Method for preparing soybean protein with thermal stability based on crowding effect

Abstract

The invention discloses a method for preparing soybean protein with thermal stability based on crowding effect, which comprises the following steps: mixing PEG (polyethylene glycol) with the molecular weight of 10000-20000, PEG dispersion liquid with the mass concentration of 20-40% and soybean protein dispersion liquid with the mass concentration of 5%, uniformly stirring, heating at 100 DEG C for 30 minutes, and then carrying out acid precipitation, centrifugation, dispersion, redissolution and drying to obtain the soybean protein with thermal stability. The thermal-stability soybean protein prepared by the method has good thermal stability, the thermal-stability soybean protein has good fluidity after being heated, and even if the soybean protein with the concentration of 2.5% is modified, the prepared thermal-stability soybean protein does not gelate after being heated at the temperature of 100 DEG C for 30 minutes at the mass concentration of 10%. The prepared soybean protein with thermal stability can be widely applied to beverages containing protein, and the stability of related products in the thermal processing process is improved while the protein content is increased.

Description

Technical Field

[0001] The invention relates to the field of plant protein processing, and in particular to a method for preparing heat-stable soybean protein based on crowding effect. Background Art

[0002] Soybean is the most widely distributed and economically profitable legume. Soy protein is one of the most important food protein resources. It contains a variety of essential amino acids for humans, has good nutritional value and functional properties, and is widely used in food processing to improve the sensory properties of food. Heat treatment is a very important operation process in processing soy protein products. It can improve the digestibility of soy protein, reduce the beany smell and play a sterilizing role. However, heat treatment is also the main factor leading to protein aggregation, which will have an adverse effect on the sensory and nutritional properties of the product, which further limits its application in high-concentration protein beverages.

[0003] Patent publication CN109553676A discloses a method for inhibiting the thermal denaturation and aggregation of fish myosin. The method in the invention involves gradient heating and heat preservation dialysis, and a stabilizer needs to be added during the gradient heating process, and a permeabilizer is added during dialysis. The implementation process is relatively cumbersome and not suitable for large-scale industrial production. Patent CN 109770041 A discloses a method for preparing heat-stable soybean protein. The heat stability of soybean protein can be improved by heat-treating and modifying soybean protein with a concentration of 0.1-1.5% (w / w, g / g), and the prepared heat-stable soybean protein can maintain a certain thermal stability at a concentration of 10%. However, in the actual study of the performance of soybean protein, it was found that the soybean meal used to extract soybean protein has a great influence on the stability of soybean protein. The higher the degree of oxidation of the soybean meal, the better the stability of the extracted soybean protein. The degree of oxidation of the soybean meal can be reflected by the total thiol content of the extracted soybean protein, such as Figure 1 As shown, the higher the degree of oxidation of soybean meal, the lower the total thiol content of the extracted soy protein. This may be because, in soybean meal with a higher degree of oxidation, the thiol group is oxidized into a disulfide bond, resulting in a decrease in the total thiol content of the finally extracted soy protein. By studying the performance of soy protein from soybean meal with different degrees of oxidation, it was found that the lower the degree of oxidation of soybean meal, the higher the total thiol content in the extracted soy protein. When the total thiol content in soy protein is greater than 1.5 μmol / g, the thermal stability of soy protein is very poor. Even if the soy protein with a concentration of 1% is heat-treated and modified according to the method of patent CN 109770041A, the modified soy protein dispersion will still gel when heated at a concentration of 10%. Therefore, it is urgent to find a method that can improve the thermal stability of soy protein with a high thiol content and is simple and easy to operate to improve the performance of soy protein. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing heat-stable soy protein based on the crowding effect, which is committed to solving the problem of gelation or aggregation of soy protein with a high thiol content (-SH group content greater than 1.5 μmol / g) when heated at a high protein concentration, thereby preparing heat-stable soy protein.

[0005] To achieve the above object, the present invention provides a method for preparing heat-stable soybean protein based on crowding effect, comprising the following specific steps:

[0006] S1, mixing: taking the soybean protein dispersion and the PEG dispersion and mixing them evenly to obtain a mixed solution A;

[0007] S2, heat treatment: heating the mixed solution A in step S1 at 95-100° C. for 25-30 min to obtain a mixed solution B;

[0008] S3, acid precipitation: the pH of the mixed solution B obtained in step S2 is adjusted to 4.0-4.5 with 1 mol / L HCl to obtain a mixed solution C;

[0009] S4, centrifugation: centrifuge the mixed solution C in step S3 to collect the precipitate;

[0010] S5, dispersion: adjust the pH of deionized water to 4.0-4.5 with 0.1 mol / L HCL, and disperse the precipitate obtained in step S4 in deionized water at pH 4.0-4.5 for 20 min to remove polyethylene glycol;

[0011] S6, centrifugation: centrifuging the product obtained in step S5 to collect the precipitate;

[0012] S7, re-dissolving: adding water to the precipitate obtained in step S6, adjusting the pH to 7.0-7.5 with 2 mol / L NaOH for dispersion and re-dissolution to obtain a protein solution;

[0013] S8, drying: drying the protein solution obtained in step S7 to obtain heat-stable soy protein.

