 250 rpm and a temperature of 25℃. Adjust the pH to 6.5 to obtain an egg white-derived lysozyme dispersion. Add β-lactoglobulin to distilled water at a mass ratio of 1:99, then add 0.2wt% NaCl, and stir for 2 hours at a stirring speed of 250 rpm and a temperature of 25℃. Adjust the pH to 6.5 to obtain a β-lactoglobulin dispersion. 2) Mix the egg white lysozyme dispersion and the β-lactoglobulin dispersion at a mass ratio of 1:2, and then stir for 3 minutes at a stirring speed of 150 rpm and a temperature of 25°C until liquid-liquid phase separation occurs. Then centrifuge for 15 minutes at a centrifugation speed of 4000 rpm and a temperature of 20°C. Then take the lower layer product and heat it in a water bath at 75°C for 25 minutes to crosslink, thus obtaining a protein gel.

[0046] Comparative Example 1: A food protein mixed dispersion liquid was prepared as follows: 1) Lysozyme from egg white was added into distilled water, the mass ratio of lysozyme from egg white to distilled water was 1:99, 0.2wt% NaCl was further added, then the mixture was stirred at a stirring rate of 300 rpm and a temperature of 25℃ for 3h, and the pH value was adjusted to 9, to obtain a lysozyme from egg white dispersion liquid; β-lactoglobulin was added into distilled water, the mass ratio of β-lactoglobulin to distilled water was 1:99, 0.2wt% NaCl was further added, then the mixture was stirred at a stirring rate of 300 rpm and a temperature of 25℃ for 3h, and the pH value was adjusted to 9, to obtain a β-lactoglobulin dispersion liquid; 2) The lysozyme from egg white dispersion liquid and the β-lactoglobulin dispersion liquid were mixed according to a mass ratio of 1:1, then the mixture was stirred at a stirring rate of 200 rpm and a temperature of 25℃ for 3min (no liquid-liquid phase separation occurred), and then the mixture was heated in a water bath at 80℃ for 30min (gelation failed), to obtain a food protein mixed dispersion liquid (the reason why the protein gel failed to form was that the lysozyme from egg white dispersion liquid and the β-lactoglobulin mixed dispersion liquid did not have phase separation conditions, and the total concentration of the protein in the system was lower than the critical concentration required for gelation, so it was difficult to form a continuous protein gel network structure).

[0047] Comparative Example 2: A β-lactoglobulin gel was prepared as follows: β-lactoglobulin was added into distilled water, the mass ratio of β-lactoglobulin to distilled water was 40:60, then the mixture was stirred at a stirring rate of 300 rpm and a temperature of 25℃ for 4h, and then the mixture was heated in a water bath at 80℃ for 30min, to obtain a β-lactoglobulin gel.

[0048] Comparative Example 3: A β-lactoglobulin gel (chemical cross-linking) was prepared as follows: 1) β-lactoglobulin was added into distilled water, the mass ratio of β-lactoglobulin to distilled water was 40:60, then the mixture was stirred at a stirring rate of 300 rpm and a temperature of 25℃ for 4h, to obtain a β-lactoglobulin dispersion liquid; 2) Glutaraldehyde aqueous solution was slowly added into the stirring β-lactoglobulin dispersion liquid until the mass fraction of glutaraldehyde in the system was 0.5%, then the mixture was stirred at 25℃ for 2h, and was left to stand, to obtain a β-lactoglobulin gel.

[0049] Performance test: 1) The actual pictures of the children's toys made of the protein gels of Examples 1-3 and the β-lactoglobulin gels of Comparative Examples 2-3 are as follows: Figure 3(shown in Figure 1).

[0050] It can be seen from Figure 3 that the protein gels of Examples 1-3 are suitable for preparing children's toys.

[0051] 2) The compression and tensile properties of the protein gels of Examples 1-3 and the β-lactoglobulin gels of Comparative Examples 2-3 were determined using a universal material testing machine (test temperature: 25°C), and the test results are shown in Figure 2. Figure 4

[0052] It can be seen from Figure 4 that: a) The compression stress of the protein gels of Examples 1-3 is greater than 2 MPa, and the tensile stress at break is greater than 1 MPa, and the mechanical properties are excellent, because the protein aggregation microdroplets generated in the liquid-liquid phase separation process constitute a locally highly crowded molecular environment, which significantly promotes the strong interaction between protein molecules and the formation of high crosslinking density in the subsequent heating process, and the aggregation microdroplets are further transformed into interconnected spherical aggregates, ultimately constructing a three-dimensional particle gel network structure with small pore size and relatively uniform distribution, so that the protein gels exhibit high compression and tensile properties; b) The compression stress of the β-lactoglobulin gel of Comparative Example 2 is 1.2 MPa, and the tensile stress at break is 0.8 MPa, which is significantly poorer than the protein gels of Examples 1-3, because the mass fraction of protein in the system of Comparative Example 2 is high (about 40%), and there is a certain molecular crowding effect, but the gelation mechanism is direct heat-induced denaturation, and the protein molecules aggregate and crosslink in a relatively random manner, forming a disordered network structure with wide pore size distribution, and the degree of compaction and crosslinking uniformity are lower than the particle gels induced by phase separation, so the mechanical properties are relatively weak; c) The compression stress of the β-lactoglobulin gel of Comparative Example 3 is 1.9 MPa, and the tensile stress at break is 1.1 MPa, which is excellent, because the interaction between protein molecules and the rigid covalent crosslinking of glutaraldehyde in Comparative Example 3 synergistically act, so as to exhibit excellent mechanical properties.

