A method for preparing a protein-based gel system for efficiently loading soybean isoflavones

Abstract

The present invention discloses a method for preparing a protein-based gel system for efficiently loading soybean isoflavones, and belongs to the technical field of functional factor stabilization processing. The present invention first adopts a pH-driven method to prepare soybean isoflavone-loaded protein nanoparticles, and then induces the nanoparticle system to form a gel system with uniform texture by glucono-δ-lactone, thereby significantly improving the embedding rate and loading amount of soybean isoflavones, and realizing its controlled release under simulated digestive tract conditions. The present invention is simple to operate, green and environmentally friendly, realizes efficient embedding and delivery of soybean isoflavones, and can significantly improve the use value of soybean isoflavones in functional food processing.

Description

Technical Field

[0001] The invention relates to the technical field of functional factor stabilization processing, and in particular to a method for preparing a protein-based gel system for efficiently loading soybean isoflavones. Background Art

[0002] Soy isoflavones are secondary metabolites produced during the growth of soybeans. They are also called "phytoestrogens" because they have a similar structure to estrogen. Studies have shown that soy isoflavones have a variety of biological activities that are beneficial to health, such as antioxidant, anti-tumor, anti-allergic, osteoporosis prevention, and blood sugar reduction.

[0003] Theoretically, soy isoflavones have the potential to be developed into functional foods. However, they have low water solubility and are difficult to add to food; they have a bitter taste and are difficult for consumers to accept; they have a polyhydroxy structure and are unstable in light, high temperature, and alkaline environments; especially when passing through the upper digestive tract, they are decomposed by pH changes and digestive enzymes, thereby reducing intestinal absorption and resulting in reduced bioavailability. These inherent defects limit their use in functional foods. Therefore, how to promote the absorption of soy isoflavones and improve their bioavailability is a huge challenge in expanding their application in the food and pharmaceutical fields.

[0004] Using food-grade proteins, polysaccharides, lipids, etc. as raw materials, delivery systems with different structures can be prepared for the embedding, protection and delivery of active compounds, and improve their water solubility, stability and bioavailability. At present, scientists have developed different types of soy isoflavone delivery systems: commonly used preparation techniques include anti-solvent precipitation, ion gel and emulsification evaporation; carrier types include particles, inclusion compounds, gels, liposomes, etc. These delivery systems can achieve the embedding, protection, controlled release and bioavailability improvement of soy isoflavones to a certain extent. However, there are still obvious deficiencies in the current research on soy isoflavone delivery systems: ① There are few studies on highly nutritious and easily accessible milk proteins as carrier matrices; ② The preparation process involves the use of organic solvents, which does not meet the requirements of green, low-carbon and sustainable development concepts; ③ The stability of the soy isoflavone overload-induced system is low, which leads to the problem of low embedding rate that has not yet been solved. Therefore, adopting reasonable technical solutions to solve the above problems has important practical value for expanding the application of soy isoflavones in functional foods. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a protein-based gel system for efficiently loading soybean isoflavones, so as to solve the problems existing in the above-mentioned prior art. By adopting a simple, green, low-energy pH-driven process, combined with a mild glucono-δ-lactone cross-linking technology, the protein-based gel system for loading soybean isoflavones is prepared. The gel system has high encapsulation efficiency and loading capacity and good stability, which is of great significance for expanding the application of soybean isoflavones in functional foods.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] The present invention provides a method for preparing a protein-based gel system for efficiently loading soybean isoflavones, comprising the following steps:

[0008] Soy isoflavone-loaded protein nanoparticles were prepared by a pH-driven method, and glucono-δ-lactone was then added to induce the soy isoflavone-loaded protein nanoparticle system to form a protein-based gel system that efficiently loads soy isoflavones.

[0009] Preferably, the preparation of soybean isoflavone-loaded protein nanoparticles by the pH-driven method comprises the following steps:

[0010] The protein is dispersed in deionized water, hydrated, and then soybean isoflavones are added and stirred evenly. The pH value of the mixed suspension is adjusted to be alkaline, and then the pH value of the mixed suspension is adjusted to be neutral or close to neutral, and stirring is continued to obtain soybean isoflavones-loaded protein nanoparticles.

[0011] Preferably, the mass volume percentage of the protein dispersed in deionized water is 4%-10%, and the hydration conditions are: hydration at 4° C. for 8-12 hours.

[0012] Preferably, the mass ratio of the soy isoflavones to the protein is 1:(5-100).