[0014] The crowding effect involved in the present invention refers to placing the soy protein isolate in a highly crowded state, that is, there is a high concentration of polyethylene glycol in a mixed solution of the soy protein isolate and polyethylene glycol, and the polyethylene glycol forms a hydration layer in water. The higher the concentration and molecular weight of the polyethylene glycol, the more volume it occupies, the more water molecules it binds, and the larger the volume of the solution it occupies, resulting in a large part of the total volume of the mixed solution being occupied by the polyethylene glycol and unable to be used by the protein molecules, thereby improving the problem of easy aggregation of the soy protein isolate and improving the thermal stability of the soy protein isolate.

[0015] In one embodiment of the present invention, the mass concentration of soybean protein in the soybean protein dispersion in step S1 is 2-5%, and the mass concentration of PEG in the PEG dispersion is 20-40%.

[0016] In one embodiment of the present invention, the preparation method of the soy protein dispersion is to take soy protein, uniformly disperse it in water at a mass concentration of 2-5% (w / w, g / g), and adjust the pH to 7.0 to obtain the soy protein dispersion.

[0017] In one embodiment of the present invention, the extraction method of soybean protein is as follows: defatted soybean meal is added to deionized water at a ratio of 1:12 (w / v, g / ml), 2mol / L NaOH solution is used to adjust pH7.0-8.5, stirred at room temperature for 1h, centrifuged at 15800g and 4°C for 30min, and the supernatant is taken; the supernatant is adjusted to pH4-5 with 2mol / L HCl, 3000-15800g, 4°C centrifuged for 5-120min to obtain a precipitate; the precipitate is dissolved with deionized water and the pH of the solution is adjusted to 6.5-8.0, and the solution is frozen or spray-dried to obtain soybean protein. The freeze-drying parameters are -50--80°C, vacuum degree 0.01Pa-50Pa, and drying for 24-72h; the spray-drying parameters are: inlet air temperature 195°C, outlet air temperature 95°C, and feed rate 20mL / min.

[0018] In one embodiment of the present invention, the total thiol content of the soy protein isolate is greater than 1.5 μmol / g, preferably 3-5 μmol / g.

[0019] In one embodiment of the present invention, the pH of the PEG dispersion is 7.0, and the molecular weight of the PEG is 10,000 to 20,000.

[0020] In one embodiment of the present invention, the preparation method of the PEG dispersion is to take PEG with a molecular weight of 10,000 to 20,000, uniformly disperse it in water at a mass concentration of 20 to 40%, and adjust the pH to 7.0 to obtain the PEG dispersion.

[0021] In one embodiment of the present invention, the volume ratio of the soybean protein dispersion to the PEG dispersion in the mixed solution A described in step S1 is 0.8-1.2:1.

[0022] In one embodiment of the present invention, the centrifugal speed in step S4 is 3000-15800 g, and the centrifugal time is 5-120 min.

[0023] In one embodiment of the present invention, the weight ratio of the precipitate to water in step S5 is 1:(5-10).

[0024] In one embodiment of the present invention, the centrifugal speed in step S6 is 3000-15800 g, and the centrifugal time is 5-120 min.

[0025] In one embodiment of the present invention, the weight ratio of the precipitate to water in step S7 is 1:(5-10).

[0026] In one embodiment of the present invention, the drying in step S8 is freeze drying or spray drying; the spray drying is specifically: -50 to -80°C, vacuum degree 0.01Pa to 50Pa, and drying for 24 to 72 hours; the spray drying is specifically: inlet air temperature 180 to 200°C, outlet air temperature 80 to 100°C, and feed rate 15 to 30mL / min.

[0027] The present invention also provides a heat-stable soybean protein prepared by the method.

[0028] The present invention also provides an application of the heat-stable soybean protein in the food field.

[0029] In one embodiment of the present invention, the food comprises a swallowable food or a high-protein food, and the high-protein food comprises a high-protein beverage.

[0030] Beneficial effects:

[0031] 1. The present invention improves the thermal stability of soybean protein by adding PEG dispersion to the soybean protein dispersion and combining heat treatment. The soybean protein prepared by the method of the present invention has good thermal stability. Even if the soybean protein dispersion with a concentration of 10% is heated (100°C for 30 minutes), the soybean protein dispersion still has good fluidity and will not gel.

