阅读说明：本技术 一种大豆分离蛋白-金雀异黄素纳米乳液的制作方法 (Preparation method of soybean protein isolate-genistein nanoemulsion ) 是由 李杨 李礼佳 吴长玲 和铭钰 冯旭梅 于 2021-08-30 设计创作，主要内容包括：本发明公开了一种大豆分离蛋白-金雀异黄素纳米乳液的制作方法,包括以下步骤：(1)大豆分离蛋白提取；(2)大豆分离蛋白-金雀异黄素复合物制备；(3)大豆分离蛋白-金雀异黄素纳米乳液制备；(4)高压均质；(5)调节pH；(6)抑菌处理；(7)恒温冷藏。本发明以大豆分离蛋白和金雀异黄素为主要原料,通过二者制成的复合物进一步制成纳米乳液,并对其加工制备条件和配方进行优化,所制备的纳米乳液具有较低的过氧化值,和优秀的储存稳定性、pH稳定性、离子稳定性及热稳定性且工艺简单、生产成本低、可以丰富金雀异黄素的保护手段并推动纳米乳液的发展,同时为大豆副产物的利用和开发提供一定的参考依据。(The invention discloses a preparation method of a soybean protein isolate-genistein nanoemulsion, which comprises the following steps: (1) extracting isolated soy protein; (2) preparing a soy protein isolate-genistein compound; (3) preparing a soy protein isolate-genistein nanoemulsion; (4) homogenizing under high pressure; (5) adjusting the pH value; (6) performing bacteriostatic treatment; (7) and (5) refrigerating at constant temperature. The invention takes soybean protein isolate and genistein as main raw materials, further prepares nano emulsion by a compound prepared from the soybean protein isolate and the genistein, optimizes the processing and preparation conditions and the formula of the nano emulsion, has lower peroxide value, excellent storage stability, pH stability, ionic stability and thermal stability, simple process and low production cost, can enrich the protection means of the genistein and promote the development of the nano emulsion, and simultaneously provides a certain reference basis for the utilization and development of soybean byproducts.)

1. A preparation method of a soybean protein isolate-genistein nanoemulsion is characterized by comprising the following steps: (1) extracting isolated soy protein; (2) preparing a soy protein isolate-genistein compound; (3) preparing a soy protein isolate-genistein nanoemulsion; (4) homogenizing under high pressure; (5) adjusting the pH value; (6) performing bacteriostatic treatment; (7) and (5) refrigerating at constant temperature.

2. The method for preparing the isolated soy protein-genistein nanoemulsion of claim 1, wherein: the extraction step of the isolated soy protein in the step (1) is as follows: crushing soybeans to obtain dry powder, sieving by using a separation sieve, mixing the soybeans and n-hexane according to a material-liquid ratio of 1:3, then carrying out centrifugal deoiling, dissolving the deoiled soybean meal in deionized water according to a material-liquid ratio of 1:20, adjusting the pH value to 8.0 by using sodium hydroxide, stirring for 1h, centrifuging, taking a supernatant, adjusting the pH value of the supernatant to 4.5 by using hydrogen chloride, stirring for 1h, centrifuging to obtain a precipitate, drying and washing the precipitate for three times by using deionized water, drying and weighing the precipitate, dissolving the precipitate by using the deionized water, adjusting the pH value to 7.0 by using the sodium hydroxide, centrifuging, collecting the supernatant, freeze-drying the collected supernatant to obtain soybean protein isolate powder for later use, wherein the first centrifugation rotation speed is 4500 Xg, the time is 15min, the second centrifugation rotation speed is 9000 Xg, the time is 30min, the third centrifugation rotation speed is 7500 Xg, the time is 30min, the fourth centrifugation rotation speed is 4500 Xg, the time is 15min, the fifth centrifugation speed was 9000 Xg for 30 min.

