Oil-soluble purple sweet potato pigment emulsion and preparation method thereof

Abstract

The application discloses an oil-soluble purple sweet potato pigment emulsion and a preparation method thereof, and belongs to the technical field of natural pigment preparation. The emulsion is prepared from 20-40 parts of deionized water, 10-30 parts of purple sweet potato pigment powder, 30-50 parts of corn oil, 15-45 parts of single and double glycerol fatty acid ester and 10-20 parts of active components by weight percentage. The active components are mainly modified rapeseed proteins treated by freeze-thaw assisted ultrasonic treatment. The emulsifying property and antioxidant capacity of the modified rapeseed proteins are improved, so that the stability of the emulsion is promoted, and the oxidation and damage of the pigment are prevented. The application provides a new idea for the development and utilization of high-quality plant protein rapeseed protein. The preparation method is simple in operation and low in cost. The stability of the purple sweet potato pigment is improved, the special smell of the purple sweet potato pigment is avoided, the oil solubility of the purple sweet potato pigment is improved, and the application range of the purple sweet potato pigment is widened.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of natural pigment preparation, and particularly relates to an oil-soluble purple sweet potato pigment emulsion and a preparation method thereof. BACKGROUND

[0002] Natural pigments have the advantages of high safety, harmonious and bright color compared with synthetic pigments, and some specific natural pigments also have physiological active ingredients to provide nutrition and health care functions, so the research on the field of natural pigments has become a hot spot. However, natural pigments have the defects of poor stability and poor preservation, and light, temperature and oxygen are easy to cause the loss and fading of natural pigments, which restricts the application of natural pigments.

[0003] Purple sweet potato pigment belongs to anthocyanin pigment, and is obtained by drying and crushing purple sweet potato tubers, then extracting with water or weak acid water, concentrating and drying. The product is not soluble in water but soluble in oil, is relatively good in light resistance and heat resistance, and has a slight special odor. Due to good heat resistance, the product can withstand the pasteurization temperature in the food industry, and is commonly used in ice cream, dairy products, beverages, jelly, candy and other foods, and can also be used as a functional ingredient of health food.

[0004] Purple sweet potato pigment has been applied in the market to a certain extent, but the problems of poor oil solubility, special odor and instability of natural pigments still exist, and it is necessary to further improve the quality of purple sweet potato pigment to broaden its application range. SUMMARY

[0005] The present application provides an oil-soluble purple sweet potato pigment emulsion and a preparation method thereof, which improves the stability and quality of the purple sweet potato pigment, improves the oil solubility of the purple sweet potato pigment, and expands the application range of the purple sweet potato pigment.

[0006] TECHNICAL SOLUTION

[0007] The oil-soluble purple sweet potato pigment emulsion is prepared by embedding 20-40 parts of deionized water, 10-30 parts of purple sweet potato pigment powder, 30-50 parts of oil phase components, 15-45 parts of emulsifying components and 10-20 parts of active components; the modified rapeseed protein is used as a solid particle and a mono-diglyceride fatty acid ester to wrap the water phase containing the purple sweet potato pigment in the hydrophilic end of the structure, and the lipophilic end is on the outside to separate the oil phase, that is, the purple sweet potato pigment is dispersed and dissolved in the oil in macroscopic view.

[0008] Of the components described above, the purple sweet potato pigment powder is a commercially available E100 common purple sweet potato pigment; the oil phase component is corn oil; the emulsifying component is mono- and diglyceride fatty acid esters; and the active component is one or a mixture of two of rapeseed protein and trehalose extracted from rapeseed meal.

[0009] The preparation method of the purple sweet potato pigment emulsion described above includes the following steps:

[0010] S1. Preparation of purple sweet potato pigment solution: Prepare purple sweet potato pigment and active components by placing them in deionized water on a magnetic stirrer and dissolving them thoroughly. Set the conditions as follows: heating temperature 50℃, speed 600rpm. After thorough dissolution, add the active components and continue dissolving. Keep warm at 50℃ for later use.

[0011] S2. Preparation of the oil phase system: Add the emulsified components to the oil phase system, heat and mix evenly, and keep warm at 50°C for later use;

[0012] S3. Emulsification: While keeping the solution obtained in S1 at a low speed (400 rpm), slowly add the oil phase in the same direction. After the addition is complete, keep it in a 50°C water bath for 20 min, and then use a high-shear emulsifier at 12000 r / min for 10 min to obtain purple sweet potato pigment emulsion.