[0032] 2. The present invention uses the preheating synergistic crowding effect to prepare heat-stable soy protein, which significantly improves the thermal stability of the soy protein. After adding PEG, even if the concentration of the soy protein is as high as 2.5%, the heat-treated soy protein can still maintain good thermal stability at a concentration of 10%. The heat-treated soy protein is heated at a concentration of 10% for 30 minutes, and the soy protein dispersion can still maintain good fluidity.

[0033] 3. For soy protein with a total thiol content (3.46 μmol / g), even if the concentration of soy protein before heat treatment is only 1%, the soy protein after heat treatment will still gel when heated at a concentration of 10%. In the present invention, based on the crowding effect combined with heat treatment, the concentration of soy protein before heat treatment can be as high as 2.5%, which significantly improves the thermal stability of soy protein.

[0034] 4. The heat-stable soybean protein obtained by the present invention has a small change in particle size before and after heating (e.g. Fig.14 , Fig.15 As shown in FIG. 1 , in addition to being applied to milk beverages, the present invention can also be applied to transparent protein beverage systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 These are the measurement results of total thiol content of soy protein isolate extracted from soybean meal with different oxidation degrees, where soybean meal 1 is soybean meal with a low oxidation degree, and soybean meal 2 is soybean meal with a high oxidation degree.

[0036] Figure 2 This is the storage modulus measurement result of the heat-stable soy protein obtained in Example 1 of the present invention after heating.

[0037] Figure 3 The viscosity measurement result of the heat-stable soy protein obtained in Example 1 of the present invention after heating.

[0038] Figure 4 This is the storage modulus measurement result of the heat-stable soy protein obtained in Example 2 of the present invention after heating.

[0039] Figure 5 The viscosity measurement result of the heat-stable soy protein obtained in Example 2 of the present invention after heating.

[0040] Figure 6 This is the measurement result of the storage modulus of the heat-stable soy protein obtained in Example 3 of the present invention after heating.

[0041] Figure 7 The viscosity measurement result of the heat-stable soy protein obtained in Example 3 of the present invention after heating is shown.

[0042] Figure 8 The storage modulus measurement result of the modified soy protein obtained in Comparative Example 1 of the present invention after heating.

[0043] Fig. 9 The viscosity measurement result of the modified soybean protein obtained in Comparative Example 1 of the present invention after heating.

[0044] Fig.10 The storage modulus measurement result of the modified soy protein obtained in Comparative Example 2 of the present invention after heating.

[0045] Fig.11 The viscosity measurement result of the modified soybean protein obtained in Comparative Example 2 of the present invention after heating.

[0046] Fig.12 The storage modulus measurement result of the modified soy protein obtained in Comparative Example 3 of the present invention after heating.

[0047] Fig.13The viscosity measurement result of the modified soybean protein obtained in Comparative Example 3 of the present invention after heating.

[0048] Fig.14 The particle size measurement results of the heat-stable soybean protein obtained in the examples of the present invention are shown in FIG.

[0049] Fig.15 The particle size measurement results of the heat-stable soy protein after heating obtained in the examples of the present invention are shown in FIG.

[0050] Fig.16 This is a schematic diagram of the fluidity of the heat-stable soy protein obtained in Example 1 of the present invention.

[0051] Fig.17 This is a schematic diagram of the fluidity of the heat-stable soy protein obtained in Example 2 of the present invention.

[0052] Fig.18 This is a schematic diagram of the fluidity of the heat-stable soy protein obtained in Example 3 of the present invention.

[0053] Fig.19 This is a schematic diagram of the fluidity of the modified soy protein obtained in Comparative Example 1 of the present invention.

[0054] Fig. 20 This is a schematic diagram of the fluidity of the modified soy protein obtained in Comparative Example 2 of the present invention.

[0055] Fig.21 This is a schematic diagram of the fluidity of the modified soy protein obtained in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0056] The present invention will be further described below through specific implementation examples:

[0057] Example 1

[0058] A method for preparing heat-stable soybean protein comprises the following steps:

[0059] S1. Soy protein extraction: defatted soybean meal was added to deionized water at a ratio of 1:12 (w / v, g / mL), the pH was adjusted to 7.5 with 2 mol / L NaOH solution, stirred at room temperature for 1 h, and centrifuged (15800 g, 30 min, 4°C) to remove insoluble matter to obtain a supernatant; the supernatant was adjusted to pH 4.0 with 2 mol / L HCl, and centrifuged (15800 g, 5 min, 4°C) to obtain a precipitate; the precipitate was dissolved with deionized water and the pH of the solution was adjusted to 7.0 with 1 mol / L NaOH, and the solution was freeze-dried to obtain soy protein; the freeze-drying parameters were -80°C, 50 Pa, and 72 h; the total thiol content of the soy protein was 3.46 μmol / g;

