Method for extracting and purifying 1-deoxynojirimycin from black mulberry leaf tablets

Abstract

The invention provides a method for extracting and purifying 1-deoxynojirimycin from black mulberry leaves, and belongs to the technical field of alkaloid extraction and purification. The method for extracting and purifying 1-deoxynojirimycin from black mulberry leaves comprises the following steps: sequentially soaking and decocting black mulberry leaves with water to obtain a black mulberry leaf extracting solution containing 1-deoxynojirimycin, and concentrating the black mulberry leaf extracting solution to obtain a black mulberry leaf extract; and mixing the black mulberry leaf extract with an acid solution, loading the obtained black mulberry leaf extract solution on a cation exchange resin adsorption column, and eluting by using a triethylamine aqueous solution as an eluent to obtain the 1-deoxynojirimycin. The method provided by the invention is simple and efficient, the purity of the obtained 1-deoxynojirimycin is high, the yield of the 1-deoxynojirimycin can be improved, and the recovery rate is high.

Description

Technical Field

[0001] The invention belongs to the technical field of alkaloid extraction and purification, and particularly relates to a method for extracting and purifying 1-deoxynojirimycin from black mulberry leaves. Background Art

[0002] 1-Deoxynojirimycin (1-DNJ) is an alkaloid extracted from the leaves and root bark of Morus plants. It is an effective α-glucosidase inhibitor and has a significant hypoglycemic effect. After entering the human body, 1-deoxynojirimycin can inhibit the decomposition of starch and sugar by sucrase, maltase, α-glucosidase, and α-amylase in the human body, thereby blocking the body's absorption of sugar, inhibiting the rise of blood sugar, and achieving the effect of preventing and treating diabetes.

[0003] The content of 1-deoxynojirimycin in black mulberry leaves is significantly higher than that in other mulberry plants, and can be used as a raw material for extracting 1-deoxynojirimycin. At present, the commonly used method for separating and purifying 1-deoxynojirimycin is: extraction with ethyl acetate or dichloromethane, and then separation by silica gel column chromatography, but the recovery rate of 1-deoxynojirimycin obtained in this way is low. Summary of the invention

[0004] The object of the present invention is to provide a method for extracting and purifying 1-deoxynojirimycin from black mulberry leaves. The method provided by the present invention is simple and efficient, and can improve the yield of 1-deoxynojirimycin.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for extracting and purifying 1-deoxynojirimycin from black mulberry leaves, comprising the following steps:

[0007] The black mulberry leaf is sequentially soaked and boiled in water to obtain a black mulberry leaf extract containing 1-deoxynojirimycin;

[0008] Concentrating the black mulberry leaf extract to obtain a black mulberry leaf extract;

[0009] The black mulberry leaf extract is mixed with an acid solution, the obtained black mulberry leaf extract solution is loaded onto a cation exchange resin adsorption column, and eluted with a triethylamine aqueous solution as an eluent to obtain 1-deoxynojirimycin.

[0010] Preferably, the soaking temperature is 20-35° C. and the soaking time is 20-30 min.

[0011] Preferably, the decoction extraction includes a first extraction, a second extraction and a third extraction performed in sequence; the solid-liquid ratio of the first extraction is 1g:15-17mL, the solid-liquid ratio of the second extraction is 1g:10-13mL, and the solid-liquid ratio of the third extraction is 1g:10-13mL.

[0012] Preferably, the temperatures of the first extraction, the second extraction and the third extraction are independently 96-98° C., and the times are independently 1.3-1.6 h.

[0013] Preferably, the acid solution is hydrochloric acid or acetic acid aqueous solution; the mass fraction of the acid solution is 10% to 15%; the solid-liquid ratio of the black mulberry leaf extract to the acid solution is 1g:10 to 12mL.

[0014] Preferably, the cation exchange resin in the cation exchange resin adsorption column is 001×7 strong acid styrene cation exchange resin;

[0015] Preferably, the mass fraction of the triethylamine aqueous solution is 2% to 4%.

[0016] Preferably, before the soaking, the method further comprises grinding the black mulberry leaves to obtain a ground material; the particle size of the ground material is ≤100 mesh.

[0017] Preferably, the cation exchange resin is sequentially subjected to a first acid treatment, an alkali treatment and a second acid treatment before use; the reagents used in the first acid treatment and the second acid treatment are hydrochloric acid, and the reagent used in the alkali treatment is a sodium hydroxide aqueous solution.

