Method for extracting redbud anthocyanin based on ultrasonic-assisted deep-eutectic solvent

Abstract

A method for extracting redbud anthocyanin based on an ultrasonic-assisted deep-eutectic solvent comprises the following steps: firstly, extracting an anthocyanin crude extract in redbud through the ultrasonic-assisted deep-eutectic solvent, then purifying the anthocyanin crude extract based on column chromatography and activated macroporous resin, and removing an elution solvent after purification to obtain the redbud anthocyanin. And carrying out freeze drying to obtain purified redbud anthocyanin. The method is used for improving the extraction efficiency and purity of the redbud anthocyanin.

Description

TECHNICAL FIELD

[0001] The present application relates to anthocyanin extraction technology field, specifically a kind of method for extracting purple king flower anthocyanin based on ultrasonic assisted low eutectic solvent. BACKGROUND

[0002] Purple king flower has the effects of clearing heat and resolving toxicity, promoting dampness and relieving stranguria, and is suitable for rheumatic bone pain, nasal ulcers, etc. Its flowers are colorful and have high pigment content, containing anthocyanins, flavonoids and other functional active substances. Anthocyanins have the effects of anti-inflammatory, antibacterial, protecting vision, reducing blood sugar, etc. However, the crude extract of anthocyanins usually contains impurities such as fat, organic acid, protein and free sugar, which directly affects the stability and other biological activities of purple king flower anthocyanins. Therefore, the crude extract of anthocyanins needs to be purified to improve the stability of anthocyanins.

[0003] Traditional methods for extracting purple king flower anthocyanins mostly use organic solvents, which can effectively dissolve anthocyanins, but there are solvent residues, and the organic solvents are not enough to destroy the cell wall, resulting in incomplete release of anthocyanins and low extraction efficiency. SUMMARY

[0004] The present application aims to provide a method for extracting purple king flower anthocyanins based on ultrasonic assisted low eutectic solvent, to improve the extraction efficiency and purity of purple king flower anthocyanins.

[0005] To solve the above technical problems, the specific scheme adopted by the present application is as follows: a method for extracting purple king flower anthocyanins based on ultrasonic assisted low eutectic solvent, first, the crude extract of anthocyanins in purple king flower is extracted by ultrasonic assisted low eutectic solvent, then the crude extract of anthocyanins is purified based on column chromatography and activated macroporous resin, after the purification treatment, the eluent is removed, and then the purified purple king flower anthocyanins are obtained by freeze-drying.

[0006] Preferably, the low eutectic solvent includes hydrogen bond acceptor and hydrogen bond donor, the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is any one or any combination of two or more of lactic acid, ethylene glycol, glucose, urea and 1,4-butanediol.

[0007] Preferably, the hydrogen bond donor is 1,4-butanediol, and the volume ratio of hydrogen bond acceptor to hydrogen bond donor is 1:(3.8-4.2), and the water content of the low eutectic solvent is 40%-60%.

[0008] Preferably, the conditions for extracting the crude extract of anthocyanins in purple king flower by ultrasonic assisted low eutectic solvent are as follows: ultrasonic frequency is 260W-455W, ultrasonic temperature is ≤55℃, and ultrasonic time is 9-11min.

[0009] Preferably, the ultrasonic frequency is 325W, and the ultrasonic temperature is 45℃.

[0010] Preferably, the redbud flowers are made into redbud flower freeze-dried powder before being added into the eutectic solvent, and the ratio of the redbud flower freeze-dried powder to the eutectic solvent is 1g:(30-50mL).

[0011] Preferably, the elution solvent is 90% ethanol solution with pH=1 adjusted by concentrated hydrochloric acid.

[0012] The present application can significantly improve the extraction rate of anthocyanins based on the ultrasonic-assisted eutectic solvent, and can also avoid the residue of organic solvents, and is safe.

[0013] In addition, the present application also significantly shortens the extraction time, can control the extraction time within 10 minutes, improves the extraction efficiency, and is helpful for factory scale production. Through experiments, the content of the extracted anthocyanins is 3.1974mg / g, and the main components of the anthocyanins include seven pigments, i.e., petunidin-3, 5-diglucoside, malvidin-3, 5-diglucoside, malvidin-3-O-glucoside, delphinidin-3-O-glucoside, delphinidin, and cyanidin-3-O-glucoside. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is the influence of DES on the extraction amount of redbud flower anthocyanins in the example group 1.

[0015] Figure 2 is the influence of ultrasonic power on the extraction amount of redbud flower anthocyanins in the example group 1.