[0013] Preferably, the pH value of the mixed suspension is first adjusted to 10-12 and maintained for 5-30 minutes, and then the pH value of the mixed suspension is adjusted to 6.5-7.5, and stirring is continued for 1-30 minutes to obtain the soy isoflavone-loaded protein nanoparticles.

[0014] Preferably, the mass volume percentage of the glucono-δ-lactone in the soy isoflavone-loaded protein nanoparticles is 0.2%-1.2%.

[0015] Preferably, the induction condition is: heat treatment at 65-90°C for 2-30 min.

[0016] Preferably, the protein comprises whey protein isolate, soy protein, sodium caseinate, egg white protein or bovine serum albumin.

[0017] The invention also provides a protein-based gel system for efficiently loading soybean isoflavones, which is prepared by the preparation method.

[0018] The mechanism of action of the present invention is as follows: under the induction of a strong alkaline environment, the hydroxyl groups of soy isoflavones are deprotonated and dissolved; at the same time, the subunits of whey protein isolate are highly dissociated, resulting in a significant increase in protein solubility. In the process of adjusting the pH back to neutral, the subunits of whey protein isolate are bound by non-covalent interactions; at the same time, the hydroxyl groups of soy isoflavones are reprotonated. Then, during the aggregation of protein subunits, soy isoflavones are wrapped inside the subunits to form a reconstituted nanoparticle structure. Further, gluconic acid is produced by decomposing glucono-δ-lactone to induce protein particles to aggregate into a gel system, so that more soy isoflavones are bound to the gel matrix, thereby obtaining a whey protein isolate-based gel system that efficiently loads soy isoflavones.

[0019] The present invention discloses the following technical effects:

[0020] (1) The present invention adopts pH-driven combined glucono-δ-lactone cross-linking technology to prepare a soy isoflavone-loaded whey protein isolate cold gel system, which gets rid of the dependence on organic solvents and has the advantages of simple operation, greenness, and low energy consumption.

[0021] (2) The method for preparing a whey protein isolate cold gel system loaded with soy isoflavones by using a pH-driven combined glucono-δ-lactone crosslinking technology proposed in the present invention solves the problem that the particle loading system induces particle instability and leads to a decrease in the embedding rate when soy isoflavones are added in large quantities, and has the characteristics of high embedding rate and loading capacity. When the mass ratio of soy isoflavones to whey protein isolate is 1:20, the embedding rate and loading capacity of soy isoflavones are 94.32% and 4.49%, respectively, which are 30.22% and 30.14% higher than the existing method for preparing soy isoflavone-loaded whey protein nanoparticles only by a pH-driven method (when the mass ratio of soy isoflavones to whey protein isolate is 1:20, the embedding rate and loading capacity of soy isoflavones are 72.43% and 3.45%, respectively). After parameter optimization, the embedding rate of soybean isoflavones can reach 90.63%, and the loading capacity is as high as 15.11%. The loading capacity is greatly improved on the basis of ensuring the embedding rate, which is of great significance for realizing the medicinal value or edible value of soybean isoflavones. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 The effect of the mass ratio of soy isoflavones to whey protein on the scanning electron microscope image of the gel system; 1: empty gel; 2: mass ratio 1:80; 3: mass ratio 1:40; 4: mass ratio 1:20;

[0024] Figure 2 The effect of the mass ratio of soy isoflavones to whey protein on the encapsulation efficiency and loading capacity of the gel system;

[0025] Figure 3 To investigate the effect of the mass ratio of soy isoflavones to whey protein on the release rate of soy isoflavones during simulated gastrointestinal digestion. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0029] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0030] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0031] Example 1

[0032] A method for preparing a protein-based gel system for efficiently loading soybean isoflavones comprises the following steps:

[0033] (1) Preparation of soy isoflavone-loaded whey protein isolate nanoparticles:

[0034] Disperse whey protein isolate in deionized water at a concentration of 5% (w / v) and hydrate overnight at 4°C. Add soy isoflavones to a mass ratio of 1:80 to protein, stir evenly, adjust the pH of the suspension to 12 and maintain for 15 minutes (the pH needs to be kept constant during this period) to deprotonate and dissolve the soy isoflavones and dissociate the protein subunits. Then, adjust the pH value of the mixed solution to 7.0 and continue stirring for 30 minutes to aggregate the protein subunits and embed the re-protonated soy isoflavones inside the protein particles.