[0013] The preparation method of the above-mentioned active component, rapeseed protein, includes the following steps:

[0014] (1) Extraction and preparation of rapeseed protein: Rapeseed protein was extracted from rapeseed meal using the alkali dissolution and acid precipitation method. The rapeseed meal was placed in a Soxhlet extraction device, petroleum ether was added, and the meal was defatted by Soxhlet extraction. The defatted meal was air-dried, pulverized, and passed through an 80-mesh sieve. The meal was dissolved in distilled water at a ratio of 1:10 (w:v). The pH of the system was adjusted to 11 with 1M NaOH. The mixture was stirred at room temperature for 2 hours, centrifuged at 10,000 r / min for 25 minutes, and the supernatant was taken and the pH was adjusted to the isoelectric point of 4.5 with 1M. The mixture was allowed to stand at room temperature for 2 hours. After centrifugation, the precipitate was taken and washed three times with alcohol. The precipitate was adjusted to pH 7.0 with a small amount of distilled water, dialyzed, and then freeze-dried to obtain rapeseed protein.

[0015] (2) Modification of rapeseed protein: Rapeseed protein was treated using a physical method of ultrasonic-assisted freeze-thaw cycle. Different ultrasonic powers of 100W, 200W, and 300W were selected for ultrasonic time of 5min, 10min, and 15min, respectively, and the solubility was measured and calculated. Each time, 20mL of rapeseed protein solution with a concentration of 1mg / mL was placed in a 50mL beaker for ultrasonic treatment. The distance between the ultrasonic probe and the liquid surface was 1.5cm, and the interval between freeze-thaw cycles was 12h. The ultrasonically treated rapeseed protein was repeatedly placed in liquid nitrogen and at room temperature for 2, 3, and 4 freeze-thaw cycles.

[0016] Beneficial effects: This invention provides an oil-soluble purple sweet potato pigment emulsion and its preparation method, which has the following advantages compared with the prior art:

[0017] 1. The oil-soluble purple sweet potato pigment prepared by this invention contains rapeseed protein, which has good antioxidant properties and excellent emulsifying properties, thus improving the stability of the purple sweet potato pigment emulsion; at the same time, the addition of trehalose can remove the taste to a certain extent.

[0018] 2. The added active component is mainly modified rapeseed protein treated with freeze-thaw assisted ultrasound. After modification, its emulsifying and antioxidant properties are enhanced, promoting emulsion stability and preventing pigment oxidation and degradation, providing a new approach for the development and utilization of high-quality plant protein, rapeseed protein. This preparation method is simple to operate and low in cost. While improving the stability of purple sweet potato pigment and avoiding its distinctive odor, it also improves the oil solubility of purple sweet potato pigment, expanding its application range.

[0019] 3. This invention incorporates modified rapeseed protein and mono- and diglycerides of fatty acids. The former, after being subjected to freeze-thaw assisted ultrasound, has its structural integrity disrupted, exposing internal hydrophobic groups that increase the speed and quantity of their approach to the oil phase interface. This leads to the aggregation of these groups at the oil-water interface, forming a liquid film that makes the oil-water interface more stable. The latter, as a co-emulsifier, further increases the surface tension between the aqueous and oil phases. Both improve the solubility of purple sweet potato pigment in oil-based foods, enabling it to be uniformly dispersed in the oil phase and expanding its application range.

[0020] 4. The active substance rapeseed protein contained in this invention has a rich and reasonable amino acid composition, which improves the nutritional quality of purple sweet potato pigment. At the same time, the rapeseed protein selected in this invention has improved solubility due to the ultrasonic-assisted freeze-thaw treatment during the preparation process, which provides a feasible approach for the rational and efficient utilization of high-quality plant protein resources. Attached Figure Description

[0021] Appendix Figure 1 This is a schematic diagram showing the comparison results of DPPH· free radical scavenging rate in an embodiment of the present invention. Detailed Implementation

[0022] The invention will now be further described with reference to the accompanying drawings.

