PH response type rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenol

Abstract

A preparation method of the sweet potato stem and leaf polyphenol-loaded pH-responsive rice bran albumin nanoparticles comprises the following steps: sequentially adding tannic acid, glycyrrhizic acid and sweet potato stem and leaf polyphenol into a rice bran albumin solution, carrying out hydration reaction, dialyzing, and freeze-drying to obtain the sweet potato stem and leaf polyphenol-loaded pH-responsive rice bran albumin nanoparticles. The pH response type rice bran albumin nanoparticles loaded with the sweet potato stem and leaf polyphenol are obtained. Vegetable protein is modified and loaded with the sweet potato stem and leaf polyphenol, so that the stability and functional characteristics of the sweet potato stem and leaf polyphenol are improved, and the disubstituted caffeoylquinic acid can be directionally released in intestinal tracts in the digestion process.

Description

Technical Field

[0001] The invention relates to the field of food technology, and in particular to pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols. Background Art

[0002] Sweet potato stems and leaves are the aboveground parts of sweet potatoes (Ipomoea batatas (L.) Lam). They have strong stress resistance, rich nutrition, strong palatability and high yield. However, a large number of sweet potato stems and leaves cannot be properly handled after harvest. In addition, due to the extremely high water content in sweet potato stems and leaves, they are difficult to preserve for a long time after harvest, which not only causes this valuable resource to be abandoned, but also pollutes the environment. Therefore, the development of deep processing technology for sweet potato stems and leaves deserves more in-depth and extensive research.

[0003] Sweet potato stems and leaves contain a large number of polyphenol compounds, mainly caffeoylquinic acid and its derivatives, which have multiple biological activities including antioxidant, anti-inflammatory, antibacterial, hypoglycemic and anti-cancer activities. Among them, di-substituted caffeoylquinic acid is more active, but it has inherent defects such as poor water solubility, easy decomposition and low bioavailability. The stability and bioaccessibility of sweet potato stem and leaf polyphenols are low, so sweet potato stems and leaves are difficult to utilize.

[0004] Rice bran, as one of the common by-products in rice processing, contains a large amount of protein, among which albumin has relatively good water solubility and biological activity. As a plant-based protein, rice bran albumin has similar nutritional value to egg yolk protein and similar emulsifying properties to whey protein, which makes it capable of becoming a carrier of bioactive ingredients.

[0005] Therefore, it is necessary to provide a method for improving the stability and bioaccessibility of sweet potato stem and leaf polyphenols by utilizing rice bran albumin, and to achieve the comprehensive utilization of rice bran albumin and sweet potato stem and leaf polyphenols. Summary of the invention

[0006] In view of this, the present application provides a pH-responsive rice bran albumin nanoparticle loaded with sweet potato stem and leaf polyphenols, which is used to solve the problem of how to improve the stability and bioaccessibility of sweet potato stem and leaf polyphenols.

[0007] In order to achieve the above technical objectives, this application adopts the following technical solutions: In the first aspect, the present application provides a method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols, comprising the following steps: adding tannic acid, glycyrrhizic acid and sweet potato stem and leaf polyphenols in sequence to a rice bran albumin solution, and performing a hydration reaction, and then dialyzing and freeze-drying to obtain pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols.

[0008] Preferably, the mass ratio of rice bran albumin, tannic acid, sweet potato stem and leaf polyphenols and glycyrrhizic acid is 10:2:2:(0.5-3).

[0009] Preferably, the preparation method of rice bran albumin comprises: adding water to defatted rice bran powder for extraction and centrifugation to obtain a supernatant; adding ammonium sulfate to the supernatant for sedimentation treatment, centrifuging to obtain a precipitate, then redissolving and freeze-drying to obtain rice bran albumin. Adding ammonium sulfate for sedimentation can improve the solubility of rice bran protein.

[0010] Preferably, the mass ratio of defatted rice bran powder to water is 1:(5-10), the extraction temperature is 55-60° C., the extraction time is 120-150 min; and the mass of ammonium sulfate is 30-40% of the mass of the defatted rice bran powder.

