A casein-sodium alginate complex, its preparation method and application

Abstract

This invention provides a casein-sodium alginate complex, its preparation method, and its applications, relating to the fields of food, health food, and pharmaceuticals. The raw materials include casein, sodium alginate, and a eutectic solvent, wherein the ratio of casein, sodium alginate, and eutectic solvent is 1.0–2.0 g: 1.0–3.0 g: 30–70 mL. Sodium alginate binds to casein through electrostatic adsorption, and the eutectic solvent further promotes the self-assembly of casein and sodium alginate to form a complex, significantly improving the emulsifying properties and solubility of the emulsion based on this complex. The casein-sodium alginate complex provided by this invention, when used as an emulsifier, can significantly improve the stability of the emulsion. When using this emulsion to load lipophilic active ingredients, compared to emulsions prepared using the casein-sodium alginate complex without the addition of a eutectic solvent, the bioactivity of the lipophilic active ingredients can be significantly improved.

Description

Technical Field

[0001] This invention relates to the fields of food, health food, or pharmaceuticals, specifically to a casein-sodium alginate complex, its preparation method, and its application. Background Technology

[0002] Emulsion delivery systems possess good stability and carrying capacity, serving as important carriers for fat-soluble active substances. They can effectively improve the water solubility, stability, and bioavailability of these substances, overcoming potential problems such as easy decomposition upon exposure to light, easy oxidation upon contact with air, and poor absorption due to strong hydrophobicity. Therefore, they have significant application prospects and potential in the food, health food, and pharmaceutical fields. The performance of an emulsion is usually closely related to the effectiveness of the emulsifier.

[0003] Proteins typically possess emulsifying properties, and due to their green and safe characteristics, their application as emulsifiers has been widely studied in recent years. Casein is the most abundant protein in milk, and it has advantages such as wide availability, easy extraction, low price, and high nutritional value. Its monomers exhibit amphiphilicity, spontaneously forming a micelle structure with a hydrophilic outer layer and a lipophilic inner layer. This cavity structure has the function of protecting and loading bioactive small molecules, therefore, casein micelle systems can be used as nanocarriers for lipid-soluble bioactive substances.

[0004] Previous studies have found that casein alone, when used as an emulsifier, forms emulsions with poor stability, easily exhibiting sedimentation, flocculation, and aggregation, thus limiting its application in emulsions. Polysaccharides can bind to proteins through electrostatic adsorption; therefore, introducing polysaccharides (such as sodium alginate) can improve the emulsifying ability of proteins. However, sodium alginate has limited effectiveness in improving the emulsifying ability of casein and requires further improvement. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the limitation of sodium alginate in improving the emulsification ability of casein in the prior art, thereby providing a casein-sodium alginate complex based on a eutectic solvent, its preparation method and application.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a casein-sodium alginate complex, the raw materials for which include: casein, sodium alginate and a eutectic solvent, wherein the ratio of casein, sodium alginate and eutectic solvent is 1.0~2.0 g: 1.0~3.0 g: 30~70 mL, and the hydrogen bond donor and hydrogen bond acceptor combination of the eutectic solvent is: ethylene glycol-choline chloride, ethylene glycol-urea, ethanolamine-choline chloride, tert-butanol-choline chloride, tert-butanol-urea, lactate-choline chloride or malate-choline chloride, and the molar ratio of hydrogen bond donor to hydrogen bond acceptor in the eutectic solvent is 2:1.

[0008] Furthermore, the ratio of casein, sodium alginate, and eutectic solvent is 1.0~2.0 g: 1.0~3.0 g: 50~70 mL.

[0009] Furthermore, the ratio of casein, sodium alginate, and eutectic solvent is 1.0 g: 1.0 g: 50~70 mL.

[0010] Furthermore, the ratio of casein, sodium alginate, and eutectic solvent is 1.0 g: 1.0 g: 50 mL, 1.0 g: 1.0 g: 60 mL, 1.0 g: 1.0 g: 70 mL, 1.5 g: 1.0 g: 50 mL, 2.0 g: 1.0 g: 50 mL, 1.0 g: 2.0 g: 50 mL, or 1.0 g: 3.0 g: 50 mL.

[0011] Further, each 1.0~2.0 g of casein is dispersed in 100 mL of water; each 1.0~3.0 g of sodium alginate is dissolved in 100 mL of water. Preferably, each 1.0 g, 1.5 g, or 2.0 g of casein is dispersed in 100 mL of water; each 1.0 g, 2.0 g, or 3.0 g of sodium alginate is dissolved in 100 mL of water.

[0012] Furthermore, the method for preparing the eutectic solvent includes: mixing the hydrogen bond donor and the hydrogen bond acceptor, and heating and stirring at a temperature of 80-100°C until a uniform and transparent system is formed. Preferably, the heating and stirring temperature is 80°C.

[0013] Secondly, the present invention provides a method for preparing the casein-sodium alginate complex, comprising the following steps:

[0014] Casein was dispersed in water to obtain a casein suspension, and sodium alginate was dissolved in water to obtain a sodium alginate solution.

[0015] The casein suspension, sodium alginate solution and eutectic solvent were mixed in proportion and stirred to obtain a casein-sodium alginate complex solution.

[0016] The casein-sodium alginate complex solution was dialyzed and freeze-dried to obtain the casein-sodium alginate complex.

[0017] Further, the stirring conditions are: stirring at 300~500 rpm for 2~5 h. Preferably, the stirring conditions are: stirring at 400 rpm for 3 h.

[0018] Further, the dialysis conditions are as follows: the casein-sodium alginate complex solution is placed in a dialysis bag with a molecular weight cutoff of 30 kD, immersed in deionized water, and dialyzed at 2-8°C for 10-18 h, with the water changed every 1-2 h. Preferably, the dialysis conditions are as follows: the casein-sodium alginate complex solution is placed in a 30 kD dialysis bag, immersed in deionized water, and dialyzed at 4°C for 12-18 h, with the water changed every 2 h.