[0023] Example 1

[0024] An oil-soluble purple sweet potato pigment was prepared by embedding 20 parts by weight of deionized water, 10 parts by weight of purple sweet potato pigment solution, 30 parts by weight of corn oil, 15 parts by weight of mono- and diglyceride fatty acid esters, and 10 parts by weight of modified rapeseed protein. The specific steps are as follows:

[0025] 1. Preparation of purple sweet potato pigment solution: Prepare 10g of purple sweet potato pigment and active components and place them in 20g of deionized water on a magnetic stirrer to dissolve them completely. Set the conditions as follows: heating temperature 50℃, speed 600rpm. After complete dissolution, add the active components and continue dissolving. Keep warm at 50℃ for later use.

[0026] 2. Preparation of the oil phase system: Add the emulsifying component to the oil phase system, heat and mix evenly, and keep warm at 50℃ for later use;

[0027] 3. Emulsification: The purple sweet potato pigment solution was slowly added in the same direction while maintaining a low rotation speed (400 rpm). After the addition was completed, the solution was kept in a 50°C water bath for 20 min. Subsequently, the emulsion was obtained by passing the solution through a high-shear emulsifier at 12000 r / min for 10 min.

[0028] Example 2

[0029] An oil-soluble purple sweet potato pigment was prepared by embedding 30 parts by weight of deionized water, 20 parts by weight of purple sweet potato pigment solution, 40 parts by weight of corn oil, 30 parts by weight of mono- and diglyceride fatty acid esters, and 15 parts by weight of modified rapeseed protein. The specific steps are as follows:

[0030] 1. Preparation of purple sweet potato pigment solution: Prepare 20g of purple sweet potato pigment and active components and place them in 30g of deionized water on a magnetic stirrer to dissolve them completely. Set the conditions as follows: heating temperature 50℃, speed 600rpm. After complete dissolution, add the active components and continue dissolving. Keep warm at 50℃ for later use.

[0031] 2. Preparation of the oil phase system: Add the emulsifying component to the oil phase system, heat and mix evenly, and keep warm at 50℃ for later use;

[0032] 3. Emulsification: The purple sweet potato pigment solution was slowly added in the same direction while maintaining a low rotation speed (400 rpm). After the addition was completed, the solution was kept in a 50°C water bath for 20 min. Subsequently, the emulsion was obtained by passing the solution through a high-shear emulsifier at 12000 r / min for 10 min.

[0033] Example 3

[0034] An oil-soluble purple sweet potato pigment was prepared by embedding 40 parts by weight of deionized water, 30 parts by weight of purple sweet potato pigment powder, 50 parts by weight of corn oil, 45 parts by weight of mono- and diglyceride fatty acid esters, and 20 parts by weight of modified rapeseed protein. The specific steps are as follows:

[0035] 1. Preparation of purple sweet potato pigment solution: Prepare 30g of purple sweet potato pigment and active components and place them in 40g of deionized water on a magnetic stirrer to dissolve them completely. Set the conditions as follows: heating temperature 50℃, speed 600rpm. After complete dissolution, add the active components and continue dissolving. Keep warm at 50℃ for later use.

[0036] 2. Preparation of the oil phase system: Add the emulsifying component to the oil phase system, heat and mix evenly, and keep warm at 50℃ for later use;

[0037] 3. Emulsification: The purple sweet potato pigment solution was slowly added in the same direction while maintaining a low rotation speed (400 rpm). After the addition was completed, the solution was kept in a 50°C water bath for 20 min. Subsequently, the emulsion was obtained by passing the solution through a high-shear emulsifier at 12000 r / min for 10 min.

[0038] Example 4

[0039] A method for preparing an oil-soluble purple sweet potato pigment, characterized in that, by weight, it is prepared from 30 parts deionized water, 20 parts purple sweet potato pigment solution, 40 parts corn oil, 30 parts mono- and diglyceride fatty acid esters, 15 parts modified rapeseed protein, and 5 parts trehalose encapsulation; the specific steps are as follows:

[0040] 1. Preparation of purple sweet potato pigment solution: Prepare 20g of purple sweet potato pigment and active components and place them in 30g of deionized water on a magnetic stirrer to dissolve them completely. Set the conditions as follows: heating temperature 50℃, speed 600rpm. After complete dissolution, add the active components and continue dissolving. Keep warm at 50℃ for later use.

[0041] 2. Preparation of the oil phase system: Add the emulsifying component to the oil phase system, heat and mix evenly, and keep warm at 50℃ for later use;

[0042] 3. Emulsification: The purple sweet potato pigment solution was slowly added in the same direction while maintaining a low rotation speed (400 rpm). After the addition was completed, the solution was kept in a 50°C water bath for 20 min. Subsequently, the emulsion was obtained by passing the solution through a high-shear emulsifier at 12000 r / min for 10 min.

