Purple sweet potato leaf water extract with uric acid reducing effect and preparation method of purple sweet potato leaf water extract

Abstract

The invention relates to a preparation method of a purple sweet potato leaf water extract with a uric acid reducing effect, and belongs to the field of food processing. Comprising the following steps: carrying out superfine grinding on dried purple sweet potato leaves; the purple sweet potato leaf superfine powder is added into 4 g / L of 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid according to the solid-liquid ratio of 1: 10 (g: mL), meanwhile, high-voltage pulse treatment is conducted, the pulse frequency is 1000-1200 Hz, the pulse width is 30-40 microseconds, the flow velocity is 200-500 L / h, the electric field intensity is 30-50 kV / cm, the pulse treatment time is 70-350 microseconds, and extraction is conducted for 20 min at the temperature of 25 DEG C. Filtering an extracting solution, recovering liquid, and performing vacuum reduced-pressure concentration. The concentrated solution is poured into an extraction kettle of supercritical CO2 extraction equipment, the extraction temperature is 60 DEG C, the extraction time is 1 h, the extraction pressure is 40 Mpa, cyclic extraction is conducted three times, liquid is collected, and the purple sweet potato leaf water extract is obtained. According to the method, active substances such as chlorogenic acid in the raw materials are promoted to be dissolved out, green and pollution-free efficient operation is achieved in the whole process, and a new technical approach is provided for efficient and accurate utilization of purple sweet potato leaves for inhibiting uric acid.

Description

Technical Field

[0001] The invention relates to a purple sweet potato leaf water extract having a uric acid-reducing effect and a preparation method thereof, and belongs to the technical field of deep processing of agricultural products. Background Art

[0002] Purple sweet potato is an annual herb of the genus Ipomoea, Convolvulaceae. Purple sweet potato leaves are the tender leaves and stems of purple sweet potato, a type of sweet potato leaves, which have traditional records of being eaten as vegetables in many countries and regions. For example, in Hubei Province of my country, people usually call the tender leaves of sweet potato plants "tiao jian" and cook them as vegetables. Modern research has found that sweet potato leaves also contain a large amount of antioxidants, which have the effects of promoting metabolism, improving immunity, and regulating sugar and lipid metabolism. Therefore, they are also called "longevity vegetables" and have potential development value. However, purple sweet potato leaves are mostly agricultural by-products that have not been deeply processed and have low added value. It is necessary to implement the comprehensive utilization of purple sweet potato leaf by-products.

[0003] Hyperuricemia is usually caused by purine metabolism disorder in the body, and gout caused by it is called the second largest metabolic disease. Hyperuricemia is mainly manifested by excessive uric acid production in the body or blocked uric acid excretion. Among them, xanthine oxidase is the key enzyme for uric acid production in purine metabolism, and proteins that transport or reabsorb urate in the kidney can regulate renal uric acid excretion. In addition, uric acid can be decomposed into allantoin by urate oxidase, and allantoin can be excreted through the kidney without the property of reabsorption. Therefore, inhibiting xanthine oxidase and promoting uric acid excretion have become the key directions for the treatment of hyperuricemia. In recent years, natural products in medicinal and edible resources have a definite therapeutic effect on hyperuricemia, with few toxic and side effects, and gradually show greater research and development advantages. In particular, studies have shown that plant-derived compounds such as alkaloids, flavonoids, and polyphenols have a significant effect on lowering blood uric acid. Studies have found that purple sweet potato leaf polyphenols have an improving effect on hyperuricemia, and HPLC-MS analysis shows that they are mainly composed of caffeoylquinic acid derivatives. In vivo, purple sweet potato leaf polyphenols can significantly inhibit the uric acid level of hyperuricemia mice from 209.6 to 166.6 μM and significantly interfere with the activity of xanthine oxidase (XOD) in the liver. Therefore, the natural active ingredients in purple sweet potato leaves have great potential to improve hyperuricemia.