3. The method of claim 1, wherein the soy protein isolate-genistein nanoemulsion comprises: the preparation method of the soy isolate protein-genistein compound in the step (2) comprises the following steps: accurately weighing 2g of soybean protein isolate powder, dissolving the soybean protein isolate powder in mL deionized water, stirring the mixture for 2h at 25 ℃, adding 0.02g of sodium azide to inhibit bacterial growth, adjusting the pH to 7.0, standing the mixture overnight at 4 ℃ until the mixture is fully hydrated, carrying out high-pressure homogenization on the protein solution twice under the homogenization pressure of 120MPa, weighing 1g of genistein to dissolve in ethanol, fully oscillating the mixture, uniformly mixing the mixture until the volume is 100mL to obtain a genistein solution, taking 5mL of the treated soybean protein isolate solution, adding 1500uL of genistein solution, carrying out constant volume to ensure that the concentration of the genistein in the mixed system is 0.15 percent, stirring the mixture for 1h, standing the mixture for 4h in a dark place after full mixing, centrifuging the mixture for 20min at 4 ℃ and 8000 Xg to remove free genistein, freezing the sample in an ultra-low temperature refrigerator at-80 ℃ for 6h, and then carrying out vacuum freeze drying to obtain the isolated soybean protein-genistein compound powder, wherein the vacuum freeze-drying parameters are as follows: the vacuum degree is 50Pa, the temperature of the plate layer is-30 ℃, and the condensation temperature is-50 ℃.

4. The method of claim 1, wherein the soy protein isolate-genistein nanoemulsion comprises: the preparation method of the soy isolate protein-genistein nanoemulsion described in the step (3) comprises the following steps: accurately weighing 1g of soybean protein isolate-genistein sample, dissolving in 100mL of deionized water, mixing soybean oil and the complex solution according to a ratio of 1:9, and shearing for 1min at 10000rpm by a high-speed shearing homogenizer to obtain colostrum.

5. The method of claim 1, wherein the soy protein isolate-genistein nanoemulsion comprises: the high-pressure homogenizing step in the step (4) comprises the following steps: homogenizing the primary emulsion twice with a high pressure homogenizer under 40 MPa.

6. The method of claim 1, wherein the soy protein isolate-genistein nanoemulsion comprises: the pH adjusting step in the step (5) is as follows: the emulsion pH was adjusted to 7.0 with sodium hydroxide or hydrogen chloride.

7. The method of claim 1, wherein the soy protein isolate-genistein nanoemulsion comprises: the bacteriostatic treatment step in the step (6) is as follows: sodium azide was added to the emulsion in an amount of 0.02%.

8. The method of claim 1, wherein the soy protein isolate-genistein nanoemulsion comprises: the constant-temperature refrigeration parameters in the step (7) are as follows: 4 ℃ is prepared.

Technical Field

The invention relates to a preparation method of a soybean protein isolate-genistein nanoemulsion, belonging to the technical field of protein-polyphenol compound processing.

Background

Genistein is a naturally occurring phenolic compound, also known as genistein, 4, 5, 7-trihydroxyisoflavone. Soybeans, fava beans, lupins, psoralea corylifolia and pueraria lobata are excellent food sources for genistein and belong to the flavonoid family. Because genistein has the same distance between the phenolic ring base and the 4'-7' -hydroxyl group as the human sex hormone 17 β -estradiol, these features give it the ability to have estrogen receptors. Therefore, it has potent estrogenic activity and is therefore considered to be a phytoestrogen. A great deal of evidence indicates that genistein has various biological activities and pharmacological actions, so that the molecule becomes a potential drug for preventing and treating various chronic diseases. The genistein has good effects on cardiovascular diseases, osteoporosis, climacteric problems, tumor, reproductive health and metabolic diseases, and has high activity due to its phenolic hydroxyl group with high reactivity and free radical scavenging ability. As a fat-soluble bioactive substance, its water solubility and stability are poor, and its application in food is also limited.