[0043] Comparative Example 1

[0044] An oil-soluble purple sweet potato pigment was prepared by embedding 30 parts by weight of deionized water, 20 parts by weight of purple sweet potato pigment solution, 40 parts by weight of corn oil, 30 parts by weight of mono- and diglyceride fatty acid esters, and 5 parts by weight of trehalose. The specific steps are as follows:

[0045] 1. Preparation of purple sweet potato pigment solution: Prepare 20g of purple sweet potato pigment and active components and place them in 30g of deionized water on a magnetic stirrer to dissolve them completely. Set the conditions as follows: heating temperature 50℃, speed 600rpm. After complete dissolution, add the active components and continue dissolving. Keep warm at 50℃ for later use.

[0046] 2. Preparation of the oil phase system: Add the emulsified components to the oil phase system, heat and mix evenly, and keep warm at 50°C for later use.

[0047] 3. Emulsification: The purple sweet potato pigment solution was slowly added in the same direction while maintaining a low rotation speed (400 rpm). After the addition was completed, the solution was kept in a 50°C water bath for 20 min. Subsequently, the emulsion was obtained by passing the solution through a high-shear emulsifier at 12000 r / min for 10 min.

[0048] Comparative Example 2

[0049] A method for preparing an oil-soluble purple sweet potato pigment, characterized in that, by weight, it is prepared from 30 parts deionized water, 20 parts purple sweet potato pigment solution, 40 parts corn oil, 30 parts mono- and diglyceride fatty acid esters, 15 parts rapeseed protein, and 5 parts trehalose encapsulation. The specific steps are as follows:

[0050] 1. Preparation of purple sweet potato pigment solution: Prepare 20g of purple sweet potato pigment and active components and place them in 30g of deionized water on a magnetic stirrer to dissolve them completely. Set the conditions as follows: heating temperature 50℃, speed 600rpm. After complete dissolution, add the active components and continue dissolving. Keep warm at 50℃ for later use.

[0051] 2. Preparation of the oil phase system: Add the emulsifying component to the oil phase system, heat and mix evenly, and keep warm at 50℃ for later use;

[0052] 3. Emulsification: The purple sweet potato pigment solution was slowly added in the same direction while maintaining a low rotation speed (400 rpm). After the addition was completed, the solution was kept in a 50°C water bath for 20 min. Subsequently, the emulsion was obtained by passing the solution through a high-shear emulsifier at 12000 r / min for 10 min.

[0053] Comparative Example 3

[0054] A method for preparing an oil-soluble purple sweet potato pigment, characterized in that it is prepared by encapsulation of 30 parts by weight of deionized water, 20 parts by weight of purple sweet potato pigment solution, 40 parts by weight of corn oil, and 30 parts by weight of mono- and diglyceride fatty acid esters. The specific steps are as follows:

[0055] 1. Preparation of purple sweet potato pigment solution: Dissolve 20g of purple sweet potato pigment and active ingredients in 30g of deionized water on a magnetic stirrer. Set the conditions as follows: heating temperature 50℃, stirring speed 600rpm. After complete dissolution, add the active ingredients and continue dissolving. Keep warm at 50℃ for later use.

[0056] 2. Preparation of the oil phase system: Add the emulsified components to the oil phase system, heat and mix evenly, and keep warm at 50°C for later use.

[0057] 3. Emulsification: The purple sweet potato pigment solution was slowly added in the same direction while maintaining a low rotation speed (400 rpm). After the addition was completed, the solution was kept in a 50°C water bath for 20 min. Subsequently, the emulsion was obtained by passing the solution through a high-shear emulsifier at 12000 r / min for 10 min.

[0058] Performance evaluation

[0059] 1. Identification of emulsion stability

[0060] The prepared emulsions (including the examples and comparative examples) were placed in centrifuge tubes and centrifuged at 3000 r / min for 20 min. The layering phenomenon was observed in each centrifuge tube. At the same time, storage experiments were carried out. The emulsions were placed in the dark under room temperature and low temperature (0-4℃) conditions. The viscosity change rate was used to characterize the emulsion. The greater the emulsion stability, the smaller the viscosity change. The results are shown in Table 1.