[0004] At present, different extraction methods are often used according to the target natural products, and the selection of methods usually follows the principle of high efficiency and no pollution. As an emerging non-thermal treatment technology, the high-voltage pulsed electric field extraction method has the characteristics of short processing time and low energy consumption. It mainly uses the raw materials as electrolytes and destroys the plant cell membrane or cell wall through the perforation effect of pulsed electric fields and magnetic fields, so that the natural products can be efficiently dissolved. Andreou et al. used the pulsed electric field method to extract olive residues. After the pulsed electric field treatment, the total phenol content increased by 91.6% and the protein content increased by 100% compared with the untreated control group, indicating that the pulsed electric field can effectively improve the traditional extraction process. Patent Publication No. CN115671787A discloses a method for accurately controlling the graded extraction of bioactive substances from purple kaempferia using a high-voltage pulsed electric field. By adjusting the energy of the pulsed electric field, the pore size range of the plant cell wall is accurately controlled, and the graded extraction of polyphenol flavonoids, essential oils, and polysaccharides in purple kaempferia is achieved. The ionic liquid extraction method has the characteristics of extremely low saturated vapor pressure, extremely low volatility, no pollution, and recyclability. It has good solubility for organic substances and is an excellent green extraction solvent. Ionic liquids can produce van der Waals forces, electrostatic forces, and other interactions with the groups of natural products, and can dissolve cellulose in the cell wall, so that the chemical components are fully dissolved. Ionic liquids are mainly used to extract phenylpropanoids, phenolic compounds, terpenes, etc. from natural products. Zhou Huiyan et al. studied the extraction of chlorogenic acid from honeysuckle and found that ionic liquids can extract chlorogenic acid from honeysuckle efficiently and quickly. Li Wanhua et al. studied the extraction of betulinic acid derivatives from traditional Chinese medicine by ionic liquids and traditional ethanol solvents. The results showed that the extraction efficiency of 1-ethyl-3-methylimidazole bromide ([EMIM]Br) was significantly improved compared with ethanol extraction. With the help of the binding ability of the C2 structure of the imidazole ring in the ionic liquid with carbon dioxide, exogenous ions can be specifically removed. At present, ionic liquids, supercritical CO2 and hydrogen peroxide are called the three major green solvents for chemical industry in the 21st century. Although the above methods can significantly improve the extraction efficiency of active substances, most of the single methods fail to achieve precise control of extraction. Therefore, in order to fully extract the active substances in purple sweet potato leaves, the method of efficient combination of multiple physical fields will be able to effectively improve the uric acid-lowering biological activity of purple sweet potato leaf water extract. Summary of the invention

[0005] Purpose of the invention: In view of the above-mentioned existing problems and shortcomings, the purpose of the present invention is to provide a method for preparing a purple sweet potato leaf water extract with a uric acid-lowering effect, thereby improving the dissolution of active substances in purple sweet potato leaves, minimizing the loss of phenolic substances, improving the in vitro xanthine oxidase inhibition rate, enhancing the uric acid decomposition ability, and having the potential for regulating the biological activity of uric acid metabolism.

[0006] Technical solution: To achieve the above-mentioned invention object, the present invention adopts the following technical solution:

[0007] A method for preparing a purple sweet potato leaf water extract having a uric acid-lowering effect comprises the following steps:

[0008] Step 1: Take fresh purple sweet potato leaves, wash and dry them;

[0009] Step 2: Ultrafinely grind the dried purple sweet potato leaves obtained in step 1 to a particle size of 20 to 30 μm, and sieve through a 600-mesh sieve for use;

[0010] Step 3: adding the sieved purple sweet potato leaf powder in step 2 to an aqueous solution of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) with a mass concentration of 4 g / L, and adjusting the pH value to 4-6 to obtain an ionic liquid extraction system;

[0011] Step 4: subject the ionic liquid extraction system obtained in step 3 to high-voltage pulse treatment, and place the suspension in the treatment chamber of the high-voltage pulse treatment device to ensure smooth flow of the liquid. The pulse frequency is 1000-1200 Hz, the pulse width is 30-40 μs, the flow rate is 200-500 L / h, and the electric field strength is 30-50 kV / cm. After the pulse treatment for 70-350 μs, the liquid is drained out and continued to be extracted at 25° C. for 20 minutes, followed by centrifugation at 3000 rpm for 10 minutes, and the supernatant is collected to obtain the purple sweet potato leaf extract.

