Xanthophyll-embedded rice bran protein emulsion gel and preparation method thereof

Abstract

The invention discloses a lutein-embedded rice bran protein emulsion gel preparation method, which comprises: 1, dissolving rice bran protein in distilled water, adjusting the pH value of the protein solution to be acidic, and diluting the supernatant with distilled water according to the target protein concentration; 2, heating the diluted rice bran protein solution, and continuously stirring in the heating process; after heating is completed, the rice bran protein solution is immediately cooled, and a high-flexibility rice bran protein solution A is obtained; step 3, adding lutein into soybean oil, and fully stirring to obtain a solution B; and step 4, mixing the solution A and the solution B, and homogenizing in a high-speed homogenizer to obtain the rice bran protein emulsion gel embedded with xanthophyll. According to the method provided by the invention, the stability and oxidation resistance of the xanthophyll are improved through the high-flexibility rice bran protein emulsion gel system, and the method can be widely applied to development of functional foods.

Description

Technical Field

[0001] The invention discloses the technical field of protein modification and application, and in particular relates to a rice bran protein emulsion gel embedded with lutein. Background Art

[0002] Lutein is a carotenoid widely found in fruits and flowers and is considered a nutritional supplement. It has potential health benefits, such as age-related macular degeneration, diabetic retinopathy, retinopathy of prematurity, myopia and cataracts. Lutein cannot be synthesized in the human body and is mainly obtained through food. Nutritionists recommend taking 6 mg of lutein daily to meet daily needs. Although lutein is widely found in the daily diet, its content is relatively low and cannot achieve the expected health benefits. In addition, during food processing, degradation reactions may reduce the lutein content. Lutein, as a fat-soluble pigment, is highly hydrophobic and sensitive to light and heat. It is easily reduced in biological activity due to oxidation, which limits its application in food. Studies have found that adding a certain amount of lutein to food and beverages as a dietary supplement is beneficial to muscle degeneration, age-related vision loss and blindness, cell aging and the enhancement of the body's immune system. Lutein has excellent antioxidant properties and can protect the skin from sunburn very well. It is usually added to nutritional supplements or various skin care products to reduce the damage to the human body from radiation from computer screens, TV screens and excessive ultraviolet radiation. It has obvious anti-radiation protection, moisturizing the skin and anti-aging effects.

[0003] Protein emulsion gel can provide a stable network structure and improve the physicochemical stability and texture of the material. Protein emulsion gel has adjustable viscoelasticity and can be used for stable loading and controlled release of functional substances. Current research mainly focuses on the construction of polyemulsion gel and the encapsulation of functional ingredients to obtain functional foods with ideal texture. However, when natural plant protein is used to construct emulsion gel, its stable emulsion gel system is unstable due to its low solubility in water, poor emulsification and stability.

[0004] Rice bran protein is heated in a water bath at pH 1.0 to 4.0 for a period of time. This operation can denature the rice bran protein and increase the flexibility of the rice bran protein. The protein structure contains flexible intervals and rigid intervals. The flexible interval refers to the part of the protein structure that is easy to change, while the rigid interval refers to the part of the protein structure that is not easy to change. The higher the ratio of the flexible interval to the rigid interval in the protein structure, the stronger the plasticity of the protein. The principle of increasing the flexible structure of rice bran protein is that it has abundant disulfide bonds and a high tendency to form aggregates. A variety of structures are formed during the protein aggregation process, including flexible scaffolds, linear fibrils, branched structures, and random aggregations. This aggregation can change the properties of the protein system. The driving forces in the modification process of rice bran protein include van der Waals and hydrophobic attraction between side chain and main chain atoms, minimizing steric clashes and energetically unfavorable bond torsion angles, maximizing hydrogen bonding, maximizing (maximizing) electrostatic repulsion (attraction), minimizing unfavorable interactions between amino acids and solvents (water) and their co-solutes, and these interactions between amino acids in proteins also exist between amino acids in neighboring proteins. This process can be mediated by charge-charge interactions, covalent bonds of hydrophilic and hydrophobic residues, or dynamic changes in protein conformation. Importantly, interactions between disulfide bonds, and hydrophobic and electrostatic interactions are important in the formation of highly flexible rice bran protein.

