A soy protein isolate and its preparation method

Abstract

This invention provides a method for preparing soy protein isolate, comprising the following steps: A) first extraction of alcohol-based soy protein concentrate to obtain a first-extract material; B) high-temperature refolding of the first-extract material to obtain a refolded protein solution; the high-temperature refolding temperature is 85℃~130℃, the time is 4s~8s, and the vacuum degree is -0.05~-0.08MPa; C) continuous extraction of the refolded protein solution to obtain an extracted mixed soy milk; D) acid precipitation and neutralization of the extracted mixed soy milk to obtain a neutralized material; E) flash sterilization and homogenization of the neutralized material, followed by spray drying to obtain soy protein isolate. The soy protein isolate preparation method provided by this invention is safe and simple, yields high protein, has low equipment requirements, and produces soy protein isolate with high whiteness.

Description

Technical Field

[0001] This invention belongs to the field of food technology, specifically relating to a soy protein isolate and its preparation method. Background Technology

[0002] Traditional soy protein isolate production process uses low-temperature defatted soybean meal as raw material, and is produced through processes such as extraction, alkali dissolution and acid precipitation, and high-temperature spray drying. During this process, soy isoflavones and phenolic substances in the soybean meal undergo oxidative browning under high temperature conditions to produce colored substances. At the same time, the Maillard reaction between amino groups and sugars in the protein deepens the color of soy protein isolate, making it difficult for the whiteness of soy protein isolate to meet the requirements of high-end food.

[0003] Existing technologies can improve the whiteness of soy protein isolate to a certain extent, but they still have certain limitations: While ozone gas treatment can oxidize and degrade some colored substances, the strong oxidizing properties of ozone can easily alter the molecular structure of soy protein isolate, reducing its key functional properties such as emulsification and water retention. Too low an ozone concentration will result in insufficient oxidation of colored substances, limiting the whiteness improvement. Furthermore, ozone treatment requires a closed, high-pressure environment, placing high demands on the equipment. Activated carbon adsorption, while removing chromogenic components, also non-specifically adsorbs some small-molecule proteins and functional components, leading to a decrease in protein yield. Additionally, multiple water washes are required to remove residual activated carbon, making the process cumbersome and inefficient. Alcohol leaching can effectively reduce harmful components, but the protein's nitrogen solubility index is very low, severely impacting protein yield during subsequent extraction. Other methods to improve soy protein isolate whiteness include alcohol washing of soybean meal, low-temperature extraction, and water washing of coagulated milk; however, these methods have very limited whiteness improvement effects and require high-quality equipment, and the alcohol-water mixture poses a significant risk.

[0004] Therefore, providing a safe and simple preparation method for high-whiteness soy protein isolate with high protein yield and low equipment requirements has become a problem that needs to be solved. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing soy protein isolate. The method for preparing soy protein isolate provided by the present invention is safe and simple, has a high protein yield, does not require high equipment, and produces soy protein isolate with high whiteness.

[0006] This invention provides a method for preparing soy protein isolate, comprising the following steps:

[0007] A) The alcohol-based soy protein concentrate is subjected to a first extraction to obtain the first-extract material;

[0008] B) The first-extracted material is subjected to high-temperature refolding to obtain a refolded protein solution; the high-temperature refolding temperature is 85℃~130℃, the time is 4s~8s, and the vacuum degree is -0.05~-0.08MPa.

[0009] C) The refolded protein solution is continuously extracted to obtain the extracted mixed soy milk;

[0010] D) The extracted mixed soy milk is subjected to acid precipitation and neutralization to obtain neutralized material;

[0011] E) After the neutralized material is subjected to flash sterilization and homogenization, it is spray-dried to obtain soy protein isolate.

[0012] Preferably, the proportion of the un-ultra-finely pulverized alcohol-based soy protein concentrate passing through a 100-mesh sieve is ≤30%.

[0013] Preferably, the method for preparing the un-ultra-finely pulverized alcohol-based soy protein concentrate includes the following steps:

[0014] Using low-temperature defatted soybean meal as raw material, it is extracted with 72%~74% ethanol solution at a material-to-solvent ratio of 1:(6~7) for 120~150 min. After desolventizing, the dry basis protein content of the extracted soybean protein is not less than 65%.

[0015] Preferably, the extractant for the first extraction is water, with a material-to-water mass ratio of 1:9 to 1:16, an extraction temperature of 35°C to 38°C, and stirring for 10 to 15 minutes.

[0016] Preferably, the high-temperature remodeling is carried out in a flash tank with a liquid level of 20% to 30%.

[0017] Preferably, the continuous extraction includes:

[0018] After refolding, the protein solution is adjusted to pH 7.0-8.0 with liquid alkali and subjected to primary extraction in a first extraction tank at a stirring speed of 50-60 r / min for 20-30 min. The solid phase is then transferred to a second extraction tank for complete extraction at a stirring speed of 50-60 r / min for 10-20 min. The water added for complete extraction is room temperature water, and the amount of water added is 3-4 times the amount of protein concentrated by the alcohol method. The extracts from the two extractions are combined to obtain the extracted mixed soy milk.

