Preparation method of soybean protein isolate

Abstract

The present invention provides a soybean protein isolate preparation method, which comprises: precipitating agent treatment: mixing a soybean meal extraction supernatant and a precipitating agent, mixing for a period of time, and separating to obtain a supernatant; wherein the precipitant is calcium chloride or calcium chloride and urea; carrying out acid precipitation treatment; the alkali extraction treatment comprises the following steps: adding water and epsilon-polylysine into the precipitate obtained by the acid precipitation treatment, and adjusting the pH value of the obtained mixture to be alkaline, so as to carry out the alkali extraction treatment. The soybean protein isolate prepared by the method has relatively low viscosity, and can still form enzyme gel with good fracture resistance in a salt environment.

Description

Technical Field

[0001] The invention relates to a method for preparing isolated soybean protein. Background Art

[0002] Soy protein isolate (SPI) is a common food ingredient with good gel properties. SPI can form a gel with a chewy texture under the action of transglutaminase (TGase), and is therefore widely used in the preparation of foods such as Chiba tofu, surimi products, and hot pot meatballs.

[0003] Many gel foods contain a certain amount of salt for seasoning. Although the enzyme gel formed by SPI under the action of TG enzyme has good hardness and elasticity, the gel structure is unstable in a salty system. Typical quality degradation is that in a salty environment, the SPI enzyme gel structure becomes rough, the toughness decreases, and the gel becomes easy to break, resulting in a decrease in the appearance and taste of the food. In order to solve this problem, US2002160097A1 and EP1671552A1 improve the salt tolerance of the composition by compounding soy protein with sugars, emulsifiers, etc., but the structure of the protein itself is not optimized and will affect the color of the product. CN107439788A changes the protein structure by heating SPI in a high pH environment to improve its gel salt tolerance. However, heating under alkaline conditions can cause the viscosity of the protein to increase significantly, thereby increasing the difficulty of material transportation, concentration and drying in subsequent production.

[0004] Therefore, there is an urgent need in the art for a method for preparing SPI that can not only effectively improve the anti-fracture performance of SPI salt-containing enzyme gel, but also overcome the problem of a sudden increase in protein viscosity caused by alkaline heat treatment. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing soy protein isolate (SPI). The soy protein isolate prepared by the method has lower viscosity and can still form enzyme gel with good anti-fracture performance in a salt environment.

[0006] In a first aspect of the present invention, a method for preparing soy protein isolate is provided, characterized in that the method comprises:

[0007] Step a): precipitant treatment, comprising: mixing the soybean meal extraction supernatant with a precipitant, mixing for a period of time and separating to obtain a supernatant; wherein the precipitant is calcium chloride, or calcium chloride and urea;

[0008] Step b): acid precipitation; and

[0009] Step c): alkaline extraction treatment, comprising: adding water and ε-polylysine to the precipitate obtained by the acid precipitation treatment, and adjusting the pH of the obtained mixture to alkaline, thereby performing alkaline extraction treatment.

[0010] In one or more embodiments, in step a), the concentration of calcium chloride is 1-5 mM, more preferably 2-4 mM; the concentration of urea is 5-80 mM, more preferably 10-50 mM, most preferably 20-50 mM, 10-35 mM or 35-50 mM.

[0011] In one or more embodiments, the mass percentage of ε-polylysine in step c) is 0.02% to 0.2%, preferably 0.05 to 0.15%, and more preferably 0.05 to 0.10%.

[0012] In one or more embodiments, in step b), the acid precipitation treatment comprises: adjusting the pH of the supernatant to acidic, standing for a period of time and separating to obtain a precipitate; preferably, the adjusted pH is 4.0-5.0, more preferably 4.0-4.5.

[0013] In one or more embodiments, in step c), the pH of the mixture after adjustment is 8.5 to 10.0, preferably 9.0 to 9.5.

[0014] In one or more embodiments, the method further comprises one or more of the following steps:

[0015] Step d): extraction treatment, preferably comprising: extracting low-temperature defatted soybean meal with water, and filtering to obtain the soybean meal extraction supernatant;

[0016] Step e): heat treatment, preferably comprising: heating the solution obtained by alkali extraction treatment to 80-150° C., preferably 100-140° C., and maintaining it for 10 seconds to 15 minutes, and then cooling it to below 50° C.;

[0017] Optional step f): pH adjustment, preferably comprising: adjusting the pH value of the cooled solution obtained in the heat treatment step to a weakly alkaline pH; more preferably, the weakly alkaline pH is 8.0 to 8.5;

[0018] Step g): drying, preferably comprises: drying the protein solution; more preferably, step g) is performed after step e) or step f).

[0019] In a second aspect of the present invention, a soy protein isolate is provided, which is prepared by the method described in the present invention.

[0020] In a third aspect of the present invention, a method for preparing enzyme gel is provided, which comprises the steps of mixing the soy protein isolate according to the present invention, salt and TG enzyme to form a gel.

[0021] In one or more embodiments, the mass percentage concentration of the soy protein isolate is 3-10%, the added amount of the salt is 0.3-1.0% or 0.4-0.8% of the mass of the protein solution, and / or the added amount of the TG enzyme is 0.1-0.6% or 0.2-0.5% of the mass of the soy protein isolate solution.

