Method for preparing thermal-stability soybean protein through cooperation of preheating and disulfide bond cleavage

Abstract

The invention discloses a method for preparing thermal-stability soybean protein by synergistic preheating and disulfide bond cleavage, which comprises the following steps: mixing Na2S2O5 dispersion liquid with the concentration of 2-20mM / L and soybean protein dispersion liquid, uniformly stirring, heating at 100 DEG C for 30 minutes, and then carrying out acid precipitation, centrifugation, dispersion, redissolution and drying to obtain the thermal-stability soybean protein. 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% 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 by preheating and coordinated disulfide bond cleavage. Background Art

[0002] Soybean is the most widely planted and economically valuable legume crop. Soy protein is a high-quality plant protein that contains essential amino acids required by the human body. Soy protein can improve food texture and increase satiety. It is a high-quality substitute for meat and dairy products and is widely used in nutritional supplements and low-fat foods. Heat treatment is a very important step in processing soy protein products. It can not only improve the digestibility of soy protein in the human body, but also reduce the beany smell and sterilize. However, during the heat processing of soy protein, heat treatment will cause protein molecules to aggregate, further leading to precipitation or gelation in the product, thus affecting the sensory and nutritional properties of the product.

[0003] Patent CN110679725A discloses a method for preparing heat-stable soy protein isolate. The invention adds modified starch to the soy protein to improve its heat stability. However, starch is a polysaccharide. Excessive intake of sugars may lead to obesity, which is contrary to the original intention of eating high-protein foods. At the same time, as consumers pay more and more attention to the sugar content of food, sugar-free foods are favored because of their low calories and health properties. Patent CN 109770041 A discloses a method for preparing heat-stable soy protein. The heat stability of soy protein can be improved by heat-treating and modifying soy protein with a concentration of 0.1-1.5% (w / w, g / g), and the prepared heat-stable soy protein can maintain a certain heat stability at a concentration of 10%. However, in the actual study of the performance of soy protein, it was found that the soybean meal used to extract soy protein has a great influence on the stability of soy protein. The higher the degree of oxidation of the soybean meal, the better the stability of the extracted soy protein. The degree of oxidation of the soybean meal can be reflected by the total thiol content of the extracted soy protein, such as Figure 1As 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 groups are oxidized into disulfide bonds, 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 improve the performance of soy protein without adding sugary substances. 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 by preheating synergistic disulfide bond cleavage, which is committed to solving the problem of gelation or aggregation of soy protein with high thiol content (-SH group content greater than 1.5 μmol / g) when heated at 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 by preheating and synergistic disulfide bond cleavage, comprising the following specific steps:

[0006] S1. Mixing: Mix the soybean protein dispersion and the Na2S2O5 dispersion, and stir 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: adjusting the pH of the mixed solution B obtained in step S2 to 4.0-4.5 to obtain a mixed solution C;

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

[0010] S5, dispersion: using 1 mol / L HCl to adjust the pH of deionized water to 4.0-4.5, and dispersing the precipitate obtained in step S4 in deionized water with a pH of 4.0-4.5;

[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 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] In one embodiment of the present invention, in step S1, the mass concentration of soybean protein in the soybean protein dispersion is 1.5-4%, and the concentration of Na2S2O5 in the Na2S2O5 dispersion is 4-20 mmol / L.

[0015] In one embodiment of the present invention, in step S1, the volume ratio of the soybean protein dispersion to the Na2S2O5 dispersion in the mixed solution A is 0.8-1.2:1.

[0016] In one embodiment of the present invention, the method for preparing the soy protein dispersion in step S1 is to take soy protein, uniformly disperse it in water at a mass concentration of 1.5-4% (w / w, g / g), and adjust the pH to 7.0 to obtain a soy protein dispersion;

[0017] In one embodiment of the present invention, the pH of the Na2S2O5 dispersion in step S1 is 7 and the concentration is 2 to 10 (mmol / L); the preparation method is to take Na2S2O5, uniformly disperse it in water at a concentration of 4 to 20 (mmol / L), and adjust the pH to 7.0 to obtain a Na2S2O5 dispersion.