[0011] Preferably, the preparation method of sweet potato stem and leaf polyphenols comprises: adding ethanol aqueous solution to sweet potato stem and leaf powder, performing ultrasonic extraction, and then centrifuging to obtain a supernatant; concentrating and purifying the supernatant using an AB-8 column, and freeze-drying to obtain sweet potato stem and leaf polyphenols.

[0012] Preferably, the mass ratio of sweet potato stem and leaf powder to ethanol is 1:40-50, the volume concentration of ethanol aqueous solution is 70-75%; the temperature of ultrasonic extraction is 40-45°C, the time of ultrasonic extraction is 30-40min, and the frequency of ultrasonic extraction is 45-50kHz.

[0013] Preferably, the pH value of the rice bran albumin solution is 3-4.

[0014] In a second aspect, the present application provides a pH-responsive rice bran albumin nanoparticle loaded with sweet potato stem and leaf polyphenols.

[0015] In a third aspect, the present application provides an oil-in-water emulsion comprising pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols. The oil-in-water emulsion is a pH-responsive rice bran albumin emulsion loaded with sweet potato stem and leaf polyphenols.

[0016] Preferably, the composition comprises the following components in parts by mass: 18-20 parts of water, 70-80 parts of corn oil, and 2-5 parts of pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols.

[0017] The beneficial effects of the present application are as follows: the present application utilizes the cross-linking characteristics of tannic acid and the pH-responsive characteristics of glycyrrhizic acid to prepare modified rice bran albumin nanoparticles, and uses them to load sweet potato stem and leaf polyphenols, thereby obtaining pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols. The pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols effectively stabilize the sweet potato stem and leaf polyphenols in an acidic microenvironment due to the presence of glycyrrhizic acid in the rice bran albumin particles, and inhibit the degradation of phenolic acid during storage, thereby improving the stability of the sweet potato stem and leaf polyphenols. The pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols of the present application can be anchored on the interface layer to form a stable water-in-oil Pickering emulsion, and its dense structure inhibits the aggregation between the particles. At the same time, since the pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols of the present application have different surface adsorption behaviors on emulsion droplets at different pH values, the formed Pickering emulsion can exist stably in simulated gastric fluid but can be slowly hydrolyzed in simulated intestinal fluid. Therefore, the pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols of the present application give the sweet potato stem and leaf polyphenols the ability of targeted release in the intestine, thereby making them have good bioaccessibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The results show the effect of glycyrrhizic acid addition on the emulsion embedding efficiency; Figure 2 The results show the effect of glycyrrhizic acid addition on emulsification ability and emulsion stability; Figure 3 is the UV stability test result; Figure 4 for Na + Effect of ion stability on test results; Figure 5 Ca + Ion stability test results; Figure 6 is the thermal stability test result; Figure 7 This is the storage stability test result; Figure 8 The response ability test result of pH value; Fig. 9 This is the test result of polyphenol release during digestion. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] Source of raw materials Sweet potato stems and leaves: sweet potato stems and leaves of Ecaishu No. 10, provided by the Institute of Grain Crops, Hubei Academy of Agricultural Sciences.

[0021] Rice bran: Ezhong No. 5 rice bran, provided by the Institute of Grain Crops, Hubei Academy of Agricultural Sciences.

[0022] Tannic acid: provided by Shanghai Aladdin Biochemical Technology Co., Ltd.

[0023] Glycyrrhizic acid: provided by Shanghai Aladdin Biochemical Technology Co., Ltd.

[0024] The preparation method of rice bran albumin is as follows: take 200g defatted rice bran powder, add 2000mL distilled water, stir evenly and place in a constant temperature water bath, extract at 55°C for 2h, centrifuge to obtain the supernatant, add 35% ammonium sulfate by mass for precipitation, take the precipitate after centrifugation and redissolve it in distilled water, dialyze and freeze-dry to obtain rice bran albumin.