[0022] In one or more embodiments, the method further comprises: a step of preparing the soy protein isolate; more preferably, the step of preparing the soy protein isolate is as described in the present invention.

[0023] In a fourth aspect of the present invention, an enzyme gel is provided, which contains the soy protein isolate of the present invention, or is prepared by the method of the present invention.

[0024] In a fifth aspect of the present invention, a soy protein isolate product is provided, which contains the soy protein isolate described in the present invention, or contains the enzyme gel described in the present invention.

[0025] In one or more embodiments, the soy protein isolate product is a food additive, a food, a pharmaceutical product or a nutritional supplement composition.

[0026] In one or more embodiments, the isolated soy protein product is a food, including hot pot products, dairy products, bakery products, candy products, bean products, sauce products, beverage products and chocolate products.

[0027] In one or more embodiments, the food is fish paste, hot pot meatballs or Chiba tofu.

[0028] In a sixth aspect of the present invention, there is provided a use selected from the following:

[0029] (1) Use of a precipitant in the preparation of soy protein isolate, wherein the precipitant is calcium chloride or calcium chloride and urea, and wherein the enzyme gel prepared using the soy protein isolate has improved salt tolerance;

[0030] (2) Application of ε-polylysine in the preparation of soy protein isolate; preferably: application of ε-polylysine in the process of preparing soy protein isolate by alkali extraction and acid precipitation principle to inhibit the increase of protein viscosity caused by alkali heat treatment;

[0031] (3) Use of a precipitant and ε-polylysine in the preparation of soy protein isolate or soy protein isolate products, wherein the precipitant is calcium chloride or calcium chloride and urea; wherein the enzyme gel prepared using the soy protein isolate has improved salt tolerance, and the increase in protein viscosity caused by alkali heat treatment during the preparation of the soy protein isolate is suppressed;

[0032] (4) Application of the soy protein isolate of the present invention in the preparation of enzyme gel with improved salt tolerance and strength;

[0033] (5) Application of the soy protein isolate described in the present invention in the preparation of soy protein isolate products with improved salt tolerance and strength.

[0034] In one or more embodiments, the concentration of calcium chloride is 1-5 mM, more preferably 2-4 mM; the concentration of urea is 5-80 mM, more preferably 10-50 mM, most preferably 20-50 mM, 10-35 mM or 35-50 mM; and / or the mass percentage of ε-polylysine is 0.02%-0.2%, preferably 0.05-0.15%, more preferably 0.05-0.10%.

[0035] Other aspects of the present invention will be apparent to those skilled in the art in view of the disclosure herein. DETAILED DESCRIPTION

[0036] The present invention finds that, in the preparation process of soy protein isolate, treatment with a precipitant before the acid precipitation step can improve the salt resistance of the enzyme gel formed by the soy protein isolate; and adding a certain amount of ε-polylysine in the neutralization step can significantly reduce the increase in protein viscosity caused by heat treatment without affecting the gel performance of the soy protein isolate. Thus, the present invention is completed.

[0037] Therefore, the present invention provides a method for preparing soybean protein isolate, which is mainly based on the principle of alkali extraction and acid precipitation, that is, dissolving the protein in defatted soybeans in a dilute alkali solution, separating and removing insoluble matter in soybean meal, obtaining a soybean protein extract, and then adjusting the pH value of the soybean protein extract to the isoelectric point of the soybean protein with an acid to precipitate the soybean protein, and then separating and washing, adjusting the pH to obtain a powdered soybean protein isolate.

[0038] Different from the prior art, the method for preparing the soy protein isolate of the present invention further comprises the following two steps: a step of adding a precipitant and a step of adding ε-polylysine during the neutralization step.

[0039] The precipitating agents used herein include calcium chloride and urea, and calcium chloride can be used alone or both can be used simultaneously.

[0040] In some embodiments, the concentration of calcium chloride in the system may be 1-5 mM, preferably 2-4 mM.

[0041] In some embodiments, when added, the concentration of urea in the system may be 5 to 80 mM, preferably 10 to 50 mM, more preferably 20 to 50 mM, 10 to 35 mM or 35 to 50 mM.

[0042] Herein, the step of adding the precipitant is usually performed after the okara separation. Specifically, the precipitant can be added to the supernatant obtained after the okara separation. Preferably, the pH of the supernatant is between 7.2 and 8.0, such as between 7.5 and 8.0. An appropriate amount of precipitant can be added to the supernatant so that the concentration of the precipitant in the resulting solution (system) is within the range described herein. After the addition and dissolution of the precipitant, the reaction conditions such as the amount of the reactants can be stirred for a period of time, such as 10 to 60 minutes or 10 to 30 minutes, and then the supernatant is separated for acid precipitation treatment. Separation can be performed by centrifugation.

[0043] Herein, the neutralization step can be carried out in a manner well known in the art. Unlike the conventional neutralization step, the present application adds an appropriate amount of ε-polylysine to the reaction system of the neutralization step. The ε-polylysine suitable for use herein is the ε-polylysine well known in the art, which is a homomonomer polymer of 25 to 30 lysine residues. Commercially available ε-polylysine can be used to implement the present invention.

[0044] In the neutralized reaction system, the concentration (mass percentage) of ε-polylysine can be in the range of 0.02-0.20%, for example, in the range of 0.05-0.15% or 0.05-0.10%. Generally, the pH of the neutralized reaction system is 8.5-10.0, preferably 9.0-9.5, and the concentration of protein in the system can be 8-10wt%. The pH value of the reaction system can be adjusted in a manner well known to those skilled in the art, for example, by using NaOH.