[0005] Proteins are important functional macromolecules in organisms, and their three-dimensional structure and dynamic properties determine the biological functions of proteins. Protein flexibility refers to the reversible changes in protein structure under certain conditions. This flexibility has an important influence on the function of proteins, such as the catalytic activity of enzymes and the binding ability of proteins to ligands. In the prior art, although there are some methods that can be used to study and regulate protein flexibility, there are still problems such as poor stability and single regulatory means.

[0006] Therefore, the present invention provides a new protein flexible regulation method to solve the deficiencies in the prior art. Summary of the invention

[0007] In view of this, the present invention provides a rice bran protein emulsion gel encapsulating lutein and a preparation method thereof, so as to improve the stability and antioxidant property of lutein.

[0008] The technical solution provided by the present invention is specifically a method for preparing a rice bran protein emulsion gel encapsulating lutein, comprising:

[0009] Step 1: dissolving rice bran protein in distilled water to obtain a protein solution, adjusting the pH of the protein solution to be acidic, fully stirring and hydrating, stirring the hydrated protein solution and then centrifuging to obtain a supernatant, determining the protein concentration in the supernatant, and diluting the supernatant with distilled water according to the target protein concentration;

[0010] Step 2: heating the diluted rice bran protein solution and continuously stirring it during the heating process; after the heating is completed, immediately cooling the rice bran protein solution to obtain a highly flexible rice bran protein solution A;

[0011] Step 3: Add lutein to soybean oil and stir thoroughly to obtain solution B;

[0012] Step 4: Mix solution A and solution B, and homogenize them in a high-speed homogenizer to obtain a rice bran protein emulsion gel encapsulating lutein.

[0013] Preferably, in step 1, the method for extracting rice bran protein comprises:

[0014] Step 11: using an organic reagent to remove oil from fresh rice bran to obtain defatted rice bran;

[0015] Step 12: extracting protein from the deesterified rice bran by alkali dissolution and acid precipitation to obtain a protein precipitate, and then freeze-drying the protein precipitate to obtain rice bran protein;

[0016] The method of extracting protein from deesterified rice bran by alkali dissolution and acid precipitation comprises:

[0017] The defatted rice bran was dissolved in distilled water to obtain a rice bran solution, and the pH of the rice bran solution was adjusted to 10.0 with a 2.0 mol / L NaOH solution. After stirring for 4 hours, the solution was centrifuged at 4000 r / min to obtain a supernatant. The pH of the supernatant was adjusted to 4.6 with a 2.0 mol / L HCl solution, and the solution was centrifuged at 4000 r / min to obtain a protein precipitate.

[0018] Preferably, in step 1, the pH of the protein solution is adjusted to 1.0-4.0 using HCl solution, wherein the concentration of the HCl solution is 0.05-2.0 mol / L.

[0019] Preferably, the target protein concentration in step 1 is 0.01-20 mg / ml.

[0020] Preferably, in step 1, the hydrated solution is stirred for more than 12 hours, and then centrifuged at 10000 r / min for 10 min to obtain a supernatant, and the supernatant is diluted with distilled water at pH 2.0 to obtain a rice bran protein solution with a target protein concentration.

[0021] Preferably, in step 2, the heating process of the rice bran protein solution is: using a water bath temperature of 75-95° C., a heating time of 0-24 h, and after the heating is completed, placing the rice bran protein solution in an ice water bath for cooling.

[0022] Preferably, the mass percentage of lutein added to soybean oil in step 3 is 0.1-2.0%.

[0023] Preferably, in step 4, the mixing volume ratio of solution A to solution B is one of 7.5:2.5, 7:3, and 6.5:3.5.

[0024] Preferably, the homogenization speed in step 4 is 6000-20000 r / min, and the homogenization time is 30-300 s.

[0025] The invention also provides a lutein-embedded rice bran protein emulsion gel prepared by the method.

