Soybean protein isolate and preparation method thereof

Abstract

The invention discloses soybean protein isolate as well as a preparation method and application thereof. The preparation method of the soybean protein isolate sequentially comprises the steps of extraction, acid precipitation, neutralization, sterilization, flash evaporation, temperature holding reaction, homogenization and drying. In the preparation process of the soybean protein isolate, protein polyphenols are removed, an acyl transfer reaction between proteins is catalyzed and protein-composite gel covalent cross-linking is improved through a specific protein modification technology and a polysaccharide covalent modification technology, so that the physicochemical properties of high purity, excellent dispersity, no lumps during stirring and the like of the proteins are ensured; the whiteness of the protein and the proper gel performance in the instant noodles are remarkably improved, and the technical problems that when the soybean protein isolate is directly applied to the instant noodles at present, the solubility and the gelation characteristic are not well matched with the texture of the noodles, and the protein powder is dark in color are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of food processing, and particularly relates to soy protein isolate and a preparation method thereof. Background Art

[0002] As a kind of instant food, the nutrition and taste of instant noodles have always been the focus of consumers' attention. Traditional instant noodles mostly use wheat flour as the main raw material, which has problems such as limited nutritional value, relatively low protein content, and easy soft collapse after cooking.

[0003] Soy protein isolate (SPI) is a high-purity plant protein, and its protein content usually exceeds 90%. In the food industry, it has a wide range of applications due to its unique functional properties. Soy protein isolate has good water solubility and water retention, and can effectively absorb and retain water, which is crucial for maintaining the humidity and freshness of food, especially during processing and storage. The good emulsifying property and foam stability of soy protein isolate can stabilize the oil-water interface and improve the emulsifying performance of food, which plays an important role in enhancing the taste and texture of food. In baked products, soy protein isolate can increase the expansibility and stability of dough, and has the ability to form gels. This property is particularly important in imitation meat products, cheese substitutes, and vegetarian products. It can also improve the texture and taste of instant noodles, making the product more firm and chewy, and at the same time improving the boil resistance of the product. The better nutritional fortification effect of soy protein isolate, as a complete protein source containing all essential amino acids for the human body, can significantly increase the protein content and nutritional value of food, and is an ideal choice for vegetarians or consumers seeking a healthy diet.

[0004] Although soy protein isolate has been applied in the food industry as a high-quality plant protein source, its direct application in instant noodles faces technical obstacles such as poor solubility, poor matching of gelation characteristics with noodle texture, and dark color of the protein powder, which limits its application. Therefore, developing a special soy protein isolate that can not only maintain the nutritional value of soy protein but also be well compatible with the instant noodle production process has become an urgent need in the industry.

[0005] Chinese Patent Document CN106798072A provides a highly dispersed soy protein isolate. Its main feature is to improve the dispersibility through the granulation aqueous phase spraying technology. This process can promote dispersion, but there is a phenomenon of powder lumps in water during the tumbling application stirring, and the color of the protein slurry is dark. Most importantly, the granulation process is prone to problems of excessive microorganisms during production operation, and it is easy to breed microorganisms if the cleaning control is not in place; Chinese Patent Document CN101735313A (Application No. CN200910262596.1) mainly has an acid precipitation pH of 4.2 - 4.6, acid precipitation and water washing, and its ash content is 4.0% - 4.5%, which belongs to a conventional water washing product and fails to solve the above problems of dissolution, dispersion, gelation, etc. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a soy protein isolate and its preparation method, which solves the technical problems such as poor matching of solubility, gelation characteristics with noodle texture and dark color of the protein powder when the current soy protein isolate is directly applied in instant noodles.

[0007] The preparation method of a soy protein isolate provided by the present invention successively includes the following steps:

[0008] Extraction step: Take an alkaline solution with a pH of 11.5 - 13, mix the soybean meal with the alkaline solution for extraction to obtain a first extraction solution, centrifuge the first extraction solution to obtain a first liquid phase and a first solid phase, mix the first solid phase with water, and perform extraction at natural pH to obtain a second extraction solution. Centrifuge the second extraction solution to obtain a second liquid phase and a second solid phase, and mix the first liquid phase and the second liquid phase to obtain a mixed soy milk emulsion;

[0009] Acid precipitation step: Adjust the pH value of the mixed soy milk emulsion, perform centrifugation to recover the solid phase, and obtain a curd solid phase;

[0010] Neutralization step: Mix the curd solid phase with water and a sodium hydroxide solution, adjust the pH and sugar content to obtain a neutralized solution;

[0011] Sterilization, flash evaporation, holding temperature reaction, homogenization, drying step: Subject the neutralized solution to sterilization, flash evaporation, holding temperature reaction, homogenization, drying, and spraying in sequence to obtain the soy protein isolate.