Soy is one of the most important and widely used food protein sources, of which soy protein isolate is a traditional food additive, an attractive food ingredient due to its high nutritional value, functional properties and desirable flavor in food products. Soy protein isolate has two of the most important protein components: beta-glycinin (7S) and glycinin (11S), together comprising about 70-80% of the soy protein isolate. 11S comprises up to twelve subunits, six of which are acidic, six of which are basic, and 7S consists of three subunits: the α, α', and β subunits. Soy protein isolate is considered to be the most nutritionally valuable protein with a good balance in amino acid composition, is rich in essential amino acids such as lysine and glutamic acid, is similar to the amino acid composition in the human body, and has physiologically beneficial components that reduce cholesterol levels and the risk of hyperlipidemia and cardiovascular disease. In addition to health-promoting benefits, it is biocompatible, biodegradable, safe, inexpensive, and has excellent functional properties such as gelling, emulsifying, and amphiphilic properties. The stable emulsion system of the soy protein isolate is very sensitive to the environment, and the stability of the soy protein isolate is easily influenced. Genistein has limited its use in food products due to its low bioavailability, pH and heat sensitivity, susceptibility to oxidation and chemical degradation. Interactions between proteins and polyphenols may lead to changes in protein function and also to increased bioavailability of polyphenols.

The invention takes soybean protein isolate and genistein as main raw materials, further prepares nano emulsion by a compound prepared from the soybean protein isolate and the genistein, optimizes the processing and preparation conditions and the formula of the nano emulsion, has lower peroxide value, excellent storage stability, pH stability, ionic stability and thermal stability, simple process and low production cost, can enrich the protection means of the genistein and promote the development of the nano emulsion, and simultaneously provides a certain reference basis for the utilization and development of soybean byproducts.

Disclosure of Invention

In order to enrich the development and utilization of protein-polyphenol compounds, improve the protection means of genistein and promote the development of nanoemulsion, the invention provides a preparation method of soybean protein isolate-genistein nanoemulsion, and the adopted technical scheme is as follows:

the method comprises the following steps: extracting isolated soy protein: crushing soybeans to obtain dry powder, sieving by using a separation sieve, mixing the soybeans and n-hexane according to a material-liquid ratio of 1:3, then carrying out centrifugal deoiling, dissolving the deoiled soybean meal in deionized water according to a material-liquid ratio of 1:20, adjusting the pH value to 8.0 by using sodium hydroxide, stirring for 1h, centrifuging, taking a supernatant, adjusting the pH value of the supernatant to 4.5 by using hydrogen chloride, stirring for 1h, centrifuging to obtain a precipitate, drying and washing the precipitate for three times by using deionized water, drying and weighing the precipitate, dissolving the precipitate by using the deionized water, adjusting the pH value to 7.0 by using the sodium hydroxide, centrifuging, collecting the supernatant, freeze-drying the collected supernatant to obtain soybean protein isolate powder for later use, wherein the first centrifugation rotation speed is 4500 Xg, the time is 15min, the second centrifugation rotation speed is 9000 Xg, the time is 30min, the third centrifugation rotation speed is 7500 Xg, the time is 30min, the fourth centrifugation rotation speed is 4500 Xg, the time is 15min, the fifth centrifugation rotation speed is 9000 Xg, and the time is 30 min;

step two: preparation of a soy protein isolate-genistein complex: accurately weighing 2g of soybean protein isolate powder, dissolving the soybean protein isolate powder in 100mL of deionized water, stirring the mixture for 2h at 25 ℃, adding 0.02g of sodium azide to inhibit bacterial growth, adjusting the pH to 7.0, standing the mixture overnight at 4 ℃ to complete hydration, continuously processing the protein solution under the homogenization pressure of 120MPa twice at high pressure, weighing 1g of genistein, dissolving the genistein in ethanol, fully oscillating the mixture, uniformly mixing the mixture until the volume is 100mL to obtain a genistein solution, taking 5mL of the processed soybean protein isolate solution, adding 1500uL of genistein solution to the mixture, fixing the volume to ensure that the concentration of the genistein in the mixed system is 0.15 percent, stirring the mixture for 1h, standing the mixture in the dark after fully mixing, centrifuging the mixture for 20min at 4 ℃ and 8000 Xg to remove free genistein, freezing the sample in an ultra-low temperature refrigerator at-80 ℃ for 6h, and then carrying out vacuum freeze drying to obtain the isolated soybean protein-genistein compound powder, wherein the vacuum freeze-drying parameters are as follows: the vacuum degree is 50Pa, the temperature of the plate layer is-30 ℃, and the condensation temperature is-50 DEG C