[0026] The present invention provides a rice bran protein emulsion gel encapsulating lutein and a preparation method thereof. The method improves the stability and antioxidant properties of lutein through a highly flexible rice bran protein emulsion gel system and can be widely used in the development of functional foods.

[0027] The emulsion gel prepared by the present invention can also be applied to the cosmetics industry, and has a simple preparation process, low cost, and is suitable for industrial production. It can also simultaneously embed and deliver a variety of water-soluble or fat-soluble bioactive substances that are beneficial to the human body.

[0028] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 The present invention is a process flow chart for preparing a rice bran protein emulsion gel with lutein embedded therein;

[0032] Figure 2 The test results of the flexibility of rice bran protein obtained by processing in Examples 1, 2 and 3 are as follows;

[0033] Figure 3 The test results of rice bran protein emulsification activity and emulsification stability obtained by processing in Examples 1, 2 and 3 are as follows;

[0034] Figure 4The test results of Example 1 on the hydrophobicity of the rice bran protein surface after heating the rice bran protein for different time periods;

[0035] Figure 5 The test results of the ThT fluorescence intensity of the rice bran protein dispersion after heating the rice bran protein for different time periods in Example 1 are as follows; Figure 6 The results of the transmission electron microscope of the rice bran protein under heating for different time periods in Example 1 are shown;

[0036] Figure 7 The test results of the lutein embedding efficiency of the emulsion gel prepared by rice bran protein in Examples 1, 2 and 3;

[0037] Figure 8 These are the results of measuring the degradation rate of lutein in the emulsion gels prepared from rice bran protein in Examples 1, 2, and 3. DETAILED DESCRIPTION

[0038] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are merely examples of methods consistent with some aspects of the present invention as detailed in the appended claims.

[0039] This embodiment provides a method for preparing a rice bran protein emulsion gel embedded with lutein, comprising the following steps:

[0040] The rice bran protein extracted by alkali dissolution and acid precipitation is dissolved in water, the pH is adjusted with HCl solution, and the mixture is fully stirred for hydration.

[0041] The hydrated solution was centrifuged at 10000r / min for 10min, the protein concentration of the supernatant was determined by Bradford method, and the rice bran protein was adjusted to the desired concentration with distilled water at pH 2.0.

[0042] After the protein concentration was determined by the Bradford method, the supernatant was diluted with distilled water at pH 2.0 to ensure consistent experimental conditions.

[0043] A rice bran protein solution with a determined concentration is heated in a water bath for an appropriate period of time to obtain a highly flexible rice bran protein.

[0044] Preferably, the protein concentration of the rice bran protein solution is in the range of 0.01 to 20 mg / ml.

[0045] Preferably, the pH of the rice bran protein solution is adjusted to be in the range of 1.0 to 4.0, and the concentration of the hydrochloric acid used is in the range of 0.05 to 2.0 mol / L.

[0046] Preferably, the water bath temperature of the rice bran protein solution during heating is within the range of 75 to 95° C., the heating time is within the range of 0 to 24 hours, and magnetic stirring is continuously performed during the heating process. After heating, the rice bran protein solution is immediately added to an ice water bath for cooling to obtain a highly flexible rice bran protein solution A.

[0047] Add a certain amount of lutein into the soybean oil and stir thoroughly to mix them evenly.

[0048] Preferably, the amount of lutein added to the soybean oil is 0.1-2.0% to obtain solution B.

[0049] Solution A and solution B are mixed in a certain ratio and averaged using a homogenizer.

[0050] Preferably, solution A and solution B are mixed in a ratio of 7.5:2.5, 7:3, or 6.5:3.5 (v / v).

[0051] Preferably, in the above homogenization process, the speed of the homogenizer is 6000-20000 r / min and the homogenization time is 30-300 s.

[0052] Before extracting rice bran protein by alkali dissolution and acid precipitation, organic reagents are used to remove the oil in fresh rice bran to ensure that the rice bran protein in the rice bran is not destroyed by oil oxidation. Ether, n-hexane, petroleum ether and other organic reagents can be used to soak fresh rice bran, and the oil in the rice bran can be removed by the principle of like dissolves like, so as to prevent the rice bran protein from being destroyed due to oil oxidation and rancidity.