[0019] Further, the freeze-drying conditions are: freeze-drying at -30 to -10°C and 10 to 100 Pa for 18 to 30 hours. Preferably, the freeze-drying conditions are: freeze-drying at -30°C and 20 Pa for 24 to 30 hours.

[0020] Thirdly, the present invention provides the application of the casein-sodium alginate complex or the casein-sodium alginate complex obtained by the preparation method as an emulsifier.

[0021] Fourthly, the present invention provides a method for preparing an emulsion based on a casein-sodium alginate complex, wherein the emulsion / emulsion gel uses the casein-sodium alginate complex or the casein-sodium alginate complex obtained by the preparation method as an emulsifier.

[0022] The preparation method includes the following steps:

[0023] The casein-sodium alginate complex was dissolved in water to obtain an aqueous solution;

[0024] A fat-soluble active substance is mixed with oil to obtain an oil phase solution;

[0025] The aqueous solution and the oil solution were mixed and homogenized to obtain an emulsion / emulsion gel based on the casein-sodium alginate complex.

[0026] Furthermore, the mass fraction of the casein-sodium alginate complex in the aqueous solution is 0.5% to 4.0%, preferably 1.0%.

[0027] Furthermore, the mass fraction of the fat-soluble active substance in the oil phase solution is 5% to 10%, preferably 6%.

[0028] Furthermore, the fat-soluble active substance includes at least one of coenzyme Q10, astaxanthin, lutein, and paclitaxel.

[0029] Furthermore, the oil includes at least one of corn oil, sunflower oil, soybean oil, and flaxseed oil.

[0030] Furthermore, the volume ratio of the aqueous phase solution to the oil phase solution of the emulsion is 7:3.

[0031] Further, the homogenization conditions are: homogenization at 8000~12000 rpm for 3~5 min. Preferably, the homogenization conditions are: homogenization at 10000 rpm for 5 min.

[0032] Fifthly, the present invention provides a method for preparing an emulsion gel based on a casein-sodium alginate complex, wherein the emulsion obtained by the preparation method is heated at 50-90°C for 0.5-2 h, cooled to room temperature, and placed at 2-8°C for 6-10 h to form an emulsion gel.

[0033] Furthermore, the heating temperature is 60℃ and the heating time is 1 hour.

[0034] Furthermore, after being placed at 4°C for 8 hours, an emulsion gel was formed.

[0035] Sixthly, the present invention provides the application of the casein-sodium alginate complex-based emulsion obtained by the preparation method described above in the preparation of food, health food or pharmaceuticals.

[0036] In a seventh aspect, the present invention provides the application of the casein-sodium alginate complex-based emulsion gel obtained by the preparation method described above in the preparation of food, health food or pharmaceuticals.

[0037] The technical solution of this invention has the following advantages:

[0038] 1. The casein-sodium alginate complex provided by the present invention comprises casein, sodium alginate and eutectic solvent as raw materials. Sodium alginate binds to casein through electrostatic adsorption, and the eutectic solvent further promotes the self-assembly of casein and sodium alginate to form a complex, thereby significantly improving the emulsification properties and solubility of the emulsion based on the complex.

[0039] 2. The casein-sodium alginate complex provided by this invention, when used as an emulsifier, can significantly reduce the average particle size of the emulsion and improve its stability. When this emulsion is used to load lipophilic active ingredients, compared with emulsions prepared using the casein-sodium alginate complex without the addition of a eutectic solvent, the bioactivity of the lipophilic active ingredients can be significantly improved. For example, when using this emulsifier to prepare an emulsion loaded with coenzyme Q10, its antioxidant properties are significantly improved.

[0040] 3. The casein-sodium alginate complex provided by the present invention can significantly improve the storage stability of emulsions and emulsion gels when used as an emulsifier. The morphology remains stable after continuous storage at room temperature for 7 days. It can also significantly reduce the centrifugation loss and heating loss of emulsion gels, and has outstanding stability advantages.

[0041] 4. The preparation method of the casein-sodium alginate complex provided by the present invention only requires dispersing casein in water to obtain a casein suspension, dissolving sodium alginate in water to obtain a sodium alginate solution, and mixing and stirring the casein suspension, sodium alginate solution, and eutectic solvent to allow casein and sodium alginate to self-assemble into a complex. The complex solution is then dialyzed and freeze-dried to obtain casein-sodium alginate complex particles, which can be reconstituted with water before use. This method is simple to operate, easy to promote, and has good application prospects.

[0042] 5. The emulsion or emulsion gel based on casein-sodium alginate complex provided by the present invention can load fat-soluble active substances. Depending on the type, use, and efficacy of the active substances, the emulsion or emulsion gel can be used to prepare food, health food, pharmaceuticals, etc., with a wide range of applications and can more fully exert the role of active substances. Detailed Implementation

[0043] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0044] The reagents and their sources used in the specific embodiments of this invention are shown in Table 1.

[0045] Table 1. Reagent Sources

[0046]

[0047] The instruments and their sources used in the specific embodiments of this invention are shown in Table 2.

[0048] Table 2. Instrument Sources

[0049]

[0050] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. All raw materials or instruments used are commercially available conventional products, including but not limited to those used in the embodiments of this application.

[0051] Example 1

[0052] This embodiment provides a casein-sodium alginate complex, the preparation method of which is as follows:

[0053] (1) Preparation of eutectic solvent: Ethylene glycol and choline chloride were mixed in a molar ratio of 2:1 and placed in a round-bottom flask. The mixture was heated in an oil bath at 80°C and stirred until a uniform and transparent system was formed to obtain the eutectic solvent for later use.

[0054] (2) Preparation of casein suspension: Disperse 1.0 g of casein in 100 mL of pure water to obtain casein suspension, and store it at 4℃ for later use;

[0055] (3) Preparation of sodium alginate solution: Dissolve 1.0 g of sodium alginate in 100 mL of pure water to obtain sodium alginate solution, and store it at 4℃ for later use;

[0056] (4) Preparation of casein-sodium alginate complex: Take 100 mL of casein suspension, 100 mL of sodium alginate solution and 50 mL of eutectic solvent respectively, mix them and stir at 400 rpm for 3 h to obtain casein-sodium alginate complex solution. Use a dialysis bag with a molecular weight cutoff of 30 kD to load the complex solution, immerse the dialysis bag in deionized water and dialyze at 4℃ for 12 h, change the water every 2 h. After dialysis, freeze dry the solution in the dialysis bag at -30℃ and 20 Pa for 24 h to obtain casein-sodium alginate complex.