[0035] (2) Preparation of soy isoflavone-loaded whey protein isolate cold gel system:

[0036] 0.6% (w / v) glucono-δ-lactone was added to the nanoparticle dispersion and heated at 85°C for 30 min to reduce the pH of the dispersion to the isoelectric point of the protein, thereby inducing the aggregation of the protein particles into a uniform gel system. The freshly prepared gel system was directly used for analysis or freeze-dried into powder using a freeze dryer.

[0037] According to the test, the embedding rate and loading amount of the gel system for soybean isoflavones under this condition are 98.79% and 1.22%, respectively. This is 7.03% and 7.02% higher than the method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method only (the embedding rate and loading amount of soybean isoflavones are 92.30% and 1.14%, respectively). The specific method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method is the same as step (1) of Example 1.

[0038] Example 2

[0039] A method for preparing a protein-based gel system for efficiently loading soybean isoflavones comprises the following steps:

[0040] (1) Preparation of soy isoflavone-loaded whey protein isolate nanoparticles:

[0041] Disperse whey protein isolate in deionized water at a concentration of 5% (w / v) and hydrate overnight at 4°C. Add soy isoflavones to a mass ratio of 1:40 to protein, stir evenly, adjust the pH of the suspension to 12 and maintain for 15 minutes (the pH needs to be kept constant during this period) to deprotonate and dissolve the soy isoflavones and dissociate the protein subunits. Then, adjust the pH value of the mixed solution to 7.0 and continue stirring for 30 minutes to aggregate the protein subunits and embed the protonated soy isoflavones again inside the protein particles.

[0042] (2) Preparation of soy isoflavone-loaded whey protein isolate cold gel system:

[0043] 0.6% (w / v) glucono-δ-lactone was added to the nanoparticle dispersion and heated at 85°C for 30 min to reduce the pH of the dispersion to the isoelectric point of the protein, thereby inducing the aggregation of the protein particles into a uniform gel system. The freshly prepared gel system was directly used for analysis or freeze-dried into powder using a freeze dryer.

[0044] According to the test, the embedding rate and loading amount of the gel system for soybean isoflavones under this condition are 96.17% and 2.35%, respectively. This is 15.73% and 18.69% higher than the method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method only (the embedding rate and loading amount of soybean isoflavones are 83.10% and 1.98%, respectively). The specific method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method is the same as step (1) of Example 2.

[0045] Example 3

[0046] A method for preparing a protein-based gel system for efficiently loading soybean isoflavones comprises the following steps:

[0047] (1) Preparation of soy isoflavone-loaded whey protein isolate nanoparticles:

[0048] Disperse whey protein isolate in deionized water at a concentration of 5% (w / v) and hydrate overnight at 4°C. Add soy isoflavones to a mass ratio of 1:20 to protein, stir evenly, adjust the pH of the suspension to 12 and maintain for 15 minutes (the pH needs to be kept constant during this period) to deprotonate and dissolve the soy isoflavones and dissociate the protein subunits. Then, adjust the pH value of the mixed solution to 7.0 and continue stirring for 30 minutes to aggregate the protein subunits and embed the protonated soy isoflavones again inside the protein particles.

[0049] (2) Preparation of soy isoflavone-loaded whey protein isolate cold gel system:

[0050] 0.6% (w / v) glucono-δ-lactone was added to the nanoparticle dispersion and heated at 85°C for 30 min to reduce the pH of the dispersion to the isoelectric point of the protein, thereby inducing the aggregation of the protein particles into a uniform gel system. The freshly prepared gel system was directly used for analysis or freeze-dried into powder using a freeze dryer.

[0051] According to the test, the embedding rate and loading amount of the gel system for soybean isoflavones under this condition were 94.32% and 4.49%, respectively. This was 30.22% and 30.14% higher than the method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method only (the embedding rate and loading amount of soybean isoflavones were 72.43% and 3.45%, respectively). The specific method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method was the same as step (1) of Example 3.

[0052] Example 4

[0053] A method for preparing a protein-based gel system for efficiently loading soybean isoflavones comprises the following steps:

[0054] (1) Preparation of soy isoflavone-loaded whey protein isolate nanoparticles:

[0055] Disperse whey protein isolate in deionized water at a concentration of 5% (w / v) and hydrate overnight at 4°C. Add soy isoflavones to a mass ratio of 1:80 to protein, stir evenly, adjust the pH of the suspension to 11 and maintain for 20 minutes (the pH needs to be kept constant during this period) to deprotonate and dissolve the soy isoflavones and dissociate the protein subunits. Then, adjust the pH value of the mixed solution to 7.0 and continue stirring for 30 minutes to aggregate the protein subunits and embed the protonated soy isoflavones again inside the protein particles.

