Antioxidant sheep milk casein-ursolic acid compound, product and application

Abstract

The invention provides an antioxidant sheep milk casein-ursolic acid compound, a product and application, a sheep milk casein solution and an ursolic acid solution are mixed in an isovolumetric mode, incubation is conducted in a dark environment, and a sheep milk casein-ursolic acid compound solution is obtained. And the structural stability of the casein is improved by utilizing the natural active component ursolic acid. The sheep milk casein serves as a natural emulsifier and carrier and has the potential of improving the solubility and stability of hydrophobic compounds, the solubility and stability of the compound can be improved by combining ursolic acid with the sheep milk casein, the digestion characteristic of the sheep milk casein can be utilized, and the solubility and stability of the compound can be improved. The release and absorption of the sheep milk casein-ursolic acid compound in gastrointestinal tracts are synergistically promoted, so that the bioavailability of the sheep milk casein-ursolic acid compound is improved, and a theoretical basis and a technical support are provided for innovation of the sheep milk product industry.

Description

Technical Field

[0001] The invention belongs to the technical field of dairy product processing, and in particular belongs to an antioxidant goat milk casein-ursolic acid complex, a product and an application thereof. Background Art

[0002] Goat milk casein (CN) is the main protein component in goat milk. Due to its unique nutritional value and functional properties, it has received increasing attention in the food industry in recent years. Compared with bovine milk casein, goat milk casein has a smaller fat globule size, a softer curd structure, and a higher content of short-chain fatty acids. These characteristics make it easier for the human body to digest and absorb, and it is particularly suitable for infants, the elderly, and people with weak digestive functions. In addition, goat milk casein also has good emulsification, gelation, and stability, and is widely used in the production of dairy products such as cheese, yogurt, and milk powder. However, despite the significant advantages of goat milk casein in terms of nutrition and digestibility, it still has some defects and deficiencies that need to be addressed in practical applications.

[0003] First, the physical and chemical stability of goat milk casein is poor. Similar to bovine milk casein, the structure of goat milk casein is also easily affected by environmental factors (such as pH, temperature, ionic strength, etc.). For example, under acidic conditions, goat milk casein tends to aggregate and form insoluble precipitates, which not only affects the appearance and texture of the product, but also reduces its nutritional value and market acceptance. In addition, during high-temperature treatment, the structure of goat milk casein may also undergo irreversible denaturation, resulting in a significant decrease in its functional properties (such as emulsification and gelation). These stability issues severely limit the application of goat milk casein in functional dairy products.

[0004] Secondly, the functional properties of existing goat milk products are relatively simple. Although goat milk casein itself has good digestibility, its antioxidant and other functional properties (such as anti-inflammatory, immunomodulatory, etc.) are relatively limited and cannot meet consumers' diverse needs for healthy food. In order to improve the functional properties of goat milk products, existing technologies usually achieve this by adding chemical stabilizers or modifiers. However, these methods have certain limitations: on the one hand, the introduction of chemical additives may bring food safety risks and is not in line with modern consumers' pursuit of natural and healthy foods; on the other hand, these additives can often only improve one aspect of performance (such as stability), but cannot comprehensively improve the antioxidant activity and other functional properties of goat milk products.

[0005] Ursolic acid (UA) is a natural pentacyclic triterpenoid compound that is widely found in plants and has significant antioxidant, anti-inflammatory and anti-cancer biological activities. However, as a hydrophobic compound, ursolic acid has a low solubility in water, which limits its absorption and bioavailability in the human body, resulting in low bioavailability. This not only affects its health care function, but also limits its application in the food industry. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present invention provides an antioxidant goat milk casein-ursolic acid complex, product and application, and utilizes the natural active ingredient ursolic acid to improve the structural stability of casein. As a natural emulsifier and carrier, goat milk casein has the potential to improve the solubility and stability of hydrophobic compounds. By combining ursolic acid with goat milk casein, not only the solubility and stability of the complex can be improved, but also the digestive characteristics of goat milk casein can be utilized to synergistically promote the release and absorption of the goat milk casein-ursolic acid complex in the gastrointestinal tract, thereby improving its bioavailability, and providing a theoretical basis and technical support for the innovation of the goat milk product industry.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for improving the stability of goat milk casein, comprising mixing equal volumes of a goat milk casein solution and an ursolic acid solution, incubating the mixture in a dark environment, and obtaining a goat milk casein-ursolic acid complex solution.