[0045] The method for preparing soy protein isolate of the present invention further comprises one or more steps of conventional soybean meal extraction, soybean dregs separation, acid precipitation, heat treatment, cooling, pH adjustment and drying.

[0046] An exemplary soybean meal extraction comprises mixing low-temperature defatted soybean meal with water at a material-liquid ratio (mass ratio) of 1:5 to 15, such as 1:10 to 15, adjusting the pH to 7.5 to 8.0, and then stirring and extracting at room temperature. The extraction time can be determined according to factors such as the amount of material used, and an exemplary time is 60 to 90 minutes. Herein, various low-temperature defatted soybean meals for preparing soy protein isolate known in the art can be used to implement the present invention.

[0047] An exemplary okara separation comprises filtering the mixture after leaching, centrifuging, and collecting the supernatant. For example, the mixture can be passed through an 80-mesh filter, such as a filter cloth, and centrifuged at 3000-5000 rpm for 10-30 minutes. The pH of the obtained supernatant is adjusted to between 7.2 and 8.0, such as between 7.5 and 8.0, for the next step of precipitant treatment.

[0048] An exemplary acid precipitation comprises adjusting the pH of the supernatant obtained by the treatment with the precipitant to 4.0 to 5.0, preferably 4.0 to 4.5, with an acid, and separating and obtaining a precipitate after standing for a period of time. The acid precipitation treatment can be carried out using an acid commonly used in the acid precipitation step, such as hydrochloric acid. The standing time can be selected according to factors such as the material, such as generally standing for 20 to 60 minutes. The precipitate can be collected by centrifugation, such as centrifugation at 2500 to 3500 rpm for 5 to 15 minutes.

[0049] An exemplary heat treatment includes heating the neutralized mixed solution to 80-150° C. (e.g., 100-140° C.) and maintaining it for 10 seconds to 15 minutes, such as 1-15 minutes or 5-10 minutes. After heating, the material is cooled to below 50° C. The material can be quickly cooled to below 50° C. using running water.

[0050] An exemplary pH adjustment step includes adjusting the pH of the material cooled after heat treatment to a range of 8.0 to 8.5. Generally speaking, the pH of the heat-treated material is alkaline, and therefore, an acid such as hydrochloric acid can be used to adjust its pH value to a range of 8.0 to 8.5. It is preferred to implement a pH adjustment step, which helps to improve the salt tolerance of the enzyme gel. In some embodiments, the pH adjustment step may not be performed.

[0051] Drying can be carried out by drying methods well known in the art, such as spray drying.

[0052] Therefore, in some embodiments, the present invention provides a method for preparing soy protein isolate using the principle of alkali extraction and acid precipitation, the method comprising treating the separated soybean meal extraction supernatant with the precipitant described herein, subjecting the separated supernatant after treatment to acid precipitation, and adding ε-polylysine to the system of the alkali extraction (neutralization) step for neutralization.

[0053] More specifically, the method comprises:

[0054] (1) Additive treatment, comprising: mixing the soybean meal extraction supernatant with the precipitant described herein, mixing for a period of time and separating to obtain a supernatant;

[0055] (2) acid precipitation; and

[0056] (3) Alkali extraction (neutralization) treatment, comprising: adding water and ε-polylysine to the precipitate obtained by acid precipitation treatment, and adjusting the pH of the resulting mixture to 8.5-10.0, preferably 9.0-9.5, thereby performing alkaline extraction treatment.

[0057] In some embodiments, the additive treatment step further includes a leaching step: leaching low-temperature defatted soybean meal with water, and filtering to obtain the soybean meal extraction supernatant.

[0058] In some embodiments, the alkali extraction step further includes a heat treatment step: heating the solution obtained by the alkali extraction treatment to 80-150°C (eg, 100-140°C), maintaining it for 10 seconds to 15 minutes, and then cooling it to below 50°C.

[0059] In some embodiments, the heat treatment step further includes a pH adjustment step, which includes adjusting the pH of the cooled solution obtained in the heat treatment step to 8.0-8.5.

[0060] In some embodiments, the method further comprises the step of drying the protein solution.

[0061] The enzyme gel formed by the soy protein isolate obtained by the method of the present invention has improved salt tolerance, increased strength and reduced viscosity. Therefore, in some embodiments, the present invention provides a method for preparing an enzyme gel, the method comprising mixing the soy protein isolate, salt and TG enzyme described in any embodiment of the present invention to form a gel step. Generally, a soy protein isolate solution of the present invention with a protein mass percentage concentration of 3 to 10% can be prepared, and then an appropriate amount of salt and TG enzyme are added to the protein solution, and mixed evenly to prepare the enzyme gel of the present invention. The amount of salt and TG enzyme added can be the conventional amount in the art. For example, based on the mass of the protein solution, the amount of salt added can be 0.3 to 1.0% or 0.4 to 0.8%, and the amount of TG enzyme added can be 0.1 to 0.6%, such as 0.2 to 0.5%. TG enzyme can be the TG enzyme conventionally used in the art, and its enzyme activity can be 80 to 200 U / g. After mixing, the resulting mixture can be reacted at a temperature of, for example, 10° C. or lower for 5 to 30 hours, then placed in a water bath at 80° C. or higher for 5 to 60 minutes, and then cooled to obtain the enzyme gel.