[0060] S2, dispersion: the soybean protein obtained in S1 is uniformly dispersed in water at a mass concentration of 5% (w / w, g / g), and the pH is adjusted to 7.0 to obtain a protein dispersion 1;

[0061] S3, dispersion: take PEG with a molecular weight of 10000, uniformly disperse it in water at a mass concentration of 30% (w / w, g / g), and adjust the pH to 7.0 to obtain a PEG dispersion;

[0062] S4, mixing: mixing equal volumes of the protein dispersion 1 obtained in step S2 and the PEG dispersion obtained in step S3, and stirring evenly to obtain a mixed solution;

[0063] S5, heat treatment: heating the mixed solution obtained in step S4 at 100° C. for 30 min;

[0064] S6, acid precipitation: the mixed solution obtained in step S5 is adjusted to pH 4.5 with 2 mol / L HCl;

[0065] S7, centrifugation: centrifuge the product obtained in step S6 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0066] S8, dispersion: adjust the pH of deionized water to 4.5 with 0.1 mol / L HCL, mix the precipitate obtained in step S7 with deionized water at a mass ratio (w / w) of 1:5 and disperse for 20 min to remove polyethylene glycol;

[0067] S9, centrifugation: centrifuge the product obtained in step S8 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0068] S10, re-dissolving: the precipitate obtained in step S9 was mixed with deionized water at a mass ratio (w / w) of 1:5, and the pH was adjusted to 7.0 with 2 mol / L NaOH for dispersion and re-dissolution to obtain a protein solution;

[0069] S11, drying: the protein solution obtained in step S10 is subjected to vacuum freeze drying (-80°C, 0.01Pa, 24h) to obtain heat-stable soy protein.

[0070] The heat-stable soy protein prepared in this example was prepared into an aqueous solution with a protein concentration of 10% (w / v, g / mL). The solution was heated at 100°C for 30 minutes, cooled and placed in a refrigerator at 4°C for 24 hours, and the storage modulus and viscosity were measured. At the same time, untreated soy protein was taken as a control, heated at 100°C for 30 minutes at the same protein concentration, cooled and placed in a refrigerator at 4°C for 24 hours, and the storage modulus and viscosity were measured. The storage modulus measurement results are shown in FIG. Figure 2 As shown, the storage modulus of the untreated soy protein after heating is significantly higher than that of the heat-stable soy protein prepared in this example; Fig.16As shown in the figure, the soy protein in the left bottle forms a hot gel after heating, while the heat-stable soy protein obtained in the right bottle in this example remains in a fluid state after heating and does not gel. Figure 3 As shown, the viscosity of the heat-stable soy protein obtained in this example is much lower than that of the untreated soy protein after heat treatment. In summary, the dispersion of the heat-stable soy protein obtained in this example has high thermal stability.

[0071] Example 2

[0072] A method for preparing heat-stable soybean protein comprises the following steps:

[0073] S1. Soy protein extraction: defatted soybean meal was added to deionized water at a ratio of 1:12 (w / v, g / mL), the pH was adjusted to 8.0 with 1 mol / L NaOH solution, stirred at room temperature for 1 h, and centrifuged (15800 g, 30 min, 4°C) to remove insoluble matter to obtain a supernatant; the supernatant was adjusted to pH 4.5 with 1 mol / L HCl, and centrifuged (3000 g, 120 min, 4°C) to obtain a soybean protein precipitate; the soybean protein precipitate was dissolved with deionized water and the pH of the solution was adjusted to 7.0, and the solution was spray-dried (inlet air temperature 195°C, outlet air temperature 95°C, feed rate 20 mL / min) to obtain soybean protein; the total thiol content of the soybean protein was 3.46 μmol / g;

[0074] S2, dispersion: soybean protein was uniformly dispersed in water at a mass concentration of 5% (w / w, g / g), and the pH was adjusted to 7.0 to obtain a protein dispersion 1;

[0075] S3, dispersion: take PEG with a molecular weight of 10000, uniformly disperse it in water at a mass concentration of 40% (w / w, g / g), and adjust the pH to 7.0 to obtain a PEG dispersion;

[0076] S4, mixing: mixing equal volumes of the protein dispersion 1 obtained in step S2 and the PEG dispersion obtained in step S3, and stirring evenly to obtain a mixed solution;

[0077] S5, heat treatment: heating the mixed solution obtained in step S4 at 100° C. for 30 min;

[0078] S6, acid precipitation: the mixed solution obtained in step S5 is adjusted to pH 4.5 with 2 mol / L HCl;