[0061] Table 1. Stability test results of the emulsions prepared in the examples and comparative examples.

[0062]

[0063] The comparison between the results of Example 1 and Comparative Example 1 shows that the presence of modified rapeseed protein treated with freeze-thaw assisted ultrasound has a positive effect on emulsion stability. The results of Example 4 and Comparative Example 2 indicate that unmodified rapeseed protein contributes to emulsion stability, but the effect is not as good as that achieved by modified rapeseed protein. This is because the structural integrity of rapeseed protein is disrupted after freeze-thaw assisted ultrasound treatment, exposing internal hydrophobic groups. This leads to an increase in the speed and quantity of the protein approaching the oil phase interface, resulting in the formation of a liquid film at the oil-water interface, making the interface more stable and improving emulsification. In summary, the purple sweet potato pigment emulsion prepared by this invention exhibits excellent stability and can significantly improve the solubility of purple sweet potato pigment in oil-based foods.

[0064] 2. Photothermal stability experiment of oil-soluble purple sweet potato pigment

[0065] (1) Light stability experiment

[0066] The prepared emulsions (including those in the examples and comparative examples) and the original pigments were placed in a constant temperature and humidity chamber equipped with mercury lamps for 8 days of light treatment. The absorbance values ​​before and after treatment were measured at the maximum absorption wavelength of 420 nm to determine the pigment retention rate. The experimental results are shown in Table 2.

[0067] Table 2. Results of photostability tests on the emulsions prepared in the examples and comparative examples.

[0068] Category Pigment retention Example One 70.5％ Example Two 74.9％ Example Three 77.4％ Example Four 79.2％ Comparative Example One 68.9％ Comparative Example Two 69.5％ Comparative Example Three 67.9％ Original pigment 63.2％

[0069] The results above show that the pigment retention rate after oil-soluble treatment is higher than that of the untreated original pigment. This may be related to the formation of the emulsion system. The lightfastness of the prepared oil-soluble purple sweet potato pigment is improved, the quality is improved, and it is easier to store.

[0070] (2) Thermal stability test

[0071] The prepared emulsions (including those in the examples and comparative examples) and the original pigments were heated at 20℃, 40℃, and 60℃ for 2 hours, respectively, and the absorbance values ​​before and after heating were measured to determine the pigment retention rate. The experimental results are shown in Table 3.

[0072] Table 3. Thermal stability test results of the emulsions prepared in the examples and comparative examples.

[0073]

[0074] The results above show that purple sweet potato pigment is quite sensitive to temperature; the pigment retention rate gradually decreases with increasing temperature. Furthermore, compared to the original pigment, the pigment retention rate of oil-treated purple sweet potato pigment decreased less significantly. These results indicate that, under the same light-shielding conditions, the heat resistance of the purple sweet potato pigment emulsion prepared by oil-treated purple sweet potato pigment emulsion is improved to some extent compared to the original pigment.

[0075] 3. Antioxidant activity of oil-soluble purple sweet potato emulsion

[0076] The strength of DPPH· free radical scavenging ability, ·OH free radical scavenging ability, and superoxide free radical scavenging ability is often used as an evaluation index of the antioxidant capacity of a substance. This invention verifies the antioxidant activity of oil-soluble purple sweet potato pigment through the DPPH free radical scavenging effect.

[0077] A certain amount of the emulsions from Example 4, Comparative Example 1, and Comparative Example 2 was added to a 10 mL brown test tube. Then, 2 mL of 0.2 mM DPPH was added to the test tube, and the mixture was shaken for 2 minutes to achieve homogeneity. The mixture was then kept at room temperature in the dark for 30 minutes. The absorbance was then measured at 595 nm. The DPPH free radical scavenging rate was determined according to the following formula:

[0078]

[0079] like Figure 1 As shown, the comparison between Comparative Example 1 and the Example shows that the purple sweet potato pigment itself has a certain degree of antioxidant activity, and the added modified rapeseed protein also has a certain degree of antioxidant activity. The synergistic effect of the two improves the antioxidant activity of the purple sweet potato pigment emulsion. At the same time, the results of Example 4 and Comparative Example 2 show that the antioxidant capacity of rapeseed protein after freeze-thaw assisted ultrasonic modification is improved. Because the internal structure of the protein breaks down after modification, the ability of amino acid residues to donate hydrogen protons is enhanced, which reduces free radicals and achieves the effect of reducing or inhibiting free radicals.