Step three: preparing a soy protein isolate-genistein nanoemulsion: accurately weighing 1g of soybean protein isolate-genistein sample, dissolving in 100mL of deionized water, mixing soybean oil and the compound solution according to a ratio of 1:9, and shearing for 1min at 10000rpm by using a high-speed shearing homogenizer to obtain colostrum;

step four: high-pressure homogenization: homogenizing the primary emulsion twice with a high pressure homogenizer under 40 MPa;

step five: adjusting the pH value: adjusting the pH of the emulsion to 7.0 with sodium hydroxide or hydrogen chloride;

step six: and (3) bacteriostatic treatment: adding sodium azide into the emulsion, wherein the addition amount is 0.02%;

step seven: and (5) constant temperature refrigeration: the temperature is 4 ℃;

the invention has the beneficial effects

The invention takes soybean protein isolate and genistein as main raw materials, further prepares nano emulsion by a compound prepared from the soybean protein isolate and the genistein, optimizes the processing and preparation conditions and the formula of the nano emulsion, has lower peroxide value, excellent storage stability, pH stability, ionic stability and thermal stability, simple process and low production cost, can enrich the protection means of the genistein and promote the development of the nano emulsion, and simultaneously provides a certain reference basis for the utilization and development of soybean byproducts.

Detailed description of the preferred embodiments

The present invention will be further described with reference to the following specific examples, but the present invention is not limited to these examples. The following examples used the following main raw materials, reagents and experimental equipment:

(1) main raw materials and reagents: selecting soybean, n-hexane, hydrogen chloride, sodium hydroxide, sodium azide, genistein, soybean oil and deionized water;

(2) experimental equipment: centrifuge, freeze dryer, high pressure homogenizer, ultra-low temperature freezer, electronic analytical balance, pH meter, high speed stirrer, high speed shearing homogenizer.

Example 1:

the embodiment provides a preparation method of a soy isolate protein-genistein nanoemulsion, which comprises the following specific steps:

the method comprises the following steps: extracting isolated soy protein: crushing soybeans to obtain dry powder, sieving by using a separation sieve, mixing the soybeans and n-hexane according to a material-liquid ratio of 1:3, then carrying out centrifugal deoiling, dissolving the deoiled soybean meal in deionized water according to a material-liquid ratio of 1:20, adjusting the pH value to 8.0 by using sodium hydroxide, stirring for 1h, centrifuging, taking a supernatant, adjusting the pH value of the supernatant to 4.5 by using hydrogen chloride, stirring for 1h, centrifuging to obtain a precipitate, drying and washing the precipitate for three times by using deionized water, drying and weighing the precipitate, dissolving the precipitate by using the deionized water, adjusting the pH value to 7.0 by using the sodium hydroxide, centrifuging, collecting the supernatant, freeze-drying the collected supernatant to obtain soybean protein isolate powder for later use, wherein the first centrifugation rotation speed is 4500 Xg, the time is 15min, the second centrifugation rotation speed is 9000 Xg, the time is 30min, the third centrifugation rotation speed is 7500 Xg, the time is 30min, the fourth centrifugation rotation speed is 4500 Xg, the time is 15min, the fifth centrifugation rotation speed is 9000 Xg, and the time is 30 min;