[0019] Preferably, the pH of the acid precipitation is 4.4 to 4.5;

[0020] The acid used for acid precipitation is hydrochloric acid solution.

[0021] Preferably, the neutralization includes:

[0022] Adjust the pH of the curd obtained from acid precipitation to 6.5-7.0, and adjust the solid content to 9.5%-12.5% ​​with water.

[0023] Preferably, after acid precipitation, wet soybean residue is obtained, which is then subjected to deodorization, steaming, washing, pressing, drying, cooling, and pulverizing to obtain soybean dietary fiber.

[0024] The present invention also provides a soy protein isolate prepared by the above preparation method, wherein the whiteness of the soy protein isolate is above 65.

[0025] Compared with existing technologies, this invention provides a method for preparing soy protein isolate, comprising the following steps: A) first extraction of un-ultra-finely pulverized alcohol-based soy protein concentrate to obtain a first-extract material; B) high-temperature refolding of the first-extract material to obtain a refolded protein solution; the high-temperature refolding temperature is 85℃~130℃, the time is 4s~8s, and the vacuum degree is -0.05~-0.08MPa; C) continuous extraction of the refolded protein solution to obtain an extracted mixed soy milk; D) acid precipitation and neutralization of the extracted mixed soy milk to obtain a neutralized material; E) flash sterilization and homogenization of the neutralized material, followed by spray drying to obtain soy protein isolate. This invention uses alcohol-based soy protein concentrate as raw material, and through high-temperature, short-time refolding, induces the unfolding and re-aggregation of protein molecules, effectively exposing the hydrophobic groups of the protein, improving the emulsifying properties of soy protein isolate and the water-binding properties of soy dietary fiber; passivating the color reaction of the protein, reducing the formation of colored substances, and improving the whiteness of the product. The method for preparing soy protein isolate provided by this invention is safe, simple, and yields high protein output with low equipment requirements. Furthermore, the soy protein isolate produced by this invention exhibits high whiteness, improved emulsification performance (35.8%), and increased crude protein yield (58.7%). This enhances the appearance compatibility of end-use products, ensures stable food texture, and improves production efficiency. The soy dietary fiber produced by this invention also boasts high whiteness, improved swelling capacity (46.9%), and increased water-holding capacity (55.6%), thereby enhancing the product's application value. Detailed Implementation

[0026] This invention provides a method for preparing soy protein isolate, comprising the following steps:

[0027] A) The un-ultra-finely pulverized alcohol-based soy protein concentrate is subjected to a first extraction to obtain the first-extract material;

[0028] B) The first-extracted material is subjected to high-temperature refolding to obtain a refolded protein solution; the high-temperature refolding temperature is 85℃~130℃, the time is 4s~8s, and the vacuum degree is -0.05~-0.08MPa.

[0029] C) The refolded protein solution is continuously extracted to obtain the extracted mixed soy milk;

[0030] D) The extracted mixed soy milk is subjected to acid precipitation and neutralization to obtain neutralized material;

[0031] E) After the neutralized material is subjected to flash sterilization and homogenization, it is spray-dried to obtain soy protein isolate.

[0032] This invention prepares soy protein isolate using un-ultra-finely ground alcohol-based soy protein concentrate as raw material. The method for preparing the un-ultra-finely ground alcohol-based soy protein concentrate includes the following steps:

[0033] Using low-temperature defatted soybean meal as raw material, extract with 72%~74% ethanol solution at a material-to-solution ratio of 1:(6~7) for 120~150 min. The material-to-solution ratio can be any ratio between 1:6, 1:6.2, 1:6.5, 1:6.8, 1:7, or 1:(6~7). The extraction time can be any value between 120, 130, 140, 150, or 120~150 min.

[0034] After desolventizing, an alcohol-based soy protein concentrate with a dry-basis protein content of not less than 65% is obtained. Desolventizing is preferably performed by extrusion and drying.

[0035] In this invention, the percentage of the un-ultra-finely pulverized alcohol-based soybean protein concentrate passing through a 100-mesh sieve is ≤30%.

[0036] After obtaining un-ultra-finely ground alcohol-based soy protein concentrate, the un-ultra-finely ground alcohol-based soy protein concentrate is subjected to a first extraction. The extractant for the first extraction is water, with a material-to-water mass ratio of 1:9 to 1:16, which can be 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, or any value between 1:9 and 1:16. The extraction temperature is 35℃ to 38℃, which can be 35, 36, 37, 38, or any value between 35℃ and 38℃. The stirring time is 10 to 15 minutes, which can be 10, 11, 12, 13, 14, 15, or any value between 10 and 15 minutes.