[0025] The preparation method of sweet potato stem and leaf polyphenols includes: taking 1g of sweet potato stem and leaf powder, adding 40mL of ethanol aqueous solution (70%, v / v), ultrasonically extracting (45kHz) for 30min in an environment of 45°C, repeating the process twice, combining the extracts and centrifuging, purifying the supernatant through an AB-8 column, and concentrating and freeze-drying to obtain sweet potato stem and leaf polyphenols.

[0026] If no specific experimental steps or conditions are specified in the examples or experimental examples of this application, the conventional experimental steps or conditions described in the literature in this field can be used. The raw materials or instruments used are all conventional products that can be obtained commercially, including but not limited to the raw materials or instruments used in the examples or experimental examples of this application.

[0027] The present solution is further described below through specific embodiments.

[0028] Example 1 A preparation method of pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols comprises the following steps: adjusting the pH value of a rice bran albumin solution to 3, adding tannic acid and stirring for 30 minutes, then adding glycyrrhizic acid and stirring for 30 minutes to obtain modified rice bran albumin nanoparticles, then adding sweet potato stem and leaf polyphenols and stirring for 30 minutes, and then dialyzing and freeze-drying to obtain pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols; wherein the mass ratio of rice bran albumin, tannic acid, glycyrrhizic acid and sweet potato stem and leaf polyphenols is 10:2:2:0.5.

[0029] Example 2 A method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols, wherein other contents are the same as those in Example 1, except that the mass ratio of rice bran albumin, tannic acid, glycyrrhizic acid and sweet potato stem and leaf polyphenols is 10:2:2:1.

[0030] Example 3 A method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols, wherein other contents are the same as those in Example 1, except that the mass ratio of rice bran albumin, tannic acid, glycyrrhizic acid and sweet potato stem and leaf polyphenols is 10:2:2:1.5.

[0031] Example 4 A method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols, wherein other contents are the same as those in Example 1, except that the mass ratio of rice bran albumin, tannic acid, glycyrrhizic acid and sweet potato stem and leaf polyphenols is 10:2:2:2.

[0032] Example 5 A method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols, wherein other contents are the same as those in Example 1, except that the mass ratio of rice bran albumin, tannic acid, glycyrrhizic acid and sweet potato stem and leaf polyphenols is 10:2:2:2.5.

[0033] Example 6 A method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols, wherein other contents are the same as those in Example 1, except that the mass ratio of rice bran albumin, tannic acid, glycyrrhizic acid and sweet potato stem and leaf polyphenols is 10:2:2:3.

[0034] Comparative Example 1 A method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols, wherein other contents are the same as those of Example 4, except that glycyrrhizic acid is not added, that is, the mass ratio of rice bran albumin, tannic acid, glycyrrhizic acid and sweet potato stem and leaf polyphenols is 10:2:0:2.

[0035] Test and Evaluation The pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols obtained in Examples 1-6 and Comparative Example 1 were fully mixed with distilled water and corn oil in a ratio of 2:18:70, homogenized at 13000 r / min, and the pH value of the product was adjusted to 4 to obtain an oil-in-water emulsion.

[0036] The effect of glycyrrhizic acid addition on the embedding efficiency, emulsification performance and emulsion stability index of the emulsion was tested. The experimental samples were the oil-in-water emulsions prepared in Examples 1-6 and Comparative Example 1.

[0037] The method for determining the emulsion embedding efficiency is as follows: 1 mL of the emulsion sample was diluted 10 times and then 5 mL of methanol was added to break the emulsion, followed by centrifugation at 14000 rpm for 10 min, and the total phenol content in the supernatant was determined.

[0038] The emulsifying performance of the emulsion was determined as follows: 100 μl of the emulsion was added to 20 mL of 0.1% sodium dodecyl sulfate (SDS) solution, and the absorbance of the solution at 500 nm was measured. 0 , the calculation formula is as follows:

[0039] Where φ is the volume fraction of oil and C is the protein concentration in the water phase (g / m3 ).