step two: preparation of a soy protein isolate-genistein complex: accurately weighing 2g of soybean protein isolate powder, dissolving the soybean protein isolate powder in 100mL of deionized water, stirring the mixture for 2h at 25 ℃, adding 0.02g of sodium azide to inhibit bacterial growth, adjusting the pH to 7.0, standing the mixture overnight at 4 ℃ to complete hydration, continuously processing the protein solution under the homogenization pressure of 120MPa twice at high pressure, weighing 1g of genistein, dissolving the genistein in ethanol, fully oscillating the mixture, uniformly mixing the mixture until the volume is 100mL to obtain a genistein solution, taking 5mL of the processed soybean protein isolate solution, adding 1500uL of genistein solution to the mixture, fixing the volume to ensure that the concentration of the genistein in the mixed system is 0.15 percent, stirring the mixture for 1h, standing the mixture in the dark after fully mixing, centrifuging the mixture for 20min at 4 ℃ and 8000 Xg to remove free genistein, freezing the sample in an ultra-low temperature refrigerator at-80 ℃ for 6h, and then carrying out vacuum freeze drying to obtain the isolated soybean protein-genistein compound powder, wherein the vacuum freeze-drying parameters are as follows: the vacuum degree is 50Pa, the temperature of the plate layer is-30 ℃, and the condensation temperature is-50 DEG C

Step three: preparing a soy protein isolate-genistein nanoemulsion: accurately weighing 1g of soybean protein isolate-genistein sample, dissolving in 100mL of deionized water, mixing soybean oil and the compound solution according to a ratio of 1:9, and shearing for 1min at 10000rpm by using a high-speed shearing homogenizer to obtain colostrum;

step four: high-pressure homogenization: homogenizing the primary emulsion twice with a high pressure homogenizer under 40 MPa;

step five: adjusting the pH value: adjusting the pH of the emulsion to 7.0 with sodium hydroxide or hydrogen chloride;

step six: and (3) bacteriostatic treatment: adding sodium azide into the emulsion, wherein the addition amount is 0.02%;

step seven: and (5) constant temperature refrigeration: the temperature is 4 ℃;

example 2:

the embodiment provides a preparation method of a soy protein isolate-genistein nanoemulsion subjected to single high-pressure homogenization treatment, which comprises the following specific steps:

the method comprises the following steps: extracting isolated soy protein: crushing soybeans to obtain dry powder, sieving by using a separation sieve, mixing the soybeans and n-hexane according to a material-liquid ratio of 1:3, then carrying out centrifugal deoiling, dissolving the deoiled soybean meal in deionized water according to a material-liquid ratio of 1:20, adjusting the pH value to 8.0 by using sodium hydroxide, stirring for 1h, centrifuging, taking a supernatant, adjusting the pH value of the supernatant to 4.5 by using hydrogen chloride, stirring for 1h, centrifuging to obtain a precipitate, drying and washing the precipitate for three times by using deionized water, drying and weighing the precipitate, dissolving the precipitate by using the deionized water, adjusting the pH value to 7.0 by using the sodium hydroxide, centrifuging, collecting the supernatant, freeze-drying the collected supernatant to obtain soybean protein isolate powder for later use, wherein the first centrifugation rotation speed is 4500 Xg, the time is 15min, the second centrifugation rotation speed is 9000 Xg, the time is 30min, the third centrifugation rotation speed is 7500 Xg, the time is 30min, the fourth centrifugation rotation speed is 4500 Xg, the time is 15min, the fifth centrifugation rotation speed is 9000 Xg, and the time is 30 min;

step two: preparation of a soy protein isolate-genistein complex: accurately weighing 2g of soybean protein isolate powder, dissolving the soybean protein isolate powder in 100mL of deionized water, stirring the mixture for 2h at 25 ℃, adding 0.02g of sodium azide to inhibit bacterial growth, adjusting the pH to 7.0, standing the mixture overnight at 4 ℃ to complete hydration, continuously processing the protein solution under the homogenization pressure of 120MPa twice at high pressure, weighing 1g of genistein, dissolving the genistein in ethanol, fully oscillating the mixture, uniformly mixing the mixture until the volume is 100mL to obtain a genistein solution, taking 5mL of the processed soybean protein isolate solution, adding 1500uL of genistein solution to the mixture, fixing the volume to ensure that the concentration of the genistein in the mixed system is 0.15 percent, stirring the mixture for 1h, standing the mixture in the dark after fully mixing, centrifuging the mixture for 20min at 4 ℃ and 8000 Xg to remove free genistein, freezing the sample in an ultra-low temperature refrigerator at-80 ℃ for 6h, and then carrying out vacuum freeze drying to obtain the isolated soybean protein-genistein compound powder, wherein the vacuum freeze-drying parameters are as follows: the vacuum degree is 50Pa, the temperature of the plate layer is-30 ℃, and the condensation temperature is-50 DEG C