[0012] Optionally, the temperature of the soybean meal is 40°C.

[0013] Optionally, in the neutralization step, the neutralization conditions are a solid content of 11.5wt% - 15.5wt%, a pH of 7.2 - 7.7, and the sodium hydroxide solution is added continuously.

[0014] Optionally, the sterilization temperature is 148°C - 155°C, the time is 15s - 60s, and the flash evaporation temperature is 70°C - 93°C.

[0015] Optionally, the sterilization, flash evaporation, holding reaction, homogenization, and drying steps include: the rotation speed of the holding reaction is 200r / min. At the pipeline where the flash-evaporated material enters the reaction tank, one or two of mannan and trehalose are continuously added in a diluted manner at a rate of 1‰ / ton - 10‰ / ton based on the mass of the polysaccharide dry basis, and the reaction time is 15min - 60min.

[0016] Optionally, the spraying liquid used for spraying is one or more of modified liquid phospholipids, sorbitan monostearate, sorbitan monooleate, mono- and diglycerol fatty acid esters, and soybean oil.

[0017] Optionally, the spraying liquid includes modified liquid phospholipids, sorbitan monostearate, sorbitan monooleate, mono- and diglycerol fatty acid esters, and soybean oil, and the weight ratio of the modified liquid phospholipids, sorbitan monostearate, sorbitan monooleate, mono- and diglycerol fatty acid esters, and soybean oil is 5:1.5:1.5:2:1.

[0018] Optionally, the spraying method of the spraying liquid during spraying is spraying on the drying tower body. During spraying, the spraying liquid is kept at a constant temperature of 60°C - 80°C, and the spraying amount of the spraying liquid is 0.5‰ - 4‰ / ton of protein.

[0019] In addition, the present invention also provides a soy protein isolate, which is prepared by the preparation method described above.

[0020] In addition, the present invention also provides an application of the soy protein isolate as described above in instant noodles.

[0021] The soy protein isolate, its preparation method, and application provided by the embodiments of the present invention have the following advantages compared with the prior art:

[0022] In the embodiments of the present invention, the preparation method of the soy protein isolate includes an extraction step, an acid precipitation step, a neutralization step, sterilization, flash evaporation, a holding reaction, homogenization, and a drying step. In the preparation process of the soy protein isolate of the present invention, through specific protein modification techniques and polysaccharide covalent modification techniques, protein polyphenolic substances are removed, the acyl transfer reaction between proteins is catalyzed, and the covalent cross-linking of protein-composite gels is improved. This not only ensures the high purity, excellent dispersibility, and no lumps during stirring of the protein, but also significantly improves the protein whiteness and suitable gel performance in instant noodles. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a process flow chart of the soy protein isolate in the embodiments of the present invention. Detailed implementation mode

[0024] As described in the background art, the direct application of soy protein isolate in instant noodles on the market currently faces technical obstacles such as poor solubility, gelation properties, and mismatch of noodle texture, as well as dark color of the protein powder, which limits its application. Therefore, there is an urgent need to develop a special soy protein isolate that can not only maintain the nutritional value of soy protein but also be well compatible with the instant noodle production process.

[0025] The inventors found through research that the protein content in current instant noodles is about 7 wt%, mainly from wheat or added vital wheat gluten. It cannot meet the protein requirement for one meal. To enhance the protein content in noodle products, additional protein raw materials need to be added, but the addition of exogenous protein will seriously affect the texture of the noodles, such as toughness, smoothness, and elasticity. Therefore, the technical problems of the present invention cannot be solved by adding exogenous protein.

[0026] The inventors further found that through specific protein modification technology and polysaccharide covalent modification technology, removing protein polyphenols, catalyzing acyl transfer reactions between proteins, and improving covalent cross-linking of protein - composite gels can improve the application performance of soy protein isolate in instant noodles.