[0062] In some embodiments, the method for preparing enzyme gel further comprises the step of preparing the soy protein isolate by using the method for preparing soy protein isolate described in any embodiment herein.

[0063] In some embodiments, the present invention also provides soy protein isolate and enzyme gel prepared by the method described in any embodiment of the present invention.

[0064] In some embodiments, the present invention also provides the use of the precipitant described herein in the preparation of soy protein isolate, wherein the soy protein isolate product prepared from the soy protein isolate has improved salt resistance. In some embodiments, the present invention also provides the use of ε-polylysine in suppressing the increase in protein viscosity caused by alkali heat treatment during the preparation of soy protein isolate using the alkali extraction and acid precipitation principle. In some embodiments, the present invention also provides the use of the precipitant described herein and ε-polylysine in the preparation of soy protein isolate or soy protein isolate products, wherein the soy protein isolate product prepared from the soy protein isolate has improved salt resistance, strength and reduced viscosity. In some embodiments, the present invention also provides the use of soy protein isolate prepared by the method described in any embodiment of the present invention in the preparation of soy protein isolate products with improved salt resistance and strength and reduced viscosity.

[0065] Herein, the soy protein isolate product contains the soy protein isolate described in any embodiment of the present invention. An exemplary soy protein isolate product includes the enzyme gel described in any embodiment of the present invention.

[0066] In some embodiments, the present invention provides a product containing the soy protein isolate described in any embodiment herein. The soy protein isolate product can be a food additive, food, pharmaceutical product, and nutritional supplement composition containing the soy protein isolate described in any embodiment herein.

[0067] As a food additive, the isolated soy protein product of the present invention can be used in the form of soft capsules, tablets, syrups or any other common dietary supplement delivery systems.

[0068] As food, the soy protein isolate product of the present invention can be incorporated into and used in various foods. The food includes but is not limited to hot pot products (such as fish paste products, hot pot meatballs), dairy products, milk beverages, ice cream, baked products, candy products, biscuits, soy products (such as Chiba tofu), cakes (such as cakes, crisp desserts, croissants and butterfly crisps) and bread, soy sauce, seasonings, fillings, oils (such as shortening) and fats, margarine, sauces (such as mayonnaise), cereals, beverages and mixed drinks, oils and fats, infant formulas, baby food (biscuits, vegetable purees and fruit purees, cereals), bar foods, snacks, candies and chocolate products.

[0069] As a pharmaceutical product, the soy protein isolate product of the present invention can be delivered orally, intravenously or by any other conventional or special administration route, and can be in the form of liquid oil, powder, granules, wax, paste, oily or aqueous emulsion, and any other form that enables it to be used for the intended purpose.

[0070] As a nutritional supplement food composition, the soy protein isolate product of the present invention can be in the form of soft capsules, tablets, syrups or any other common dietary supplement delivery systems.

[0071] The pharmaceutical or nutritional supplement food composition containing the soy protein isolate product of the present invention may include physiologically acceptable free-flowing agents, other additives, excipients, desiccants and diluents, colorants, flavor and taste ingredients, and any ingredients for controlling physiological, sensory and other properties, as well as additional active ingredients, such as minerals, vitamins, and other nutritional additives.

[0072] Compared with the prior art, the present invention has advantages or positive effects.

[0073] (1) A certain amount of calcium chloride and optionally urea are added to the soybean meal alkaline extract. When urea is used, low concentrations of urea induce moderate exposure of highly hydrophobic components in soybean protein, which combine with calcium ions to form insoluble matter, which is removed by centrifugation; subsequently, further alkali heat treatment is combined to effectively improve the hydrophilicity and salt tolerance of soybean protein.

[0074] (2) Soy protein and ε-polylysine were co-heat treated at high pH. ε-polylysine inhibited the sudden increase in protein viscosity caused by alkaline heat treatment and did not affect the improvement of protein gel properties.

[0075] (3) When pH adjustment is performed, the size and charge state of protein thermal aggregates can be optimized, further improving the salt resistance of SPI enzyme gel.

[0076] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial sources.

[0077] Experimental methods

[0078] Preparation of SPI enzyme gel: Weigh 2.5g of soy protein isolate powder, add 47.5g of deionized water (containing 0.02% NaN3), prepare a solution with a protein concentration of 5% (w / w), and stir thoroughly to dissolve the protein. Centrifuge the protein solution at 3000rpm for 3min to remove bubbles, and then pour 40g of protein solution into a 50ml beaker. Add 0.6% (w / w) sodium chloride (the normal salt content of foods such as Chiba tofu and hot pot meatballs) and 0.3% (w / w) TG enzyme (100U / g) to the beaker, mix well, seal the beaker, place it at 4℃ for reaction for 20h, 90℃ water bath for 30min, take out the beaker and place it in an ice bath to cool for 20min.

[0079] SPI enzyme gel texture test: Use a blade to take out the cylindrical protein gel from the beaker along the wall of the beaker and place it on the stage of the texture analyzer TA.Xt plus. Use P / 0.5S probe, one-time pressing mode, test parameters: 1.5mm / s before / during the test, 10mm / s after the test, pressing distance 26mm, trigger stress 5g, record stress-time curve. The pressing distance (rupture distance) corresponding to the gel fracture reflects the toughness of the gel.