[0057] This embodiment also provides an emulsion and emulsion gel based on a casein-sodium alginate complex, the preparation method of which is as follows:

[0058] (1) The casein-sodium alginate complex prepared in this embodiment was reconstituted with pure water to obtain an aqueous solution with a complex mass fraction of 1.0%;

[0059] (2) Dissolve coenzyme Q10 in corn oil to obtain an oil phase solution with a coenzyme Q10 mass fraction of 6%;

[0060] (3) Mix the aqueous phase solution and the oil phase solution at a volume ratio of 7:3 and homogenize at 10,000 rpm for 5 min to obtain casein-sodium alginate emulsion; heat the emulsion in a water bath at 60℃ for 1 h, cool it to room temperature, and then place it at 4℃ for 8 h to form an emulsion gel, which is then stored at 4℃ for later use.

[0061] Example 2

[0062] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that the amount of eutectic solvent used in step (4) is 60 mL.

[0063] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0064] Example 3

[0065] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that the amount of eutectic solvent used in step (4) is 70 mL.

[0066] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0067] Example 4

[0068] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that in step (1), urea is used instead of choline chloride to prepare an ethylene glycol-urea eutectic solvent.

[0069] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0070] Example 5

[0071] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that in step (1), ethanolamine is used instead of ethylene glycol to prepare an ethanolamine-choline chloride eutectic solvent.

[0072] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0073] Example 6

[0074] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that in step (1), tert-butanol is used instead of ethylene glycol to prepare tert-butanol-choline chloride eutectic solvent.

[0075] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0076] Example 7

[0077] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that in step (1), tert-butanol is used instead of ethylene glycol and urea is used instead of choline chloride to prepare the tert-butanol-urea eutectic solvent.

[0078] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0079] Example 8

[0080] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that in step (1), lactic acid is used instead of ethylene glycol to prepare a lactic acid-choline chloride eutectic solvent.

[0081] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0082] Example 9

[0083] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that in step (1), malic acid is used instead of ethylene glycol to prepare a malic acid-choline chloride eutectic solvent.

[0084] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0085] Example 10

[0086] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that in step (2), the casein suspension is obtained by dispersing 1.5 g of casein in 100 mL of pure water.

[0087] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0088] Example 11

[0089] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that in step (2), the casein suspension is obtained by dispersing 2.0 g of casein in 100 mL of pure water.

[0090] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0091] Example 12

[0092] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that in step (3), the sodium alginate solution is obtained by dissolving 2.0 g of sodium alginate in 100 mL of pure water.

[0093] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0094] Example 13

[0095] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that in step (3), the sodium alginate solution is obtained by dissolving 3.0 g of sodium alginate in 100 mL of pure water.

[0096] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0097] Example 14

[0098] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that the dialysis time in step (4) is 18 h.

[0099] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0100] Example 15

[0101] This embodiment provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that the freeze-drying time in step (4) is 30 h.

[0102] This embodiment also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared in this embodiment, the preparation method of which is the same as in Example 1.

[0103] Comparative Example 1

[0104] This comparative example provides a casein-sodium alginate complex, the preparation method of which is as follows:

[0105] (1) Preparation of casein suspension: Disperse 1.0 g of casein in 100 mL of pure water to obtain casein suspension, and store at 4℃ for later use;

[0106] (2) Preparation of sodium alginate solution: Dissolve 1.0 g of sodium alginate in 100 mL of pure water to obtain sodium alginate solution, and store it at 4℃ for later use;

[0107] (3) Preparation of casein-sodium alginate complex: Take 100 mL of casein suspension and 100 mL of sodium alginate solution respectively, mix them and stir at 400 rpm for 3 h to obtain casein-sodium alginate complex solution. Use a dialysis bag with a molecular weight cutoff of 30 kD to load the complex solution, immerse the dialysis bag in deionized water and dialyze at 4℃ for 12 h, changing the water every 2 h. After dialysis, freeze-dry the solution in the dialysis bag at -30℃ and 20 Pa for 24 h to obtain casein-sodium alginate complex.

[0108] This comparative example also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared based on this comparative example, the preparation method of which is the same as in Example 1.

[0109] Comparative Example 2

[0110] This comparative example provides a casein-sodium alginate complex, the preparation method of which is as follows:

[0111] (1) Preparation of casein solution: Disperse 1.0 g of casein in 100 mL of pure water, add 2 mol / L NaOH solution to adjust the pH to 7.0, and store at 4℃ for later use;

[0112] (2) Preparation of sodium alginate solution: Dissolve 1.0 g of sodium alginate in 100 mL of pure water to obtain sodium alginate solution, and store it at 4℃ for later use;

[0113] (3) Preparation of casein-sodium alginate complex: Take 100 mL of casein solution and 100 mL of sodium alginate solution respectively, mix them and stir at 400 rpm for 3 h to obtain casein-sodium alginate complex solution. Use a dialysis bag with a molecular weight cutoff of 30 kD to load the complex solution, immerse the dialysis bag in deionized water and dialyze at 4℃ for 12 h, changing the water every 2 h. After dialysis, freeze-dry the solution in the dialysis bag at -30℃ and 20 Pa for 24 h to obtain casein-sodium alginate complex.

[0114] This comparative example also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared based on this comparative example, the preparation method of which is the same as in Example 1.

[0115] Comparative Example 3

[0116] This comparative example provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that step (1) is omitted and an equal amount of ethylene glycol is used to replace the eutectic solvent in step (4).

[0117] This comparative example also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared based on this comparative example, the preparation method of which is the same as in Example 1.

[0118] Comparative Example 4

[0119] This comparative example provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that the molar ratio of ethylene glycol to choline chloride in step (1) is 5:1.