[0027] To solve the above technical problems, the preparation method of the soy protein isolate provided by the present invention includes an extraction step, an acid precipitation step, a neutralization step, sterilization, flash evaporation, holding temperature reaction, homogenization, and drying steps. In the preparation process of the soy protein isolate of the present invention, through specific protein modification technology and polysaccharide covalent modification technology, removing protein polyphenols, catalyzing acyl transfer reactions between proteins, and improving covalent cross-linking of protein - composite gels not only ensure the high purity of the protein and excellent physical and chemical properties such as good dispersibility and no lumps during stirring, but also significantly improve the whiteness of the protein and the suitable gel properties in instant noodles.

[0028] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be described in detail below with reference to the drawings and specific implementation modes.

[0029] The raw materials, samples, reagents, and equipment used in the embodiments of the present invention are all commercially available products that can be purchased on the market unless otherwise specified. Among them, the modified liquid phospholipid is produced by Hebei Huaxia Houde.

[0030] Please refer to Figure 1 , Figure 1 which is the process flow chart of the soy protein isolate in the embodiments of the present invention.

[0031] As described below, the present invention provides a method for preparing a soy protein isolate, including the following steps.

[0032] S100, Extraction step: Take alkaline water with a pH of 11.5 - 13, mix the soybean meal with the alkaline water and then conduct extraction to obtain a first extract. Centrifuge the first extract to obtain a first liquid phase and a first solid phase. Mix the first solid phase with water and conduct extraction at natural pH to obtain a second extract. Centrifuge the second extract to obtain a second liquid phase and a second solid phase. Mix the first liquid phase and the second liquid phase to obtain a mixed soybean milk emulsion.

[0033] Optionally, in some embodiments, the soybean meal is low-temperature soybean meal and the temperature of the soybean meal is 40°C. The inventor found that by adjusting the temperature of the soybean meal during the reaction, the extraction rate can be improved. Compared with the normal temperature of 25°C, 40°C can increase the yield of soy protein isolate by about 0.5% - 1% and can improve the color of soy protein isolate. Compared with the normal temperature of 25°C, the whiteness value of the powder increases by 5% - 10%.

[0034] In addition, it should be noted that the inventor found that by adjusting the pH of the alkaline water in the extraction step, the performance of soy protein isolate can be improved. By using the pH value of the present invention, the dissolution rate of protein is increased, and there are more macromolecular proteins, and the gel property of soy protein isolate is good.

[0035] S200, Acid precipitation step: Adjust the pH value of the mixed soybean milk emulsion, conduct centrifugation to recover the solid phase, and obtain a curd solid phase.

[0036] S300, Neutralization step: Mix the curd solid phase with water and sodium hydroxide solution, and adjust the pH and sugar content to obtain a neutralized liquid.

[0037] In one embodiment, in the neutralization step, the neutralization conditions are that the solid content is 11.5wt% - 15.5wt%, the pH is 7.2 - 7.7, and the addition method of the sodium hydroxide solution is continuous alkali addition. It should be noted that the solid content is the total solid matter after removing water after mixing the curd solid phase with water and sodium hydroxide solution. The continuous alkali addition is automated continuous alkali addition, that is, control the continuous addition of sodium hydroxide solution within a certain time and make the pH at the end of the step be 7.2 - 7.7.

[0038] S400, Sterilization, flash evaporation, holding temperature reaction, homogenization, drying steps: Subject the neutralized liquid to sterilization, flash evaporation, holding temperature reaction, homogenization, drying, and spraying in sequence to obtain the soy protein isolate.

[0039] Specifically, in some embodiments, the sterilization temperature is 148°C - 155°C, the time is 15s - 60s, and the flash evaporation temperature is 70°C - 93°C.

[0040] Specifically, in some embodiments, the steps of sterilization, flash evaporation, holding temperature reaction, homogenization, and drying include: the rotation speed of the holding temperature reaction is 200 r / min. At the pipeline where the flash evaporation material enters the reaction tank, one or both of mannan and trehalose are continuously added in a dilution manner at a rate of 1‰ / ton to 10‰ / ton of the polysaccharide dry basis mass, and the reaction time is 15 min - 60 min.