[0080] SPI viscosity test: The viscosity of the heated soy protein solution (8%, w / w) in the heat treatment step was tested. A rotational viscometer (Brookfield DV2T-LV) was used for the measurement: probe 62#, constant shear rate 100 rpm, and the average viscosity within 60 seconds was recorded.

[0081] Preparation and texture test of Chiba tofu: Weigh 45g of protein powder, add 292.42g of ice-water mixture (205g water + 87.42g ice), and chop at 10000rpm for 3min. Add 22.5g soybean oil and chop at 10000rpm for 2min; add 0.76g monosodium glutamate and 1.14g white sugar and chop at 10000rpm for 1min; add 15.2g of acetylated distarch phosphate (modified cassava starch) and 1.14g TG enzyme (100U / g), chop at 10000rpm for 2min; finally add 1.9g salt and chop at 10000rpm for 1min; vacuum degas the resulting slurry, fill it in a texture tank, and react at 4℃ overnight. After the reaction, heat the texture tank at 85℃ for 45min and cool it with running water. Use a blade to take out the protein gel block along the wall of the texture tank and place it on the stage of the texture analyzer TA.Xt plus. The texture test method of Chiba tofu is the same as that of SPI enzyme gel. The stress at the time of gel fracture reflects the strength of the gel, and the corresponding downward pressure distance (fracture distance) reflects the toughness of the gel.

[0082] Example 1

[0083] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0084] Okara separation: The extracted mixture was filtered through an 80-mesh filter cloth, the filtrate was centrifuged at 4000 rpm for 20 min, and the supernatant was collected and adjusted to pH 7.5.

[0085] Add precipitant: add anhydrous calcium chloride and urea to the supernatant to make the concentration of calcium chloride in the system 4mM and the concentration of urea 20mM. Stir and dissolve, react for 20min, centrifuge at 5000rpm for 10min, and collect the supernatant.

[0086] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0087] Neutralization: Add a certain amount of water and ε-polylysine to the acid curd precipitate, adjust the pH to 9.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w) and an ε-polylysine concentration of 0.1% (w / w).

[0088] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0089] pH adjustment: Adjust the pH of the cooled protein solution to 8.5 with hydrochloric acid.

[0090] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder A.

[0091] Example 2

[0092] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0093] Okara separation: The mixed material after extraction was filtered through 80-mesh filter cloth, the obtained filtrate was centrifuged at 4000 rpm for 20 min, the supernatant was collected, and the pH of the supernatant was adjusted to 7.5.

[0094] Add precipitant: add anhydrous calcium chloride and urea to the above supernatant to make the concentration of calcium chloride in the system 4mM and the concentration of urea 20mM. Stir and dissolve, react for 20min, centrifuge at 5000rpm for 10min, and collect the supernatant.

[0095] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0096] Neutralization: Add a certain amount of water and ε-polylysine to the acid curd precipitate, adjust the pH to 9.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w) and an ε-polylysine concentration of 0.05% (w / w).

[0097] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0098] pH adjustment: Adjust the pH of the cooled protein solution to 8.5 with hydrochloric acid.

[0099] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder B.

[0100] Example 3

[0101] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0102] Okara separation: The mixed material after extraction was filtered through 80-mesh filter cloth, the obtained filtrate was centrifuged at 4000 rpm for 20 min, the supernatant was collected, and the pH of the supernatant was adjusted to 7.5.

[0103] Add precipitant: add anhydrous calcium chloride and urea to the above supernatant to make the concentration of calcium chloride in the system 2mM and the concentration of urea 50mM. Stir and dissolve, react for 20 minutes, centrifuge at 5000 rpm for 10 minutes, and collect the supernatant.

[0104] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0105] Neutralization: Add a certain amount of water and ε-polylysine to the acid curd precipitate, adjust the pH to 9.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w) and an ε-polylysine concentration of 0.1% (w / w).

[0106] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0107] pH adjustment: Adjust the pH of the cooled protein solution to 8.5 with hydrochloric acid.

[0108] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder C.

[0109] Example 4

[0110] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0111] Okara separation: The extracted mixture was filtered through an 80-mesh filter cloth, the filtrate was centrifuged at 4000 rpm for 20 min, the supernatant was collected, and the pH of the supernatant was adjusted to 8.0.

[0112] Add precipitant: add anhydrous calcium chloride and urea to make the concentration of calcium chloride in the system 3mM and the concentration of urea 35mM. Stir and dissolve, react for 20 minutes, centrifuge at 5000 rpm for 10 minutes, and collect the supernatant.

[0113] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0114] Neutralization: Add a certain amount of water and ε-polylysine to the acid curd precipitate, adjust the pH to 9.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w) and an ε-polylysine concentration of 0.1% (w / w).

[0115] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0116] pH adjustment: Adjust the pH of the cooled protein solution to 8.5 with hydrochloric acid.

[0117] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder D.

[0118] Example 5

[0119] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0120] Okara separation: The mixed material after extraction was filtered through 80-mesh filter cloth, the obtained filtrate was centrifuged at 4000 rpm for 20 min, the supernatant was collected, and the pH of the supernatant was adjusted to 7.5.