[0018] In one embodiment of the present invention, the extraction method of soybean protein is as follows: defatted soybean meal is added to deionized water in a ratio of 1:12 (w / v, g / ml), 2mol / L NaOH solution is used to adjust the pH to 7.0-8.5, stirring at room temperature for 1h, centrifuging at 15800g and 4°C for 30min, and taking the supernatant; the supernatant is adjusted to pH 4-5 with 2mol / L HCl, and centrifuged at 3000-15800g and 4°C 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 dried to obtain soybean protein.

[0019] In one embodiment of the present invention, the drying in the soy protein extraction method is freeze drying or spray drying; the parameters of the freeze drying are -50 to -80°C, vacuum degree 0.01Pa to 50Pa, and drying for 24 to 72 hours; the parameters of the spray drying are: inlet air temperature 195°C, outlet air temperature 95°C, and feed rate 20mL / min.

[0020] 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.

[0021] In one embodiment of the present invention, the weight ratio of the precipitate to water in step S5 is 1:(5-10).

[0022] 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.

[0023] In one embodiment of the present invention, the weight ratio of the precipitate to water in step S7 is 1:(5-10).

[0024] 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.

[0025] The present invention also provides a heat-stable soybean protein prepared by the method.

[0026] The present invention also provides an application of the heat-stable soybean protein in the food field.

[0027] In one embodiment of the present invention, the application includes preparing a high-protein beverage or a swallowable food using the heat-stable soy protein.

[0028] Beneficial effects:

[0029] 1. The present invention improves the thermal stability of soybean protein by adding Na2S2O5 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.

[0030] 2. The present invention uses preheating to coordinate the cleavage of disulfide bonds to prepare heat-stable soy protein. The addition of the reducing agent Na2S2O5 is helpful for the cleavage of disulfide bonds, which significantly improves the heat stability of the soy protein. After adding the reducing agent Na2S2O5, even if the concentration of the soy protein is as high as 2%, the heat-treated soy protein can still maintain good heat 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.

[0031] 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, the addition of a reducing agent combined with heat treatment can make the concentration of soy protein before heat treatment as high as 2%, significantly improving the thermal stability of soy protein.

[0032] 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

[0033] Figure 1 These are the measurement results of total thiol content of soy protein isolate extracted from soybean meals 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.

[0034] 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.

[0035] Figure 3 The viscosity measurement result of the heat-stable soy protein obtained in Example 1 of the present invention after heating.

[0036] 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.

[0037] Figure 5 The viscosity measurement result of the heat-stable soy protein obtained in Example 2 of the present invention after heating.

[0038] Figure 6 This is the storage modulus measurement result of the heat-stable soy protein obtained in Example 3 of the present invention after heating.

[0039] Figure 7 The viscosity measurement result of the heat-stable soy protein obtained in Example 3 of the present invention after heating is shown.

[0040] Figure 8 The storage modulus measurement result of the modified soy protein obtained in Example 4 of the present invention after heating.

[0041] Fig. 9 The viscosity measurement result of the modified soybean protein obtained in Example 4 of the present invention after heating is shown.

[0042] Fig.10 The storage modulus measurement result of the modified soy protein obtained in Comparative Example 1 of the present invention after heating.

[0043] Fig.11 The viscosity measurement result of the modified soybean protein obtained in Comparative Example 1 of the present invention after heating.

[0044] Fig.12 The storage modulus measurement result of the modified soy protein obtained in Comparative Example 2 of the present invention after heating.

[0045] Fig.13 The viscosity measurement result of the modified soybean protein obtained in Comparative Example 2 of the present invention after heating.

[0046] Fig.14 These are the particle size measurement results of the heat-stable soybean proteins obtained in Examples 1 to 3 of the present invention.

[0047] Fig.15 These are the particle size measurement results of the heat-stable soybean proteins obtained in Examples 1 to 3 of the present invention after heating.

[0048] Fig.16 This is a schematic diagram of the fluidity of the heat-stable soy protein obtained in Example 1 of the present invention.

[0049] Fig.17 This is a schematic diagram of the fluidity of the heat-stable soy protein obtained in Example 2 of the present invention.