[0053] 3) The cyclic compression properties of the protein gels of Examples 1-3 and the β-lactoglobulin gels of Comparative Examples 2-3 were determined using a universal material testing machine (test temperature: 25°C, set compression strain of 30%, cyclic compression for 10 times), and the test results are shown in Figure 3. Figure 5

[0054] It can be seen from Figure 5 that: ​​a) The maximum compression stress of the protein gels of Examples 1-3 under the first compression condition was about 2.2 MPa, and the compression stress slightly decreased with the increase of the cycle number, and the compression stress could still be stabilized at 1.9 MPa after 10 cycles of compression, and the cycle compression performance was excellent, because the protein condensed droplets generated by liquid-liquid phase separation were converted into a network of interconnected granular gels under subsequent heat treatment, and the network had both a dense granular phase with high cross-linking density and a certain energy dissipation capacity, had a relatively high bearing capacity when first loaded, and dissipated part of the stress through the micro rearrangement between particles and interfaces during the cycle loading process, so that a relatively high and relatively stable residual stress could be maintained after multiple cycles of compression; b) The maximum compression stress of the β-lactoglobulin gel of Comparative Example 2 under the first compression condition was 1 MPa, and the compression stress gradually decreased with the increase of the cycle number, and finally stabilized at 0.8 MPa, and the cycle compression performance was poor, because the gel network of the β-lactoglobulin gel of Comparative Example 2 was composed of randomly aggregated cross-linking generated by heat-induced denaturation, and the structure was disordered and the pore size was large, and the weak connection and large pore region in the network was easy to be gradually destroyed and irreversibly deformed during the cycle compression process, resulting in a continuous decrease in the compression stress under a compression strain of 30%, and only a low level could be stabilized; c) The maximum compression stress of the β-lactoglobulin gel of Comparative Example 3 under the first compression condition was 1.9 MPa, close to that of the protein gels of Examples 1-3, but the compression stress would suddenly decrease during the first 5 cycles of compression, and then the compression stress would gradually stabilize at about 0.9 MPa, because although the rigid covalent cross-linking in Comparative Example 3 could obtain a high initial compression stress, the network flexibility and structure rearrangement ability were insufficient, and micro cracks and brittle fractures were easy to occur at the stress concentration sites during the first few cycles of compression, causing the bearing skeleton to rapidly degrade, so the compression stress would suddenly decrease during the first few cycles of compression, and finally could only be stabilized at a low level.

[0055] 4) 1 g of the protein gels of Examples 1-3 and the β-lactoglobulin gels of Comparative Examples 2-3 were made into samples of the same shape and immersed in deionized water at 4°C for 12 d, then the samples were taken out, the water on the surface of the samples was absorbed clean with filter paper, and then the samples were weighed to test the long-term mass stability in the water environment, and the test results are shown in Table 2. Figure 6

[0056] It can be seen from Table 2 that: Figure 6 ​​a) The protein gels of Examples 1-3 showed very little change in mass (less than 10%) after being stored in an aqueous environment at 4°C for 12 days. This is because the molecular crowding environment formed by the lysozyme droplets generated by the liquid-liquid phase separation promoted strong interactions and high cross-linking density between proteins during the heating process, ultimately forming a three-dimensional network structure with small pore size (about 10 μm in diameter) and relatively uniform pore size. This three-dimensional network structure can effectively bind internal water molecules and resist the expansion stress caused by external water penetration by relying on its rigid mechanical framework, thus exhibiting excellent quality stability in an aqueous environment. b) The β-lactoglobulin gel of Comparative Example 2 showed a mass change of up to 60% after being stored in an aqueous environment at 4°C for 12 days. The reason is that the β-lactoglobulin gel of Comparative Example 2 is a network formed by thermally induced random aggregation in a homogeneous solution. The cross-linking density is relatively insufficient and the pore size is large. Such a large-pore structure lacks sufficient elastic contraction force to resist the osmotic pressure drive of water. Therefore, it will continue to absorb water during storage until it reaches swelling equilibrium, resulting in a significant increase in mass and exhibiting poor mass stability. c) The β-lactoglobulin gel of Comparative Example 3 showed a mass change of up to 30% after being stored in an aqueous environment at 4°C for 12 days. This is because the β-lactoglobulin gel of Comparative Example 3 forms a high cross-linking density and a stable covalent cross-linking network under the action of glutaraldehyde. The network retains a large number of hydrophilic groups and a porous structure that can retain water, so it will also undergo significant water absorption and swelling and mass increase in an aqueous environment. However, the increase in mass is controlled by the cross-linking density, so its mass stability is slightly better than that of the β-lactoglobulin gel of Comparative Example 2.