[0121] Add precipitant: add anhydrous calcium chloride and urea to make the concentration of calcium chloride in the system 4mM and the concentration of urea 20mM. Stir and dissolve, react for 20min, centrifuge at 5000rpm for 10min, and collect the supernatant.

[0122] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0123] Neutralization: Add a certain amount of water and ε-polylysine to the acid curd precipitate, adjust the pH to 9.0 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w) and an ε-polylysine concentration of 0.1% (w / w).

[0124] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0125] pH adjustment: Use hydrochloric acid to adjust the cooled protein solution to pH 8.0.

[0126] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder E.

[0127] Example 6: No pH correction

[0128] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0129] Okara separation: The mixed material after extraction was filtered through 80-mesh filter cloth, the obtained filtrate was centrifuged at 4000 rpm for 20 min, the supernatant was collected, and the pH of the supernatant was adjusted to 7.5.

[0130] Add precipitant: add anhydrous calcium chloride and urea to make the concentration of calcium chloride in the system 4mM and the concentration of urea 20mM. Stir and dissolve, react for 20min, centrifuge at 5000rpm for 10min, and collect the supernatant.

[0131] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0132] Neutralization: Add a certain amount of water and ε-polylysine to the acid curd precipitate, adjust the pH to 9.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w) and an ε-polylysine concentration of 0.1% (w / w).

[0133] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0134] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder F.

[0135] Example 7: No Urea

[0136] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0137] Okara separation: The extracted mixture was filtered through an 80-mesh filter cloth, the filtrate was centrifuged at 4000 rpm for 20 min, and the supernatant was collected and adjusted to pH 7.5.

[0138] Add precipitant: add anhydrous calcium chloride to the supernatant to make the calcium chloride concentration in the system 4mM. Stir and dissolve, react for 20 minutes, centrifuge at 5000 rpm for 10 minutes, and collect the supernatant.

[0139] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0140] Neutralization: Add a certain amount of water and ε-polylysine to the acid curd precipitate, adjust the pH to 9.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w) and an ε-polylysine concentration of 0.1% (w / w).

[0141] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0142] pH adjustment: Adjust the pH of the cooled protein solution to 8.5 with hydrochloric acid.

[0143] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder G.

[0144] Example 8: 0.02% ε-polylysine

[0145] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0146] Okara separation: The extracted mixture was filtered through an 80-mesh filter cloth, the filtrate was centrifuged at 4000 rpm for 20 min, and the supernatant was collected and adjusted to pH 7.5.

[0147] Add precipitant: add anhydrous calcium chloride and urea to the supernatant to make the concentration of calcium chloride in the system 4mM and the concentration of urea 20mM. Stir and dissolve, react for 20min, centrifuge at 5000rpm for 10min, and collect the supernatant.

[0148] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0149] Neutralization: Add a certain amount of water and ε-polylysine to the acid curd precipitate, adjust the pH to 9.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w) and an ε-polylysine concentration of 0.02% (w / w).

[0150] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0151] pH adjustment: Adjust the pH of the cooled protein solution to 8.5 with hydrochloric acid.

[0152] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder H.

[0153] Example 9: 0.2% ε-polylysine

[0154] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0155] Okara separation: The extracted mixture was filtered through an 80-mesh filter cloth, the filtrate was centrifuged at 4000 rpm for 20 min, and the supernatant was collected and adjusted to pH 7.5.

[0156] Add precipitant: add anhydrous calcium chloride and urea to the supernatant to make the concentration of calcium chloride in the system 4mM and the concentration of urea 20mM. Stir and dissolve, react for 20min, centrifuge at 5000rpm for 10min, and collect the supernatant.

[0157] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0158] Neutralization: Add a certain amount of water and ε-polylysine to the acid curd precipitate, adjust the pH to 9.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w) and an ε-polylysine concentration of 0.2% (w / w).

[0159] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0160] pH adjustment: Adjust the pH of the cooled protein solution to 8.5 with hydrochloric acid.

[0161] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder I.

[0162] Comparative Example 1: Ordinary Process SPI

[0163] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0164] Okara separation: The extracted mixture was filtered through an 80-mesh filter cloth, the filtrate was centrifuged at 4000 rpm for 20 min, and the supernatant was collected.

[0165] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0166] Neutralization: Add a certain amount of water to the acid curd precipitate, adjust the pH to 7.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w).

[0167] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0168] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder J.

[0169] Comparative Example 2: Alkali-heat Process SPI

[0170] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0171] Okara separation: The extracted mixture was filtered through an 80-mesh filter cloth, the filtrate was centrifuged at 4000 rpm for 20 min, and the supernatant was collected.

[0172] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0173] Neutralization: Add a certain amount of water to the acid curd precipitate, adjust the pH to 9.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w).

[0174] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0175] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder K.

[0176] Comparative Example 3: No calcium chloride and urea

[0177] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0178] Okara separation: The extracted mixture was filtered through an 80-mesh filter cloth, the filtrate was centrifuged at 4000 rpm for 20 min, and the supernatant was collected.

[0179] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0180] Neutralization: Add a certain amount of water and ε-polylysine to the acid curd precipitate, adjust the pH to 9.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w) and an ε-polylysine concentration of 0.1% (w / w).

[0181] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0182] pH adjustment: Adjust the pH of the cooled protein solution to 8.5 with hydrochloric acid.

[0183] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder L.