[0053] The method of extracting rice bran protein by alkali dissolution and acid precipitation is as follows: the rice bran solution is adjusted to a pH of 10.0 with a 2.0 mol / L NaOH solution, stirred for 4 hours, and then centrifuged in a centrifuge at 4000 r / min to obtain a supernatant, which is adjusted to a pH of 4.6 with a 2.0 mol / L HCI solution, and centrifuged in a centrifuge at 4000 r / min to obtain a precipitate, which is then dried using a freeze dryer.

[0054] The present invention aims at the defect that the emulsion gel prepared by traditional natural plant protein has poor performance, and provides a rice bran protein modified by acid-heat treatment, which enhances the flexible structure of rice bran protein and improves the stability of emulsion gel. The present invention relates to a protein flexibility regulation method, which controls the flexible state of protein through specific chemical modification and conditions. The flexible rice bran protein emulsion gel obtained by the method of the present invention has good stability and makes an important contribution to the stability of lutein embedded therein. Specifically, on the basis of natural rice bran protein, the present invention modifies rice bran protein by acid-heat treatment, destroys the protein structure during heating, exposes the hydrophobic groups, and hydrolyzes the acidic amino acids in the rice bran protein in an acidic environment. After heating, the rice bran protein is placed in an ice water bath to enhance the hydrogen bonding between the rice bran proteins. In this process, the secondary structure of the rice bran protein is transformed, mainly from the α-helix to the β-folded structure.

[0055] Example 1

[0056] Preparation of rice bran protein solution: Rice bran protein was dissolved in water, adjusted to pH 2.0 with 2.0 mol / L HCl solution, the protein concentration was measured by Bradford method, and the solution was diluted to a concentration of 10 mg / ml.

[0057] Preparation of highly flexible rice bran protein solution: The above rice bran protein solution was heated in a 90°C water bath for 0, 2, 4, 6, 8, 10, and 12 hours, and then placed in an ice water bath to cool to room temperature. The flexibility of rice bran protein with different treatment times was measured, and it was found that the rice bran protein with the highest flexibility was obtained when the heating time was 12 hours.

[0058] Preparation of soybean oil-lutein mixed solution: add 0.1% (mass fraction) lutein into soybean oil, heat and stir at 120° C. in the dark for 2 min to completely dissolve it.

[0059] The highly flexible rice bran protein solution obtained by heating for 12 hours was mixed with the soybean oil-lutein mixed solution in a ratio of 2.5:7.5, and then averaged for 40 seconds at an average condition of 16000 r / min to obtain an emulsion gel.

[0060] Example 2

[0061] Preparation of rice bran protein solution: Rice bran protein is dissolved in water, adjusted to pH 7.0 with 2.0 mol / L HCI solution or 2.0 mol / L NaOH solution, the protein concentration is measured by Bradford method, and the solution is diluted to a concentration of 10 mg / ml.

[0062] Preparation of highly flexible rice bran protein solution: The above rice bran protein solution was heated in a 90°C water bath for 0, 2, 4, 6, 8, 10, and 12 hours, then placed in an ice water bath and cooled to room temperature. The flexibility of the rice bran protein after different treatment times was measured to obtain rice bran protein solutions with different softness.

[0063] Preparation of soybean oil-lutein mixed solution: add 0.1% (mass fraction) lutein into soybean oil, heat and stir at 120° C. in the dark for 2 min to completely dissolve it.

[0064] Preparation of high-flexibility rice bran protein emulsion gel encapsulating lutein: The high-flexibility rice bran protein solution obtained by heating for 12 hours and the soybean oil-lutein mixed solution are mixed in a ratio of 2.5:7.5, and then averaged for 40 seconds at an average condition of 16000r / min to obtain an emulsion gel.

[0065] Example 3

[0066] Preparation of rice bran protein solution: Rice bran protein was dissolved in water, adjusted to pH 2.0 with 2.0 mol / L HCl solution, the protein concentration was measured by Bradford method, and the solution was diluted to a concentration of 10 mg / ml.