[0120] This comparative example also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared based on this comparative example, the preparation method of which is the same as in Example 1.

[0121] Comparative Example 5

[0122] This comparative example provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that in step (1), oxalic acid dihydrate is used instead of ethylene glycol to prepare oxalic acid dihydrate-choline chloride eutectic solvent.

[0123] This comparative example also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared based on this comparative example, the preparation method of which is the same as in Example 1.

[0124] Comparative Example 6

[0125] This comparative example provides a casein-sodium alginate complex, the preparation method of which is the same as in Example 1, except that urea is used instead of ethylene glycol in step (1) to prepare a urea-choline chloride eutectic solvent.

[0126] This comparative example also provides an emulsion and emulsion gel of casein-sodium alginate complex prepared based on this comparative example, the preparation method of which is the same as in Example 1.

[0127] Comparative Example 7

[0128] This comparative example provides an emulsion and emulsion gel based on a casein-sodium alginate complex. The preparation method is the same as in Example 1, except that in step (3), the aqueous phase solution and the oil phase solution are mixed at a volume ratio of 5:5.

[0129] Comparative Example 8

[0130] This comparative example provides an emulsion and emulsion gel based on a casein-sodium alginate complex. The preparation method is the same as in Example 1, except that in step (3), the aqueous phase solution and the oil phase solution are mixed at a volume ratio of 6:4.

[0131] Comparative Example 9

[0132] This comparative example provides an emulsion and emulsion gel based on a casein-sodium alginate complex. The preparation method is the same as in Example 1, except that in step (3), the aqueous phase solution and the oil phase solution are mixed at a volume ratio of 8:2.

[0133] Comparative Example 10

[0134] This comparative example provides an emulsion and emulsion gel based on a casein-sodium alginate complex. The preparation method is the same as in Example 1, except that in step (3), the aqueous phase solution and the oil phase solution are mixed at a volume ratio of 9:1.

[0135] Experimental Example 1: Emulsifying properties and solubility of emulsions based on casein-sodium alginate complex

[0136] I. Experimental Objective

[0137] This experiment aims to test the emulsification properties and solubility of the casein-sodium alginate complex-based emulsions prepared in Examples 1-15 and Comparative Examples 1-10. The test indicators include emulsification activity (EAI), emulsification stability (ESI), and solubility.

[0138] II. Experimental Methods

[0139] 1. Emulsification property testing

[0140] Dissolve 0.1 g of emulsion sample in 100 mL of pure water to obtain a sample solution. Take 30 mL of the prepared sample solution and add 10 mL of soybean oil. Homogenize at 8000 rpm for 1 min. Take 100 μL of the bottom layer solution and dilute it 100 times with 0.1% sodium dodecyl sulfate solution (SDS). Measure the absorbance at 500 nm. After standing for 30 min, measure the absorbance again and calculate the corresponding emulsifying activity and emulsifying stability.

[0141]

[0142] In the formula:

[0143] EAI: Emulsifying activity, m 2 / g;

[0144] ESI: Emulsification stability, %

[0145] C: Sample mass concentration, g / mL;

[0146] The oil phase ratio in the emulsion is set to 0.25.

[0147] L: Optical path length of the cuvette, cm;

[0148] DF: Dilution factor, set to 100;

[0149] A1: Absorbance of the emulsion;

[0150] A2: Absorbance of the emulsion after standing for 30 minutes.

[0151] 2. Solubility test

[0152] The emulsion sample was stirred at room temperature for 20 min, then centrifuged at 10,000 rpm for 30 min, and the supernatant was collected. 5 mL of G-250 reagent was mixed with 1 mL of the supernatant, and the mixture was reacted at room temperature for 15 min. The absorbance at 595 nm was measured. 10 mg of BSA was dissolved in distilled water and brought to a final volume of 100 mL to prepare a 0.1 mg / mL standard stock solution. This stock solution was then serially diluted to obtain a series of standard solutions with concentrations ranging from 0.02 to 0.10 mg / mL. A standard curve was plotted with the concentration of the standard solution on the x-axis and the absorbance of the standard solution at 595 nm on the y-axis. The casein mass concentration C1 in the supernatant was determined from the absorbance of the supernatant at 595 nm and the standard curve.

[0153] Take a certain volume of emulsion sample, add 4 volumes of cold methanol (pre-placed at -20℃), and quickly vortex for 20 s; then incubate on ice for 30 min to promote protein precipitation and oil phase aggregation; centrifuge at 10000 rpm, 4℃ for 10 min, and carefully discard the supernatant (containing oil phase and solvent) to obtain the precipitate; add 3 volumes of cold methanol to the precipitate for washing, vortex for 10 s, centrifuge at 10000 rpm for 5 min, and discard the supernatant to remove residue; release the organic reagents from the obtained precipitate in a fume hood for about 2 min; add a certain volume of buffer (50 mM Tris-HCl, pH 7.5), and vortex to redissolve the precipitate (if insoluble particles are encountered, centrifuge at 10000 rpm for 5 min and collect the supernatant); quantitatively determine the protein concentration according to the aforementioned G-250 method, and use a sample solution without casein and with the same other components as a control, subtract the matrix background, and calculate the total casein mass concentration C2 in the emulsion.

[0154] Calculate the sample solubility S using the following formula.

[0155] S = C1 / C2 × 100%

[0156] In the formula:

[0157] S: solubility, %

[0158] C1: Casein mass concentration in the supernatant, mg / mL;

[0159] C2: Total casein protein concentration in the emulsion, mg / mL.

[0160] All experiments were performed in triplicate, and the results are expressed as mean ± standard deviation.

[0161] III. Experimental Results

[0162] Table 3. Results of emulsification and solubility tests of emulsions (mean ± standard deviation)

[0163]

[0164] Note: In each column, different letters indicate a significant difference between groups (P < 0.05), while identical or overlapping letters indicate no significant difference between groups.