[0037] After obtaining the first extract, the first extract is subjected to high-temperature refolding to obtain a refolded protein solution. The high-temperature refolding temperature is 85℃~130℃, which can be any value between 85, 90, 95, 100, 105, 110, 115, 120, 125, 130℃, or 85℃~130℃; the time is 4s~8s, which can be any value between 4, 5, 6, 7, 8s, or 4s~8s; and the vacuum degree is -0.05~-0.08MPa, which can be any value between -0.05, -0.06, -0.07, -0.08, or -0.05~-0.08MPa. The first extract is then introduced into a flash evaporator, with the liquid level at 20%~30%, which can be any value between 20%, 25%, 30%, or 20%~30%.

[0038] The refolded protein solution is continuously extracted to obtain extracted mixed soy milk. The continuous extraction includes:

[0039] After refolding, the pH of the protein solution is adjusted to 7.0-8.0 using liquid alkali. The pH can be 7.0, 7.2, 7.4, 7.5, 7.6, 7.8, 8.0, or any value between 7.0 and 8.0. Primary extraction is performed in a first-stage extraction tank with a stirring speed of 50-60 rpm (50, 55, 60, or any value between 50 and 60 rpm) and a time of 20-30 min (20, 25, 30, or any value between 20 and 30 min). The solid phase is then transferred to a second-stage extraction tank for complete extraction with a stirring speed of 50-60 rpm (50, 55, 60, or any value between 50 and 60 rpm) and a time of 10-20 min (10, 15, 20, or any value between 10 and 20 min).

[0040] In the process of complete extraction, room temperature water is added, and the amount of water added is 3 to 4 times the amount of protein concentrated by the alcohol method. The extracts from the two extractions are combined to obtain the extracted mixed soy milk.

[0041] The extracted mixed soy milk was subjected to acid precipitation and neutralization to obtain neutralized material.

[0042] The extracted mixed soy milk was thoroughly mixed, the pH was adjusted to 4.4-4.5, and centrifuged to obtain curd and wet soy residue. The acid used was hydrochloric acid solution.

[0043] Adjust the pH of the obtained curd with an alkaline solution to 6.5-7.0, which can be 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, or any value between 6.5 and 7.0. Adjust the solid content with water to 9.5%-12.5%, which can be 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, or any value between 9.5% and 12.5%.

[0044] After neutralization, the material is subjected to flash sterilization and homogenization, and then spray-dried to obtain soy protein isolate.

[0045] Soybean dietary fiber is obtained from wet soybean residue after deodorization, steaming, washing, pressing, drying, cooling, and pulverizing.

[0046] This invention uses alcohol-based soy protein concentrate as raw material. Through high-temperature, short-time refolding, the protein molecular structure unfolds and re-aggregates, effectively exposing the hydrophobic groups of the protein, improving the emulsifying properties of soy protein isolate and the water-binding properties of soy dietary fiber; it also passivates the colorimetric reaction of the protein, reducing the formation of colored substances and improving product whiteness. The soy protein isolate preparation method provided by this invention is safe and simple, with high protein yield and low equipment requirements. Furthermore, the soy protein isolate produced by this invention has high whiteness, improved emulsifying performance by 35.8%, and increased crude protein yield by 58.7%. This can improve the appearance adaptability of end-use products, ensure food texture stability, and improve production efficiency. The soy dietary fiber produced by this invention has high whiteness, improved swelling capacity by 46.9%, and improved water-holding capacity by 55.6%, enhancing the application value of the product.

[0047] To further understand the present invention, the following embodiments illustrate the soy protein isolate and its preparation method provided by the present invention. The scope of protection of the present invention is not limited by the following embodiments.

[0048] The alcohol-based soy protein concentrate used in the following examples and comparative examples was prepared according to the following method:

[0049] Using low-temperature defatted soybean meal as raw material, it is extracted with 72%~74% ethanol solution at a material-to-solvent ratio of 1:6 for 2 hours. After desolventizing, an alcohol-based soybean protein concentrate with a dry basis protein content of not less than 6% is obtained.

[0050] The preparation methods for alcohol-based soybean protein concentrate, acid-based soybean protein concentrate, and the low-temperature defatted soybean meal raw material used in Comparative Example 4 are as follows:

[0051] Using non-GMO soybeans as raw material, the process involves impurity removal, softening, crushing, peeling, and rolling. Hexane is used as the leaching solvent for desolventizing, with an immersion temperature of 55-60℃ and a leaching time of 120 minutes, yielding wet meal. The wet meal is then subjected to vacuum low-temperature desolventizing at a temperature of 70-85℃, a desolventizing time of 15-20 minutes, and a negative pressure of -0.5 to -1 kPa, resulting in low-temperature defatted soybean meal. The defatted soybean meal has a dry basis crude protein content ≥53%, NSI ≥65%, moisture ≤10%, and impurity content ≤0.1%.