[0056] (2) Preparation of soy isoflavone-loaded whey protein isolate cold gel system:

[0057] Same as step (2) of Example 1.

[0058] According to the test, the embedding rate and loading amount of the gel system for soybean isoflavones under this condition are 97.13% and 1.20%, respectively. This is 7.65% and 8.11% higher than the method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method only (the embedding rate and loading amount of soybean isoflavones are 90.23% and 1.11%, respectively). The specific method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method is the same as step (1) of Example 4.

[0059] Example 5

[0060] A green preparation method for a protein-based gel system efficiently loaded with soybean isoflavones comprises the following steps:

[0061] (1) Preparation of soy isoflavone-loaded whey protein isolate nanoparticles:

[0062] Disperse whey protein isolate in deionized water at a concentration of 5% (w / v) and hydrate overnight at 4°C. Add soy isoflavones to a mass ratio of 1:80 to protein, stir evenly, adjust the pH of the suspension to 10 and maintain for 30 minutes (the pH needs to be kept constant during this period) to deprotonate and dissolve the soy isoflavones and dissociate the protein subunits. Then, adjust the pH value of the mixed solution to 7.0 and continue stirring for 30 minutes to aggregate the protein subunits and embed the protonated soy isoflavones again inside the protein particles.

[0063] (2) Preparation of soy isoflavone-loaded whey protein isolate cold gel system:

[0064] Same as step (2) of Example 1.

[0065] According to the test, the embedding rate and loading amount of the gel system for soybean isoflavones under this condition are 96.73% and 1.19%, respectively. This is 7.95% and 8.18% higher than the method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method only (the embedding rate and loading amount of soybean isoflavones are 89.61% and 1.10%, respectively). The specific method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method is the same as step (1) of Example 5.

[0066] Example 6

[0067] A method for preparing a protein-based gel system for efficiently loading soybean isoflavones comprises the following steps:

[0068] (1) Preparation of soy isoflavone-loaded whey protein isolate nanoparticles:

[0069] Same as (1) of Example 1.

[0070] (2) Preparation of soy isoflavone-loaded whey protein isolate cold gel system:

[0071] 0.8% (w / v) glucono-δ-lactone was added to the nanoparticle dispersion and heated at 85°C for 20 min to reduce the pH of the dispersion to the isoelectric point of the protein, thereby inducing the aggregation of the protein particles into a uniform gel system. The freshly prepared gel system was directly used for analysis or freeze-dried into powder using a freeze dryer.

[0072] According to the test, the embedding rate and loading amount of the gel system for soybean isoflavones under this condition are 98.79% and 1.22%, respectively. This is 7.03% and 7.02% higher than the method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method only (the embedding rate and loading amount of soybean isoflavones are 92.30% and 1.14%, respectively). The specific method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method is the same as step (1) of Example 6.

[0073] Example 7

[0074] A green preparation method for a protein-based gel system efficiently loaded with soybean isoflavones comprises the following steps:

[0075] (1) Preparation of soy isoflavone-loaded whey protein isolate nanoparticles:

[0076] Same as (1) of Example 1.

[0077] (2) Preparation of soy isoflavone-loaded whey protein isolate cold gel system:

[0078] 1.0% (w / v) glucono-δ-lactone was added to the nanoparticle dispersion and heated at 90°C for 15 min to reduce the pH of the dispersion to the isoelectric point of the protein, thereby inducing the aggregation of the protein particles into a uniform gel system. The freshly prepared gel system was directly used for analysis or freeze-dried into powder using a freeze dryer.

[0079] According to the test, the embedding rate and loading amount of the gel system for soybean isoflavones under this condition are 98.79% and 1.22%, respectively. This is 7.03% and 7.02% higher than the method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method only (the embedding rate and loading amount of soybean isoflavones are 92.30% and 1.14%, respectively). The specific method of preparing soybean isoflavone-loaded whey protein nanoparticles by pH-driven method is the same as step (1) of Example 7.