[0040] The stability of the emulsion was determined as follows: 100 μl of the emulsion was added to 20 mL of 0.1% SDS solution, and the absorbance of the solution at 500 nm was measured after mixing. 0 After the original emulsion was allowed to stand for 10 min, 100 μl of the emulsion was added to 20 mL of 0.1% SDS solution and its absorbance at 500 nm was measured again. 10 , the calculation formula is as follows:

[0041] The results are as follows Figure 1-2 shown.

[0042] like Figure 1 As shown in the figure, the encapsulation efficiency of the emulsion first increased and then decreased with the increase of the amount of glycyrrhizic acid added. When the addition ratio of rice bran albumin: tannic acid: sweet potato stem and leaf polyphenols: glycyrrhizic acid was 10:2:2:2, it had the strongest encapsulation ability for phenolic compounds.

[0043] like Figure 2 As shown in the figure, the emulsifying ability and stability of the emulsion first increase and then decrease with the increase of the amount of glycyrrhizic acid added. When the addition ratio of rice bran albumin: tannic acid: sweet potato stem and leaf polyphenols: glycyrrhizic acid is 10:2:2:2, it has relatively good emulsifying ability and stability.

[0044] By adding glycyrrhizic acid to rice bran albumin nanoparticles, the phenolic hydroxyl groups in tannic acid are able to interact with the disubstituted glucuronic acid of glycyrrhizic acid nanofibers, thereby spontaneously forming a denser tannic acid-glycyrrhizic acid cross-linked network. When the concentration of glycyrrhizic acid is low, the content of nanoparticles anchored on the emulsion will significantly decrease, and the cross-linked network will become loose, causing the oxidants in the environment to diffuse to the loading center of the nanoparticles, resulting in the degradation of phenolic compounds. This shows that an appropriate amount of glycyrrhizic acid has a positive effect on the embedding efficiency of the emulsion. Therefore, the amount of glycyrrhizic acid added in Example 1 is optimal.

[0045] Test the effect of emulsification on the UV stability and ionic stability of nanoparticles (Na + and Ca + ), thermal stability, storage stability, pH stability and simulated digestion bioaccessibility. The experimental samples were the pH-responsive rice bran white nanoparticles loaded with sweet potato stem and leaf polyphenols in Example 1 (referred to as original nanoparticles) and the corresponding water-in-oil emulsion ( Figure 3-9 (recorded in Chinese as 10:2:2:2).

[0046] The method for determining the UV stability of the emulsion is as follows: add 10 g of the experimental sample to a beaker containing 50 mL of normal saline, treat it with UV for 30 min in a light-proof environment, and measure the total phenol content in the normal saline at 0, 5, 10, 15, 20, 25 and 30 min of treatment.

[0047] Emulsion Na + The method for determining ionic stability is as follows: add 10 g of the experimental sample to a beaker containing 50 mL of distilled water, add NaCl to it to make the final concentration reach 0.1 M, incubate at 37°C for 30 min, and measure the total phenol content in the physiological saline at 0, 5, 10, 15, 20, 25 and 30 min of incubation.

[0048] Emulsion Ca + The ionic stability was determined as follows: 10 g of the experimental sample was added to a beaker containing 50 mL of distilled water, CaCl was added to it to make the final concentration reach 0.5 M, and the mixture was incubated at 37 °C for 30 min. The total phenol content in the saline was measured at 0, 5, 10, 15, 20, 25 and 30 min of incubation.

[0049] The method for determining the thermal stability of the emulsion is as follows: a beaker containing 50 mL of normal saline is heated to 37°C, 45°C, 50°C and 55°C, respectively, and then 10 g of the experimental sample is added and kept for 5 minutes. The beaker is then placed in an ice water bath and cooled for 10 minutes, and the total phenol content in the normal saline is measured.

[0050] The storage stability of the emulsion was determined as follows: 10 g of the test sample was placed in a beaker containing 50 mL of saline and stored at 4°C for 6 days. The sample was taken out at 0 days, 2 days, 4 days and 6 days of storage, and the total phenol content in the saline was measured.