[0041] It should be noted that the holding temperature reaction is to maintain the flash evaporation temperature. In some embodiments, the mannan is konjac glucomannan. It should be noted that by adding one or both of mannan and trehalose in the above steps, through protein modification technology and polysaccharide covalent modification technology, protein polyphenolic substances can be removed, the acyl transfer reaction between proteins can be catalyzed, and the covalent cross-linking of protein-composite gels can be improved. This not only ensures the high purity, excellent dispersibility, and no lumps during stirring of the protein, but also significantly improves the protein whiteness and the suitable gel performance in instant noodles, and enhances the application performance of soy protein isolate in instant noodles.

[0042] In addition, the thermal denaturation process of protein involves the dissociation of soy protein subunits and the recombination of protein polymers through hydrophobic interactions and disulfide bonds. In the present invention, by further controlling the thermal denaturation at a certain temperature during sterilization, flash evaporation, and holding temperature reaction, the sulfhydryl groups originally buried inside are exposed after the protein molecules are partially unfolded. With the extension of a certain heating time, the sulfhydryl groups within or between protein molecules cross-link to form S-S, and the total sulfhydryl groups decrease, so that the gel properties of soy protein isolate are maintained at a certain level.

[0043] Hydrophobic interactions and intermolecular disulfide bonds are the main forces maintaining the structure of soy protein gels. When polysaccharides undergo covalent cross-linking reactions with soy protein isolate, the polysaccharides can be covalently bound to protein molecules, increasing the content of long-chain hydrophobic groups and enhancing the hydrophobic interaction forces during gel formation, so the protein-composite hydrogel of soy protein isolate will be improved. Mannan has high viscosity, swelling rate, and water absorption capacity, which helps in the formation of protein-composite hydrogels. At the same time, mannan has good synergistic effects with proteins and starches, which helps in the formation of gels. Therefore, such proteins have more application advantages.

[0044] It should be noted that in this step, the protein is mixed with water and exists in the form of a slurry. The polysaccharide dry basis mass means that the addition of polysaccharides in this step is calculated according to the protein dry matter content.

[0045] Furthermore, the spraying liquid used for spraying is one or more of modified liquid phospholipids, sorbitan monostearate, sorbitan monooleate, mono- and diglycerol fatty acid esters, and soybean oil.

[0046] Specifically, in one embodiment, the spraying liquid includes modified liquid phospholipid, sorbitan monostearate, sorbitan monooleate, mono- and diglycerol fatty acid esters, and soybean oil. The weight ratio of the modified liquid phospholipid, sorbitan monostearate, sorbitan monooleate, mono- and diglycerol fatty acid esters, and soybean oil is 5:1.5:1.5:2:1.

[0047] Specifically, in some embodiments, the spraying method of the spraying liquid during spraying is spraying on the drying tower body. During spraying, the spraying liquid is kept at a constant temperature of 60°C - 80°C, and the spraying amount of the spraying liquid is 0.5‰ - 4‰ per ton of protein.

[0048] In addition, an embodiment of the present invention also provides a soy protein isolate, which is prepared by the preparation method described in the embodiment of the present invention.

[0049] In addition, an embodiment of the present invention also provides an application of the soy protein isolate in instant noodles, and the soy protein isolate is the soy protein isolate prepared in the embodiment of the present invention.

[0050] Example 1 Preparation of Soy Protein Isolate

[0051] (1) Extraction: Adjust the pH of the alkaline water to 11.5, mix the low-temperature soybean meal at 40°C with water, and the weight ratio of the low-temperature soybean meal to water is 6.8:1. Perform the first extraction for 30 minutes, and then perform centrifugal separation. The obtained liquid phase 1 enters the soybean milk storage tank, and the obtained solid phase 1 is subjected to the second extraction: Mix the solid phase 1 with water at a weight ratio of 4.5:1, and perform natural pH extraction, followed by centrifugal separation. The obtained solid phase 2 is a by-product, and the obtained liquid phase 2 enters the soybean milk storage tank and is mixed with the liquid phase 1 to obtain a mixed soybean milk.

[0052] (2) Acid precipitation: Adjust the pH value of the mixed soybean milk to 4.5, and perform horizontal screw centrifugal separation. The parameters of the centrifugal separation are 3000 revolutions per minute, and the solid phase is recovered to obtain the curd solid phase 3.

[0053] (3) Neutralization: Mix the curd solid phase 3 with water and 30wt% sodium hydroxide solution, and adjust the pH to 7.3 to obtain a neutralized solution. The neutralization conditions are a solid content of 11.5wt% and a pH of 7.3, and the alkali addition method is continuous alkali addition.