[0016] Figure 3 is the influence of the water content of DES on the extraction amount of redbud flower anthocyanins in the example group 1.

[0017] Figure 4 is the influence of ultrasonic temperature on the extraction amount of redbud flower anthocyanins in the example group 1.

[0018] Figure 5 is the influence of the ratio of material to liquid on the extraction amount of redbud flower anthocyanins in the example group 1.

[0019] Figure 6 is the infrared spectrum of the purified anthocyanins in the example group 2.

[0020] Figure 7 is the mass spectrum of the purified anthocyanins in the example group 2.

[0021] Figure 8 is the ion mass spectrum at peak A and the structure diagram of petunidin-3, 5-diglucoside.

[0022] Figure 9 is the ion mass spectrum at peak B and the structure diagram of malvidin-3, 5-diglucoside.

[0023] Figure 10 is the ion mass spectrum at peak C and the structure of malvidin-3-O-glucoside.

[0024] Figure 11 is the ion mass spectrum at peak D and the structure of violin-3-O-glucoside.

[0025] Figure 12 is the ion mass spectrum at peak E and the structure of violin.

[0026] Figure 13 is the ion mass spectrum at peak F and the structure of cyanidin-3-O-glucoside.

[0027] Figure 14 is the ion mass spectrum at peak G and the structure of cyanidin. DETAILED DESCRIPTION

[0028] The application discloses a method for extracting anthocyanins from Bauhinia Blake flowers based on an ultrasonic-assisted deep eutectic solvent, and the anthocyanins are extracted from the Bauhinia Blake flowers based on the ultrasonic-assisted deep eutectic solvent, and then the anthocyanin crude extract is purified by using activated macroporous resins to obtain purified anthocyanins, and the method specifically comprises the following steps.

[0029] In the first step, the deep eutectic solvent is added into the freeze-dried powder of the Bauhinia Blake flowers, and the anthocyanin crude extract is obtained after ultrasonic treatment for a certain time; the deep eutectic solvent comprises a hydrogen bond acceptor and a hydrogen bond donor, the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor comprises any one of lactic acid, ethylene glycol, glucose, urea and 1,4-butanediol.

[0030] The ultrasonic condition is that the ultrasonic frequency is 260 W-455 W, the ultrasonic temperature is less than or equal to 55 DEG C, and the ultrasonic time is 10 min; preferably, the ultrasonic frequency is 325 W, the ultrasonic temperature is 45 DEG C, and the ultrasonic time is 10 min.

[0031] The ratio of the Bauhinia Blake flowers (freeze-dried powder) to the deep eutectic solvent is 1 g:50 mL-1 g:30 mL.

[0032] In the second step, the anthocyanin crude extract is separated and purified based on column chromatography and activated macroporous resins, the anthocyanin eluent is collected, the elution solvent is removed, and the purified Bauhinia Blake flower anthocyanins are obtained by freeze-drying.

[0033] In the application, the activation of the macroporous resin (AB-8 type is adopted) comprises the following steps: anhydrous ethanol is added into the macroporous resin, and the macroporous resin is completely immersed; the macroporous resin is placed at room temperature for 24 h; the ethanol is filtered out; the macroporous resin is washed with deionized water; then the macroporous resin is soaked in a 5% hydrochloric acid solution at room temperature for 5 h; the macroporous resin is filtered and washed with deionized water until neutral; then the macroporous resin is soaked in a 5% NaOH solution at room temperature for 5 h; the macroporous resin is filtered and washed with distilled water until neutral; finally, the macroporous resin is dried to a constant weight and is ready for use.

[0034] In the present application, the wet method of packing the macroporous resin column comprises the following steps: adding anhydrous ethanol into the macroporous resin and ensuring that the macroporous resin is immersed, standing for 30 min to make the macroporous resin fully swell; slowly pouring the swelled macroporous resin into a chromatographic column, discharging the anhydrous ethanol, adding an appropriate amount of distilled water into the chromatographic column to clean the resin layer after the anhydrous ethanol is completely discharged, and simultaneously, gently knocking the column wall to discharge the air bubbles in the resin layer, repeatedly cleaning the resin layer until the effluent has no alcohol smell, and then performing dynamic adsorption and desorption.

[0035] After packing, the extract is added into the chromatographic column in batches, and the flow rate of the sample loading is controlled to be 2 mL / min; after the sample loading is completed, 90% ethanol with pH = 1.0 is used as an eluent (adjusted by 36.5% hydrochloric acid) to elute, and the flow rate of the eluent is 1 mL / min; the eluent is collected, the ethanol is removed by rotary evaporation, and then the purified anthocyanins are obtained after freeze-drying.