[0008] Furthermore, a goat milk casein solution with a concentration of 3 mg / mL and an ursolic acid solution with a concentration of 0.25 mg / mL to 1.0 mg / mL were mixed in equal volumes and incubated in a dark environment to obtain a goat milk casein-ursolic acid complex solution.

[0009] The present invention also provides a method for improving the digestion property of goat milk casein, comprising mixing a goat milk casein solution and an ursolic acid solution in equal volumes, incubating the mixture in a dark environment, and obtaining a goat milk casein-ursolic acid complex solution.

[0010] Furthermore, a goat milk casein solution with a concentration of 3 mg / mL and an ursolic acid solution with a concentration of 0.25 mg / mL to 1.0 mg / mL were mixed in equal volumes and incubated in a dark environment to obtain a goat milk casein-ursolic acid complex solution.

[0011] The present invention also provides an antioxidant goat milk casein-ursolic acid complex. The goat milk casein solution and the ursolic acid solution are mixed in equal volumes and incubated in a dark environment to obtain the goat milk casein-ursolic acid complex solution.

[0012] Furthermore, a goat milk casein solution with a concentration of 3 mg / mL and an ursolic acid solution with a concentration of 0.25 mg / mL to 1.0 mg / mL were mixed in equal volumes and incubated in a dark environment to obtain a goat milk casein-ursolic acid complex solution.

[0013] Furthermore, the solvents of the goat milk casein solution and the ursolic acid solution are both phosphate buffer solutions with a concentration of 0.1 M and a pH value of 7.40.

[0014] The present invention also provides a functional dairy product, which is prepared by adding the antioxidant sheep milk casein-ursolic acid complex into a dairy product to obtain the functional dairy product with antioxidant function.

[0015] Furthermore, the addition ratio of the goat milk casein-ursolic acid complex is 0.1% to 1.0%.

[0016] Furthermore, the dairy product is goat milk.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention significantly improves the solubility and stability of casein by combining ursolic acid with goat milk casein. As a natural emulsifier and carrier, goat milk casein has the potential to improve the solubility and stability of hydrophobic compounds. After ursolic acid is combined with it, it effectively overcomes the problem of poor self-solubility by virtue of the characteristics of goat milk casein. At the same time, by utilizing the digestive characteristics of goat milk casein, the release and absorption of the goat milk casein-ursolic acid complex in the gastrointestinal tract can be promoted, thereby greatly improving the bioavailability of ursolic acid and casein. This advantage enables ursolic acid to better exert its efficacy in the human body, providing a more efficient solution for related health care and medical applications.

[0018] In terms of dairy products, the goat milk casein-ursolic acid complex (CN-UA complex) prepared by the present invention brings many advantages to dairy products. On the one hand, the complex significantly improves the structural stability of dairy products during processing and storage, effectively avoids precipitation and stratification problems, and ensures the quality of dairy products. On the other hand, the CN-UA complex exhibits strong antioxidant capacity during in vitro digestion, can effectively remove free radicals, delay the oxidation and deterioration of dairy products, and meet consumers' demand for healthy food. In addition, the complex also improves the digestion and absorption rate of goat milk casein through synergistic effects, enhances the nutritional utilization of dairy products, and is particularly suitable for people with weak digestive function, providing strong support for the innovative development of the dairy industry.