[0054] (4) Sterilization: Control the sterilization temperature at 150°C and the time at 20 seconds.

[0055] (5) Flash evaporation: The flash evaporation temperature is 80°C.

[0056] (6) Holding temperature reaction: Control the constant temperature stirring reaction of the material after flash evaporation, maintain a constant temperature of 80 °C, rotation speed of 200 r / min. At the pipeline where the flash-evaporated material enters the reaction tank, prepare a mixed solution according to konjac glucomannan: trehalose: water = 1:1:5, add the mixed solution at 1‰ per ton of polysaccharide dry basis mass, and the reaction time is 20 minutes;

[0057] (7) Homogenization: Homogenize the product of the holding temperature reaction using a high-pressure homogenizer, with a pressure of 24 mPa;

[0058] (8) Drying: Feed the homogenized material into a pressure spray drying tower for drying and spraying. The air supply temperature is 195 °C, the spraying amount of the spraying liquid is 1‰ per ton of protein. The spraying liquid is modified liquid phospholipid, sorbitan monostearate, sorbitan monooleate, mono- and diglycerol fatty acid esters, and soybean oil, with a weight ratio of 5:1.5:1.5:2:1. Keep the spraying liquid at a constant temperature of 80 °C to obtain soy protein isolate.

[0059] Preparation of soy protein isolate in Example 2

[0060] (1) Extraction: Adjust the pH of the alkaline water to 11.8, mix low-temperature soybean meal at 40 °C with water, the weight ratio of low-temperature soybean meal to water is 6.8:1, conduct the first extraction, with an extraction time of 30 minutes, and perform centrifugal separation. The obtained liquid phase 1 enters the soybean milk storage tank, and the obtained solid phase 1 undergoes a second extraction: mix according to raw material soybean meal and water at 4.5:1, extract at natural pH, and perform centrifugal separation. The obtained solid phase 2 is a by-product, and the obtained liquid phase 2 enters the soybean milk storage tank and is mixed with liquid phase 1 to obtain a mixed soybean milk solution.

[0061] (2) Acid precipitation: Adjust the pH value of the mixed soybean milk solution to 4.5, conduct horizontal screw centrifugal separation, and the parameters of the centrifugal separation are 3000 r / min. Recover the solid phase to obtain the curd solid phase 3.

[0062] (3) Neutralization: Mix the solid phase 3 with water and 30 wt% sodium hydroxide solution, adjust the pH to 7.4 to obtain a neutralized solution. The neutralization conditions are a solid content of 12.5 wt% and a pH of 7.4, and the alkali addition method is continuous alkali addition.

[0063] (4) Sterilization: Control the sterilization temperature at 150 °C and the time at 22 seconds.

[0064] (5) Flash evaporation: The flash evaporation temperature is 75 °C.

[0065] (6) Holding temperature reaction: Control the constant temperature stirring reaction of the material after flash evaporation, maintain a constant temperature of 80 °C, rotation speed of 200 r / min. At the pipeline where the flash-evaporated material enters the reaction tank, prepare a mixed solution according to konjac glucomannan: trehalose: water = 1:1:5, add the mixed solution at 1‰ per ton of polysaccharide dry basis mass, and the reaction time is 30 minutes;

[0066] (7) Homogenization: The temperature-maintained reaction product is homogenized using a high-pressure homogenizer, with a pressure of 24 mPa;

[0067] (8) Drying: The homogenized material enters a pressure spray drying tower for drying and spraying. The air supply temperature is 190 °C, the spraying amount of the spraying liquid is 1.5‰ per ton of protein, and the spraying liquid is modified liquid phospholipid, sorbitan monooleate, mono- and diglycerol fatty acid esters, and soybean oil, with a weight ratio of 5:1.5:2:1. The spraying liquid is maintained at a constant temperature of 80 °C to obtain soy protein isolate.