[0051] The method for determining the pH stability of the emulsion is as follows: 10 g of the experimental sample was added to a beaker containing 50 mL of distilled water, and the pH value of the system was adjusted to 3, 5, and 7, respectively, using 0.1 M HCl and 1 M NaOH solutions. After incubation at 37°C for 30 min, the total phenol content in the solution was measured.

[0052] The in vitro digestion method of emulsion was as follows: 4 mL of the sample to be tested was diluted to 15 mL, 15 mL of α-amylase solution (0.03 g / mL) was added and the pH value was adjusted to 6.8, and the mixture was placed in a shaker at 37°C and 120 rpm to start the oral digestion stage. After incubation for 3 minutes, the supernatant was centrifuged and the total phenolic and free fatty acid contents were determined; NaCl (2 g / L) was dissolved in deionized water and the pH value was adjusted to 2.0 to prepare simulated gastric fluid, and then protease was added to it to make the final concentration reach 3.2 mg / mL, 15 mL of oral digestion fluid was mixed with 15 mL of simulated gastric fluid and its pH value was kept at 2.0, and the mixture was placed at 37°C and 120 The gastric digestion stage was started by shaking at rpm. After incubation for 120 min, the supernatant was centrifuged and the total phenolic and free fatty acid contents were determined. The pH value of the gastric digestion fluid was adjusted to 7 and mixed with 3.5 mL of bile salt solution (53.6 mg / mL) and 1.5 mL of electrolyte solution (NaCl concentration was 210.1 mg / mL and CaCl 2 The intestinal digestion reaction was started by adding 2.5 mL of lipase solution (60 mg / mL) and incubating at 37 °C for 120 min. The supernatant was then centrifuged to determine its total phenol content.

[0053] Method for determining total phenol content: After the extracted polyphenol solution is concentrated and freeze-dried, a certain amount of sample is weighed and added to distilled water, vortexed to mix, centrifuged at 8000rpm and 4℃ for 10min, 0.5mL of supernatant is added to 4mL of 10% folin phenol solution and 3mL of 7.5% sodium carbonate solution, incubated at 50℃ for 10min, and then the absorbance is measured at 525nm.

[0054] The results are as follows Figure 3-9 shown.

[0055] like Figure 3 As shown in the figure, with the extension of UV irradiation time, the contents of phenolic compounds in the emulsion and nanoparticles decreased to varying degrees. The polyphenol retention rate of the emulsion at 30 minutes was 70.33%, which was better than the protective effect of the nanoparticles. It can be seen that the emulsion significantly improved the UV stability of sweet potato stem and leaf polyphenols.

[0056] like Figure 4 and 5 As shown in Figure 2, with the extension of treatment time, metal ions caused the emulsion to break and the nanoparticles to decompose to varying degrees, among which Na + and Ca + After 30 minutes, the polyphenol content in the emulsion decreased by 28% and 29%, respectively, but was still significantly higher than the loss of polyphenol content in the nanoparticles. Therefore, the emulsion significantly improved the ionic stability of sweet potato stem and leaf polyphenols.

[0057] like Figure 6 As shown, the increase in ambient temperature caused the content of phenolic compounds in the emulsion and nanoparticles to decrease. Compared with 37°C, the polyphenol retention capacity of the nanoparticles incubated at 55°C decreased by 28.19%, but the polyphenol retention capacity of the emulsion only decreased by 10.94%. In addition, the stability of the nanoparticles at 37°C was much lower than that of the emulsion. Therefore, the emulsion significantly improved the thermal stability of sweet potato stem and leaf polyphenols.

[0058] like Figure 7 As shown in the figure, with the extension of storage time, the polyphenol retention capacity of the emulsion and nanoparticles decreased. The emulsion still loaded more than 90% of phenolic compounds after storage for 6 days, while this value was only 45.24% in the nanoparticles. It can be seen that the emulsion significantly improved the storage stability of sweet potato stem and leaf polyphenols.