Step three: preparing a soy protein isolate-genistein nanoemulsion: accurately weighing 1g of soybean protein isolate-genistein sample, dissolving in 100mL of deionized water, mixing soybean oil and the compound solution according to a ratio of 1:9, and shearing for 1min at 10000rpm by using a high-speed shearing homogenizer to obtain colostrum;

step four: high-pressure homogenization: homogenizing the primary emulsion once with a high pressure homogenizer under 40 MPa;

step five: adjusting the pH value: adjusting the pH of the emulsion to 7.0 with sodium hydroxide or hydrogen chloride;

step six: and (3) bacteriostatic treatment: adding sodium azide into the emulsion, wherein the addition amount is 0.02%;

step seven: and (5) constant temperature refrigeration: the temperature is 4 ℃;

example 3:

the embodiment provides a preparation method of a soybean protein isolate-genistein nanoemulsion which is not subjected to high-pressure homogenization treatment, and the preparation method comprises the following specific steps:

the method comprises the following steps: extracting isolated soy protein: crushing soybeans to obtain dry powder, sieving by using a separation sieve, mixing the soybeans and n-hexane according to a material-liquid ratio of 1:3, then carrying out centrifugal deoiling, dissolving the deoiled soybean meal in deionized water according to a material-liquid ratio of 1:20, adjusting the pH value to 8.0 by using sodium hydroxide, stirring for 1h, centrifuging, taking a supernatant, adjusting the pH value of the supernatant to 4.5 by using hydrogen chloride, stirring for 1h, centrifuging to obtain a precipitate, drying and washing the precipitate for three times by using deionized water, drying and weighing the precipitate, dissolving the precipitate by using the deionized water, adjusting the pH value to 7.0 by using the sodium hydroxide, centrifuging, collecting the supernatant, freeze-drying the collected supernatant to obtain soybean protein isolate powder for later use, wherein the first centrifugation rotation speed is 4500 Xg, the time is 15min, the second centrifugation rotation speed is 9000 Xg, the time is 30min, the third centrifugation rotation speed is 7500 Xg, the time is 30min, the fourth centrifugation rotation speed is 4500 Xg, the time is 15min, the fifth centrifugation rotation speed is 9000 Xg, and the time is 30 min;

step two: preparation of a soy protein isolate-genistein complex: accurately weighing 2g of soybean protein isolate powder, dissolving the soybean protein isolate powder in 100mL of deionized water, stirring the mixture for 2h at 25 ℃, adding 0.02g of sodium azide to inhibit bacterial growth, adjusting the pH to 7.0, standing the mixture overnight at 4 ℃ to complete hydration, continuously processing the protein solution under the homogenization pressure of 120MPa twice at high pressure, weighing 1g of genistein, dissolving the genistein in ethanol, fully oscillating the mixture, uniformly mixing the mixture until the volume is 100mL to obtain a genistein solution, taking 5mL of the processed soybean protein isolate solution, adding 1500uL of genistein solution to the mixture, fixing the volume to ensure that the concentration of the genistein in the mixed system is 0.15 percent, stirring the mixture for 1h, standing the mixture in the dark after fully mixing, centrifuging the mixture for 20min at 4 ℃ and 8000 Xg to remove free genistein, freezing the sample in an ultra-low temperature refrigerator at-80 ℃ for 6h, and then carrying out vacuum freeze drying to obtain the isolated soybean protein-genistein compound powder, wherein the vacuum freeze-drying parameters are as follows: the vacuum degree is 50Pa, the temperature of the plate layer is-30 ℃, and the condensation temperature is-50 DEG C