[0068] Preparation of Soy Protein Isolate in Example 3

[0069] (1) Extraction: Adjust the pH of the alkaline water to 11.8, mix the low-temperature soybean meal at 40 °C with water, with a weight ratio of low-temperature soybean meal to water of 6.8:1, conduct the first extraction for 30 minutes, and perform centrifugal separation. The obtained liquid phase 1 enters the soybean milk storage tank, and the obtained solid phase 1 is subjected to a second extraction, mixed with water at a ratio of raw soybean meal to water of 4.5:1, and extracted at natural pH, followed by centrifugal separation. The obtained solid phase 2 is a by-product, and the obtained liquid phase 2 enters the soybean milk storage tank and is mixed with liquid phase 1 to obtain a mixed soybean milk emulsion.

[0070] (2) Acid precipitation: Adjust the pH value of the mixed soybean milk emulsion to 4.6, conduct horizontal screw centrifugal separation at a speed of 3000 rpm, and recover the solid phase to obtain the curd solid phase 3.

[0071] (3) Neutralization: Mix the curd solid phase 3 with water and a 30 wt% sodium hydroxide solution, adjust the pH to 7.3 to obtain a neutralized solution. The neutralization conditions are a solid content of 13.0 wt% and a pH of 7.4, and the alkali addition method is continuous alkali addition.

[0072] (4) Sterilization: Control the sterilization temperature at 150 °C and the time at 30 seconds.

[0073] (5) Flash evaporation: The flash evaporation temperature is 70 °C.

[0074] (6) Temperature-maintained reaction: Control the constant-temperature stirring reaction of the flash-evaporated material, maintain a constant temperature of 80 °C, and a rotation speed of 200 rpm. At the pipeline where the flash-evaporated material enters the reaction tank, a mixed solution is prepared according to konjac glucomannan:trehalose:water = 1:1:5, and the mixed solution is added at 5‰ per ton of polysaccharide dry basis mass, and the reaction time is 30 minutes;

[0075] (7) Homogenization: The temperature-maintained reaction product is homogenized using a high-pressure homogenizer, with a pressure of 26 mPa;

[0076] (8) Drying: The homogenized material enters a pressure spray drying tower for drying and spraying. The air supply temperature is 190 °C, the spraying amount of the spraying liquid is 1.5‰ per ton of protein, and the spraying liquid is modified liquid phospholipid, sorbitan monooleate, mono- and diglycerol fatty acid esters, and soybean oil, with a weight ratio of 5:1.5:2:1. The spraying liquid is kept at a constant temperature of 80 °C to obtain soy protein isolate.

[0077] Example 4 High-protein Fried Instant Noodles

[0078] 1. Formula

[0079] 250 Kg of wheat flour, 25 Kg of soy protein isolate prepared in Example 1, 90 Kg of water, and 8.46 Kg of other auxiliary materials.

[0080] The other auxiliary materials are mixed according to the ratio of 6.2 Kg of salt, 1.2 Kg of thickener, 1.00 Kg of acidity regulator, and 0.06 Kg of pigment. Among them, the thickener is xanthan gum, guar gum, sodium alginate, and sodium carboxymethylcellulose; the acidity regulator is sodium carbonate, potassium carbonate, and phosphate; the pigment is gardenia yellow and riboflavin. There are no special restrictions on the thickener, acidity regulator, and pigment in this application, and generally commercially available products can be used.

[0081] 2. Preparation method

[0082] Weigh the raw materials according to the formula and mix them in a continuous dough mixer to obtain dough;

[0083] Let the dough go through proofing, compounding, rolling, and cutting successively to make raw noodles with a length of 30 cm, a thickness of 1.2 mm, and a width of 1.5 mm;

[0084] Place the raw noodles in a steamer at a temperature of 100 °C, a steamer pressure of 9 KPa, and a saturated steam flow rate of 800 Kg / h for 3 minutes for α - gelatinization to obtain α - gelatinized noodles;

[0085] Place the α - gelatinized noodles in a frying box for frying. The frying temperature for the first gradient is 110 °C - 125 °C, and the frying time is 35 s; the frying temperature for the second gradient is 125 °C - 135 °C, and the frying time is 40 s; the frying temperature for the third gradient is 135 °C - 152 °C, and the frying time is 35 s. Then the high - protein fried instant noodles are obtained.

[0086] Comparative Example 1 and Comparative Example 2

[0087] The differences between Comparative Example 1 and Comparative Example 2 and Example 1 are that (1) the pH value of the alkaline water in the extraction step is different. The pH of the alkaline water used in Comparative Example 1 is 9.0, and the pH of the alkaline water used in Comparative Example 2 is 11.0. Other steps are the same as those in Example 1.