[0012] Step 5: Filter the purple sweet potato leaf extract obtained in step 4, and concentrate under vacuum, with a vacuum degree of 0.01 to 0.08 MPa and a temperature of 30 to 60° C., and concentrate under vacuum until the concentrate is 1 / 10 to 1 / 15 of the volume of the feed liquid, to obtain a purple sweet potato leaf concentrate;

[0013] Step 6: Pour the purple sweet potato leaf concentrate obtained in step 5 into the extraction kettle of the supercritical CO2 extraction equipment, with an extraction temperature of 60°C, an extraction time of 1h, an extraction pressure of 40Mpa, high-pressure pumping of CO2, and cyclic extraction for 3 times, and collect the liquid to obtain the purple sweet potato leaf water extract.

[0014] Furthermore, in the step 3, [Bmim]BF4 is prepared by reacting a BF4 salt with a halide ionic liquid (X-generation 1-butyl-3-methylimidazole) to obtain the target ionic liquid [Bmim]BF4.

[0015] Furthermore, in step 3, the aqueous solution of [Bmim]BF4 is an ionic liquid having a mass concentration of 4 g / L in water.

[0016] Furthermore, the aqueous solution of [Bmim]BF4 is added in step 3 at a material-liquid ratio of purple sweet potato leaves to ionic liquid of 1:10 (g:mL).

[0017] Furthermore, the purple sweet potato leaf extract was added to a xanthine oxidase reaction system to detect its ability to inhibit xanthine oxidase and the amount of allantoin generated; it was added to a uric acid system to detect its ability to decompose uric acid. The contents of uric acid and allantoin were determined using a liquid-mass spectrometer.

[0018] Furthermore, the half inhibition concentration of xanthine oxidase in the finished product of purple sweet potato leaf water extract is 48.25 mg / mL, and when the concentration of purple sweet potato leaf extract is 70 mg / mL, the allantoin production content is as high as 40.91 mg / mL.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following advantages: the cell wall of purple sweet potato leaves is precisely broken by ultrafine grinding combined with a high-voltage pulse electric field, and the active substances in the purple sweet potato leaves are more easily dissolved. The method of ionic liquid combined with supercritical carbon dioxide extraction is low temperature and easy to control, which can effectively reduce the loss of extraction solvents and efficiently retain active substances. In addition, the extraction solvents are all recognized as "green solvents for chemical industry in the 21st century", which are healthy and pollution-free. Compared with other single-phase extractions, this method has better repeatability, better biological activity in regulating uric acid metabolism, and has industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 . Schematic diagram of the preparation of purple sweet potato leaf water extract

[0021] Figure 2 . LC-MS ion spectrum of purple sweet potato leaf extract

[0022] Figure 3 .Uric acid inhibition rate and allantoin production curves at different concentrations of purple sweet potato leaf extract

[0023] Figure 4 .Liquid chromatography of allantoin under the intervention of allantoin standard and purple sweet potato leaf extract of different concentrations

[0024] Figure 5 . Liquid chromatography of allantoin in 70 mg / mL purple sweet potato leaf extract

[0025] Figure 6 .Proteomic mass spectrum of purple sweet potato leaf extract DETAILED DESCRIPTION

[0026] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0027] like Figure 1The steps shown are a method for preparing a purple sweet potato leaf water extract having a uric acid-lowering effect, and 4 examples are given below for illustration.