[0079] S7, centrifugation: centrifuge the product obtained in step S6 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0080] S8, dispersion: adjust the pH of deionized water to 4.5 with 0.1 mol / L HCL, mix the precipitate obtained in step S7 with deionized water at a mass ratio (w / w) of 1:5 and disperse for 20 min to remove polyethylene glycol;

[0081] S9, centrifugation: centrifuge the product obtained in step S8 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0082] S10, re-dissolving: the precipitate obtained in step S9 was mixed with deionized water at a mass ratio (w / w) of 1:5, and the pH was adjusted to 7.0 with 2 mol / L NaOH for dispersion and re-dissolution to obtain a protein solution;

[0083] S11, drying: the protein solution obtained in step S10 is subjected to vacuum freeze drying (-80°C, 0.01Pa, 24h) to obtain heat-stable soy protein.

[0084] The heat-stable soy protein prepared in this example was prepared into an aqueous solution with a protein concentration of 10% (w / v, g / mL). The solution was heated at 100°C for 30 minutes, cooled and placed in a 4°C refrigerator for 24 hours, and the storage modulus and viscosity were measured. At the same time, soy protein was taken as a control, and the storage modulus and viscosity were measured at the same protein concentration at 100°C for 30 minutes, cooled and placed in a 4°C refrigerator for 24 hours. The storage modulus measurement results are shown in FIG. Figure 4 The viscosity measurement results are shown in Figure 5 As shown, the storage modulus and viscosity values ​​of the heat-stable soy protein prepared in this example after heat treatment are much smaller than those of the untreated soy protein dispersion; Fig.17 It shows that compared with the untreated soy protein, the heat-stable soy protein on the right did not gel after heating, and showed a colloidal dispersion state with good fluidity and uniform dispersion.

[0085] Example 3

[0086] A method for preparing heat-stable soybean protein comprises the following steps:

[0087] S1. Soy protein extraction: defatted soybean meal was added to deionized water at a ratio of 1:12 (w / v, g / mL), the pH was adjusted to 8.0 with 2 mol / L NaOH solution, stirred at room temperature for 1 h, and centrifuged (15800 g, 30 min, 4°C) to remove insoluble matter to obtain a supernatant; the supernatant was adjusted to pH 5.0 with 2 mol / L HCl, and centrifuged (6000 g, 15 min, 4°C) to obtain a soy protein precipitate; the soy protein precipitate was dissolved with deionized water and the pH of the protein solution was adjusted to 7.0, and the protein solution was freeze-dried to obtain soy protein, and the freeze-drying was specifically -80°C, 0.01 Pa, 24 h; the total thiol content of the soy protein was 3.46 μmol / g;

[0088] S2, dispersion: soybean protein was uniformly dispersed in water at a mass concentration of 5% (w / w, g / g), and the pH was adjusted to 7.0 to obtain a protein dispersion 1;

[0089] S3, dispersion: take PEG with a molecular weight of 20000, uniformly disperse it in water at a mass concentration of 20% (w / w, g / g), and adjust the pH to 7.0 to obtain a PEG dispersion;

[0090] S4, mixing: mixing equal volumes of the protein dispersion 1 obtained in step S2 and the PEG dispersion obtained in step S3, and stirring evenly to obtain a mixed solution;

[0091] S5, heat treatment: heating the mixed solution obtained in step S4 at 100° C. for 30 min;

[0092] S6, acid precipitation: the mixed solution obtained in step S5 is adjusted to pH 4.5 with 2 mol / L HCl;

[0093] S7, centrifugation: centrifuge the product obtained in step S6 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0094] S8, dispersion: adjust the pH of deionized water to 4.5 with 0.1 mol / L HCL, mix the precipitate obtained in step S7 with deionized water at a mass ratio (w / w) of 1:5 and disperse for 20 min to remove polyethylene glycol;

[0095] S9, centrifugation: centrifuge the product obtained in step S8 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0096] S10, re-dissolving: the precipitate obtained in step S9 was mixed with deionized water at a mass ratio (w / w) of 1:5, and the pH was adjusted to 7.0 with 2 mol / L NaOH for dispersion and re-dissolution to obtain a protein solution;

[0097] S11, drying: the protein solution obtained in step S10 is subjected to vacuum freeze drying (-80°C, 0.01Pa, 24h) to obtain heat-stable soy protein.