[0036] The present application will be described in detail below with reference to the accompanying drawings. It should be pointed out that the reagents and experimental instruments used in the present application are all common commercially available reagents or instruments in existing laboratories. It should be pointed out that the extraction amount of the redbud flower anthocyanins is calculated by the pH differential method in the present application:

[0037] Two 1 mL anthocyanin extracts (i.e. the extract after suction filtration) are respectively put into two 10 mL volumetric flasks, and are respectively diluted to volume with potassium chloride-hydrochloric acid buffer solution with pH = 1.0 and acetic acid-sodium acetate buffer solution with pH = 4.5;

[0038] After dilution, the extract is placed in the dark for 30 min, and then the absorbance values of the extract at 521 nm and 700 nm are measured, and the content C of the redbud flower anthocyanins is calculated according to the absorbance values, which is calculated as follows:

[0039]

[0040] A=(A 521 -A 700 ) pH1.0 -(A 521 -A 700 ) pH4.5

[0041] In the formula: C is the content of total anthocyanins in the sample, mg / g; A is the difference between the absorbance values of the sample under two pH conditions, L / (g·cm); M W is the molecular weight of cyanidin-3-O-glucoside, 449 g / mol; DF is the dilution factor; V is the total volume of the extract, mL; M is the mass of the redbud flowers, g; ε is the molar extinction coefficient, 26900 L / (mol·cm); and L is the light range, 1 cm.

[0042] Example 1: Extraction of redbud flower anthocyanins

[0043] 1. The effect of deep eutectic solvent (DES) on the extraction rate of crepe myrtle anthocyanins

[0044] Add 1.0 g of crepe myrtle powder to DES with a water content of 30%, the solid-liquid ratio is 1 g:30 mL, ultrasonic extraction once: ultrasonic power 300 W, ultrasonic extraction time 10 min, ultrasonic extraction temperature 50℃;

[0045] Among them, the hydrogen bond acceptor of DES is choline chloride, and the hydrogen bond donor is lactic acid, 1,4-butanediol, urea, glucose, citric acid and ethylene glycol, respectively. The hydrogen bond acceptor and the hydrogen bond donor are mixed in a certain volume ratio to obtain five groups of DES, which are: DES-1 choline chloride: urea = 1:2; DES-2: choline chloride: lactic acid = 1:1; DES-3: choline chloride: 1,4-butanediol = 1:4; DES-4: choline chloride: ethylene glycol = 1:3; DES-5: choline chloride: glucose = 1:1; Add purified water to the five groups of DES, and adjust the water content of each DES to 30%;

[0046] After the extraction is completed (once), the solid is removed by suction filtration to obtain the anthocyanin extract (i.e. the filter core after suction filtration), and the extraction amount of crepe myrtle anthocyanins is calculated by pH differential method, and the specific results are shown in Figure 1 . It can be seen from Figure 1 that the anthocyanin content of DES-3 (i.e. choline chloride: 1,4-butanediol = 1:4) is the largest and reaches 3.1103 mg / g; followed by DES-2 (choline chloride: lactic acid = 1:1) combination, and the anthocyanin contents of the two groups are similar. Therefore, DES-2 and DES-3 are used as the preferred deep eutectic solvent for extracting crepe myrtle anthocyanins. In addition, the inventors found in the test process that although an acidic environment is conducive to the stability of anthocyanins, the viscosity of DES-2 is relatively large, which may hinder the penetration of the solvent in the extraction matrix to a certain extent. Therefore, DES-3 (i.e. choline chloride: 1,4-butanediol = 1:4) is used as the best solvent in the present application.

[0047] 2. The effect of ultrasonic power on the yield of crepe myrtle anthocyanins

[0048] During the ultrasonic action, the ultrasonic energy provides energy, transmits strong vibration to the crepe myrtle powder and the solvent, causes partial destruction of the raw material cells, accelerates the release of intracellular substances, and enhances the diffusion of solutes. The present application considers the effect of different ultrasonic powers on the yield of crepe myrtle anthocyanins, which specifically includes the following contents:

[0049] Add DES-3 with a water content of 30% to each 1.0g of Bauhinia flower powder at a material-to-liquid ratio of 1g:30mL. Perform ultrasonic extraction once: extraction time 10min, extraction temperature 50℃. Investigate the effect of ultrasonic power on anthocyanin yield, using ultrasonic powers of 260W, 325W, 390W, 455W, and 520W respectively. After extraction, filter to obtain the anthocyanin extract, and determine and calculate the anthocyanin yield. Results are shown below. Figure 2 .