[0088] Comparative Example 3

[0089] The difference between Comparative Example 3 and Example 1 lies in that (8) there is no spraying during drying, and the other steps are the same as those in Example 1.

[0090] Comparative Examples 4 to 6 are existing fried instant noodles

[0091] 1. Formulation

[0092] Except for the different soy protein isolates, the other formulations of Comparative Examples 4 to 6 are the same as those in Example 4. See Table 1.

[0093] Comparative Example 4 adds high-gel soy protein isolate, Comparative Example 5 adds highly denatured soy protein isolate, and Comparative Example 6 does not add soy protein isolate, which has little effect on the taste of instant noodles and can therefore be used as a reference.

[0094] Table 1 Formulation composition of Comparative Examples 4 to 6

[0095]

[0096] 2. Preparation method

[0097] Same as Example 4 and will not be elaborated here.

[0098] Effect Example 1

[0099] According to the preparation methods of Example 1, Comparative Example 1 and Comparative Example 2, soy protein was prepared separately in multiple production cycles, and each production cycle was 12 h. Calculate the yield of soy protein isolate. Yield (%) = output quantity of soy protein / input quantity of soybean meal * 100, and the yield results are shown in Table 2.

[0100] Table 2 Yields of soy protein isolate in different production cycles of Example 1, Comparative Example 1 and Comparative Example 2

[0101]

[0102] According to the results in Table 2, it can be seen that by utilizing the solubility characteristics of soy protein at different pH values to achieve extraction and separation, the solubility of protein in soybean meal increases with the increase of pH value. When the pH value is higher than the isoelectric point (isoelectric point = 4.5), the protein molecules carry negative charges, and the hydroxide ions (OH⁻) in the solution will interact with the positive charge groups on the protein molecules, which also enhances the electrostatic repulsion between protein molecules, increases the solubility of protein, and thus increases the yield.

[0103] Effect Example 2

[0104] Respectively take the soy protein isolate samples prepared in Example 1 and Comparative Example 3, and test their solubility in parallel.

[0105] Solubility test method: Take 5 g of soy protein isolate samples respectively, dissolve them in 100 mL of water respectively, stir with a stirring rod, and record the time when there is no dry powder on the surface as the dispersion time. After stirring for 1 minute, filter with a 40-mesh sieve (pore size 380 μm), weigh the residue on the sieve, and its solubility can be evaluated. The results are shown in Table 3.

[0106] Table 3 Comparison of the solubility of soy protein isolate between Example 1 and Comparative Example 3

[0107]

[0108] It can be seen from the results in Table 3 that the spraying process of the present application can significantly improve the solubility of the prepared soy protein isolate.

[0109] Effect Example 3

[0110] Next, the fried instant noodles prepared in Example 4 of the present invention and the fried instant noodles prepared in Comparative Examples 4 to 6 are subjected to sensory evaluation and noodle texture property measurement to illustrate the advantages of the soy protein isolate provided in the examples of the present invention in the field of instant noodle application.

[0111] 1. Sensory evaluation

[0112] The instant noodles prepared in Example 4 and Comparative Examples 4 to 6 are subjected to sensory evaluation. Evaluation method: The sensory scoring measurement method refers to "GB / T 25005-2010 Sensory analysis - Sensory evaluation method for instant noodles", and the specific scoring criteria are shown in Table 4 below. The scoring rules are: low (1 - 3 points), medium (4 - 6 points), high (7 - 9 points). The sensory evaluation results are shown in Table 5.

[0113] Table 4 Scoring rules for sensory evaluation of instant noodles

[0114]

[0115] Table 5 Sensory evaluation results of instant noodles in Example 4 and Comparative Examples 4 to 6

[0116]

[0117] It can be seen from the sensory evaluation results of instant noodles in Example 4 and Comparative Examples 4 to 6 in Table 5 that the soy protein isolate produced by the process of this patent has little influence on the taste of instant noodles when applied to instant noodles and is suitable for instant noodles.

[0118] 2. Evaluation of TPA noodle texture property measurement

[0119] (1) Instrument

[0120] Texture analyzer manufacturer SMS (stable Micro System), model TA.XT.plus

[0121] (2) Measurement method

[0122] Sample placement method: Take 3 soaked instant noodle samples and place them side by side without gaps on the texture analyzer detection platform for TPA texture property testing. The same sample is tested 5 times in parallel. The meanings of the parameters in the texture analyzer are shown in Table 6.