[0080] Example 8

[0081] A green preparation method for a protein-based gel system efficiently loaded with soybean isoflavones comprises the following steps:

[0082] (1) Preparation of soy isoflavone-loaded whey protein isolate nanoparticles:

[0083] Disperse whey protein isolate in deionized water at a concentration of 4% (w / v) and hydrate overnight at 4°C. Add soy isoflavones to a mass ratio of 1:100 to protein, stir evenly, adjust the pH of the suspension to 10 and maintain for 5 minutes (the pH needs to be kept constant during this period) to deprotonate and dissolve the soy isoflavones and dissociate the protein subunits. Then, adjust the pH value of the mixed solution to 6.5 and continue stirring for 30 minutes to aggregate the protein subunits and embed the re-protonated soy isoflavones inside the protein particles.

[0084] (2) Preparation of soy isoflavone-loaded whey protein isolate cold gel system:

[0085] 0.2% (w / v) glucono-δ-lactone was added to the nanoparticle dispersion and heated at 65°C for 2 min to reduce the pH of the dispersion to the isoelectric point of the protein, thereby inducing the aggregation of the protein particles into a uniform gel system. The freshly prepared gel system was directly used for analysis or freeze-dried into powder using a freeze dryer. According to the test, the embedding rate and loading capacity of the gel system for soy isoflavones under this condition were 95.63% and 0.95%, respectively. This was 7.78% and 9.20% higher than the method of preparing soy isoflavone-loaded whey protein nanoparticles only by pH-driven method (the embedding rate and loading capacity of soy isoflavones were 88.73% and 0.87%, respectively).

[0086] Example 9

[0087] A method for preparing a protein-based gel system for efficiently loading soybean isoflavones comprises the following steps:

[0088] (1) Preparation of soy isoflavone-loaded whey protein isolate nanoparticles:

[0089] Disperse whey protein isolate in deionized water at a concentration of 10% (w / v) and hydrate overnight at 4°C. Add soy isoflavones to a mass ratio of 1:5 to protein, stir evenly, adjust the pH of the suspension to 12 and maintain for 30 minutes (the pH needs to be kept constant during this period) to deprotonate and dissolve the soy isoflavones and dissociate the protein subunits. Then, adjust the pH value of the mixed solution to 7.5 and continue stirring for 30 minutes to aggregate the protein subunits and embed the protonated soy isoflavones again inside the protein particles.

[0090] (2) Preparation of soy isoflavone-loaded whey protein isolate cold gel system:

[0091] 1.2% (w / v) glucono-δ-lactone was added to the nanoparticle dispersion and heated at 90°C for 30 min to reduce the pH of the dispersion to the isoelectric point of the protein, thereby inducing the aggregation of the protein particles into a uniform gel system. The freshly prepared gel system was directly used for analysis or freeze-dried into powder using a freeze dryer. According to the test, the embedding rate and loading capacity of the gel system for soy isoflavones under this condition were 90.63% and 15.11%, respectively. This was 61.32% and 61.43% higher than the method of preparing soy isoflavone-loaded whey protein nanoparticles only by pH-driven method (the embedding rate and loading capacity of soy isoflavones were 56.18% and 9.36%, respectively).

[0092] From the above experimental data analysis, it can be known that the mass ratio of soy isoflavones to whey protein isolate of the present invention and the alkali treatment pH value of the suspension of the two are key factors affecting the formation, stability and embedding effect of soy isoflavones in nanoparticles. The larger the mass ratio of soy isoflavones to whey protein isolate, the slower the protein dissociation and soy isoflavone dissolution under the same alkali treatment pH conditions, the larger the particle size of the formed nanoparticles, the lower the stability, and the lower the embedding rate of soy isoflavones. When the mass ratio of soy isoflavones to whey protein isolate is fixed, the higher the alkali treatment pH, the faster and more thorough the protein dissociation and soy isoflavone dissolution, the faster the preparation of nanoparticles, and the better the stability and embedding effect of soy isoflavones. If the method for preparing nanoparticles remains unchanged, only changing the amount of glucono-δ-lactone added and the heat treatment temperature will not affect the embedding rate and loading capacity of the gel system. However, the amount of glucono-δ-lactone added and the heat treatment temperature will affect the generation rate of gluconic acid, and then affect the formation speed and structure of the gel. The larger the amount of glucono-δ-lactone added and the higher the heat treatment temperature, the faster the gel is formed and the harder the texture.