[0059] like Figure 8 As shown in the figure, with the change of environmental pH value, the polyphenol retention capacity of the emulsion and nanoparticles showed different trends, in which the emulsion tended to demulsify in a neutral pH environment to release the phenolic acid it loaded, while the nanoparticles had a stronger resistance to the acidic environment. It can be seen that the emulsion achieved a response to the change of pH value.

[0060] like Fig. 9 As shown in the figure, due to the acidic environment and the destructive effect of pepsin on proteins, nanoparticles tend to release their loaded phenolic compounds during the gastric digestion stage. However, the network structure formed by glycyrrhizic acid and tannic acid evenly covers the emulsion interface layer, blocking the contact between the internal rice bran albumin and pepsin, thereby maintaining the original form of the emulsion in the simulated gastric fluid. It can be seen that emulsions are more suitable for achieving the goal of intestinal directional release than nanoparticles.

[0061] Compared with the existing technology, the encapsulation of polyphenols with animal-derived proteins (β-lactoglobulin, whey protein isolate and ovalbumin) is highly allergenic and has the risk of spreading diseases. The present application modifies plant proteins and loads sweet potato stem and leaf polyphenols, thereby improving the stability and functional properties of sweet potato stem and leaf polyphenols, and can achieve the directional release of disubstituted caffeoylquinic acid in the intestine during digestion, which has important practical significance for promoting the application of sweet potato stem and leaf polyphenols in the food field and the development of its deep processing system.

[0062] The above are only preferred specific implementations of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols, characterized in that: The following steps are involved: Tannic acid, glycyrrhizic acid and sweet potato stem and leaf polyphenols are added to a rice bran albumin solution in sequence, and a hydration reaction is carried out. After dialysis and freeze-drying, the pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols are obtained.

2. The method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols according to claim 1, characterized in that: The mass ratio of the rice bran albumin, tannic acid, sweet potato stem and leaf polyphenols and glycyrrhizic acid is 10:2:2:(0.5-3).

3. The method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols according to claim 1, characterized in that: The preparation method of the rice bran albumin comprises: Add water to the defatted rice bran powder for extraction and centrifugation to obtain a supernatant; Ammonium sulfate is added to the supernatant to perform sedimentation treatment, and then the precipitate is taken out by centrifugation, and then redissolved and freeze-dried to obtain the rice bran albumin.

4. The method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols according to claim 3, characterized in that: The mass ratio of the defatted rice bran powder to water is 1:(5-10), the extraction temperature is 55-60° C., and the extraction time is 120-150 min; the mass of the ammonium sulfate is 30-40% of the mass of the defatted rice bran powder.

5. The method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols according to claim 1, characterized in that: The preparation method of sweet potato stem and leaf polyphenols comprises: Adding ethanol aqueous solution to the sweet potato stem and leaf powder, performing ultrasonic extraction, and then centrifuging to obtain a supernatant; The supernatant is concentrated and purified using an AB-8 column and freeze-dried to obtain the sweet potato stem and leaf polyphenols.

6. The method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols according to claim 5, characterized in that: The mass ratio of the sweet potato stem and leaf powder to ethanol is 1:40-50, and the volume concentration of the ethanol aqueous solution is 70-75%; the temperature of the ultrasonic extraction is 40-45°C, the time of the ultrasonic extraction is 30-40min, and the frequency of the ultrasonic extraction is 45-50kHz.

7. The method for preparing pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols according to claim 1, characterized in that: The pH value of the rice bran albumin solution is 3-4.

8. pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols obtained by the preparation method according to any one of claims 1 to 7.

9. An oil-in-water emulsion comprising the pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols as claimed in claim 8.

10. The oil-in-water emulsion according to claim 9, characterized in that The method comprises the following components in parts by weight: 18-20 parts of water, 70-80 parts of corn oil, and 2-5 parts of the pH-responsive rice bran albumin nanoparticles loaded with sweet potato stem and leaf polyphenols.

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