[0165] As shown in Table 3, compared with Comparative Example 1, Examples 1-9 used casein-sodium alginate complexes with added eutectic solvents such as ethylene glycol-choline chloride and ethylene glycol-urea as emulsifiers to prepare emulsions, which significantly improved the emulsification properties and solubility of the emulsions. The improvement in emulsification properties and solubility was more pronounced with the casein-sodium alginate complex with added ethylene glycol-choline chloride (molar ratio 2:1) as the emulsifier. Comparative Example 2, compared to Comparative Example 1, increased casein solubility through alkali treatment, but did not significantly improve the emulsification properties and solubility of the emulsion. Comparative Example 3, compared to Example 1, only added ethylene glycol, a hydrogen bond donor forming a eutectic solvent, during the preparation of the casein-sodium alginate complex. The resulting emulsion showed significantly reduced emulsification properties and solubility, indicating that the eutectic solvent has a significant impact on the emulsifying effect of the casein-sodium alginate complex. Comparative Example 4, compared to Example 1, altered the molar ratio of ethylene glycol to choline chloride during the preparation of the casein-sodium alginate complex. The resulting emulsion exhibited significantly reduced emulsifying properties and solubility. This is presumably because the increased proportion of ethylene glycol weakens the hydrogen bonds in the mixture, thus reducing the solvent's effect. Compared to Comparative Example 1, Comparative Example 5, using a casein-sodium alginate complex prepared with oxalate dihydrate-choline chloride eutectic solvent as an emulsifier, showed significantly worse emulsifying properties and solubility. This is presumably because the strong acidity of oxalic acid promotes denaturation of casein during prolonged contact, preventing the complex from completing its self-assembly process. Comparative Example 6, using a casein-sodium alginate complex prepared with urea-choline chloride eutectic solvent as an emulsifier, showed no significant difference in emulsifying properties and solubility compared to Comparative Example 1. This demonstrates that not all eutectic solvent combinations significantly improve the emulsifying properties and solubility of casein-sodium alginate complex-based emulsions. Combining Comparative Examples 7-10 and Example 1, the gradually increasing ratio of the aqueous phase to the oil phase resulted in a trend of first increasing and then slightly decreasing emulsification properties and solubility of the emulsion. Example 1 (water:oil = 7:3) showed the best performance, indicating that the water-oil ratio affects the emulsification performance of the emulsion. Examples 10-11 increased the concentration of casein stock solution compared to Example 1; Examples 12-13 increased the concentration of sodium alginate stock solution compared to Example 1; and Examples 14-15 extended the dialysis time and freeze-drying time compared to Example 1. Although these results differed to varying degrees from those of Example 1, they all achieved relatively ideal results.

[0166] Experimental Example 2: Antioxidant Properties of Emulsions Based on Casein-Sodium Alginate Complex

[0167] I. Experimental Objective

[0168] This experiment aims to detect the antioxidant properties of the casein-sodium alginate complex-based emulsions prepared in Examples 1-15 and Comparative Examples 1-10. The detection indicators include DPPH radical scavenging rate, hydroxyl radical scavenging rate and ABTS radical scavenging rate.

[0169] II. Experimental Methods

[0170] 1. Method for determining DPPH free radical scavenging rate (%)

[0171] Add 2 mL of a sample solution of appropriate concentration to 2 mL of freshly prepared 0.2 mmol / L DPPH solution, mix well, and incubate at 37℃ in the dark for 30 min. Measure the absorbance at 517 nm and record it as A1. For the control group, replace the DPPH solution with pure water, and record the absorbance as A2. For the blank group, replace the sample solution with pure water, and record the absorbance as A0. All experiments are performed in triplicate. The absorbance should ideally be between 0.2 and 0.8. The formula for calculating the DPPH free radical scavenging rate is as follows:

[0172] DPPH radical scavenging rate = [1 - ((A1 - A2) / A0)] × 100%

[0173] 2. Method for determining hydroxyl radical scavenging rate (%)

[0174] Prepare 8 mmol / L ferrous sulfate solution, 20 mmol / L H₂O₂ solution, 3 mmol / L salicylic acid solution, and a sample solution of appropriate concentration. Mix 0.335 mL of the sample solution with 0.1 mL of ferrous sulfate solution, 0.335 mL of salicylic acid solution, and 0.08 mL of H₂O₂ solution, and incubate at 37℃ for 30 min. After cooling, bring the volume to 1 mL, centrifuge at 8000 rpm for 10 min, and measure the absorbance of the supernatant at 510 nm, denoted as A1. Use pure water instead of the sample solution and H₂O₂ solution as the blank and control groups, respectively, and record the absorbance as A0 and A2. All experiments are performed in triplicate. The absorbance should ideally be between 0.2 and 0.8. The formula for calculating the hydroxyl radical scavenging rate is as follows:

[0175] Hydroxyl radical scavenging rate = [1 - ((A1 - A2) / A0)] × 100%

[0176] 3. Method for determining ABTS free radical scavenging rate (%)

[0177] Mix 1 mL of ABTS solution (7.4 mmol / L) with an equal volume of 2.6 mmol / L K2S2O8 solution, and let stand in the dark for 16 h to form ABTS. + Stock solution; ABTS should be diluted with anhydrous ethanol solution before use. +The stock solution was appropriately diluted to obtain an absorbance of 0.7 ± 0.02 at 734 nm, thus yielding ABTS. ＋ Working solution; add 1.980 mL of ABTS + The working solution was mixed with 20 μL of sample and reacted at 30℃ for 10 min. The absorbance at 734 nm was measured and recorded as A1. In the control group, the ABTS solution was replaced with pure water, and the absorbance was recorded as A2. In the blank group, the sample solution was replaced with pure water, and the absorbance was recorded as A0. All experiments were performed in triplicate. The formula for calculating the ABTS free radical scavenging rate is as follows:

[0178] ABTS radical scavenging rate = [1 - ((A1 - A2) / A0)] × 100%

[0179] III. Experimental Results

[0180] Table 4. Results of antioxidant activity assay of the emulsion (mean ± standard deviation)

[0181]

[0182] Note: In each column, different letters indicate a significant difference between groups (P < 0.05), while identical or overlapping letters indicate no significant difference between groups.