[0019] The present invention combines the natural ingredient ursolic acid with goat milk casein, and does not require the addition of chemical stabilizers, which meets food safety and health requirements. Moreover, the present invention not only provides a new complex, but also applies it to the development of functional dairy products, bringing new development opportunities to the goat dairy product industry. By adding the CN-UA complex to dairy products such as goat milk, functional dairy products with antioxidant functions are obtained, which further expands the functions and application scope of dairy products, and is expected to promote the goat dairy product industry to develop in a healthier and more functional direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The UV spectrum test result of the antioxidant goat milk casein-ursolic acid complex of the present invention; Figure 2 The fluorescence spectrum test results of the antioxidant goat milk casein-ursolic acid complex of the present invention; Figure 3 The molecular docking test results of the antioxidant goat milk casein-ursolic acid complex of the present invention; Figure 4 The DPPH free radical scavenging test results of the antioxidant goat milk casein-ursolic acid complex of the present invention; Figure 5 The results are the in vitro digestion test results of the antioxidant goat milk casein-ursolic acid complex of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0022] The present invention provides a method for preparing an antioxidant goat milk casein-ursolic acid complex, comprising: Step 1, extracting goat milk casein from goat milk by isoelectric precipitation method; Step 101, centrifuging the fresh goat milk at a speed of 5000 rpm for 20 minutes to remove the fat layer and other insoluble impurities in the milk; Step 102, transfer the pretreated goat milk to a beaker, slowly add 1 mol / L hydrochloric acid solution under stirring with a magnetic stirrer, and monitor the pH value with a pH meter. When the pH value of the solution reaches 4.6, goat milk casein precipitates due to the weakening of charge repulsion; Step 103, transferring the goat milk solution containing the precipitate into a centrifuge tube, and centrifuging at a speed of 8000 rpm for 20 minutes. After centrifugation, the goat milk casein is precipitated at the bottom of the centrifuge tube, and the supernatant contains other components such as whey protein. The supernatant is removed and the precipitate is retained; Step 104, adding an appropriate amount of deionized water to the centrifuge tube containing the goat milk casein precipitate, gently blowing with a pipette to resuspend the precipitate, centrifuging again, and repeating the washing 2-3 times to remove the impurities, whey protein and salt remaining in the precipitate; Step 105, dissolving the washed goat milk casein precipitate in an appropriate amount of deionized water, putting it into a dialysis bag (the molecular weight cutoff is generally 3500~8000Da), and placing it in a container filled with a large amount of deionized water for 24 hours. During this period, the dialysate is replaced 3 times to completely remove residual salt and small molecule impurities. The dialyzed goat milk casein solution is freeze-dried to obtain goat milk casein dry powder.

[0023] Step 2, mixing the extracted goat milk casein and ursolic acid in an equal volume ratio to prepare a goat milk casein-ursolic acid complex; Step 201, preparing a goat milk casein solution with a concentration of 3 mg / mL and an ursolic acid solution with a concentration of 0.25 mg / mL to 1.0 mg / mL, wherein the solvent is a phosphate buffer solution (0.1 M, pH 7.40); the prepared goat milk casein solution is a milky white liquid, and is ultrasonicated at 200 W for 30 min to completely dissolve it into a uniform solution; after adding the transparent crystalline ursolic acid to the phosphate buffer solution, it is necessary to ultrasonicate at 200 W for 40 min to dissolve it and disperse it into a uniform solution; Step 202, taking equal volumes of goat milk casein solution and ursolic acid solutions of different concentrations (0.25, 0.50, 0.75 and 1.00 mg / mL, w / v), mixing and stirring evenly; Step 203, incubating the mixed solution in the dark for 20 minutes to prepare a goat milk casein-ursolic acid complex solution showing a light milky white color; Step 204: Store the complex solution at 4° C. for subsequent analysis.

[0024] Step 3: Add the goat milk casein-ursolic acid complex to goat milk, and make functional dairy products through homogenization, sterilization and other processes.

[0025] Step 301, adding goat milk casein-ursolic acid complex to goat milk at a certain ratio (0.1%-1.0%); Step 302, uniformly dispersing the complex in the goat milk by homogenization (pressure 35MPa-45MPa, temperature 35°C-45°C); Step 303: pasteurization (70°C-75°C, 10s-20s) is used to ensure product safety; Step 304: Aseptically pack and store at 4°C to 25°C to optimize product stability and functional properties; Step 305: Prepare a functional dairy product with antioxidant function.