[0052] Example 1:

[0053] (1) Using un-ultra-finely ground alcohol-based soy protein concentrate as raw material, feed it into a mixing tank with a material-to-water ratio of 1:12, an extraction temperature of 37°C, and stirring for 10 minutes. Un-finely ground means that the proportion of the material passing through a 100-mesh sieve of alcohol-based soy protein concentrate is ≤30%.

[0054] (2) High-temperature remodeling: the material is introduced into the flash tank, the liquid level is 20%, the heating temperature of the connecting tube bundle is 120℃, the time is 6s, and the vacuum degree is -0.08MPa;

[0055] (3) Continuous extraction: After refolding, the pH of the protein solution is adjusted to 7.0 with liquid alkali. The first extraction is carried out in the first extraction tank and the complete extraction is carried out in the second extraction tank. The water added in the second extraction is room temperature water, and the amount of water added is 3 times the amount of protein concentrated by the raw material alcohol method.

[0056] (4) Separate soybean residue. Mix the extracted mixed soybean milk thoroughly, adjust the pH to 4.5, and centrifuge to obtain curd and wet soybean residue. The acid used is hydrochloric acid solution.

[0057] (5) Neutralize the resulting curd by adjusting the pH to 6.9 with an alkaline solution and adjusting the solid content to 11.5% with water;

[0058] (6) After neutralization, the material is sterilized at 135℃ for 8 seconds, vacuum controlled at -0.08MPa, homogenized at 35MPa, and then dried by hot air spray at 190℃ to obtain soy protein isolate.

[0059] (7) The wet soybean residue was conditioned with 3 times the amount of 50°C hot water, passed through a plate and frame filter press to obtain a fiber filter cake, and then dried and pulverized with 180°C hot air. The obtained fiber powder was then pulverized by ultra-fine grinding and sieved to obtain soybean dietary fiber.

[0060] Example 2:

[0061] (1) Using un-ultra-finely ground alcohol-based soy protein concentrate as raw material, feed it into a mixing tank, with a material-to-water ratio of 1:10, an extraction temperature of 37℃, and stirring for 10 minutes. Un-finely ground means that the proportion of the material passing through a 100-mesh sieve of alcohol-based soy protein concentrate is ≤30%.

[0062] (2) High-temperature remodeling: the material is introduced into the flash tank, the liquid level is 20%, the heating temperature of the connecting tube bundle is 90℃, the time is 8s, and the vacuum degree is -0.06MPa;

[0063] (3) Continuous extraction: After refolding, the protein solution is adjusted to pH 7.0 with liquid alkali and then subjected to primary extraction in a first extraction tank. The stirring speed is 50-60 r / min and the time is 30 min. The solid phase is then transferred to a second extraction tank for complete extraction. The stirring speed is 50-60 r / min and the time is 15 min. The water added in the second extraction is room temperature water, and the amount of water added is 3 times the amount of protein concentrated by the alcohol method of the raw material. All liquid phase is transferred to the soy milk tank.

[0064] (4) Separate soybean residue. Mix the extracted mixed soybean milk thoroughly, adjust the pH to 4.5, and centrifuge to obtain curd and wet soybean residue. The acid used is hydrochloric acid solution.

[0065] (5) Neutralize the resulting curd by adjusting the pH to 6.9 with an alkaline solution and adjusting the solid content to 12% with water;

[0066] (6) After neutralization, the material is sterilized at 135℃ for 8 seconds, vacuum controlled at -0.08MPa, homogenized at 35MPa, and then dried by hot air spray at 190℃ to obtain soy protein isolate.

[0067] (7) The wet soybean residue was conditioned with 3 times the amount of 50°C hot water, passed through a plate and frame filter press to obtain a fiber filter cake, and then dried and pulverized with 180°C hot air. The obtained fiber powder was then pulverized by ultra-fine grinding and sieved to obtain soybean dietary fiber.

[0068] Example 3:

[0069] (1) Using un-ultra-finely ground alcohol-based soy protein concentrate as raw material, feed it into a mixing tank, with a material-to-water ratio of 1:10, an extraction temperature of 37℃, and stirring for 10 minutes. Un-finely ground means that the proportion of the material passing through a 100-mesh sieve of alcohol-based soy protein concentrate is ≤30%.

[0070] (2) High-temperature remodeling: the material is introduced into the flash tank, the liquid level is 20%, the heating temperature of the connecting tube bundle is 105℃, the time is 6s, and the vacuum degree is -0.08MPa;

[0071] (3) Continuous extraction: After refolding, the protein solution is adjusted to pH 7.0 with liquid alkali and then subjected to primary extraction in a first extraction tank. The stirring speed is 50-60 r / min and the time is 30 min. The solid phase is then transferred to a second extraction tank for complete extraction. The stirring speed is 50-60 r / min and the time is 15 min. The water added in the second extraction is room temperature water, and the amount of water added is 3 times the amount of protein concentrated by the alcohol method of the raw material. All liquid phase is transferred to the soy milk tank.