[0067] Preparation of highly flexible rice bran protein solution: The above rice bran protein solution was heated in an 80°C water bath for 0, 2, 4, 6, 8, 10, and 12 hours, and then placed in an ice water bath to cool to room temperature. The flexibility of rice bran protein with different treatment times was measured, and it was found that the rice bran protein with the highest flexibility was obtained when the heating time was 12 hours.

[0068] Preparation of soybean oil-lutein mixed solution: add 0.1% (mass fraction) lutein into soybean oil, heat and stir at 120° C. in the dark for 2 min to completely dissolve it.

[0069] Preparation of high-flexibility rice bran protein emulsion gel encapsulating lutein: The high-flexibility rice bran protein solution obtained by heating for 12 hours and the soybean oil-lutein mixed solution are mixed in a ratio of 2.5:7.5, and then averaged for 40 seconds at an average condition of 16000r / min to obtain an emulsion gel.

[0070] It can be seen from the above Examples 1 to 3 that the rice bran protein has the highest protein flexibility when heated at pH 2.0 and 90° C. for 12 h, and has the best stabilizing effect on the emulsion gel encapsulating lutein.

[0071] The main analysis methods in the embodiments of the present invention and the comparative examples are as follows:

[0072] 1. Rice bran protein flexibility test method: The flexibility of rice bran protein molecules is judged by the degree of trypsin hydrolysis of rice bran protein. Take 250 μL 1mg / mL trypsin (dissolved in 0.05mol / L, pH 8.0 Tris-HCl buffer, enzyme activity 7852U / g) solution and add it to 4mL, 1mg / mL rice bran protein sample solution at 38℃ constant temperature enzymolysis for 2h, then add 4mL volume fraction 5% trichloroacetic acid solution to terminate the enzymolysis reaction, and centrifuge at 3000rpm for 5min. Then take the supernatant to measure its absorbance at 280nm wavelength, and use absorbance A0 to represent flexibility.

[0073] 2. Emulsifying activity and emulsifying stability test method: Accurately measure 7.5mL (10mg / ml) of rice bran protein solution and 2.5ml of soybean oil and add them to a clean centrifuge tube with a capacity of 25mL. Use a homogenizer to homogenize at 10000rpm for 1min. Immediately after homogenization, take 10uL of the newly prepared emulsion and dilute it 100 times with 0.1% (w / v) SDS solution, and measure the absorbance at 500nm with a spectrophotometer. After 10min, extract the emulsion (10μl) from the bottom and measure it in the same way. The emulsifying ability index (EAI) and emulsifying stability index (ESI) are calculated using the following formula:

[0074]

[0075] Where D is the dilution factor, A0 and A10 are the absorbance at 0 and 10 min, respectively, C is the protein concentration (g / ml), and Φ is the oil volume fraction of the emulsion.

[0076] 3. Protein surface hydrophobicity test method: ANS (8-phenylamino-1-naphthalenesulfonic acid) fluorescent probe method was used and improved. Rice bran protein sample solution and rice bran protein modified under different treatment conditions were diluted with 0.01mol / L phosphate buffer to 4 concentration samples with protein concentrations of 0.025, 0.05, 0.1, and 0.2mg / mL, respectively. Take 6mL of the diluted rice bran protein solution, add 20μL of 8mmol / L ANS solution, mix well, and keep it away from light at room temperature for 15min, then colorimetrically measure the fluorescence intensity under the conditions of excitation wavelength of 390nm, emission wavelength of 470nm, and slit of 5nm in a fluorescence spectrophotometer, and plot the fluorescence intensity with the fluorescence intensity as the ordinate and the concentration of the rice bran protein solution as the abscissa. The initial slope is the sample surface hydrophobicity value.

[0077] 4. ThT test method: Prepare a solution of 0.8 mg / mL of thiomethoxythiothioate (Th T) with 0.2 mol / L NaCl and 0.01 mol / L phosphate buffer (pH 7.0), filter with a needle with a 0.2 μm filter to remove insoluble Th T particles to prepare the Th T stock solution. Dilute the Th T stock solution 50 times with phosphate buffer (0.01 mol / L, pH 7.0, 0.15 mol / L NaCl) to prepare the Th T working solution. Mix 5 mL of the Th T working solution with 50 μL of the sample solution to be tested, vortex and react for 30 seconds, and determine the Th T value of the protein sample at an excitation wavelength of 460 nm, an emission wavelength of 490 nm, and an excitation slit and an emission slit of 5 nm.