[0026] Example 1 An antioxidant goat milk casein-ursolic acid complex, the preparation steps are as follows: Step 1, preparing goat milk casein solution and ursolic acid solution; Step 101, preparing a goat milk casein solution with a concentration of 3 mg / mL, wherein the solvent is a phosphate buffer solution (0.1 M, pH 7.40); Step 102, preparing an ursolic acid solution with a concentration of 0.25 mg / mL, wherein the solvent is a phosphate buffer solution (0.1 M, pH 7.40); Step 103: adjusting the pH values ​​of the goat milk casein solution and the ursolic acid solution as needed.

[0027] Step 2, mix the goat milk casein solution and the ursolic acid solution in a volume ratio of 1:1 and stir evenly; Step 3, incubating the mixed solution in the dark for 20 minutes to prepare a goat milk casein-ursolic acid complex solution; Step 4, adding the goat milk casein-ursolic acid complex solution into goat milk at a mass ratio of 0.5%; Step 5: Evenly disperse the complex in the goat milk by homogenization, with a homogenization pressure of 35 MPa and a temperature of 45° C. Step 6: Pasteurization is used to ensure product safety, with a sterilization temperature of 72°C and a time of 15 seconds; Step 7: Aseptically fill and store within a temperature range of 10°C to optimize product stability and functional properties.

[0028] Example 2 An antioxidant goat milk casein-ursolic acid complex, the preparation steps are as follows: Step 1, preparing goat milk casein solution and ursolic acid solution; Step 101, preparing a goat milk casein solution with a concentration of 3 mg / mL, wherein the solvent is a phosphate buffer solution (0.1 M, pH 7.40); Step 102, preparing an ursolic acid solution with a concentration of 0.5 mg / mL, wherein the solvent is a phosphate buffer solution (0.1 M, pH 7.40); Step 103: adjusting the pH values ​​of the goat milk casein solution and the ursolic acid solution as needed.

[0029] Step 2, mix the goat milk casein solution and the ursolic acid solution in a volume ratio of 1:1 and stir evenly; Step 3, incubating the mixed solution in the dark for 20 minutes to prepare a goat milk casein-ursolic acid complex solution; Step 4, adding the goat milk casein-ursolic acid complex solution into goat milk at a mass ratio of 0.5%; Step 5: Evenly disperse the complex in the goat milk by homogenization, with a homogenization pressure of 40 MPa and a temperature of 40° C. Step 6: Pasteurization is used to ensure product safety, with a sterilization temperature of 72°C and a time of 15 seconds; Step 7: Aseptically fill and store at a temperature range of 4°C to optimize product stability and functional properties.

[0030] Example 3 An antioxidant goat milk casein-ursolic acid complex, the preparation steps are as follows: Step 1, preparing goat milk casein solution and ursolic acid solution; Step 101, preparing a goat milk casein solution with a concentration of 3 mg / mL, wherein the solvent is a phosphate buffer solution (0.1 M, pH 7.40); Step 102, preparing an ursolic acid solution with a concentration of 0.75 mg / mL, wherein the solvent is a phosphate buffer solution (0.1 M, pH 7.40); Step 103: adjusting the pH values ​​of the goat milk casein solution and the ursolic acid solution as needed.

[0031] Step 2, mix the goat milk casein solution and the ursolic acid solution in a volume ratio of 1:1 and stir evenly; Step 3, incubating the mixed solution in the dark for 20 minutes to prepare a goat milk casein-ursolic acid complex solution; Step 4, adding the goat milk casein-ursolic acid complex solution into goat milk at a mass ratio of 0.5%; Step 5: Evenly disperse the complex in the goat milk by homogenization, with a homogenization pressure of 45 MPa and a temperature of 35° C. Step 6: Pasteurization is used to ensure product safety, with a sterilization temperature of 72°C and a time of 15 seconds; Step 7: Aseptically fill and store at a temperature range of 4°C to optimize product stability and functional properties.