[0098] The heat-stable soy protein prepared in this example was prepared into an aqueous solution with a protein concentration of 10% (w / v, g / mL). The solution was heated at 100°C for 30 minutes, cooled and placed in a 4°C refrigerator for 24 hours, and the storage modulus and viscosity were measured. At the same time, soy protein was taken as a control, and the storage modulus and viscosity were measured at the same protein concentration at 100°C for 30 minutes, cooled and placed in a 4°C refrigerator for 24 hours. The storage modulus measurement results are shown in FIG. Figure 6 The viscosity measurement results are shown in Figure 7As shown, the storage modulus and viscosity values ​​of the heat-stable soy protein prepared in this example after heat treatment are much smaller than those of the untreated soy protein dispersion; Fig.18 It shows that the heat-stable soy protein on the right side has not gelled after heat treatment at a higher protein concentration, showing a colloidal dispersion with good fluidity and uniform dispersion, indicating that the heat-stable soy protein after combined treatment has better fluidity and stability.

[0099] Comparative Example 1

[0100] A method for preparing soybean protein comprises the following steps:

[0101] S1. Soy protein extraction: defatted soybean meal was added to deionized water at a ratio of 1:12 (w / v, g / mL), the pH was adjusted to 7.0 with 2 mol / L NaOH solution, stirred at room temperature for 1 h, and centrifuged (15800 g, 30 min, 4°C) to remove insoluble matter to obtain a supernatant; the supernatant was adjusted to pH 4.5 with 2 mol / L HCl, and centrifuged (6000 g, 30 min, 4°C) to obtain a soybean protein precipitate; the soybean protein precipitate was dissolved with deionized water and the pH of the protein solution was adjusted to 7.0, and the protein solution was freeze-dried to obtain soybean protein, and the freeze-drying was specifically -50°C, 0.01 Pa, 24 h; the total thiol content of the soybean protein was 3.46 μmol / g;

[0102] S2, dispersion: soybean protein was uniformly dispersed in water at a mass concentration of 2.5% (w / w, g / g), and the pH was adjusted to 7.0 to obtain a protein dispersion 1;

[0103] S3, heat treatment: heating the protein dispersion 1 obtained in step S2 at 100° C. for 30 min;

[0104] S4, acid precipitation: the mixed solution obtained in step S3 is adjusted to pH 4.5 with 2 mol / L HCl;

[0105] S5, centrifugation: centrifuge the product obtained in step S4 (15800g, 30min, 4°C) to collect the precipitate;

[0106] S6, re-dissolving: mixing the precipitate obtained in step S5 with deionized water at a mass ratio (w / w) of 1:5, and adjusting the pH to 7.0 with 2 mol / L NaOH for dispersion and re-dissolution to obtain a protein solution;

[0107] S7, drying: the protein solution obtained in step S6 is subjected to vacuum freeze drying (-80°C, 0.01Pa, 24h) to obtain heat-stable soy protein.

[0108] The heat-stable soy protein prepared in this comparative example was prepared into an aqueous solution with a protein concentration of 10% (w / v, g / mL). The solution was heated at 100°C for 30 minutes, cooled and placed in a 4°C refrigerator for 24 hours, and the storage modulus and viscosity were measured. At the same time, soy protein was taken as a control, and the storage modulus and viscosity were measured at the same protein concentration at 100°C for 30 minutes, cooled and placed in a 4°C refrigerator for 24 hours. The storage modulus measurement results are shown in FIG. Figure 8 The viscosity measurement results are shown in Fig. 9 As shown, the heat-stable protein prepared in this comparative example gelled after heat treatment, and the storage modulus and viscosity values ​​were close to those of the untreated soy protein dispersion after heating; Fig.19 It is intuitively shown that the untreated soy protein on the left and the soy protein dispersion after thermal stabilization on the right both undergo gelation to varying degrees, indicating that the thermal stability of the soy protein after thermal stabilization under this condition is poor.

[0109] Comparative Example 2

[0110] A method for preparing soybean protein comprises the following steps:

[0111] S1. Soy protein extraction: defatted soybean meal was added to deionized water at a ratio of 1:12 (w / v, g / mL), the pH was adjusted to 8.0 with 2 mol / L NaOH solution, stirred at room temperature for 1 h, and centrifuged (15800 g, 30 min, 4°C) to remove insoluble matter to obtain a supernatant; the supernatant was adjusted to pH 5.0 with 2 mol / L HCl, and centrifuged (6000 g, 15 min, 4°C) to obtain a soy protein precipitate; the soy protein precipitate was dissolved with deionized water and the pH of the protein solution was adjusted to 7.0, and the protein solution was freeze-dried to obtain soy protein, and the freeze-drying was specifically -80°C, 0.01 Pa, 24 h; the total thiol content of the soy protein was 3.46 μmol / g;

[0112] S2, dispersion: soybean protein was uniformly dispersed in water at a mass concentration of 5% (w / w, g / g), and the pH was adjusted to 7.0 to obtain a protein dispersion 1;

[0113] S3, dispersion: take PEG with a molecular weight of 6000, uniformly disperse it in water at a mass concentration of 30% (w / w, g / g), and adjust the pH to 7.0 to obtain a PEG dispersion;