[0072] (4) Separate soybean residue. Mix the extracted mixed soybean milk thoroughly, adjust the pH to 4.5, and centrifuge to obtain curd and wet soybean residue. The acid used is hydrochloric acid solution.

[0073] (5) Neutralize the resulting curd by adjusting the pH to 6.9 with an alkaline solution and adjusting the solid content to 12% with water;

[0074] (6) After neutralization, the material is sterilized at 135℃ for 8 seconds, vacuum controlled at -0.08MPa, homogenized at 35MPa, and then dried by hot air spray at 190℃ to obtain soy protein isolate.

[0075] (7) The wet soybean residue was conditioned with 3 times the amount of 50°C hot water, passed through a plate and frame filter press to obtain a fiber filter cake, and then dried and pulverized with 180°C hot air. The obtained fiber powder was then pulverized by ultra-fine grinding and sieved to obtain soybean dietary fiber.

[0076] Comparative Example 1:

[0077] (1) Using un-ultra-finely ground alcohol-based soy protein concentrate as raw material, feed it into a mixing tank, with a material-to-water ratio of 1:10, an extraction temperature of 37℃, and stirring for 10 minutes. Un-finely ground means that the proportion of the material passing through a 100-mesh sieve of alcohol-based soy protein concentrate is ≤30%.

[0078] (2) Continuous extraction: After refolding, the protein solution is adjusted to pH 7.0 with liquid alkali and then subjected to primary extraction in a first extraction tank. The stirring speed is 50-60 r / min and the time is 30 min. The solid phase is then transferred to a second extraction tank for complete extraction. The stirring speed is 50-60 r / min and the time is 15 min. The water added in the second extraction is room temperature water, and the amount of water added is 3 times the amount of protein concentrated by the alcohol method of the raw material. All liquid phase is transferred to the soy milk tank.

[0079] (3) Separate soybean residue. Mix the extracted mixed soybean milk thoroughly, adjust the pH to 4.5, and centrifuge to obtain curd and wet soybean residue. The acid used is hydrochloric acid solution.

[0080] (4) Neutralize the resulting curd by adjusting the pH to 6.9 with an alkaline solution and adjusting the solid content to 12% with water;

[0081] (5) After neutralization, the material is sterilized at 135℃ for 8 seconds, vacuum controlled at -0.08MPa, homogenized at 35MPa, and then dried by hot air spray at 190℃ to obtain soy protein isolate.

[0082] (6) The wet soybean residue is conditioned with 3 times the amount of 50°C hot water, passed through a plate and frame filter press to obtain a fiber filter cake, and then the pulverized filter cake is dried with 180°C hot air. The obtained fiber powder is then pulverized by ultrafine grinding and sieved to obtain soybean dietary fiber.

[0083] Comparative Example 2:

[0084] (1) Using ultra-fine pulverized alcohol-based soy protein concentrate as raw material, feed it into a mixing tank with a material-to-water ratio of 1:10, an extraction temperature of 37℃, and stir for 10 minutes. Ultra-fine pulverization refers to the proportion of material passing through a 100-mesh sieve of alcohol-based soy protein concentrate being ≥95%.

[0085] (2) High-temperature remodeling: the material is introduced into the flash tank, the liquid level is 20%, the heating temperature of the connecting tube bundle is 105℃, the time is 6s, and the vacuum degree is -0.08MPa;

[0086] (3) Continuous extraction: After refolding, the protein solution is adjusted to pH 7.0 with liquid alkali and then subjected to primary extraction in a first extraction tank. The stirring speed is 50-60 r / min and the time is 30 min. The solid phase is then transferred to a second extraction tank for complete extraction. The stirring speed is 50-60 r / min and the time is 15 min. The water added in the second extraction is room temperature water, and the amount of water added is 3 times the amount of protein concentrated by the alcohol method of the raw material. All liquid phase is transferred to the soy milk tank.

[0087] (4) Separate soybean residue. Mix the extracted mixed soybean milk thoroughly, adjust the pH to 4.5, and centrifuge to obtain curd and wet soybean residue. The acid used is hydrochloric acid solution.

[0088] (5) Neutralize the resulting curd by adjusting the pH to 6.9 with an alkaline solution and adjusting the solid content to 12% with water;

[0089] (6) After neutralization, the material is sterilized at 135℃ for 8 seconds, vacuum controlled at -0.08MPa, homogenized at 35MPa, and then dried by hot air spray at 190℃ to obtain soy protein isolate.

[0090] (7) The wet soybean residue was conditioned with 3 times the amount of 50°C hot water, passed through a plate and frame filter press to obtain a fiber filter cake, and then dried and pulverized with 180°C hot air. The obtained fiber powder was then pulverized by ultra-fine grinding and sieved to obtain soybean dietary fiber.