[0032] Example 4 An antioxidant goat milk casein-ursolic acid complex, the preparation steps are as follows: Step 1, preparing goat milk casein solution and ursolic acid solution; Step 101, preparing a goat milk casein solution with a concentration of 3 mg / mL, wherein the solvent is a phosphate buffer solution (0.1 M, pH 7.40); Step 102, preparing an ursolic acid solution with a concentration of 1.0 mg / mL, wherein the solvent is a phosphate buffer solution (0.1 M, pH 7.40); Step 103: adjusting the pH values ​​of the goat milk casein solution and the ursolic acid solution as needed.

[0033] Step 2, mix the goat milk casein solution and the ursolic acid solution in a volume ratio of 1:1 and stir evenly; Step 3, incubating the mixed solution in the dark for 20 minutes to prepare a goat milk casein-ursolic acid complex solution; Step 4, adding the goat milk casein-ursolic acid complex solution into goat milk at a mass ratio of 0.5%; Step 5: Evenly disperse the complex in the goat milk by homogenization, with a homogenization pressure of 35 MPa and a temperature of 45° C. Step 6: Pasteurization is used to ensure product safety, with a sterilization temperature of 72°C and a time of 15 seconds; Step 7: Aseptically fill and store within a temperature range of 10°C to optimize product stability and functional properties.

[0034] The binding properties, antioxidant activity and in vitro digestion stability of the goat milk casein-ursolic acid complexes prepared in Examples 1 to 4 were tested as follows: The binding properties of the goat milk casein-ursolic acid complexes prepared in Examples 1 to 4 were studied by UV-visible spectroscopy analysis, fluorescence spectroscopy analysis, molecular docking analysis, and the like; Step 1: UV-Vis spectroscopy analysis The UV absorption spectra of the complex solutions were measured using a Puxi T9CS double-beam UV-visible spectrophotometer. The absorbance of the UA and CN complex solutions with different concentrations (0.00-1.00 mg / mL) was measured in the wavelength range of 260 nm to 500 nm.

[0035] The interaction mechanism between CN and UA was studied by UV-visible absorption spectroscopy. Figure 1 The UV-visible absorption characteristics of CN at different concentrations of UA (0.00~1.00mg / mL). A clear absorption peak appeared in the spectrum of each CN-UA complex around 280 nm. In addition, with the increase of UA concentration, the UV absorption of the complex showed an increasing trend and exhibited a slight red shift (279 ~ 281 nm). This may be due to the change in the microenvironment where the tryptophan and tyrosine residues are located due to the combination of CN and UA. In addition, the observed high UV absorption and red shift phenomenon jointly prove the binding of the two molecules.

[0036] Step 2: Fluorescence spectroscopy analysis The effect of different concentrations (0.00 to 1.00 mg / mL) of UA on CN fluorophore was measured using a fluorescence spectrophotometer (RF-6000, Shimadzu, Japan). The excitation wavelength was 280 nm. The emission wavelength was set to a fluorescence range of 300 nm to 500 nm. The excitation and emission slit widths were both set to 10 nm.

[0037] The change of fluorescence intensity was used to explore the effect of the interaction between CN and UA on conformational changes. Figure 2 As shown in the figure, with the increase of UA concentration, the fluorescence intensity of the complex gradually decreased, and the maximum absorption characteristic peak of the sample appeared near 332 nm, with a slight red shift (334 nm). The interaction between UA and the aromatic ring of CN amino acid residues will also reduce the hydrophobic microenvironment of aromatic amino acid residues, thereby affecting the microenvironment of tryptophan and tyrosine residues and quenching the fluorescence of proteins. In addition, the addition of UA may also cause changes in the spatial conformation of CN, resulting in more hydrophobic groups exposed in the protein molecular structure. This result is consistent with the results of UV-visible spectroscopy analysis.

[0038] Step 3: Molecular docking analysis To explore the interaction between CN and UA, molecular docking simulations were performed using Auto Dock Vina (version 1.5.7). The 3D structure of UA (CID: 64945) was downloaded from the PubChem database (https: / / pubchem.ncbi.nlm.nih.gov / ). Goat casein α was obtained from the Uniprot database. s1 -CN (P18626), α s2 The three-dimensional structures of the four subtypes of β-CN (P33049), β-CN (P33048) and κ-CN (P02670) were obtained. After optimizing the structures of CN and UA, CN was selected as the receptor and UA as the ligand for molecular docking analysis. During the docking calculation process, the default parameters in AutoDock Vina were used to ensure the consistency and reliability of the results. After the molecular docking was completed, PyMOL was used to further visualize and analyze the obtained docking results.