[0050] Fig.18 This is a schematic diagram of the fluidity of the heat-stable soy protein obtained in Example 3 of the present invention.

[0051] Fig.19 This is a schematic diagram of the fluidity of the heat-stable soy protein obtained in Example 4 of the present invention.

[0052] Fig. 20 This is a schematic diagram of the fluidity of the modified soy protein obtained in Comparative Example 1 of the present invention.

[0053] Fig.21 This is a schematic diagram of the fluidity of the modified soy protein obtained in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0054] The present invention will be further described below through specific implementation examples:

[0055] Example 1

[0056] A method for preparing heat-stable soybean protein comprises the following steps:

[0057] 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;

[0058] S2, dispersion: soybean protein was uniformly dispersed in water at a mass concentration of 2% (w / w, g / g), and the pH was adjusted to 7.0 to obtain a protein dispersion 1;

[0059] S3, dispersion: Na2S2O5 is uniformly dispersed in water at a concentration of 10 (mmol / L), and the pH is adjusted to 7.0 to obtain a Na2S2O5 dispersion;

[0060] S4, mixing: mixing equal volumes of the protein dispersion 1 obtained in step S2 and the Na2S2O5 dispersion obtained in step S3, and stirring evenly to obtain a mixed solution;

[0061] S5, heat treatment: heating the mixed solution obtained in step S4 at 100° C. for 30 min;

[0062] S6, acid precipitation: the mixed solution obtained in step S5 is adjusted to pH 4.5 with 2 mol / L HCl;

[0063] S7, centrifugation: centrifuge the product obtained in step S6 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0064] S8, dispersion: adjust the pH of deionized water to 4.5 using 1 mol / L HCl, mix the precipitate obtained in step S7 with deionized water at pH 4.5 at a mass ratio (w / w) of 1:5 and disperse for 20 min;

[0065] S9, centrifugation: centrifuge the product obtained in step S8 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0066] S10, re-dissolving: mixing the precipitate obtained in step S9 with deionized water at a mass ratio (w / w) of 1:5 and adjusting the pH to 7.0 for dispersion and re-dissolution to obtain a protein solution;

[0067] 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.

[0068] 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 non-heat-stabilized soy protein after heating is significantly higher than that of the heat-stabilized soy protein prepared in this example; Fig.16 As 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.

[0069] Example 2

[0070] A method for preparing heat-stable soybean protein comprises the following steps:

[0071] 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 solution pH 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;

[0072] S2, dispersion: soybean protein was uniformly dispersed in water at a mass concentration of 2% (w / w, g / g), and the pH was adjusted to 7.0 to obtain a protein dispersion 1;

[0073] S3, dispersion: Na2S2O5 is uniformly dispersed in water at a concentration of 4 (mmol / L), and the pH is adjusted to 7.0 to obtain a Na2S2O5 dispersion;

[0074] S4, mixing: mixing equal volumes of the protein dispersion 1 obtained in step S2 and the Na2S2O5 dispersion obtained in step S3, and stirring evenly to obtain a mixed solution;

[0075] S5, heat treatment: heating the mixed solution obtained in step S4 at 100° C. for 30 min;

[0076] S6, acid precipitation: the mixed solution obtained in step S5 is adjusted to pH 4.5 with 2 mol / L HCl;

[0077] S7, centrifugation: centrifuge the product obtained in step S6 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0078] S8, dispersion: adjust the pH of deionized water to 4.5 using 1 mol / L HCl, mix the precipitate obtained in step S7 with deionized water of pH 4.5 at a mass ratio (w / w) of 1:5 and disperse for 20 min;

[0079] S9, centrifugation: centrifuge the product obtained in step S8 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0080] S10, re-dissolving: mixing the precipitate obtained in step S9 with deionized water at a mass ratio (w / w) of 1:5 and adjusting the pH to 7.0 for dispersion and re-dissolution to obtain a protein solution;

[0081] 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.

[0082] 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.