[0050] Depend on Figure 2 It can be seen that within the range of ultrasonic power 260W-520W, the amount of anthocyanins extracted from Bauhinia flowers first increases slightly with the increase of ultrasonic power, reaches the highest value at 325W, then decreases slightly in the range of 325W-455W, and the anthocyanin content decreases significantly after the ultrasonic power exceeds 455W.

[0051] When the ultrasonic power is too high, excessive energy transfer leads to an increase in the temperature of the solvent system, causing anthocyanin degradation and thus reducing extraction efficiency. Therefore, in this invention, the ultrasonic power is preferably controlled below 455W, more preferably below 325W, with 325W being the optimal ultrasonic power.

[0052] 3. Effect of DES moisture content on the yield of anthocyanins from Bauhinia purpurea

[0053] DES-3 was added to 1.0 g of Bauhinia flower powder at a material-to-liquid ratio of 1 g:30 mL, and ultrasonic extraction was performed once: ultrasonic extraction time 10 min, ultrasonic extraction temperature 50℃, and ultrasonic power 325 W. The effect of DES-3 water content on anthocyanin yield was investigated, with water contents of 20%, 30%, 40%, 50%, and 60% respectively. After extraction, the anthocyanin extract was obtained by filtration, and the anthocyanin yield was determined and calculated. The results are shown in the figure. Figure 3 .

[0054] Depend on Figure 3 It is known that the extraction yield of anthocyanins from Bauhinia flowers shows a trend of first increasing and then decreasing within the range of 20%-60% water content in DES-3. The extraction yield is highest when the water content of DES-3 is 40%. This is because a suitable water content can reduce the viscosity of the solvent and enhance its penetration in the extraction medium. Furthermore, an appropriate amount of water can reduce surface tension and increase cell permeability, making it easier for biomolecules to be extracted and reducing extraction costs, which is beneficial for industrial production. However, excessively high water content can easily damage the hydrogen bond structure of DES, reducing its effectiveness and thus lowering the extraction efficiency. Therefore, in this invention, the preferred water content of DES-3 is 40%.

[0055] 4. Effect of ultrasonic temperature on the yield of anthocyanins from Bauhinia purpurea

[0056] To 1.0 g of Bauhinia championii flower powder, add DES-3 with a water content of 40%, a solid-liquid ratio of 1 g:30 mL, and ultrasonic extract once: ultrasonic extraction time 10 min, ultrasonic power 325 W, and investigate the effect of ultrasonic temperature on the yield of anthocyanins, ultrasonic temperature in turn: 40℃, 45℃, 50℃, 55℃, 60℃; After extraction, the anthocyanin extract is obtained by suction filtration, and the extraction amount of anthocyanins is determined and calculated, and the results are shown in Table 1. Figure 4 .

[0057] As shown in Figure 4 , when the ultrasonic temperature is 40℃-45℃, the content of anthocyanins in Bauhinia championii flowers gradually increases; when the ultrasonic temperature is 45℃-60℃, the extraction amount of anthocyanins in Bauhinia championii flowers gradually decreases. Generally speaking, higher temperature can increase the molecular motion rate, so that the solvent has greater fluidity, and the anthocyanin molecules in Bauhinia championii flowers can diffuse into the solvent faster, and the extraction efficiency is also improved accordingly. However, when the temperature is too high, the DES or anthocyanins may be destroyed. Therefore, the preferred ultrasonic extraction temperature of the present application is 45℃.

[0058] 5, Effect of solid-liquid ratio on the yield of anthocyanins in Bauhinia championii flowers

[0059] To 1.0 g of Bauhinia championii flower powder, add DES-3 with a water content of 40%, ultrasonic extract once: ultrasonic extraction time 10 min, ultrasonic power 325 W, and ultrasonic temperature 45℃, investigate the effect of solid-liquid ratio on the yield of anthocyanins, solid-liquid ratio in turn: 1:10, 1:20, 1:30, 1:40, 1:50; After extraction, the anthocyanin extract is obtained by suction filtration, and the extraction amount of anthocyanins is determined and calculated, and the results are shown in Table 2. Figure 5 .