[0091] Comparative Example 3:

[0092] (1) Using un-ultra-finely ground alcohol-based soy protein concentrate as raw material, feed it into a mixing tank, with a material-to-water ratio of 1:10, an extraction temperature of 37℃, and stirring for 10 minutes. Un-finely ground means that the proportion of the material passing through a 100-mesh sieve of alcohol-based soy protein concentrate is ≤30%.

[0093] (2) High-temperature remodeling: the material is introduced into the flash tank, the heating temperature of the connecting tube bundle is 80℃, the liquid level is 20%, the time is 9s, and the vacuum degree is -0.08MPa;

[0094] (3) Continuous extraction: After refolding, the protein solution is adjusted to pH 7.0 with liquid alkali and then subjected to primary extraction in a first extraction tank. The stirring speed is 50-60 r / min and the time is 30 min. The solid phase is then transferred to a second extraction tank for complete extraction. The stirring speed is 50-60 r / min and the time is 15 min. The water added in the second extraction is room temperature water, and the amount of water added is 3 times the amount of protein concentrated by the alcohol method of the raw material. All liquid phase is transferred to the soy milk tank.

[0095] (4) Separate soybean residue. After the extracted mixed soybean milk is fully mixed, it is homogenized at a homogenization pressure of 20 MPa. The pH of the soybean milk is adjusted to 4.5. The coagulated milk and wet soybean residue are separated by centrifugation. The acid used is hydrochloric acid solution.

[0096] (5) Neutralize the resulting curd by adjusting the pH to 6.9 with an alkaline solution and adjusting the solid content to 12% with water;

[0097] (6) After neutralization, the material is sterilized at 135℃ for 8 seconds, vacuum controlled at -0.08MPa, homogenized at 35MPa, and then dried by hot air spray at 190℃ to obtain soy protein isolate.

[0098] (7) The wet soybean residue was conditioned with 3 times the amount of 50°C hot water, passed through a plate and frame filter press to obtain a fiber filter cake, and then dried and pulverized with 180°C hot air. The obtained fiber powder was then pulverized by ultra-fine grinding and sieved to obtain soybean dietary fiber.

[0099] Comparative Example 4:

[0100] (1) Low-temperature defatted soybean meal was used as raw material and fed into a mixing tank with a material-to-water ratio of 1:10. The extraction temperature was 37℃ and the mixture was stirred for 10 minutes.

[0101] (2) The parameters for high-temperature refolding, extraction, neutralization, sterilization, and drying are the same as in Example 3, to obtain soy protein isolate and soy dietary fiber products.

[0102] Comparative Example 5:

[0103] (1) Using low-temperature defatted soybean meal as raw material, the protein coagulates and precipitates under a pH of about 4.5, and then neutralizes, homogenizes, sterilizes and spray-dries to obtain acid-concentrated protein. Using this acid-concentrated soybean protein as raw material, it is fed into a mixing tank with a material-to-water ratio of 1:10, an extraction temperature of 37℃ and stirring for 10 minutes. The basic production process of acid-concentrated soybean protein is as follows: using low-temperature defatted soybean meal as raw material, after crushing and sieving, it is mixed with water at a material-to-water ratio of 1:10 and then the pH is adjusted to 4.5 by hydrochloric acid for acid extraction. After separation, the obtained solid phase is neutralized to pH 7.0 by liquid alkali, and then sterilized, concentrated and dried to obtain soybean protein product.

[0104] (2) The parameters for high-temperature refolding, extraction, neutralization, sterilization, and drying are the same as in Example 3, to obtain soy protein isolate and soy dietary fiber products.

[0105] Product performance testing:

[0106] (1) Blue light whiteness and Lab value

[0107] The blue light whiteness of the powder sample was measured using an intelligent whiteness meter. The powder sample box was cleaned with a clean brush. A frosted glass plate was placed in the pressure cap, and the powder sample box was tightened. The sample to be tested was gently placed into the powder sample box, and any excess material protruding from the flat surface was scraped off. The pressure block was placed on top, and the powder compactor nut was screwed on. A "click-click" sound when the handle was turned clockwise indicated that the sample was compacted. The powder compactor handle was turned counterclockwise 720°, the powder compactor nut was loosened, the plastic cap was replaced, the powder sample box was flipped over, the pressure cap was removed, the frosted glass plate was moved horizontally, and the powder sample box was placed into the test port. The digital window immediately displayed the blue light whiteness value of the sample. Each sample was measured three times, and the average value was taken as the result.

[0108] The Lab value is determined using a colorimeter. The sample is placed in a special powder cuvette, the wall of the cuvette is tapped gently to avoid creating gaps, the bottom of the sample cuvette is wiped clean with lens paper, and then placed on the instrument. The instrument reads the value automatically. Each sample is measured three times, and the average value is taken as the result.