[0083] Example 3

[0084] A method for preparing heat-stable soybean protein comprises the following steps:

[0085] 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 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 -80° C., 0.01 Pa, 24 h;

[0086] S2, dispersion: soybean protein was uniformly dispersed in water at a mass concentration of 2% (w / w, g / g), and the pH was adjusted to 7.0 to obtain a protein dispersion 1;

[0087] S3, dispersion: Na2S2O5 is uniformly dispersed in water at a concentration of 20 (mmol / L), and the pH is adjusted to 7.0 to obtain a Na2S2O5 dispersion;

[0088] S4, mixing: mixing equal volumes of the protein dispersion 1 obtained in step S2 and the Na2S2O5 dispersion obtained in step S3, and stirring evenly to obtain a mixed solution;

[0089] S5, heat treatment: heating the mixed solution obtained in step S4 at 100° C. for 30 min;

[0090] S6, acid precipitation: the mixed solution obtained in step S5 is adjusted to pH 4.5 with 2 mol / L HCl;

[0091] S7, centrifugation: centrifuge the product obtained in step S6 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0092] S8, dispersion: adjust the pH of deionized water to 4.5 using 1 mol / L HCl, mix the precipitate obtained in step S7 with deionized water of pH 4.5 at a mass ratio (w / w) of 1:5 and disperse for 20 min;

[0093] S9, centrifugation: centrifuge the product obtained in step S8 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0094] S10, re-dissolving: mixing the precipitate obtained in step S9 with deionized water at a mass ratio (w / w) of 1:5 and adjusting the pH to 7.0 for dispersion and re-dissolution to obtain a protein solution;

[0095] 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.

[0096] 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 7 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.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.

[0097] Example 4

[0098] A method for preparing heat-stable soybean protein comprises the following steps:

[0099] 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;

[0100] S2, dispersion: soybean protein was uniformly dispersed in water at a mass concentration of 4% (w / w, g / g), and the pH was adjusted to 7.0 to obtain a protein dispersion 1;

[0101] S3, dispersion: Na2S2O5 is uniformly dispersed in water at a concentration of 20 (mmol / L), and the pH is adjusted to 7.0 to obtain a Na2S2O5 dispersion;

[0102] S4, mixing: mixing equal volumes of the protein dispersion 1 obtained in step S2 and the Na2S2O5 dispersion obtained in step S3, and stirring evenly to obtain a mixed solution;

[0103] S5, heat treatment: heating the mixed solution obtained in step S4 at 100° C. for 30 min;

[0104] S6, acid precipitation: the mixed solution obtained in step S5 is adjusted to pH 4.5 with 2 mol / L HCl;

[0105] S7, centrifugation: centrifuge the product obtained in step S6 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0106] S8, dispersion: adjust the pH of deionized water to 4.5 using 1 mol / L HCl, mix the precipitate obtained in step S7 with pH 4.5 deionized water at a mass ratio (w / w) of 1:5 and disperse in the pH 4.5 deionized water for 20 min;

[0107] S9, centrifugation: centrifuge the product obtained in step S8 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0108] S10, re-dissolving: mixing the precipitate obtained in step S9 with deionized water at a mass ratio (w / w) of 1:5, adding water, adjusting the pH to 7.0, dispersing and re-dissolving, and obtaining a protein solution;

[0109] 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.

[0110] 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 8 The viscosity measurement results are shown in Fig. 9 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.19 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.

[0111] Comparative Example 1

[0112] A method for preparing soybean protein comprises the following steps:

[0113] 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 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 -50°C, 0.01 Pa, 24 h;

[0114] S2, dispersion: soybean protein was uniformly dispersed in water at a mass concentration of 1% (w / w, g / g), and the pH was adjusted to 7.0 to obtain a protein dispersion 1;

[0115] S3, heat treatment: heating the protein dispersion 1 obtained in step S2 at 100° C. for 30 min;

[0116] S4, acid precipitation: the mixed solution obtained in step S3 is adjusted to pH 4.5 with 2 mol / L HCl;

[0117] S5, centrifugation: centrifuging the product obtained in step S4 to collect the precipitate;

[0118] S6, re-dissolving: adding water to the precipitate obtained in step S5, adjusting the pH to 7.0 for dispersion and re-dissolution to obtain a protein solution;

[0119] S7, drying: drying the protein solution obtained in step S6 to obtain heat-stable soy protein.