[0114] S4, mixing: mixing equal volumes of the protein dispersion 1 obtained in step S2 and the PEG dispersion obtained in step S3, and stirring evenly to obtain a mixed solution;

[0115] S5, heat treatment: heating the mixed solution obtained in step S4 at 100° C. for 30 min;

[0116] S6, acid precipitation: the mixed solution obtained in step S5 is adjusted to pH 4.5 with 2 mol / L HCl;

[0117] S7, centrifugation: centrifuge the product obtained in step S6 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0118] S8, dispersion: adjust the pH of deionized water to 4.5 with 0.1 mol / L HCL, mix the precipitate obtained in step S7 with deionized water at a mass ratio (w / w) of 1:5 and disperse for 20 min to remove polyethylene glycol;

[0119] S9, centrifugation: centrifuge the product obtained in step S8 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0120] S10, re-dissolving: the precipitate obtained in step S9 was mixed with deionized water at a mass ratio (w / w) of 1:5, and the pH was adjusted to 7.0 with 2 mol / L NaOH for dispersion and re-dissolution to obtain a protein solution;

[0121] S11, drying: the protein solution obtained in step S10 is subjected to vacuum freeze drying (-80°C, 0.01Pa, 24h) to obtain heat-stable soy protein.

[0122] The heat-stable soy protein prepared in this example was prepared into an aqueous solution with a protein concentration of 10% (w / v, g / mL). The solution was heated at 100°C for 30 minutes, cooled and placed in a 4°C refrigerator for 24 hours, and the storage modulus and viscosity were measured. At the same time, soy protein was taken as a control, and the storage modulus and viscosity were measured at the same protein concentration at 100°C for 30 minutes, cooled and placed in a 4°C refrigerator for 24 hours. The storage modulus measurement results are shown in FIG. Fig.10 The viscosity measurement results are shown in Fig.11 As shown, the heat-stable protein prepared in this comparative example gelled after heat treatment, and the storage modulus and viscosity values ​​were close to those of the untreated soy protein dispersion after heating; Fig. 20 It shows that the untreated soy protein on the left and the soy protein dispersion after thermal stabilization on the right both undergo gelation to varying degrees, indicating that the thermal stability of the soy protein after thermal stabilization under this condition is poor.

[0123] Comparative Example 3

[0124] A method for preparing soybean protein comprises the following steps:

[0125] S1. Soy protein extraction: defatted soybean meal was added to deionized water at a ratio of 1:12 (w / v, g / mL), the pH was adjusted to 8.0 with 2 mol / L NaOH solution, stirred at room temperature for 1 h, and centrifuged (15800 g, 30 min, 4°C) to remove insoluble matter to obtain a supernatant; the supernatant was adjusted to pH 5.0 with 2 mol / L HCl, and centrifuged (6000 g, 15 min, 4°C) to obtain a soy protein precipitate; the soy protein precipitate was dissolved with deionized water and the pH of the protein solution was adjusted to 7.0, and the protein solution was freeze-dried to obtain soy protein, and the freeze-drying was specifically -80°C, 0.01 Pa, 24 h; the total thiol content of the soy protein was 3.46 μmol / g;

[0126] S2, dispersion: soybean protein was uniformly dispersed in water at a mass concentration of 5% (w / w, g / g), and the pH was adjusted to 7.0 to obtain a protein dispersion 1;

[0127] S3, dispersion: take PEG with a molecular weight of 10000, uniformly disperse it in water at a mass concentration of 5% (w / w, g / g), and adjust the pH to 7.0 to obtain a PEG dispersion;

[0128] S4, mixing: mixing equal volumes of the protein dispersion 1 obtained in step S2 and the PEG dispersion obtained in step S3, and stirring evenly to obtain a mixed solution;

[0129] S5, heat treatment: heating the mixed solution obtained in step S4 at 100° C. for 30 min;

[0130] S6, acid precipitation: the mixed solution obtained in step S5 is adjusted to pH 4.5 with 2 mol / L HCl;

[0131] S7, centrifugation: centrifuge the product obtained in step S6 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0132] S8, dispersion: adjust the pH of deionized water to 4.5 with 0.1 mol / L HCL, mix the precipitate obtained in step S7 with deionized water at a mass ratio (w / w) of 1:5 and disperse for 20 min to remove polyethylene glycol;

[0133] S9, centrifugation: centrifuge the product obtained in step S8 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0134] S10, re-dissolving: the precipitate obtained in step S9 was mixed with deionized water at a mass ratio (w / w) of 1:5, and the pH was adjusted to 7.0 with 2 mol / L NaOH for dispersion and re-dissolution to obtain a protein solution;

[0135] S11, drying: the protein solution obtained in step S10 is subjected to vacuum freeze drying (-80°C, 0.01Pa, 24h) to obtain heat-stable soy protein.