[0109] (2) Emulsifying properties of soy protein isolate

[0110] The emulsification performance was tested by simulating milk using the actual application of soy protein isolate. 200g of ice water was weighed into a chopping cup, followed by 50g of soy protein isolate. The mixture was mixed at low speed (level 1) until no dry powder remained (approximately 90 seconds). Then, it was chopped at high speed for 2 minutes, scraping and mixing every minute. Next, 200g of pork fat (processed through a 14mm perforated meat grinder) was added, and the mixture was chopped for a total of 3 minutes, scraping and mixing every minute. Finally, 9g of salt was added, and the mixture was chopped at high speed for 80 seconds. The emulsion was then transferred to a heat-sealed bag, and a sausage filling experiment was conducted. Each sausage was 150±10mm in length and weighed 50±0.5g. After filling the intestines, they were placed in sealed bags and vacuum-sealed. They were then sterilized by steaming at 115±1℃ for 22±2 minutes. After sterilization, when the temperature of the intestines naturally dropped below 37℃, the casings were peeled open for testing. A P / 50 probe was selected, the emulsified gel was cut into 25mm pieces, the deformation of the physical property tester was set to 60%, and the peak value of the rupture strength after the test was recorded.

[0111] (3) Protein production yield

[0112] Protein production yield is calculated as crude protein yield.

[0113] Crude protein yield (%) = (finished product weight × finished product dry basis protein content) / (total raw materials × raw material dry basis protein content)

[0114] (4) Solubility of soybean dietary fiber

[0115] The swelling capacity of soybean dietary fiber was determined using the graduated cylinder method. Accurately weigh a dried, constant-weight sample m (≤1.000 g) and pour it into a 10 mL graduated cylinder. Gently tap the cylinder to allow the sample to naturally accumulate without compaction, and record the volume as V1 (mL). Add 8 mL of distilled water, gently shake the cylinder to completely disperse the sample without clumping, and add water to a final volume of 10 mL. Tighten the stopper and shake well. Let the cylinder stand upright for 12 hours, and record the volume as V2 (mL). Measure each sample three times, and take the average value as the result.

[0116] Swelling capacity (mL / g) = (V2 - V1) / m

[0117] (5) Water-holding capacity of soybean dietary fiber

[0118] The water-holding capacity of soybean dietary fiber was determined using an industry-standard centrifugation method. A dried, constant-weight sample (m) was accurately weighed into a beaker, and 50 times its volume of distilled water was added. The sample was allowed to stand at room temperature for 30 minutes. The mass of the empty centrifuge tube was recorded as m1. All samples were transferred to centrifuge tubes and centrifuged at 4000 rpm for 15 minutes to completely separate the free water from the wet residue. The free water was discarded, and the weight of the centrifuge tube plus the wet residue (m2) was measured. Each sample was measured three times, and the average value was taken as the result.

[0119] Water holding capacity (g / g) = (m2 - m1 - m) / m

[0120] (6) NSI (Nitrogen Solubility Index)

[0121] The NSI of the sample was determined using a combination of water-soluble nitrogen extraction and Kjeldahl nitrogen determination. 5.000 g of sample was accurately weighed into a 500 ml Erlenmeyer flask, dissolved in approximately 200 ml of deionized water, and shaken at 120 rpm for 120 min in a 30°C water bath. The resulting suspension was transferred to a 250 ml volumetric flask and brought to volume. The solution was then transferred to a centrifuge and centrifuged at 1500 rpm for 10 min. The supernatant was filtered, and 5.0 ml of the filtrate was transferred to a digestion tube. 5 g of catalyst was weighed, and 10 ml of concentrated sulfuric acid was added for digestion. The nitrogen content was determined using a Kjeldahl nitrogen analyzer. The measured value represents the water-soluble nitrogen content. The total nitrogen content of the sample was determined using a Kjeldahl nitrogen analyzer according to the national standard (GB 5009.5-2025).

[0122] NSI (%) = (Water-soluble nitrogen content / Total nitrogen content of sample) × 100

[0123] Table 1

[0124]

[0125] As shown in Table 1, crude protein yield reflects the final recovery efficiency of crude protein from raw materials in the entire production process. It is a core economic and technological performance indicator in the production process, related to production costs and capacity benefits. The higher the yield, the higher the utilization rate of raw material protein and the less resource waste. Compared with Comparative Example 2, Example 3 showed a 28.7% increase in protein yield, indicating that ultrafine grinding causes protein loss. Compared with Comparative Example 1, Example 3 showed a 58.7% increase in protein yield, indicating that the present invention can effectively improve the protein yield when producing soy protein isolate from alcohol-concentrated protein, which is beneficial to improving company profits. Protein content and NSI determine its application scenario. The NSI value of the product obtained in the comparative example is much lower than that of Example 3. The protein content and NSI value of Example 3 are both better, and it can be applied to end products with high protein content requirements.