[0039] Molecular docking is an effective technique to evaluate the affinity and binding energy between ligands and receptors. Figure 3 The binding configuration obtained after molecular docking simulation of CN and UA. UA showed close association and integration in the active site of CN, and a total of 22 casein residues interacted with UA. s1 -CN 7 amino acid residues (Pro162, Val153, Ala158, Tyr109, Tyr161, Tyr169, Phe165), αs2 Two amino acid residues of α-CN (Phe104, Ile101), five amino acid residues of β-CN (Leu6, Leu9, Leu12, Ala13, Arg16), and six amino acid residues of κ-CN (Phe38, Phe39, Glu36, Arg37, Asp40, Asp41) interact with UA through hydrophobic interactions. s2 -CN's two amino acid residues Tyr105 and Glu100 bind to UA through hydrogen bonds. These findings clearly indicate that the non-covalent binding between CN and UA is mainly mediated by hydrophobic interactions and hydrogen bonds.

[0040] The antioxidant activity of the goat milk casein-ursolic acid complexes prepared in Examples 1 to 4 was evaluated by DPPH free radical scavenging rate; Step 4: DPPH free radical scavenging rate analysis 0.20 mL of the sample solution was mixed with 1 mL of 0.20 mmol / L DPPH solution (prepared with anhydrous ethanol), and the mixture was allowed to react at room temperature in the dark for 30 min. The absorbance (A1) was measured at a wavelength of 517 nm. Anhydrous ethanol was used as a blank, and the absorbance of anhydrous ethanol and DPPH was measured (A0). Using water-soluble vitamin E (Trolox) as a standard, the free radical scavenging rate was calculated according to the following formula:

[0041] Oxidative stress can induce a variety of diseases, so antioxidant activity is a desirable property of food materials. Protein-polyphenol complexes have been shown to have higher antioxidant capacity than native proteins. Figure 4 In the experiment, with the increase of UA concentration, the scavenging ability of CN-UA on DPPH free radicals was significantly enhanced (p<0.05). When the UA concentration was 1.00 mg / mL, the scavenging rate of CN-UA complex on DPPH free radicals reached a maximum of 73.88±5.98%. This may be because the hydroxyl group of UA has a protective effect on CN in the complex system. This further proves that the presence of UA stabilizes the structure of CN and enhances its antioxidant capacity.

[0042] The goat milk casein-ursolic acid complex prepared in Examples 1 to 4 was subjected to in vitro digestion test to evaluate the digestion stability of the goat milk casein-ursolic acid complex; Step 5. In vitro digestion analysis Preparation of simulated digestive fluid: Na2HPO4 (1.195 g), KH2PO4 (0.095 g), α-amylase (0.05 g), and NaCl (4 g) were dissolved in ultrapure water to 500 mL, and the pH of the solution was adjusted to 6.75 with PBS buffer to prepare simulated salivary fluid (SSF). In vitro simulated gastric fluid (SGF) was prepared by dissolving NaCl (0.21 g), pepsin (0.087 g), and a small amount of 1.0 M HCl in 100 mL of double distilled water and adjusting the pH to 2.0–3.0 with 1.0 M HCl. In vitro simulated intestinal fluid (SIF) was prepared by dissolving NaH2PO4 (0.88 g), NaCl (0.876 g), and trypsin (0.1 g) in 100 mL of double distilled water and adjusting the pH to 7.0–8.0 with 1.0 M NaOH.

[0043] Simulated oral digestion: 1 mL of sample solution was mixed with 9 mL of simulated saliva (SSF) and placed in a 37 ℃ constant temperature shaking incubator for oral digestion.