[0184] Comparative Example 4: No ε-polylysine

[0185] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0186] Okara separation: The mixed material after extraction was filtered through 80-mesh filter cloth, the obtained filtrate was centrifuged at 4000 rpm for 20 min, the supernatant was collected, and the pH of the supernatant was adjusted to 7.5.

[0187] Add precipitant: add anhydrous calcium chloride and urea to the above supernatant to make the concentration of calcium chloride in the system 4mM and the concentration of urea 20mM. Stir and dissolve, react for 20min, centrifuge at 5000rpm for 10min, and collect the supernatant.

[0188] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0189] Neutralization: Add a certain amount of water to the acid curd precipitate, adjust the pH to 9.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w).

[0190] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0191] pH adjustment: Adjust the pH of the cooled protein solution to 8.5 with hydrochloric acid.

[0192] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder M.

[0193] Comparative Example 5: No Calcium Chloride

[0194] Soybean meal extraction: Mix low-temperature defatted soybean meal with water in a solid-liquid ratio of 1:10, adjust the pH to 7.5 with sodium hydroxide, and stir and extract at room temperature for 90 minutes.

[0195] Okara separation: The extracted mixture was filtered through an 80-mesh filter cloth, the filtrate was centrifuged at 4000 rpm for 20 min, and the supernatant was collected and adjusted to pH 7.5.

[0196] Add precipitant: Add urea to the supernatant to make the urea concentration in the system 20mM. Stir and dissolve, react for 20min, centrifuge at 5000rpm for 10min, and collect the supernatant.

[0197] Acid precipitation: adjust the pH of the supernatant to 4.5 with hydrochloric acid, let it stand for 30 minutes, centrifuge it at 3000 rpm for 10 minutes, and collect the acid curd precipitate.

[0198] Neutralization: Add a certain amount of water and ε-polylysine to the acid curd precipitate, adjust the pH to 9.5 with sodium hydroxide, stir thoroughly to dissolve the precipitate, and obtain a protein reconstituted solution with a protein concentration of 8% (w / w) and an ε-polylysine concentration of 0.1% (w / w).

[0199] Heat treatment: Heat the above protein reconstitution solution at 100°C for 10 min, and quickly cool the material to below 50°C using running water.

[0200] pH adjustment: Adjust the pH of the cooled protein solution to 8.5 with hydrochloric acid.

[0201] Drying: The soy protein solution is spray-dried to obtain soy protein isolate powder N.

[0202] Soy protein isolate powder AN was prepared into SPI enzyme gel samples 1-14, and enzyme gel texture test and viscosity test were carried out. The results are shown in Table 1.

[0203] Table 1: SPI enzyme gel texture and viscosity of heat-treated SPI solution

[0204]

[0205]

[0206] The results in Table 1 show that compared with the common process J, although the gel rupture distance of the alkaline heat process K is slightly improved, its viscosity increases significantly. The gel rupture distance of L is smaller than that of A, indicating that the addition of calcium chloride and urea further improves the salt tolerance of the enzyme gel of SPI on the basis of alkaline heat treatment. The gel rupture distance of M is the same as that of A, but the viscosity is significantly higher than that of A, indicating that controlling the addition range of ε-polylysine within a certain range can not only inhibit the sudden increase in protein viscosity caused by alkaline heat treatment, but also will not affect the gel properties of the protein. The rupture distance of N is smaller than that of L, indicating that the use of urea alone will reduce the salt tolerance of the enzyme gel of SPI.

[0207] Test Case

[0208] Test Example 1: Soy Protein Isolate A is used in the production of thousand-sheet tofu

[0209] According to the above method for making Chiba tofu, the soy protein isolate A obtained in Example 1 was used to make Chiba tofu, and the texture of the obtained tofu was measured. The results are shown in Table 2.

[0210] Test Example 2: Soybean Protein Isolate J is used in the production of thousand-sheet tofu

[0211] According to the above method for making Chiba tofu, the soy protein isolate J obtained in Comparative Example 1 was used to make Chiba tofu, and the texture of the obtained tofu was measured. The results are shown in Table 2.

[0212] Test Example 3: Soybean Protein Isolate K Applied in Chiba Tofu Production

[0213] According to the above method for making Chiba tofu, the soy protein isolate K obtained in Comparative Example 2 was used to make Chiba tofu, and the texture of the obtained tofu was measured. The results are shown in Table 2.

[0214] Test Example 4: Soybean Protein Isolate M is used in Chiba Tofu Production

[0215] According to the above method for making Chiba tofu, the soy protein isolate M obtained in Comparative Example 4 was used to make Chiba tofu, and the texture of the obtained tofu was measured. The results are shown in Table 2.

[0216] Table 2 Texture of Chiba tofu

[0217] Chiba Tofu Soy Protein Isolate Powder Gel strength (g) Gel rupture distance (mm) 1 (Test Example 1) A 2424 26 2 (Test Example 2) J 1473 15 3 (Test Example 3) K 1807 18 4 (Test Example 4) M 2139 22

[0218] The results in Table 2 show that the Chiba tofu made from A has the highest gel strength and toughness, and presents a good chewy texture. The Chiba tofu made from J has the worst texture, the tofu is soft and easy to break, and has poor elasticity / toughness. K is improved relative to J, but the quality is still significantly lower than A. Although the salt tolerance test result of the enzyme gel of sample M is the same as that of A, due to its high viscosity, during the process of making Chiba tofu, the sauce is unevenly dispersed within the limited chopping time, which ultimately affects the uniformity of the tofu texture. Therefore, the texture of the Chiba tofu made with it is not as good as that of sample A, reflecting that the high protein viscosity will affect the actual application effect.