[0028] Example 1.

[0029] Take fresh purple sweet potato leaves, wash and then dry them in the sun, ultrafinely grind the dried purple sweet potato leaves to a particle size of 20 μm, and use them after passing through a 600-mesh sieve; after sieving, add purple sweet potato leaf powder to a [Bmim]BF4 aqueous solution with a mass concentration of 4 g / L according to a solid-liquid ratio of 1:10 (g:mL), and adjust the pH value to 5 to obtain an ionic liquid extraction system; then, perform high-voltage pulse treatment, place the suspension in a treatment chamber of a high-voltage pulse treatment device to ensure smooth liquid flow, the pulse frequency is 1000 Hz, the pulse width is 30 μs, the flow rate is 200 L / h, and the electric field strength is 30 kV / cm. After the pulse treatment for 100 μs, drain the liquid and continue to stand and extract at 25°C for 20 minutes, then centrifuge at 3000 rpm for 10 minutes, collect the supernatant, and obtain a purple sweet potato leaf extract. The solution was filtered and concentrated under vacuum with a vacuum degree of 0.05 MPa and a temperature of 60°C. The solution was concentrated under vacuum until the concentrate was 1 / 10 of the volume of the feed liquid to obtain a purple sweet potato leaf concentrate. The solution was poured into an extraction kettle of a supercritical CO2 extraction device with an extraction temperature of 60°C, an extraction time of 1 h, an extraction pressure of 40 MPa, and CO2 was pumped in under high pressure. The extraction was cyclically performed for 3 times, and the liquid was collected to obtain a purple sweet potato leaf water extract.

[0030] The components of purple sweet potato leaf extract were determined by liquid chromatography-mass spectrometry. The HPLC detection conditions were as follows: waters HSST3 column (2.1 mm × 150 mm, 3.5 μm), column temperature 30 °C, injection volume 3 μL, mobile phase A was acetonitrile, phase B was acetonitrile-0.1% formic acid aqueous solution, flow rate 0.3 mL min -1 , isocratic elution at 10:90 for 32 min, and detection at a wavelength of 327 nm.

[0031] The mass spectrometry detection conditions are as follows: ion source: electrospray ion source (ESI), negative ion scanning; multiple reaction monitoring (MRM); capillary voltage: 4.5 kV; nebulizer pressure: 45 psi; drying gas flow rate: 10 L / min; drying gas temperature: 350 ° C; sheath gas flow rate: 10 L / min; sheath gas temperature: 300 ° C; parent ion: 353.1, daughter ion: 191, quantitative ion: 85, declustering voltage: 80 V, collision energy: 35 V. The information data dependent acquisition (IDA) mode was used to collect and analyze the data, and the ion spectrum results were obtained as follows: Figure 2As shown, through comparison with known spectra, it can be seen that the main components are caffeoylquinic acid substances, followed by DL-malic acid, caffeic acid, L-asparagine and other components, among which chlorogenic acid is the most abundant. Chlorogenic acid was detected by high-phase liquid chromatography, and the content was 8.858μg / mL, accounting for about 0.08%.

[0032] Example 2.

[0033] Take fresh purple sweet potato leaves, wash and then dry them in the sun, ultrafinely grind the dried purple sweet potato leaves to a particle size of 20 μm, and use them after passing through a 600-mesh sieve; after sieving, add purple sweet potato leaf powder to a [Bmim]BF4 aqueous solution with a mass concentration of 4 g / L according to a solid-liquid ratio of 1:10 (g:mL), and adjust the pH value to 5 to obtain an ionic liquid extraction system; then, perform high-voltage pulse treatment, place the suspension in a treatment chamber of a high-voltage pulse treatment device to ensure smooth liquid flow, the pulse frequency is 1000 Hz, the pulse width is 30 μs, the flow rate is 200 L / h, and the electric field strength is 40 kV / cm. After the pulse treatment for 200 μs, drain the liquid and continue to stand and extract at 25°C for 20 minutes, then centrifuge at 3000 rpm for 10 minutes, collect the supernatant, and obtain a purple sweet potato leaf extract. The solution was filtered and concentrated under vacuum with a vacuum degree of 0.05 MPa and a temperature of 60°C. The solution was concentrated under vacuum until the concentrate was 1 / 10 of the volume of the feed liquid to obtain a purple sweet potato leaf concentrate. The solution was poured into an extraction kettle of a supercritical CO2 extraction device with an extraction temperature of 60°C, an extraction time of 1 h, an extraction pressure of 40 MPa, and CO2 was pumped in under high pressure. The extraction was cyclically performed for 3 times, and the liquid was collected to obtain a purple sweet potato leaf water extract.