[0136] The heat-stable soy protein prepared in this example was prepared into an aqueous solution with a protein concentration of 10% (w / v, g / mL). The solution was heated at 100°C for 30 minutes, cooled and placed in a 4°C refrigerator for 24 hours, and the storage modulus and viscosity were measured. At the same time, soy protein was taken as a control, and the storage modulus and viscosity were measured at the same protein concentration at 100°C for 30 minutes, cooled and placed in a 4°C refrigerator for 24 hours. The storage modulus measurement results are shown in FIG. Fig.12 The viscosity measurement results are shown in Fig.13 As shown, the heat-stable protein prepared in this comparative example gelled after heat treatment, and the storage modulus and viscosity values ​​were close to those of the untreated soy protein dispersion after heating; Fig.21 It shows that the untreated soy protein on the left and the soy protein dispersion after thermal stabilization on the right both undergo gelation to varying degrees, indicating that the thermal stability of the soy protein after thermal stabilization under this condition is poor.

[0137] 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 heat-stable soybean protein based on crowding effect, characterized in that: The specific steps include: S1, mixing: taking the soybean protein dispersion and the PEG dispersion and mixing them evenly to obtain a mixed solution A; S2, heat treatment: heating the mixed solution A in step S1 at 95-100° C. for 25-30 min to obtain a mixed solution B; S3, acid precipitation: adjusting the pH of the mixed solution B obtained in step S2 to 4.0-4.5 to obtain a mixed solution C; S4, centrifugation: centrifuge the mixed solution C in step S3 to collect the precipitate; S5, dispersion: adjust the pH of deionized water to 4.0-4.5 with 0.1 mol / L HCL, and disperse the precipitate obtained in step S4 in deionized water at pH 4.0-4.5 for 20 min to remove polyethylene glycol; S6, centrifugation: centrifuging the product obtained in step S5 to collect the precipitate; S7, re-dissolving: adding water to the precipitate obtained in step S6, adjusting the pH to 7.0-7.5 for dispersion and re-dissolution to obtain a protein solution; S8, drying: drying the protein solution obtained in step S7 to obtain heat-stable soy protein; Wherein, the mass concentration of soybean protein in the soybean protein dispersion described in step S1 is 2-5%, the mass concentration of PEG in the PEG dispersion is 20-40%, and the molecular weight of PEG is 10000-20000.

2. The method according to claim 1, characterized in that The preparation method of the soy protein dispersion in step S1 is to take soy protein, evenly disperse it in water at a mass concentration of 2-5% (w / w, g / g), and adjust the pH to 7.0 to obtain the soy protein dispersion.

3. The method according to claim 1, characterized in that The extraction method of soybean protein is as follows: defatted soybean meal is added with deionized water at a ratio of 1:12 (w / v, g / ml), pH is adjusted to 7.0-8.5 with 2mol / L NaOH solution, stirred at room temperature for 1h, centrifuged at 15800g and 4℃ for 30min, and the supernatant is taken; the supernatant is adjusted to pH 4-5 with 2mol / L HCl, centrifuged at 3000-15800g and 4℃ for 5-120min to obtain a precipitate; the precipitate is dissolved with deionized water and the pH of the solution is adjusted to 6.5-8.0, and the solution is frozen or spray-dried to obtain soybean protein. The parameters of the freeze-drying are -50--80℃, vacuum degree 0.01Pa-50Pa, and drying for 24-72h; the parameters of the spray-drying are: inlet air temperature 195℃, outlet air temperature 95℃, and feed rate 20mL / min.

4. The method according to claim 1, characterized in that: The volume ratio of the soybean protein dispersion to the PEG dispersion in the mixed solution A described in step S1 is 0.8-1.2:

1.

5. The method according to claim 1, characterized in that The centrifugal speeds in steps S4 and S6 are both 3000-15800 g, and the centrifugal time is both 5-120 min.

6. The method according to claim 1, characterized in that The weight ratio of the precipitate to water in steps S5 and S7 is 1:(5-10).

7. The method according to claim 6, characterized in that The drying in step S8 is freeze drying or spray drying; the spray drying is specifically: -50 to -80°C, vacuum degree 0.01Pa to 50Pa, and drying for 24 to 72 hours; the spray drying is specifically: inlet air temperature 180 to 200°C, outlet air temperature 80 to 100°C, and feed rate 15 to 30mL / min.

8. The heat-stable soybean protein prepared according to the method according to any one of claims 1 to 7.

9. Use of the heat-stable soybean protein according to claim 8 in the food field.

10. The use according to claim 9, characterized in that: The food includes swallowable food or high-protein food, and the high-protein food includes high-protein beverage.

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