[0060] As can be seen from Figure 5 , within the range of 1:10-1:40 g / mL, the extraction amount of anthocyanins in Bauhinia championii flowers shows a gradually increasing trend. This is because when the solid-liquid ratio is low, the contact area between the sample and the solvent becomes smaller, and the dispersion speed of the solvent around the sample also slows down, and a smaller solid-liquid ratio also leads to an increase in the viscosity of the system, making it difficult for the extraction solution to separate from the solid; when the solid-liquid ratio reaches 1:40 g / mL, the extraction amount of anthocyanins in Bauhinia championii flowers reaches the maximum, and then decreases. Therefore, in the present application, the solid-liquid ratio is 1:50 g / mL-1:30 g / mL, preferably 1:40 g / mL-1:30 g / mL, and most preferably 1:40 g / mL.

[0061] In summary, the crude extract condition of anthocyanins in the application is: DES-3 (i.e. choline chloride: 1,4-butanediol = 1:4) is used as the best solvent in the application, the water content of DES-3 is 40%; the ultrasonic power is preferably within 455 W, more preferably within 325 W, and 325 W is the optimal ultrasonic power; the ultrasonic extraction temperature is 45°C; the solid-liquid ratio is 1:50 g / mL to 1:30 g / mL, preferably 1:40 g / mL to 1:30 g / mL, and the optimal is 1:40 g / mL.

[0062] Example group 2 purification of purple royal flower anthocyanins

[0063] I. Purification

[0064] The crude extract of purple royal flower anthocyanins contains a large amount of impurities, and the application adopts macroporous resin and column chromatography to separate and purify the crude extract to remove non-anthocyanin substances in the crude extract. The specific experimental operation is: add DES-3 with a water content of 40% to purple royal flower powder, ultrasonic extraction once: ultrasonic extraction time 10 min, ultrasonic power 325 W, ultrasonic temperature 45°C, solid-liquid ratio 1:40 g / mL, and at least 150 mL of extract is obtained; after activating 20 g of AB-8 type macroporous resin, column loading, dilute the extract;

[0065] The diluted extract is added to the chromatographic column twice, the sample flow rate is 2 mL / min; after the sample is added, elute with 90% ethanol solution (pH 1.0, adjusted with concentrated hydrochloric acid), the elution flow rate is 1 mL / min; collect the eluate, remove the ethanol by rotary evaporation, and then freeze-dry to obtain the purified anthocyanins.

[0066] II. Identification of components of purple royal flower anthocyanins

[0067] 1. The freeze-dried anthocyanins are characterized by infrared, and the results are shown in Figure 6 . It can be seen from Figure 6 that the purple royal flower anthocyanins have characteristic absorption peaks at wave numbers of 3306, 2927, 1602, 1404, 1040, 866, 815 and 514 cm -1 . Among them, the characteristic absorption peak near 3300 cm -1 corresponds to the hydroxyl group, which is attributed to the absorption of alcohol and hydroxyl group; the characteristic absorption peak at 2927 cm -1 corresponds to the carbon-hydrogen bond in methyl and methoxy; the spectral peak near 1830-1650 cm -1 corresponds to the carbon-oxygen double bond, and the absorption peak at 1602 cm -1 can be characterized as the presence of flavonoids in the extract; the wave peak at 1040 cm -1 is related to the ether bond stretching vibration in the carbon ring; the wave peak at 866 cm-1 and 815 cm -1 The results show that the molecular structure of the purpleflower anthocyanins contains hydroxyl, methyl, methoxyl, benzene ring and sugar group.

[0068] 2. UHPLC-MS / MS detection method

[0069] The anthocyanins in the purpleflower are identified by UHPLC-MS / MS, wherein the chromatographic column is a Waters C18 chromatographic column (2.1*100 mm, particle size 1.7 μm); the mobile phase is 0.1% formic acid aqueous solution (buffer A) and pure acetonitrile solution (buffer B); the injection amount is 5 μL; the column temperature is 30 DEG C; the flow rate is 0.3 mL / min; the gradient elution is 95% buffer A for 0-1 min, 95%-85% buffer A for 1-2 min, 85%-72% buffer A for 2-4 min, 72%-60% buffer A for 4-6 min, 60%-40% buffer A for 6-8 min, 60%-40% buffer A for 8-8.5 min, 40%-95% buffer A for 8.5-9 min, and 95% buffer A for 9-10 min; the ESI positive ion mode is adopted, and the mass scanning range is m / z 50-1200; and the results are shown in Figures 7-14 and Table 1.