[0034] Furthermore, the purple sweet potato leaf extract was added to a xanthine oxidase reaction system to detect its ability to inhibit xanthine oxidase. A xanthine oxidase reaction system was configured, the enzyme concentration was 50U / mg protein, the substrate was 1mmol / L xanthine, and different concentrations of purple sweet potato leaf extract were used for intervention, namely 30mg / mL, 40mg / mL, 50mg / mL, 60mg / mL, 70mg / mL, and 80mg / mL. The absorbance of xanthine oxidase was detected using a multifunctional microplate reader. As the concentration of the extract increased, the xanthine oxidase inhibition rate changed as shown in the figure. Figure 3 As shown, the half maximal inhibition concentration of xanthine oxidase was 48.25 mg / mL.

[0035] The content of allantoin generated by adding uric acid to the purple sweet potato leaf extract was determined by liquid chromatography-mass spectrometry. The high performance liquid chromatography detection conditions are as follows: Hypersil ODS column (4.6mm×250mm, 5μm), column temperature 30℃, injection volume 5μL, mobile phase A phase methanol, phase B methanol: water (volume 9:1), flow rate 0.5mL·min-1, detection at a wavelength of 224nm, the liquid chromatography results are as follows: Figure 4As shown in the figure, the concentrations of allantoin generated by the xanthine oxidase reaction system under the intervention of 30mg / mL, 40mg / mL, 50mg / mL, 60mg / mL, 70mg / mL, and 80mg / mL concentrations of purple sweet potato leaf extract were 24.76mg / mL, 34.43mg / mL, 37.76mg / mL, 40.25mg / mL, 40.91mg / mL, and 39.06mg / mL, respectively. The results of the concentration of allantoin generated as the concentration of the extract increased are shown in the figure. Figure 3 As shown in the figure, the allantoin content increases with the increase of the concentration of purple sweet potato leaf extract. When the concentration is 70 mg / mL, the allantoin content reaches the highest level, and then shows a downward trend. In order to eliminate the interference of allantoin in the purple sweet potato leaf extract, 70 mg / mL of purple sweet potato leaf water extract was used as the blank control group, and the high-performance liquid chromatography detection was performed under the same conditions. The liquid chromatography results are shown in the figure. Figure 5 As shown. The content of allantoin in purple sweet potato leaf extract is 0.327mg / mL. The results show that after intervention with purple sweet potato leaf extract, the content of allantoin decomposed from uric acid generated by xanthine is significantly increased.

[0036] Example 3.