[0123] Test conditions: Probe: A / LKB, TPA measurement parameters: Test speed (front - middle - back): 1.0 - 2.0 - 5.0 mm / s; Compression ratio: 80%; Trigger force: 5 g; Compression interval: 5 s.

[0124] Test time points: Samples are taken and tested when the instant noodles are soaked in boiling water for 4 minutes and 7 minutes. The results are shown in Table 7.

[0125] Table 6 Meanings of each parameter in the texture analyzer

[0126]

[0127] Table 7 Results of the texture test data of instant noodles

[0128]

[0129] It can be seen from the results of the texture test data of instant noodles in Table 7 that the soy protein isolate produced by the process of this patent, when applied to instant noodles, is relatively close to the texture indexes of existing instant noodles, can combine well with the protein in wheat flour, and is suitable for instant noodles.

[0130] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined by the claims.

Claims

1. A method for preparing soy protein isolate, characterized in that, It successively includes the following steps: Extraction step: Take alkaline water with a pH of 11.5 - 13, mix soybean meal with the alkaline water for extraction to obtain a first extract, centrifuge the first extract to obtain a first liquid phase and a first solid phase, mix the first solid phase with water, and perform extraction at natural pH to obtain a second extract, centrifuge the second extract to obtain a second liquid phase and a second solid phase, and mix the first liquid phase and the second liquid phase to obtain a mixed soybean milk; Acid precipitation step: Adjust the pH value of the mixed soybean milk, perform centrifugation to recover the solid phase to obtain a curd solid phase; Neutralization step: Mix the curd solid phase with water and sodium hydroxide solution, and adjust the pH and sugar content to obtain a neutralized liquid; Sterilization, flash evaporation, holding reaction, homogenization, drying steps: Subject the neutralized liquid to sterilization, flash evaporation, holding reaction, homogenization, drying, and spraying in sequence to obtain the soy protein isolate; 2. The preparation method of soy protein isolate according to claim 1, characterized in that, The temperature of the soybean meal is 40°C.

3. The preparation method of soy protein isolate according to claim 1 or 2, characterized in that, In the neutralization step, the neutralization conditions are a solid content of 11.5 wt% - 15.5 wt% and a pH of 7.2 - 7.7, and the sodium hydroxide solution is added in a continuous alkali addition manner.

4. The preparation method of soy protein isolate according to claim 1, characterized in that, The sterilization temperature is 148°C - 155°C, the time is 15 s - 60 s, and the flash evaporation temperature is 70°C - 93°C.

5. The preparation method of soy protein isolate according to claim 4, characterized in that, The sterilization, flash evaporation, holding reaction, homogenization, drying steps include: The rotation speed of the holding reaction is 200 r / min. At the pipeline where the flash-evaporated material enters the reaction tank, add one or both of mannan and trehalose in a continuous dilution manner at a rate of 1‰ / ton - 10‰ / ton based on the mass of the polysaccharide dry basis, and the reaction time is 15 min - 60 min.

6. The preparation method of soy protein isolate according to claim 1, characterized in that, The spraying liquid used for spraying is one or more of modified liquid phospholipid, sorbitan monostearate, sorbitan monooleate, mono- and diglycerol fatty acid esters, and soybean oil.

7. The preparation method of soy protein isolate according to claim 6, characterized in that, The spraying liquid includes modified liquid phospholipid, sorbitan monostearate, sorbitan monooleate, mono- and diglycerol fatty acid esters, and soybean oil, and the weight ratio of the modified liquid phospholipid, sorbitan monostearate, sorbitan monooleate, mono- and diglycerol fatty acid esters, and soybean oil is 5:1.5:1.5:2:

1.

8. The preparation method of soy protein isolate according to claim 1, wherein, During spraying, the spraying method of the spraying liquid is spraying on the drying tower body. During spraying, the spraying liquid is kept at a constant temperature of 60°C - 80°C, and the spraying amount of the spraying liquid is 0.5‰ - 4‰ / ton of protein.

9. A soy protein isolate, characterized in that, The soy protein isolate is prepared by the preparation method according to any one of claims 1 - 8.

10. An application of the soy protein isolate according to claim 9 in instant noodles.

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