[0120] 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. 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 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.

[0121] Comparative Example 2

[0122] A method for preparing soybean protein comprises the following steps:

[0123] 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 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 -80° C., 0.01 Pa, 24 h;

[0124] S2, dispersion: soybean protein was uniformly dispersed in water at a mass concentration of 2% (w / w, g / g), and the pH was adjusted to 7.0 to obtain a protein dispersion 1;

[0125] S3, dispersion: Na2S2O5 is uniformly dispersed in water at a concentration of 2 (mmol / L), and the pH is adjusted to 7.0 to obtain a Na2S2O5 dispersion;

[0126] S4, mixing: mixing equal volumes of the protein dispersion 1 obtained in step S2 and the Na2S2O5 dispersion obtained in step S3, and stirring evenly to obtain a mixed solution;

[0127] S5, heat treatment: heating the mixed solution obtained in step S4 at 100° C. for 30 min;

[0128] S6, acid precipitation: the mixed solution obtained in step S5 is adjusted to pH 4.5 with 2 mol / L HCl;

[0129] S7, centrifugation: centrifuge the product obtained in step S6 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0130] S8, dispersion: the precipitate obtained in step S7 was mixed with pH 4.5 deionized water at a mass ratio (w / w) of 1:5 and dispersed in the pH 4.5 deionized water for 20 min;

[0131] S9, centrifugation: centrifuge the product obtained in step S8 (15800 g, 30 min, 4° C.) to collect the precipitate;

[0132] S10, re-dissolving: mixing the precipitate obtained in step S9 with deionized water at a mass ratio (w / w) of 1:5, adding water, adjusting the pH to 7.0, dispersing and re-dissolving, and obtaining a protein solution;

[0133] 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.

[0134] 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. 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 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.

[0135] 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 by preheating and disulfide bond cleavage, characterized in that: The specific steps include: S1. Mixing: Mix the soybean protein dispersion and the Na2S2O5 dispersion, and stir 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: using 1 mol / L HCl to adjust the pH of deionized water to 4.0-4.5, and dispersing the precipitate obtained in step S4 in deionized water with a pH of 4.0-4.5; 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.

2. The method according to claim 1, characterized in that In step S1, the mass concentration of soybean protein in the soybean protein dispersion is 1.5-4%, and the concentration of Na2S2O5 in the Na2S2O5 dispersion is 4-20 mmol / L.

3. The method according to claim 1, characterized in that: In step S1, the volume ratio of the soybean protein dispersion to the Na2S2O5 dispersion in the mixed solution A is 0.8-1.2:

1.

4. The method according to claim 1, characterized in that: The soybean protein extraction method comprises the following steps: adding deionized water to defatted soybean meal at a ratio of 1:12 (w / v, g / ml), adjusting the pH value to 7.0-8.5 with a 2 mol / L NaOH solution, stirring at room temperature for 1 hour, centrifuging at 15800 g and 4°C for 30 minutes, and obtaining a supernatant; adjusting the pH value of the supernatant to 4-5 with 2 mol / L HCl, and centrifuging at 3000-15800 g and 4°C for 5-120 minutes to obtain a precipitate; dissolving the precipitate with deionized water and adjusting the pH value of the solution to 6.5-8.0, and subjecting the solution to freeze drying or spray drying to obtain soybean protein; the freeze drying parameters are -50--80°C, vacuum degree 0.01 Pa-50 Pa, and drying for 24-72 hours; the spray drying parameters are: inlet air temperature 195°C, outlet air temperature 95°C, and feed rate 20 mL / min.

5. The method according to claim 1, characterized in that The centrifugal speed in steps S4 and S6 is 3000-15800 g, and the centrifugal time is 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 1, 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, drying 24 to 72h; the spray drying is specifically: inlet air temperature 180 to 200°C, outlet air temperature 80 to 100°C, 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 application includes preparing high-protein beverages or swallowable foods using the heat-stable soybean protein.

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