[0093] Experimental effect test:

[0094] Taking Examples 1-3 as an example, the following related indicators were tested on the prepared soy isoflavone-loaded whey protein isolate cold gel:

[0095] (1) Scanning electron microscopy observation: The gel samples were sliced ​​and fixed with glutaraldehyde, and then sprayed with a layer of 10 nm gold nanoparticles. Electron microscopic images of different samples were obtained using a scanning electron microscope at an accelerating voltage of 5 kV under vacuum conditions.

[0096] (2) Determination of soybean isoflavone embedding rate and loading capacity: Cut a 1 cm 3The sample was added with 70% ethanol aqueous solution and ultrasonically treated (500W, 30min), and then centrifuged (10000g, 30min) to obtain the supernatant containing soybean isoflavones. The supernatant was appropriately diluted with 70% ethanol aqueous solution, and the content of soybean isoflavones was determined by liquid chromatography, and the embedding rate and loading amount were calculated according to the following formula:

[0097]

[0098]

[0099] (3) Release rate of soy isoflavones in simulated gastrointestinal digestion: 1 cm 3 The sample was mixed with 40 mL of HCl (0.1 M) and then shaken in a constant temperature shaking incubator for 10 min (37°C, 100 rpm / min). 10 mg of pepsin was added and the pH was adjusted to 2.0 to start simulated gastric fluid (SGF) digestion. After 60 min, 250 mg of pig bile salt was added, the pH was adjusted to 7.0, and shaken for 10 min. Then 20 mg of trypsin was added to start simulated intestinal fluid (SIF) digestion (120 min). Every 30 min, 0.5 mL of sample was taken from the digestion fluid and centrifuged (10000 g, 30 min) to obtain a precipitate, 70% ethanol aqueous solution was added and ultrasonically treated (500 W, 30 min), and then centrifuged (10000 g, 30 min) to obtain a supernatant containing soy isoflavones. The supernatant was appropriately diluted with 70% ethanol aqueous solution, and the content of soy isoflavones was determined by liquid chromatography, and the release rate was calculated according to the following formula:

[0100]

[0101] The results are as follows Figure 1-3 As shown: Figure 1 This reflects that as the ratio of soybean isoflavones to protein increases, the pore size of the gel gradually decreases and the structure becomes more compact; Figure 2 It can be seen that with the increase of the mass ratio of soy isoflavones to protein, the embedding rate of soy isoflavones shows a downward trend, but the loading amount shows an increasing trend. It should be noted that the embedding rate and loading amount of the gel system are greater than the embedding rate and loading amount of the particle system at the same mass ratio of soy isoflavones to protein (see Examples 1-3); Figure 3 It can be seen that with the increase of the mass ratio of soy isoflavones to protein, the release rate of soy isoflavones showed a downward trend, which may be related to the gel structure becoming more dense.

[0102] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a protein-based gel system for efficiently loading soybean isoflavones, characterized in that: The following steps are involved: The soy isoflavone-loaded protein nanoparticles were prepared by a pH-driven method, and then glucono-δ-lactone was added to induce the soy isoflavone-loaded protein nanoparticle system to form a protein-based gel system that efficiently loads soy isoflavones. The mass ratio of the soy isoflavones to the protein is 1:20; The mass volume percentage of the glucono-δ-lactone in the soy isoflavone-loaded protein nanoparticles is 0.2%-1.2%; The induction conditions are: heat treatment at 65-90°C for 2-30 minutes; The protein is whey protein isolate; The method of preparing soy isoflavone-loaded protein nanoparticles by using a pH-driven method comprises the following steps: dispersing the protein in deionized water, hydrating it, adding soy isoflavones, stirring evenly, adjusting the pH value of the mixed suspension to be alkaline, and then adjusting the pH value of the mixed suspension to be neutral or close to neutral, and continuing stirring to obtain soy isoflavone-loaded protein nanoparticles; The step of adjusting the pH value of the mixed suspension to be alkaline is to adjust the pH value of the mixed suspension to 10-12.

2. The preparation method according to claim 1, characterized in that The mass volume percentage of the protein dispersed in deionized water is 4%-10%, and the hydration conditions are: hydration at 4° C. for 8-12 hours.

3. The preparation method according to claim 1, characterized in that: First, the pH value of the mixed suspension is adjusted to 10-12 and maintained for 5-30 minutes, and then the pH value of the mixed suspension is adjusted to 6.5-7.5, and stirring is continued for 1-30 minutes to obtain the soy isoflavone-loaded protein nanoparticles.

4. A protein-based gel system for efficiently loading soybean isoflavones, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 3.

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