[0080] 4. Odor Comparison Experiment of Oil-soluble Purple Sweet Potato Emulsion

[0081] The odor of Examples 2, 4, and Comparative Example 2 was compared with that of the original purple sweet potato pigment. The specific method was as follows: 30g of the pigment was placed in an open glass dish, and the odor was smelled at the mouth of the dish, 10cm, 20cm, and 30cm. No odor was indicated by "-", and an odor by "+". "+" indicates an odor can be smelled at the mouth of the dish, "++" indicates an odor can be smelled at 10cm from the mouth, "++" indicates an odor can be smelled at 20cm from the mouth, and "+++" indicates an odor can be smelled at 30cm from the mouth. The results are shown in Table 4.

[0082] Table 4. Comparison of the odor of purple sweet potato pigments

[0083] Category Odour Example Two + Example Four — Comparative Example Two — Original pigment ++

[0084] Compared to Example 2, Example 4 contained no other ingredients besides trehalose, indicating that trehalose acted as a masking agent and was effective in masking the distinctive off-odors from plant pigment extraction. The results of Example 4 and Comparative Example 2 showed that rapeseed protein had no effect on odor removal. The difference in odor between Example 2 and the original pigment indicated that the oil-soluble purple sweet potato pigment emulsion had reduced off-odors. In summary, the addition of trehalose and other substances during the preparation of the oil-soluble purple sweet potato pigment emulsion is significant for reducing off-odors and improving pigment quality.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an oil-soluble purple sweet potato pigment emulsion, characterized in that, Includes the following steps: S1. Preparation of modified rapeseed protein with active components: Rapeseed meal was defatted using Soxhlet extraction, air-dried, pulverized, and passed through an 80-mesh sieve. The meal was dissolved in distilled water at a w:v ratio of 1:

10. The pH of the system was adjusted to 11 with 1M NaOH, stirred at room temperature for 2 h, centrifuged at 10000 r / min for 25 min, and the supernatant was adjusted to the isoelectric point of 4.5 with 1M HCl and allowed to stand at room temperature for 2 h. After centrifugation under the same conditions, the precipitate was washed three times with alcohol, and the pH of the precipitate was adjusted to 7.0 with a small amount of distilled water. After dialysis, the precipitate was freeze-dried to obtain rapeseed protein. The rapeseed protein was treated by ultrasonic-assisted freeze-thaw cycles using a physical method. The protein was sonicated at 300 W for 15 min with the ultrasonic probe 1.5 cm above the liquid surface. The ultrasonically treated rapeseed protein was repeatedly subjected to liquid nitrogen and room temperature treatment for 4 freeze-thaw cycles with an interval of 12 h to obtain modified rapeseed protein. S2. Preparation of purple sweet potato pigment solution: Prepare purple sweet potato pigment and active components by dissolving them completely in deionized water. After the purple sweet potato pigment is fully dissolved, add the active components and continue to dissolve. Keep warm at 50℃ for later use. S3. Preparation of the oil phase system: Add the emulsified component to the oil phase component, heat and mix evenly, and keep warm at 50°C for later use; S4. Emulsification: The solution obtained in S2 is kept at 400 rpm, and the oil phase is slowly added in the same direction. After the addition is completed, the solution is kept in a 50℃ water bath for 20 min. Then, the purple sweet potato pigment emulsion is obtained by passing it through a high shear emulsifier at 12000 r / min for 10 min. The purple sweet potato pigment emulsion is prepared by encapsulating 20-40 parts of deionized water, 10-30 parts of purple sweet potato pigment powder, 30-50 parts of oil phase component, 15-45 parts of emulsifying component, and 10-20 parts of active component by weight. The active component is modified rapeseed protein, and the emulsifying component is mono- and diglyceride fatty acid esters. The modified rapeseed protein, as a solid particle, and the mono- and diglyceride fatty acid esters encapsulate the aqueous phase containing purple sweet potato pigment within the hydrophilic end of their structure, while the lipophilic end separates the oil phase on the outside.

2. The method for preparing the oil-soluble purple sweet potato pigment emulsion according to claim 1, characterized in that, The dissolution process in S1 is set to a heating temperature of 50°C and a rotation speed of 600 rpm.

3. The method for preparing the oil-soluble purple sweet potato pigment emulsion according to claim 1, characterized in that, The oil phase component is corn oil.

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