[0126] Blue light whiteness represents the overall whiteness of the product, while the Lab value characterizes the detailed results of the product's color dimensions. Under the same raw material conditions, compared with Comparative Examples 1-3, the examples show higher blue light whiteness values, higher L values, and lower ab values ​​for soy protein isolate and soy dietary fiber. This indicates that the protein is light and bright in color, mainly manifested in light red and light yellow hues, with high whiteness. This reflects proper temperature and pH control during the refolding and extraction processes, resulting in good decolorization and effective control of Maillard and other color-forming reactions during production. Under different raw material conditions, compared with Comparative Examples 4-5, the examples still show a significant advantage in color, indicating that selecting alcohol-based soy concentration as a raw material according to this invention is more conducive to improving the whiteness of the finished product. Such products can enhance the color of finished products such as vegetarian meat and fish paste.

[0127] The emulsifying properties of soy protein isolate are characterized by its ability to form a stable oil-water protein gel system; the higher the breaking strength, the better the protein emulsifying performance. The emulsifying performance of Examples 1-3 of this invention is superior to that of Comparative Examples 1-5, with Example 3 showing a 35.8% improvement in emulsifying performance compared to Comparative Example 1, indicating a significant improvement in the emulsifying performance of the protein isolate prepared according to this invention.

[0128] The swelling and water-holding capacity of soybean dietary fiber directly reflect the ability of dietary fiber to interact with water. Higher swelling capacity indicates a more significant volume expansion effect after the fiber absorbs water, while higher water-holding capacity indicates a stronger water retention capacity. Among them, Example 3 exhibits the best swelling and water-holding capacity. Under this scheme, the molecular network structure of the fiber, the looseness of the particles, and the molecular expansion ability after absorbing water are all better, which plays a role in thickening, increasing volume, and improving fluffiness during food processing.

[0129] Based on the results of the above cases, the soy protein isolate produced by this invention has good whiteness, emulsifying properties, and protein yield, while also improving the whiteness, swelling properties, and water-holding capacity of the by-product soy dietary fiber, which is beneficial for industrial production and application. Example 3 is the best among these.

[0130] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing soy protein isolate, characterized in that, Includes the following steps: A) The alcohol-based soy protein concentrate is subjected to a first extraction to obtain the first-extract material; B) The first-extracted material is subjected to high-temperature refolding to obtain a refolded protein solution; the high-temperature refolding temperature is 85℃~130℃, the time is 4s~8s, and the vacuum degree is -0.05~-0.08MPa. C) The refolded protein solution is continuously extracted to obtain the extracted mixed soy milk; D) The extracted mixed soy milk is subjected to acid precipitation and neutralization to obtain neutralized material; E) After the neutralized material is subjected to flash sterilization and homogenization, it is spray-dried to obtain soy protein isolate.

2. The preparation method according to claim 1, characterized in that, The percentage of the un-ultra-finely pulverized alcohol-based soy protein concentrate passing through a 100-mesh sieve is ≤30%.

3. The preparation method according to claim 1, characterized in that, The method for preparing the alcohol-based soy protein concentrate without ultrafine grinding includes the following steps: Using low-temperature defatted soybean meal as raw material, it is extracted with 72%~74% ethanol solution at a material-to-solvent ratio of 1:(6~7) for 120~150 min. After desolventizing, the dry basis protein content of the extracted soybean protein is not less than 65%.

4. The preparation method according to claim 1, characterized in that, The extract used in the first extraction was water, with a material-to-water mass ratio of 1:9 to 1:16, an extraction temperature of 35℃ to 38℃, and stirring for 10 to 15 minutes.

5. The preparation method according to claim 1, characterized in that, The high-temperature remodeling is carried out in a flash tank with a liquid level of 20% to 30%.

6. The preparation method according to claim 1, characterized in that, The continuous extraction includes: After refolding, the protein solution is adjusted to pH 7.0-8.0 with liquid alkali and subjected to primary extraction in a first extraction tank at a stirring speed of 50-60 r / min for 20-30 min. The solid phase is then transferred to a second extraction tank for complete extraction at a stirring speed of 50-60 r / min for 10-20 min. The water added for complete extraction is room temperature water, and the amount of water added is 3-4 times the amount of protein concentrated by the alcohol method. The extracts from the two extractions are combined to obtain the extracted mixed soy milk.

7. The preparation method according to claim 1, characterized in that, The pH of the acid precipitation is 4.4~4.5; The acid used for acid precipitation is hydrochloric acid solution.

8. The preparation method according to claim 1, characterized in that, The neutralization includes: Adjust the pH of the curd obtained from acid precipitation to 6.5-7.0, and adjust the solid content to 9.5%-12.5% ​​with water.

9. The preparation method according to claim 1, characterized in that, After acid precipitation, wet soybean residue is obtained. The wet soybean residue is then deodorized, steamed, washed, squeezed, dried, cooled, and pulverized to obtain soybean dietary fiber.

10. A soy protein isolate prepared by the preparation method according to any one of claims 1 to 9, characterized in that, The whiteness of the soy protein isolate is above 65.

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