Step three: preparing a soy protein isolate-genistein nanoemulsion: accurately weighing 1g of soybean protein isolate-genistein sample, dissolving in 100mL of deionized water, mixing soybean oil and the compound solution according to a ratio of 1:9, and shearing for 1min at 10000rpm by using a high-speed shearing homogenizer to obtain colostrum;

step four: adjusting the pH value: adjusting the pH of the emulsion to 7.0 with sodium hydroxide or hydrogen chloride;

step five: and (3) bacteriostatic treatment: adding sodium azide into the emulsion, wherein the addition amount is 0.02%;

step six: and (5) constant temperature refrigeration: the temperature is 4 ℃;

example 4:

the embodiment provides a preparation method of a soy protein isolate nano-emulsion, which comprises the following specific steps:

the method comprises the following steps: extracting isolated soy protein: crushing soybeans to obtain dry powder, sieving by using a separation sieve, mixing the soybeans and n-hexane according to a material-liquid ratio of 1:3, then carrying out centrifugal deoiling, dissolving the deoiled soybean meal in deionized water according to a material-liquid ratio of 1:20, adjusting the pH value to 8.0 by using sodium hydroxide, stirring for 1h, centrifuging, taking a supernatant, adjusting the pH value of the supernatant to 4.5 by using hydrogen chloride, stirring for 1h, centrifuging to obtain a precipitate, drying and washing the precipitate for three times by using deionized water, drying and weighing the precipitate, dissolving the precipitate by using the deionized water, adjusting the pH value to 7.0 by using the sodium hydroxide, centrifuging, collecting the supernatant, freeze-drying the collected supernatant to obtain soybean protein isolate powder for later use, wherein the first centrifugation rotation speed is 4500 Xg, the time is 15min, the second centrifugation rotation speed is 9000 Xg, the time is 30min, the third centrifugation rotation speed is 7500 Xg, the time is 30min, the fourth centrifugation rotation speed is 4500 Xg, the time is 15min, the fifth centrifugation rotation speed is 9000 Xg, and the time is 30 min;

step two: preparing the soybean protein isolate nano emulsion: accurately weighing 1g of soybean protein isolate, dissolving in 100mL of deionized water, mixing soybean oil and the compound solution according to a ratio of 1:9, and shearing for 1min at 10000rpm by using a high-speed shearing homogenizer to obtain primary emulsion;

step four: high-pressure homogenization: homogenizing the primary emulsion twice with a high pressure homogenizer under 40 MPa;

step five: adjusting the pH value: adjusting the pH of the emulsion to 7.0 with sodium hydroxide or hydrogen chloride;

step six: and (3) bacteriostatic treatment: adding sodium azide into the emulsion, wherein the addition amount is 0.02%;

step seven: and (5) constant temperature refrigeration: the temperature is 4 ℃;

the following is a portion of the experimental data:

TABLE 1 comparison of the effects of the examples

Experimental group	Example 1	Example 2	Example 3	Example 4
					Peroxide number (mM)	1.05	1.49	1.59	2.51
Storage stability (%)	95.12	87.59	84.53	81.26
					pH stability (%)	90.13	84.79	82.75	78.68
Ion stability (%)	92.43	84.56	87.47	79.21
					Thermal stability (%)	92.13	88.13	87.56	81.23

As shown in the table, according to comparison of specific examples 1 to 4, it is found that the nanoemulsion prepared from the soy protein isolate-genistein has the best physicochemical indexes, and the peroxide value, the storage stability, the pH stability, the ionic stability and the thermal stability of the nanoemulsion are optimal, and the indexes are respectively: 1.05mM, 95.12%, 90.13%, 92.43% and 92.13%, and the nano emulsion prepared only by using the isolated soy protein has poor physicochemical indexes.

In conclusion, the invention takes the soy protein isolate and the genistein as main raw materials, the nano emulsion is further prepared by the compound prepared from the soy protein isolate and the genistein, and the processing and preparation conditions and the formula of the nano emulsion are optimized, the prepared nano emulsion has lower peroxide value, excellent storage stability, pH stability, ionic stability and thermal stability, simple process and low production cost, can enrich the protection means of the genistein and promote the development of the nano emulsion, and simultaneously provides a certain reference basis for the utilization and the development of the soy byproduct.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.