[0183] As shown in Table 4, compared with Comparative Example 1, Examples 1-15 showed a significant improvement in antioxidant activity when using casein-sodium alginate complexes with added eutectic solvents such as ethylene glycol-choline chloride and ethylene glycol-urea as emulsifiers to prepare emulsions. Comparative Example 2, compared with Example 1, did not add eutectic solvents when preparing the casein-sodium alginate complex and used alkali treatment to increase casein solubility. The antioxidant activity of the emulsion prepared using this casein-sodium alginate complex as an emulsifier was significantly reduced, but there was no significant difference compared to Comparative Example 1. Comparative Example 3, compared to Example 1, added only ethylene glycol, a hydrogen bond donor forming a eutectic solvent, when preparing the casein-sodium alginate complex. The antioxidant activity of the emulsion prepared using this casein-sodium alginate complex as an emulsifier was also significantly reduced, indicating that only eutectic solvents formulated with hydrogen bond donors and acceptors have a significant effect on improving the antioxidant activity of emulsions. Compared to Example 1, Comparative Example 4 increased the proportion of ethylene glycol in the preparation of the casein-sodium alginate complex. The emulsion prepared using ethylene glycol as an emulsifier exhibited poor performance and significantly reduced antioxidant activity. Compared to Comparative Example 1, Comparative Example 5 added oxalate dihydrate-choline chloride eutectic solvent in the preparation of the casein-sodium alginate complex, resulting in an emulsion with even worse antioxidant properties. Compared to Comparative Example 1, Comparative Example 6 added urea-choline chloride eutectic solvent in the preparation of the casein-sodium alginate complex, but the antioxidant properties of the emulsion prepared using urea as an emulsifier did not change significantly. These results are generally consistent with the emulsification characteristics and solubility results of the emulsion in Experimental Example 1. Compared to Example 1, Comparative Examples 7-10 adjusted the water-oil ratio during emulsion preparation, but the antioxidant properties did not change significantly.

[0184] Example 3: Average particle size of emulsions based on casein-sodium alginate complex

[0185] I. Experimental Objective

[0186] This experiment aims to detect the average particle size of the emulsions based on casein-sodium alginate complexes prepared in Examples 1-15 and Comparative Examples 1-10.

[0187] II. Experimental Methods

[0188] The particle size distribution of the emulsion was measured using a laser particle size analyzer. The emulsion was diluted 20 times with pure water and then dripped into the feed inlet of the laser particle size analyzer. The refractive indices of soybean oil and water were 1.47 and 1.33, respectively, and the particle absorption coefficient was 0.001.

[0189] All experiments were performed in triplicate, and the results are expressed as mean ± standard deviation.

[0190] III. Experimental Results

[0191] Table 5. Results of average particle size determination of emulsions (mean ± standard deviation)

[0192]

[0193] Note: In each column, different letters indicate a significant difference between groups (P < 0.05), while identical or overlapping letters indicate no significant difference between groups.

[0194] As shown in Table 5, compared with Comparative Example 1, Examples 1-15, using casein-sodium alginate complexes with added eutectic solvents such as ethylene glycol-choline chloride and ethylene glycol-urea as emulsifiers to prepare emulsions, showed significantly reduced average particle size and higher emulsion stability. Compared with Comparative Example 1, Comparative Example 5, which added oxalate dihydrate-choline chloride eutectic solvent during the preparation of the casein-sodium alginate complex, resulted in emulsions with larger average particle size and poorer stability. Compared with Comparative Example 1, Comparative Example 6, which added urea-choline chloride eutectic solvent during the preparation of the casein-sodium alginate complex, did not show a significant change in average particle size. Comparative Example 2, compared to Comparative Example 1, increased casein solubility through alkali treatment during the preparation of the casein-sodium alginate complex, resulting in a slightly reduced emulsion particle size, but without significant improvement. Compared to Example 1, Comparative Example 3, which only added ethylene glycol, a hydrogen bond donor forming a eutectic solvent, during the preparation of the casein-sodium alginate complex, showed a significantly increased emulsion particle size and poor stability. Comparative Example 4, compared to Example 1, altered the ratio of hydrogen bond donors to acceptors during the preparation of the casein-sodium alginate complex, resulting in a significantly increased emulsion particle size and also poor stability. Compared to Example 1, Comparative Examples 7-10 adjusted the water-oil ratio during emulsion preparation, resulting in either a significantly increased emulsion particle size or no significant difference.

[0195] Example 4: Storage stability of emulsions and emulsion gels based on casein-sodium alginate complexes

[0196] I. Experimental Objective

[0197] This experiment aims to study the storage stability of emulsions and emulsion gels based on casein-sodium alginate complexes prepared in Examples 1-15 and Comparative Examples 1-10.

[0198] II. Experimental Methods

[0199] Each prepared emulsion and emulsion gel sample was sealed in a sample bottle to reduce evaporation and stored at room temperature in the dark for 7 days. The state of the emulsion and emulsion gel after storage was observed with the naked eye.

[0200] III. Experimental Results

[0201] Table 6. Storage stability results of emulsions and emulsion gels

[0202]

[0203] Note: Basic stability standard for emulsion: no obvious oil-water separation, flocculation, aggregation, emulsion floating, or sedimentation; Basic stability standard for emulsion gel: relatively uniform appearance, no obvious stratification, no obvious collapse or shrinkage of the gel network, and no obvious colloidal structure destruction (gel rupture or bottom deposition).

[0204] As shown in Table 6, the emulsions and emulsion gels prepared in Comparative Examples 7-10 (water-to-oil ratios of 5:5, 6:4, 8:2, and 9:1, respectively) all exhibited stratification after 7 days of storage at room temperature, indicating poor stability. The emulsions and emulsion gels prepared in Examples 1-15 (water-to-oil ratio of 7:3) remained largely stable within 7 days of storage at room temperature, demonstrating good storage stability. This is because the interfacial area between the oil and water phases was suitable, allowing proteins to be more uniformly adsorbed at the oil-water interface, forming a tighter interfacial film. Simultaneously, the viscosity of the emulsion was appropriately increased, reducing the aggregation of water molecules and increasing its stability. Correspondingly, when preparing emulsion gels in Examples 1-15, a more stable gel network structure was formed within the emulsion. This indicates that emulsions with an appropriate oil phase fraction are more conducive to forming a stable protein gel network structure, helping to maintain the stability of the emulsion gel. The emulsions and emulsion gels prepared in Comparative Examples 3-5 also exhibited stratification after 7 days of storage at room temperature, indicating poor stability. The emulsions and emulsion gels prepared in Comparative Examples 1, 2, and 6 remained basically stable in their various forms within 7 days of storage at room temperature, demonstrating good stability.