[0057] 5) The protein gels of Examples 1-3, the food protein mixture dispersion of Comparative Example 1, and the β-lactoglobulin gels of Comparative Examples 2-3 were sterilized with ultraviolet light, then immersed in cell culture medium to prepare an extract. Mouse fibroblasts were co-cultured with the extract for 24 hours, and cell viability was then tested. The cytotoxicity test results are as follows: Figure 7 As shown.

[0058] Depend on Figure 7 It can be known that: a) The relative cell proliferation rate of the protein gels in Examples 1-3 is close to that of pure culture medium, approximately 100%, and there is no cytotoxicity. This is because the phase separation process and subsequent heat treatment process in Examples 1-3 only involve the physical interaction and rearrangement of the protein molecules themselves, without introducing any exogenous chemical cross-linking agents. The final product is pure, consisting only of natural food protein and water, and therefore has biocompatibility comparable to cell culture medium and is non-cytotoxic. b) The relative cell proliferation rate of the food protein mixture dispersion of Comparative Example 1 and the β-lactoglobulin gel of Comparative Example 2 was also around 100%, with no cytotoxicity. The reason is that although Comparative Example 1 and Comparative Example 2 were prepared by different methods, they were essentially systems formed by natural proteins through physical means (mixing or heat induction), and they also did not contain harmful chemicals, thus showing good biocompatibility. c) The β-lactoglobulin gel in Comparative Example 3 had a low cell proliferation rate of about 10% and high cytotoxicity. The reason is that glutaraldehyde, the chemical cross-linking agent in Comparative Example 3, is a highly active bifunctional aldehyde. During the cross-linking reaction, it does not react completely. Subsequently, in the hydrolysis environment, it slowly releases free aldehyde groups from the cross-linking network. These free aldehyde groups can undergo irreversible covalent cross-linking with amino groups on the cell membrane and amino groups of important intracellular enzymes and proteins, thereby damaging cell structure and key metabolic functions, ultimately leading to cell death.

[0059] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A protein gel, characterized in that, The composition includes positively charged food proteins, negatively charged food proteins, and edible inorganic salts; the positively charged food proteins are at least one of lysozyme and gelatin; the negatively charged food proteins are at least one of soy protein and whey protein.

2. The protein gel according to claim 1, characterized in that: The positively charged food protein in the protein gel has a mass percentage of 6% to 40%; the negatively charged food protein in the protein gel has a mass percentage of 6% to 40%.

3. The protein gel according to claim 1 or 2, characterized in that: The mass ratio of the positively charged food protein to the negatively charged food protein is 1:0.25 to 4.

4. The protein gel according to claim 1, characterized in that: The edible inorganic salt is at least one of sodium chloride and potassium chloride.

5. The protein gel according to claim 1 or 4, characterized in that: The edible inorganic salts constitute 0.1% to 0.3% of the protein gel by mass.

6. The protein gel according to any one of claims 1, 2, and 4, characterized in that: The pore size of the gel network in the protein gel is 1 μm to 15 μm.

7. A method for preparing a protein gel as described in any one of claims 1 to 6, characterized in that, Includes the following steps: 1) Disperse positively charged and negatively charged food proteins separately in water, then add edible inorganic salts and adjust the pH to 6-7 to obtain dispersions of positively charged and negatively charged food proteins. 2) Mix the dispersion of positively charged food protein and the dispersion of negatively charged food protein and stir until liquid-liquid phase separation occurs. Centrifuge, take the lower layer product and heat it for cross-linking to obtain protein gel.

8. The preparation method according to claim 7, characterized in that: Step 1) The mass percentage of positively charged food protein in the dispersion of the positively charged food protein is 0.1% to 2.0%; Step 1) The mass percentage of negatively charged food protein in the dispersion of the negatively charged food protein is 0.1% to 2.0%; Step 2) The mass ratio of the dispersion of the positively charged food protein to the dispersion of the negatively charged food protein is 1:0.25 to 4.

9. The preparation method according to claim 7 or 8, characterized in that: Step 2) The stirring is carried out at a stirring rate of 100 rpm to 200 rpm and a temperature of 10 ℃ to 40 ℃ for a stirring time of 1 min to 5 min; Step 2) The heating crosslinking is carried out at a temperature of 70 ℃ to 90 ℃ for a heating crosslinking time of 20 min to 30 min.

10. The use of a protein gel as described in any one of claims 1 to 6 in the preparation of food or children's toys.

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