[0070] As shown in Table 1 and Figures 7-14 It can be known that the first molecular ion peaks m / z of the anthocyanins corresponding to peak A (RT=2.08 min) and peak B (RT=2.48 min) are 641 and 655, and the second fragment ion peaks m / z are 479 / 317 and 493 / 331 respectively. According to the second fragment ion peaks, the anthocyanin glycoside bases are petunidin and malvidin respectively, and the two second fragment ion peaks correspond to the loss of two glucose, so it is inferred that the two anthocyanins are petunidin-3, 5-diglucoside and malvidin-3, 5-diglucoside;

[0071] The molecular ion peaks of peak C (RT=3.08 min), peak D (RT=4.05 min) and peak F (RT=4.85 min) are at m / z 493, 465 and 449 respectively, and there is only one second fragment ion peak at m / z 331, 303 and 287 respectively, which can correspond to the loss of one glucose. Therefore, it can be determined that the three anthocyanin components are malvidin-3-O-glucoside, delphinidin-3-O-glucoside and cyanidin-3-O-glucoside in turn;

[0072] Peaks E and F belong to anthocyanin aglycone, peak E (RT = 4.52 min) is delphinidin with a molecular ion peak at m / z 303; peak G (RT = 5.13 min) has a molecular ion peak at m / z 287, which is cyanidin. Table 1 Anthocyanin components of Bauhinia Blake flower

[0073] In conclusion, the extraction amount of the anthocyanin of Bauhinia Blake flower can reach 3.1974 mg / g based on the ultrasonic-assisted deep eutectic solvent extraction, which not only significantly improves the extraction amount of the anthocyanin of Bauhinia Blake flower, but also significantly shortens the extraction time, avoids the residue of organic solvents, has high safety, and is conducive to the large-scale production of factories. It is identified that the main components of the anthocyanin of Bauhinia Blake flower include seven pigments, i.e., petunidin-3, 5-diglucoside, malvidin-3, 5-diglucoside, malvidin-3-O-glucoside, delphinidin-3-O-glucoside, delphinidin, cyanidin-3-O-glucoside and cyanidin, which provides a basis for the in-depth research of the anthocyanin of Bauhinia Blake flower.

Claims

1. A method for extracting anthocyanins from Bauhinia flowers using ultrasound-assisted eutectic solvent, characterized in that: First, crude anthocyanin extract from Bauhinia flowers was extracted using an ultrasound-assisted eutectic solvent. Then, the crude anthocyanin extract was purified using column chromatography and activated macroporous resin. After purification, the elution solvent was removed, and the purified Bauhinia anthocyanins were obtained by freeze-drying.

2. The method for extracting anthocyanins from Bauhinia flowers using ultrasound-assisted eutectic solvent as described in claim 1, characterized in that: Eutectic solvents include hydrogen bond acceptors and hydrogen bond donors, wherein the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is any one or any combination of two or more of lactic acid, ethylene glycol, glucose, urea, and 1,4-butanediol.

3. The method for extracting anthocyanins from Bauhinia flowers using ultrasound-assisted eutectic solvent as described in claim 2, characterized in that: The hydrogen bond donor is 1,4-butanediol, and the volume ratio of hydrogen bond acceptor to hydrogen bond donor is 1:

1. (3.8-4.2), the water content of the eutectic solvent is 40%-60%.

4. The method for extracting anthocyanins from Bauhinia flowers using ultrasound-assisted eutectic solvent as described in claim 1, characterized in that: The conditions for ultrasonic-assisted eutectic solvent extraction of crude anthocyanins from Bauhinia flowers were as follows: ultrasonic frequency of 260W to 455W, ultrasonic temperature ≤55℃, and ultrasonic time of 9-11min.

5. The method for extracting anthocyanins from Bauhinia flowers using ultrasound-assisted eutectic solvent as described in claim 4, characterized in that: The ultrasonic frequency is 325W and the ultrasonic temperature is 45℃.

6. The method for extracting anthocyanins from Bauhinia flowers using ultrasound-assisted eutectic solvent as described in claim 1, characterized in that: Bauhinia flowers are made into freeze-dried Bauhinia flower powder and then added to a eutectic solvent. The ratio of freeze-dried Bauhinia flower powder to eutectic solvent is 1g:(30-50mL).

7. The method for extracting anthocyanins from Bauhinia flowers using ultrasound-assisted eutectic solvent as described in claim 1, characterized in that: The elution solvent was a 90% ethanol solution with pH=1 adjusted by concentrated hydrochloric acid.

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