[0078] 5.TEM determination method: Dilute the 3% (w / v) sample to 0.1% (w / v) with water at pH 2.0, take about 1 mL of the diluted protein sample and drop it on the copper grid dedicated to the transmission electron microscope for adsorption for 5 hours, then dry it in a sterile environment at room temperature for 12 hours, and use a transmission electron microscope (TEM) at a voltage of 100kV and adjust different observation magnifications (4000-10000 times) to observe the microstructure of the sample.

[0079] 6. Emulsion gel particle size test method: The particle size distribution was determined using a laser light scattering instrument (Master Sizer 3000, Malvern Instruments Ltd., UK). Assuming spherical particles, the refractive indices of the soybean oil phase and the water phase were 1.465 and 1.333, respectively. Three measurements were averaged.

[0080] 7. Lutein embedding rate determination method: Weigh 0.2g of freeze-dried emulsion gel, add 5mL of anhydrous ethanol, and after ultrasonic treatment for 30min, centrifuge the sample at 4500r / min for 15min. Separate the ethanol phase and repeat the extraction until the absorbance of all mixed ethanol phases at a wavelength of 448nm remains stable. Use a UV-visible spectrophotometer for analysis and draw a standard curve to calculate the lutein mass concentration.

[0081]

[0082] 8. Lutein degradation rate test method: Store the sample in the dark at 37℃ for 96h to accelerate the degradation of lutein. Extract lutein with anhydrous ethanol and measure the absorbance at 445nm. Calculate the lutein content in the emulsion according to the lutein standard curve:

[0083]

[0084] Where: C t is the lutein content after storage time t, and C0 is the lutein content during preparation.

[0085] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0086] 9. Data processing

[0087] All data in this experiment were statistically analyzed using IBM SPSS Statistics 26 software, and the Duncan method was used to analyze the significance of differences between data. The significance level was p < 0.05. Each experiment was repeated three times, and the results were expressed as mean ± standard deviation. Data were plotted using Origin 2022 software.

[0088] 10. Results

[0089] Heating can cause structural perturbations or unfolding of proteins, leading to loss of function. The concepts of flexibility and rigidity are fundamental to understanding the relationship between function, structure, and stability. Therefore, identifying and understanding the effects of acid-heat treatment on flexible regions in the structure of rice bran proteins is necessary to achieve efficient protein engineering and rational design of thermostable proteins. Figure 2 It can be seen that the flexibility of rice bran protein increased significantly when heated at 90°C for 12 h at pH 2.0, and the flexibility of rice bran protein in other examples changed slightly, among which the flexibility of rice bran protein in Example 2 changed slightly when heat-treated at pH 7.0. Figure 3 , 4 The emulsifying activity, surface hydrophobicity and Th T fluorescence intensity of the rice bran protein treated in Example 1 in , 5 are significantly different from those in Examples 2 and 3, and the increase in emulsifying activity, the decrease in surface hydrophobicity and the increase in Th T fluorescence intensity all indicate that the performance of the rice bran protein obtained by this treatment method in preparing emulsions and emulsion gels is improved. Figure 6 The projection electron microscope image can explain why the rice bran protein with the highest flexibility obtained by heating for 12 hours in Example 1 has superior performance in stabilizing the emulsion gel, namely, the interlaced network structure makes a huge contribution.

[0090] The protection and delivery ability of rice bran protein emulsion gel on lutein can be evaluated by the lutein embedding rate and lutein degradation rate. Figure 7 , 8As shown, the protection and delivery of lutein by the emulsion gel prepared by heating rice bran protein in Examples 1, 2, and 3 were tested. Example 1 had the highest lutein embedding rate, especially the rice bran protein emulsion gel obtained by heat treatment for 12 hours. Example 2 had the lowest lutein embedding rate. As shown in the figure, the degradation rate of lutein protected by Example 1 was significantly lower than that of Examples 2 and 3. Combined with the above experiments, it can be concluded that heat treatment of rice bran protein under pH 2.0 conditions can improve the protection and delivery ability of the emulsion gel prepared therefrom for lutein. The realization of this ability can be attributed to the fact that acid heat treatment improves the flexibility of rice bran protein.