[0044] Simulated gastric digestion: Oral digestive fluid was mixed with an equal volume of simulated gastric fluid (SGF) and digested in a 37 ℃ constant temperature water bath for 2 h.

[0045] Simulated intestinal digestion: An equal volume of simulated intestinal fluid (SIF) was then added to the gastric digestive fluid, and digestion was continued in a 37 °C water bath for 2 h.

[0046] Part of the digestion solution was taken from each digestion system, mixed with an equal volume of 10% trichloroacetic acid (TCA), and cooled in 4°C ice water for 30 minutes. The solution was then centrifuged (4°C, 4000 r / min, 15 minutes), and the supernatant was taken to determine the digestibility of each system using a BCA kit (Beijing Kangwei Century Biotechnology Co., Ltd.). The experiment was repeated three times, and the average value was taken as the final result.

[0047] The bioaccessibility of goat casein is higher than that of cow casein, but the digestion and absorption efficiency of UA in the human body is relatively low. Figure 5In the simulated in vitro digestion, the retention rate of CN-UA complex was significantly lower than that of the control group (p<0.05). Under the action of gastric acid and pepsin, the non-covalent binding of CN and UA has a synergistic effect on the digestion and absorption of these two substances. In addition, the retention rate of CN-UA complex in the intestine gradually decreased (from 21.10±2.00% to 15.12±1.07%). For example, after combined use with high concentration of UA (1.00 mg / mL), the retention rate of protein during intestinal digestion decreased by 1.40 times. After gastric digestion, the particle size of the complex was smaller and the structure was loose, which was more easily decomposed and absorbed by enzymes in the intestine. These results well illustrate that CN-UA complex can effectively bind and improve the bioaccessibility of proteins.

Claims

1. A method for improving the stability of goat milk casein, characterized in that: The goat milk casein solution and the ursolic acid solution were mixed in equal volumes and incubated in a dark environment to obtain a goat milk casein-ursolic acid complex solution.

2. A method for improving the stability of goat milk casein according to claim 1, characterized in that: A goat milk casein solution with a concentration of 3 mg / mL and an ursolic acid solution with a concentration of 0.25 mg / mL to 1.0 mg / mL were mixed in equal volumes, and incubated in a dark environment to obtain a goat milk casein-ursolic acid complex solution.

3. A method for improving the digestibility of goat milk casein, characterized in that: The goat milk casein solution and the ursolic acid solution were mixed in equal volumes and incubated in a dark environment to obtain a goat milk casein-ursolic acid complex solution.

4. A method for improving the digestibility of goat milk casein according to claim 3, characterized in that: A goat milk casein solution with a concentration of 3 mg / mL and an ursolic acid solution with a concentration of 0.25 mg / mL to 1.0 mg / mL were mixed in equal volumes, and incubated in a dark environment to obtain a goat milk casein-ursolic acid complex solution.

5. An antioxidant sheep milk casein-ursolic acid complex, characterized in that: The goat milk casein solution and the ursolic acid solution were mixed in equal volumes and incubated in a dark environment to obtain a goat milk casein-ursolic acid complex solution.

6. The antioxidant sheep milk casein-ursolic acid complex according to claim 5, characterized in that: A goat milk casein solution with a concentration of 3 mg / mL and an ursolic acid solution with a concentration of 0.25 mg / mL to 1.0 mg / mL were mixed in equal volumes, and incubated in a dark environment to obtain a goat milk casein-ursolic acid complex solution.

7. An antioxidant sheep milk casein-ursolic acid complex according to claim 5 or 6, characterized in that: The solvents of the goat milk casein solution and the ursolic acid solution are both phosphate buffer solutions with a concentration of 0.1 M and a pH value of 7.

40.

8. A functional dairy product, characterized in that: The antioxidant sheep milk casein-ursolic acid complex described in claim 5 or 6 is added to dairy products to prepare functional dairy products with antioxidant function.

9. A functional dairy product according to claim 8, characterized in that: The added ratio of the goat milk casein-ursolic acid complex is 0.1% to 1.0%.

10. A functional dairy product according to claim 8, characterized in that: The dairy product is goat milk.

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