[0037] Take fresh purple sweet potato leaves, wash and then dry them in the sun, ultrafinely grind the dried purple sweet potato leaves to a particle size of 20 μm, and use them after passing through a 600-mesh sieve; after sieving, add purple sweet potato leaf powder to a [Bmim]BF4 aqueous solution with a mass concentration of 4 g / L according to a solid-liquid ratio of 1:10 (g:mL), and adjust the pH value to 5 to obtain an ionic liquid extraction system; then, perform high-voltage pulse treatment, place the suspension in a treatment chamber of a high-voltage pulse treatment device to ensure smooth liquid flow, the pulse frequency is 1000 Hz, the pulse width is 30 μs, the flow rate is 200 L / h, and the electric field strength is 40 kV / cm. After the pulse treatment for 200 μs, drain the liquid and continue to stand and extract at 25°C for 20 minutes, then centrifuge at 3000 rpm for 10 minutes, collect the supernatant, and obtain a purple sweet potato leaf extract. The solution was filtered and concentrated under vacuum with a vacuum degree of 0.05 MPa and a temperature of 60°C. The solution was concentrated under vacuum until the concentrate was 1 / 10 of the volume of the feed liquid to obtain a purple sweet potato leaf concentrate. The solution was poured into an extraction kettle of a supercritical CO2 extraction device with an extraction temperature of 60°C, an extraction time of 1 h, an extraction pressure of 40 MPa, and CO2 was pumped in under high pressure. The extraction was cyclically performed for 3 times, and the liquid was collected to obtain a purple sweet potato leaf water extract.

[0038] Furthermore, the purple sweet potato leaf extract was tested by the BCA method to find that the protein content was about 15%, and the metabolomics method was used to detect the composition of the key protein components in the ingredients. The collected raw data was analyzed using the international mainstream proteomics data analysis software Proteome Discoverer, and the database used the uniprotkb_Convolvulaceae_20240115.fasta database for sequence library retrieval. Precursor mass tolerance and fragment masstolerance were set to 15ppm and 0.02Da, respectively. The proteomics map results are shown in Figure 5 shown.

[0039] Example 4.

[0040] Take fresh purple sweet potato leaves, wash and then dry them in the sun, ultrafinely grind the dried purple sweet potato leaves to a particle size of 20 μm, and use them after passing through a 600-mesh sieve; after sieving, add purple sweet potato leaf powder to a [Bmim]BF4 aqueous solution with a mass concentration of 4 g / L according to a solid-liquid ratio of 1:10 (g:mL), and adjust the pH value to 5 to obtain an ionic liquid extraction system; then, perform high-voltage pulse treatment, place the suspension in a treatment chamber of a high-voltage pulse treatment device to ensure smooth liquid flow, the pulse frequency is 1000 Hz, the pulse width is 30 μs, the flow rate is 200 L / h, and the electric field strength is 40 kV / cm. After the pulse treatment for 200 μs, drain the liquid and continue to stand and extract at 25°C for 20 minutes, then centrifuge at 3000 rpm for 10 minutes, collect the supernatant, and obtain a purple sweet potato leaf extract. The solution was filtered and concentrated under vacuum with a vacuum degree of 0.05 MPa and a temperature of 60°C. The solution was concentrated under vacuum until the concentrate was 1 / 10 of the volume of the feed liquid to obtain a purple sweet potato leaf concentrate. The solution was poured into an extraction kettle of a supercritical CO2 extraction device with an extraction temperature of 60°C, an extraction time of 1 h, an extraction pressure of 40 MPa, and CO2 was pumped in under high pressure. The extraction was cyclically performed for 3 times, and the liquid was collected to obtain a purple sweet potato leaf water extract.

[0041] Furthermore, the obtained purple sweet potato leaf extract was given to three volunteers. The dosage was once a day, 50 mL each time. After drinking it continuously for 1 month, they went to the hospital to draw blood to test the uric acid index. The uric acid indexes of the three volunteers before drinking the purple sweet potato leaf extract were 566.9 μmol / L, 490 μmol / L, and 579 μmol / L, respectively. After the purple sweet potato leaf extract drinking intervention, the test index results were 388.2 μmol / L, 428 μmol / L, and 498 μmol / L, respectively. The above results show that the purple sweet potato leaf extract extracted by this method significantly reduces the blood uric acid content in people with high uric acid.

[0042] The advantages of this solution are specifically reflected in:

[0043] 1. Purple sweet potato leaves are the tender leaves and stems of purple sweet potatoes, with high food safety and good medicinal value. Purple sweet potatoes are widely planted in my country. Purple sweet potato leaves are by-products with low prices, stable sources, and easy industrialization. This plan increases the added value of by-products and realizes the precise utilization of by-products.