[0205] Experimental Example 5: Centrifugation and heating losses of emulsion gels based on casein-sodium alginate complexes

[0206] I. Experimental Objective

[0207] This experiment aims to detect the centrifugal and heating losses of the casein-sodium alginate complex-based emulsion gels prepared in Examples 1-15 and Comparative Examples 1-10.

[0208] II. Experimental Methods

[0209] 1. Centrifugal loss rate detection

[0210] Place 5.0 g of the emulsion gel sample into a centrifuge tube and centrifuge (4℃, 8000 rpm, 15 min) to remove free water and oil from the gel. Then, carefully wipe the inside of the centrifuge tube with filter paper, record the total weight of the centrifuge tube and gel before and after centrifugation, and calculate the centrifugation loss rate according to the following formula: Centrifugation loss rate (%) = (total weight of tube and gel before centrifugation - total weight of tube and gel after centrifugation) / mass of gel × 100%.

[0211] 2. Heating loss rate test

[0212] A 5.0 g emulsion gel sample was heated at 90℃ for 0.5 h. The total weight of the glass dish and gel before and after heating was recorded, and the heating loss rate was calculated according to the following formula: Heating loss rate (%) = (Total weight of gel and dish before heating - Total weight of gel and dish after heating) / Mass of gel × 100%.

[0213] III. Experimental Results

[0214] Table 7. Centrifugation loss rate and heating loss rate of emulsion gel (mean ± standard deviation)

[0215]

[0216] Note: In each column, different letters indicate a significant difference between groups (P < 0.05), while identical or overlapping letters indicate no significant difference between groups.

[0217] The centrifugal loss rate of emulsion gels is strongly dependent on the structure of the gel network. A coarser gel structure results in a weaker ability to bind water, making it easier for water to be squeezed out by external forces. Table 7 shows that the centrifugal loss rates of the emulsion gels prepared in the examples and comparative examples differ to varying degrees, with the sample prepared in Example 2 exhibiting the lowest centrifugal loss rate. Among the casein-sodium alginate complexes prepared using different types of eutectic solvents as emulsifiers (Examples 1, 4-9 and Comparative Examples 5-6), the casein-sodium alginate complex prepared with ethylene glycol-choline chloride as the emulsifier had the lowest centrifugal loss rate, while the casein-sodium alginate complex prepared with oxalate dihydrate-choline chloride as the emulsifier had the highest centrifugal loss rate. This indicates that the type of eutectic solvent significantly affects the performance of the emulsion gel. Meanwhile, compared to Comparative Example 1 (no eutectic solvent added during emulsifier preparation) and Comparative Example 3 (only ethylene glycol, a hydrogen bond donor forming a eutectic solvent, was added during emulsifier preparation), the centrifugal losses of Examples 1, 4-9 were all reduced, indicating that using the casein-sodium alginate complex prepared with a suitable eutectic solvent as an emulsifier significantly improves the performance of the emulsion gel. Comparative Example 2, compared to Comparative Example 1, increased casein solubility through alkali treatment during the preparation of the casein-sodium alginate complex, resulting in a lower centrifugal loss rate of the emulsion gel prepared using it as an emulsifier, but it was still significantly higher than that of Examples 1-3. Comparative Example 4, compared to Example 1, changed the ratio of hydrogen bond donors and acceptors during the preparation of the casein-sodium alginate complex, but the centrifugal loss rate of the emulsion gel prepared using it as an emulsifier was still significantly increased, indicating poor stability. Furthermore, changes in the ratio of the aqueous phase to the oil phase (Comparative Examples 7-10 and Example 1) affected the centrifugal loss of the gel, with the loss rate gradually decreasing as the oil phase ratio decreased.

[0218] Emulsion gels are porous, soft substances containing a large amount of water. Generally, gels with less water loss after heating are considered to be of better quality. Sodium alginate has excellent gelatinization properties; when mixed with casein, it gels upon heating and binds with water to form a gel network that fills the gel network, increasing the binding of water molecules and reducing water loss during heating. Table 7 shows that the heating loss rates of the emulsion gels prepared in the examples and comparative examples differ to varying degrees, with the sample prepared in Example 2 exhibiting the lowest heating loss rate. Using casein-sodium alginate complexes prepared with different types of eutectic solvents as emulsifiers, the emulsion gel samples prepared using the casein-sodium alginate complex prepared with ethylene glycol-choline chloride as the emulsifier had the lowest heating loss rate, while the emulsion gel prepared with the casein-sodium alginate complex prepared with oxalate dihydrate-choline chloride as the emulsifier had the highest heating loss rate. This indicates that the type of eutectic solvent affects the performance of the emulsion gel to some extent. Meanwhile, the heating losses of Examples 1, 4-9 were lower than those of Comparative Example 1 (no eutectic solvent was added during emulsifier preparation) and Comparative Example 3 (only ethylene glycol, a hydrogen bond donor forming a eutectic solvent, was added during emulsifier preparation), indicating that using the casein-sodium alginate complex prepared with a suitable eutectic solvent as an emulsifier significantly improves the performance of the emulsion gel. Comparative Example 5 (oxalate dihydrate-choline chloride group) and Comparative Example 6 (urea-choline chloride group) showed severe heating losses, with no significant difference from Comparative Example 1. Comparative Example 2, compared to Comparative Example 1, increased casein solubility through alkali treatment during the preparation of the casein-sodium alginate complex, resulting in a lower heating loss rate for the emulsion gel prepared using it as an emulsifier, but it was still higher than that of Examples 1-3. Comparative Example 4, compared to Example 1, changed the ratio of hydrogen bond donors and acceptors during the preparation of the casein-sodium alginate complex, but the heating loss rate of the emulsion gel prepared using it as an emulsifier was still significantly increased, indicating poor stability. In addition, changes in the ratio of the aqueous phase to the oil phase (Comparative Examples 7-10 and Example 1) affected the heating loss rate of the gel, which gradually decreased as the oil phase ratio decreased.