[0091] It should be understood that the present invention is not limited to what has been described above and that various modifications and changes may be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing a rice bran protein emulsion gel for embedding lutein, characterized in that: include: Step 1: dissolving rice bran protein in distilled water to obtain a protein solution, adjusting the pH of the protein solution to be acidic, fully stirring and hydrating, stirring the hydrated protein solution and then centrifuging to obtain a supernatant, determining the protein concentration in the supernatant, and diluting the supernatant with distilled water according to the target protein concentration; Step 2: heating the diluted rice bran protein solution, stirring continuously during the heating process; After the heating is completed, the rice bran protein solution is immediately cooled to obtain a high-flexibility rice bran protein solution A; Step 3: Add lutein to soybean oil and stir thoroughly to obtain solution B; Step 4: Mix solution A and solution B, and homogenize them in a high-speed homogenizer to obtain a rice bran protein emulsion gel encapsulating lutein.

2. The method for preparing the rice bran protein emulsion gel embedded with lutein according to claim 1, characterized in that: In step 1, the method for extracting rice bran protein comprises: Step 11: using an organic reagent to remove oil from fresh rice bran to obtain defatted rice bran; Step 12: extracting protein from the deesterified rice bran by alkali dissolution and acid precipitation to obtain a protein precipitate, and then freeze-drying the protein precipitate to obtain rice bran protein; The method of extracting protein from deesterified rice bran by alkali dissolution and acid precipitation comprises: The defatted rice bran was dissolved in distilled water to obtain a rice bran solution, and the pH of the rice bran solution was adjusted to 10.0 with a 2.0 mol / L NaOH solution. After stirring for 4 hours, the solution was centrifuged at 4000 r / min to obtain a supernatant. The pH of the supernatant was adjusted to 4.6 with a 2.0 mol / L HCl solution, and the solution was centrifuged at 4000 r / min to obtain a protein precipitate.

3. The method for preparing the rice bran protein emulsion gel embedded with lutein according to claim 1, characterized in that: In step 1, the pH of the protein solution is adjusted to 1.0-4.0 using HCl solution, wherein the concentration of the HCl solution is 0.05-2.0 mol / L.

4. The method for preparing the rice bran protein emulsion gel embedded with lutein according to claim 1, characterized in that: The target protein concentration in step 1 is 0.01-20 mg / ml.

5. The method for preparing the rice bran protein emulsion gel embedded with lutein according to claim 1, characterized in that: Step 1: Stir the hydrated solution for more than 12 hours, centrifuge at 10000 r / min for 10 minutes to obtain a supernatant, and dilute the supernatant with distilled water at pH 2.0 to obtain a rice bran protein solution with a target protein concentration.

6. The method for preparing the rice bran protein emulsion gel embedded with lutein according to claim 1, characterized in that: In step 2, the heating process of the rice bran protein solution is: using a water bath temperature of 75-95° C., a heating time of 0-24 hours, and after the heating is completed, placing the rice bran protein solution in an ice water bath for cooling.

7. The method for preparing the rice bran protein emulsion gel embedded with lutein according to claim 1, characterized in that: In step 3, the added mass percentage of lutein in soybean oil is 0.1-2.0%.

8. The method for preparing the rice bran protein emulsion gel embedded with lutein according to claim 1, characterized in that: In step 4, the mixing volume ratio of solution A to solution B is one of 7.5:2.5, 7:3, and 6.5:3.

5.

9. The method for preparing the rice bran protein emulsion gel embedded with lutein according to claim 1, characterized in that: The homogenization speed in step 4 is 6000-20000 r / min, and the homogenization time is 30-300 s.

10. A rice bran protein emulsion gel embedded with lutein prepared by the method according to any one of claims 1 to 9.

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