[0044] 2. This process uses ultrafine grinding combined with high-voltage pulse processing methods, high-frequency oscillation to break the wall and destroy the purple sweet potato leaf cell membrane or cell wall through the perforation effect of pulsed electric and magnetic fields, so that the natural active substance components can be efficiently dissolved, which significantly improves the raw material utilization rate and extraction efficiency, is conducive to sustainable development, and is a green and environmentally friendly auxiliary extraction technology with high extraction efficiency.

[0045] 3. In order to increase the content of active substances, ionic liquids replace organic solvents such as ethanol, and aqueous solutions are used as solvents to reduce the edible burden of high-acid target populations, efficiently extract and reduce pollution; the obtained purple sweet potato leaf extract is further extracted by supercritical carbon dioxide injection. While fully extracting the active substances, the C2 structure of the imidazole ring in the ionic liquid implemented in this scheme specifically removes exogenous ions based on its ability to bind to carbon dioxide. It has the advantages of green and safe operation, good stability, etc., and the resulting product has high biological activity.

Claims

1. A method for preparing a purple sweet potato leaf water extract having a uric acid-lowering effect, characterized in that: The steps include: Step 1: Take fresh purple sweet potato leaves, wash and dry them; Step 2: Ultrafinely grind the dried purple sweet potato leaves obtained in step 1 to a particle size of 20 to 30 μm, and sieve through a 600-mesh sieve for use; Step 3: Add the sieved purple sweet potato leaf powder in step 2 to an aqueous solution of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) at a mass concentration of 4 g / L, and adjust the pH value to 4 to 6 to obtain an ionic liquid extraction system; Step 4: subject the ionic liquid extraction system obtained in step 3 to high-voltage pulse treatment, and place the suspension in the treatment chamber of the high-voltage pulse treatment device to ensure smooth flow of the liquid. The pulse frequency is 1000-1200 Hz, the pulse width is 30-40 μs, the flow rate is 200-500 L / h, and the electric field strength is 30-50 kV / cm. After the pulse treatment for 70-350 μs, the liquid is drained out and continued to be extracted at 25° C. for 20 minutes, followed by centrifugation at 3000 rpm for 10 minutes, and the supernatant is collected to obtain the purple sweet potato leaf extract. Step 5: Filter the purple sweet potato leaf extract obtained in step 4, and concentrate under vacuum, with a vacuum degree of 0.01 to 0.08 MPa and a temperature of 30 to 60° C., and concentrate under vacuum until the concentrate is 1 / 10 to 1 / 15 of the volume of the feed liquid, to obtain a purple sweet potato leaf concentrate; Step 6: Pour the purple sweet potato leaf concentrate obtained in step 5 into the extraction kettle of the supercritical CO2 extraction equipment, with an extraction temperature of 60°C, an extraction time of 1h, an extraction pressure of 40Mpa, high-pressure pumping of CO2, and cyclic extraction for 3 times, and collect the liquid to obtain the purple sweet potato leaf water extract.

2. The method for preparing the purple sweet potato leaf water extract according to item 1, characterized in that: The [Bmim]BF4 in step 3 is prepared by reacting a BF4 salt with a halide ionic liquid (X-generation 1-butyl-3-methylimidazole) to obtain the target ionic liquid [Bmim]BF4.

3. The method for preparing the purple sweet potato leaf water extract according to item 1, characterized in that: The aqueous solution of [Bmim]BF4) in step 3 is an ionic liquid with a mass concentration of 4 g / L in water.

4. The method for preparing the purple sweet potato leaf water extract according to item 1, characterized in that: In the step 3, the aqueous solution of [Bmim]BF4 is added according to the material-liquid ratio of purple sweet potato leaves to ionic liquid of 1:10 (g:mL).

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