[0219] In general, a suitable eutectic solvent can help improve the system's ability to bind water, reduce the mobility of water molecules, reduce water loss under the same external force, and result in lower centrifugal and heating loss rates, thus enhancing the stability of the emulsion gel.

[0220] In summary, the casein-sodium alginate complexes provided in Examples 1-15, by adding a suitable eutectic solvent to promote the self-assembly of casein and sodium alginate, and using this casein-sodium alginate complex as an emulsifier to prepare emulsions and emulsion gels, result in emulsions with excellent emulsifying properties and solubility, suitable particle size, and good storage stability. Loading coenzyme Q10 onto this emulsion significantly enhances its antioxidant activity, while the resulting emulsion gels also exhibit strong storage stability and low centrifugation and heating losses. This demonstrates that the casein-sodium alginate complex provided by this invention has many outstanding advantages as an emulsifier, and is significantly superior to complexes prepared without the addition of a eutectic solvent.

[0221] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A casein-sodium alginate complex, characterized in that, The preparation raw materials include casein, sodium alginate and a deep eutectic solvent, wherein the ratio of the casein, the sodium alginate and the deep eutectic solvent is 1.0-2.0 g: 1.0-3.0 g: 30-70 mL, the combination of the hydrogen bond donor and the hydrogen bond acceptor of the deep eutectic solvent is ethylene glycol-choline chloride, ethylene glycol-urea, ethanolamine-choline chloride, tert-butyl alcohol-choline chloride, tert-butyl alcohol-urea, lactic acid-choline chloride or malic acid-choline chloride, and the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor in the deep eutectic solvent is 2:

1.

2. The casein-sodium alginate complex according to claim 1, wherein 1.0-2.0 g of the casein is dispersed in 100 mL of water, and 1.0-3.0 g of the sodium alginate is dissolved in 100 mL of water. 1.0-2.0 g of the casein is dispersed in 100 mL of water, and 1.0-3.0 g of the sodium alginate is dissolved in 100 mL of water. The ratio of the casein, the sodium alginate and the deep eutectic solvent is 1.0-2.0 g: 1.0-3.0 g: 50-70 mL. The preparation method of the deep eutectic solvent comprises mixing the hydrogen bond donor and the hydrogen bond acceptor and heating and stirring at a temperature of 80-100 DEG C until a uniform transparent system is formed.

3. The casein-sodium alginate complex according to claim 1, wherein 1.0 g of the casein is dispersed in 100 mL of water, and 1.0 g of the sodium alginate is dissolved in 100 mL of water. The ratio of the casein, the sodium alginate and the deep eutectic solvent is 1.0 g: 1.0 g: 50-70 mL. The method comprises the following steps:

4. The method for preparing the casein-sodium alginate complex according to any one of claims 1 to 3, characterized in that, The casein is dispersed in water to obtain a casein suspension, and the sodium alginate is dissolved in water to obtain a sodium alginate solution. The casein suspension, the sodium alginate solution and the deep eutectic solvent are mixed in proportion and stirred to obtain a casein-sodium alginate complex solution. The casein-sodium alginate complex solution is subjected to dialysis and freeze-drying to obtain the casein-sodium alginate complex.

5. The method for preparing the casein-sodium alginate complex according to claim 4, wherein the stirring condition is stirring at 300-500 rpm for 2-5 h. The dialysis condition is that the casein-sodium alginate complex solution is loaded into a dialysis bag with a molecular weight cut-off of 30 kD, immersed in deionized water, dialyzed at 2-8 DEG C for 10-18 h, and the water is changed every 1-2 h. The freeze-drying condition is freeze-drying at -30 to -10 DEG C and 10-100 Pa for 18-30 h.

6. Use of the casein-sodium alginate complex according to any one of claims 1-3 or the casein-sodium alginate complex obtained by the method according to claim 4 or 5 as an emulsifier. The emulsion uses the casein-sodium alginate complex according to any one of claims 1-3 or the casein-sodium alginate complex obtained by the method according to claim 4 or 5 as an emulsifier, The method comprises the following steps:

7. A process for the preparation of a casein protein-alginate sodium complex based emulsion, characterized in that, The casein-sodium alginate complex is dissolved in water to obtain an aqueous phase solution. A fat-soluble active substance is mixed with oil to obtain an oil phase solution. ​ ​ Mixing the aqueous phase solution and the oil phase solution, homogenizing to obtain the emulsion based on casein-sodium alginate complex.

8. The preparation method of the emulsion based on casein-sodium alginate complex according to claim 7, characterized in that, the mass fraction of the casein-sodium alginate complex in the aqueous phase solution is 0.5% to 4%; the mass fraction of the fat-soluble active substance in the oil phase solution is 5% to 10%; the fat-soluble active substance comprises at least one of coenzyme Q10, astaxanthin, lutein and paclitaxel; the oil comprises at least one of corn oil, sunflower oil, soybean oil and flaxseed oil; the volume ratio of the aqueous phase solution and the oil phase solution is 7:3; the homogenization condition is 8000 to 12000 rpm for 3 to 5 min.

9. A method for the preparation of a casein protein-alginate sodium complex based emulsion gel, characterized in that, The emulsion obtained by the preparation method of claim 7 or 8 is heated at 50 to 90℃ for 0.5 to 2 h, cooled to room temperature, and placed at 2 to 8℃ for 6 to 10 h to form an emulsion gel.

10. The emulsion based on casein-sodium alginate complex obtained by the preparation method of claim 7 or 8, or the emulsion gel based on casein-sodium alginate complex obtained by the preparation method of claim 9 is applied to the preparation of food, health food or medicine.

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