[0219] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims. At the same time, all the documents mentioned in the present invention are cited as references in this application, just as each document is cited as reference separately.

Claims

1. A method for preparing soy protein isolate, characterized in that: The method comprises: Step a): precipitant treatment, comprising: mixing the soybean meal extraction supernatant with a precipitant, mixing for a period of time and separating to obtain a supernatant; wherein the precipitant is calcium chloride, or calcium chloride and urea; Step b): acid precipitation; and Step c): alkaline extraction treatment, comprising: adding water and ε-polylysine to the precipitate obtained by the acid precipitation treatment, and adjusting the pH of the obtained mixture to alkaline, thereby performing alkaline extraction treatment.

2. The method according to claim 1, characterized in that In the step a), the concentration of calcium chloride is 1-5 mM, more preferably 2-4 mM; the concentration of urea is 5-80 mM, more preferably 10-50 mM, most preferably 20-50 mM, 10-35 mM or 35-50 mM; The mass percentage of ε-polylysine in step c) is 0.02% to 0.2%, preferably 0.05 to 0.15%, and more preferably 0.05 to 0.10%.

3. The method according to claim 1, characterized in that In the step b), the acid precipitation treatment comprises: adjusting the pH of the supernatant to acidic, standing for a period of time and separating to obtain a precipitate; preferably, the adjusted pH is 4.0 to 5.0, more preferably 4.0 to 4.5; and / or In the step c), the pH of the mixture is adjusted to 8.5 to 10.0, more preferably 9.0 to 9.

5.

4. The method according to any one of claims 1 to 3, characterized in that The method further comprises one or more of the following steps: Step d): extraction treatment, preferably comprising: extracting low-temperature defatted soybean meal with water, and filtering to obtain the soybean meal extraction supernatant; Step e): heat treatment, preferably comprising: heating the solution obtained by alkali extraction treatment to 80-150° C., preferably 100-140° C., and maintaining it for 10 seconds to 15 minutes, and then cooling it to below 50° C.; Optional step f): pH adjustment, preferably comprising: adjusting the pH value of the cooled solution obtained in the heat treatment step to a weakly alkaline pH; more preferably, the weakly alkaline pH is 8.0 to 8.5; Step g): drying, preferably comprises: drying the protein solution; more preferably, step g) is performed after step e) or step f).

5. A soy protein isolate prepared by the method according to any one of claims 1 to 4.

6. A method for preparing enzyme gel, comprising the step of mixing the soy protein isolate according to claim 5, salt and TG enzyme to form a gel; Preferably, the mass percentage concentration of the soy protein isolate is 3-10%, the amount of salt added is 0.3-1.0% or 0.4-0.8% of the mass of the protein solution, and / or the amount of TG enzyme added is 0.1-0.6% or 0.2-0.5% of the mass of the soy protein isolate solution; Preferably, the method further comprises: The step of preparing the soy protein isolate; more preferably, the step of preparing the soy protein isolate is as described in any one of claims 1 to 4.

7. An enzyme gel comprising the soy protein isolate according to claim 5, or prepared by the method according to claim 6.

8. A soy protein isolate product, comprising the soy protein isolate according to claim 5, or the enzyme gel according to claim 7; Preferably, the soy protein isolate product is a food additive, a food, a medicinal product or a nutritional supplement composition; more preferably, the soy protein isolate product is a food, comprising: Hot pot products, dairy products, baked products, candy products, bean products, sauce products, beverage products and chocolate products; most preferably, the food is fish paste, hot pot meatballs or Chiba tofu.

9. Select from the following applications: (1) Application of a precipitant in the preparation of soy protein isolate, wherein: The precipitant is calcium chloride or calcium chloride and urea, and the enzyme gel prepared by using the soy protein isolate has improved salt tolerance; (2) Application of ε-polylysine in the preparation of soy protein isolate; preferably: application of ε-polylysine in the process of preparing soy protein isolate by alkali extraction and acid precipitation principle to inhibit the increase of protein viscosity caused by alkali heat treatment; (3) Use of a precipitant and ε-polylysine in the preparation of soy protein isolate or soy protein isolate products, wherein the precipitant is calcium chloride or calcium chloride and urea; wherein the enzyme gel prepared using the soy protein isolate has improved salt tolerance, and the increase in protein viscosity caused by alkali heat treatment during the preparation of the soy protein isolate is suppressed; (4) Use of the soy protein isolate according to claim 5 in the preparation of enzyme gel with improved salt tolerance and strength; (5) Use of the soy protein isolate according to claim 5 in the preparation of a soy protein isolate product with improved salt resistance and strength.

10. The use according to claim 9, characterized in that The concentration of calcium chloride is 1-5 mM, more preferably 2-4 mM; the concentration of urea is 5-80 mM, more preferably 10-50 mM, most preferably 20-50 mM, 10-35 mM or 35-50 mM; and / or, The mass percentage of the ε-polylysine is 0.02% to 0.2%, preferably 0.05 to 0.15%, and more preferably 0.05 to 0.10%.

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