[0018] The invention provides a method for extracting and purifying 1-deoxynojirimycin from black mulberry leaves, comprising the following steps: soaking and decocting black mulberry leaves in water in sequence to obtain a black mulberry leaf extract containing 1-deoxynojirimycin; concentrating the black mulberry leaf extract to obtain a black mulberry leaf extract; mixing the black mulberry leaf extract with an acid solution, loading the obtained black mulberry leaf extract solution onto a cation exchange resin adsorption column, and eluting with a triethylamine aqueous solution as an eluent to obtain 1-deoxynojirimycin. The invention uses water as a solvent and adopts a water decoction method to extract 1-deoxynojirimycin from black mulberry leaves, which is simple and efficient, has high safety and good solubility, and significantly improves the yield of 1-deoxynojirimycin. At the same time, the acid solution can dissolve the 1-deoxynojirimycin in the black mulberry leaf extract, so that the 1-deoxynojirimycin exists in the obtained black mulberry leaf extract solution in the form of ions, and because 1-deoxynojirimycin is a positively charged alkaloid, it can exchange with the cation exchange resin, and the cation exchange resin separates the positively charged 1-deoxynojirimycin ions from the negatively charged or neutral impurities to complete the purification of 1-deoxynojirimycin. The method provided by the present invention is simple to operate, and the 1-deoxynojirimycin obtained thereby has high purity and high recovery rate. The embodiment shows that according to the method provided by the present invention, 1-deoxynojirimycin in black mulberry leaves is extracted, and the yield of 1-deoxynojirimycin can reach 0.095% to 0.098%, and compared with other types of purification resins, the cation exchange resin used in the present invention has the highest recovery rate for 1-deoxynojirimycin. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0020] Figure 1 LC-MS / MS chromatograms of the 1-DNJ compound reference substance and the eluate obtained in Example 1. DETAILED DESCRIPTION

[0021] The present invention provides a method for extracting and purifying 1-deoxynojirimycin from black mulberry leaves, comprising the following steps:

[0022] The black mulberry leaf is sequentially soaked and boiled in water to obtain a black mulberry leaf extract containing 1-deoxynojirimycin;

[0023] Concentrating the black mulberry leaf extract to obtain a black mulberry leaf extract;

[0024] The black mulberry leaf extract is mixed with an acid solution, the obtained black mulberry leaf extract solution is loaded onto a cation exchange resin adsorption column, and eluted with a triethylamine aqueous solution as an eluent to obtain 1-deoxynojirimycin.

[0025] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known to those skilled in the art or are prepared by methods well known to those skilled in the art.

[0026] The invention adopts water to soak and decoct black mulberry leaves in sequence to extract black mulberry leaves, so as to obtain a black mulberry leaf extract containing 1-deoxynojirimycin.

[0027] In the present invention, the soaking step preferably includes grinding the black mulberry leaves to obtain a grinding material. In the present invention, the grinding temperature is preferably 20-35°C, more preferably 25-30°C. The auxiliary agent used for the grinding in the present invention is preferably quartz sand, and the particle size of the quartz sand is preferably 40-60 mesh, more preferably 50-60 mesh. In the present invention, the ground material is preferably passed through a 100 mesh sieve, and the undersize is collected to obtain a grinding material. The particle size of the grinding material in the present invention is preferably ≤100 mesh.

[0028] After obtaining the milled material, the present invention uses water to soak and decoct the milled material in sequence to obtain a black mulberry leaf extract containing 1-deoxynojirimycin. In the present invention, the soaking temperature is preferably 20-35°C, more preferably 25-30°C; the time is preferably 20-30min, more preferably 25-30min. In the present invention, the decoction extraction preferably includes a first extraction, a second extraction and a third extraction performed in sequence. The first extraction of the present invention is preferably carried out under water bath conditions; the material-liquid ratio of the first extraction is preferably 1g:15-17mL, specifically 1g:15mL, 1g:16mL or 1g:17mL; the temperature is preferably 96-98°C, specifically 96°C, 97°C or 98°C; the time is preferably 1.3-1.6h, specifically 1.3h, 1.4h, 1.5h or 1.6h. The second extraction of the present invention is preferably carried out under water bath conditions; the solid-liquid ratio of the second extraction is preferably 1g:10-13mL, specifically 1g:10mL, 1g:11mL, 1g:12mL or 1g:13mL; the temperature is preferably 96-98°C, specifically 96°C, 97°C or 98°C; the time is preferably 1.3-1.6h, specifically 1.3h, 1.4h, 1.5h or 1.6h. The third extraction of the present invention is preferably carried out under water bath conditions; the solid-liquid ratio of the third extraction is preferably 1g:10-13mL, specifically 1g:10mL, 1g:11mL, 1g:12 or 1g:13mL; the temperature is preferably 96-98°C, specifically 96°C, 97°C or 98°C; the time is preferably 1.3-1.6h, specifically 1.3h, 1.4h, 1.5h or 1.6h.

[0029] After obtaining the black mulberry leaf extract containing 1-deoxynojirimycin, the invention concentrates the black mulberry leaf extract to obtain a black mulberry leaf extract.

[0030] The present invention preferably includes solid-liquid separation of the black mulberry leaf extract and collecting liquid materials before concentration. In the present invention, the solid-liquid separation is preferably filtration. The concentration of the present invention is preferably dry concentration; the dry concentration is preferably carried out under vacuum conditions; the feed temperature of the dry concentration is preferably 38 to 40°C, specifically 38°C, 39°C or 40°C; the feed rate is preferably 12 to 15 mL·min -1 , specifically 12 mL·min -1 、13mL·min -1 、14mL·min -1 or 15 mL min -1 ; The conveyor belt speed is preferably 4 to 5 mm·min -1 , specifically 4mm·min -1 or 5mm·min-1 The drying and concentration time is preferably 20 to 30 minutes, more preferably 25 to 30 minutes.

[0031] After obtaining the black mulberry leaf extract, the invention mixes the black mulberry leaf extract with an acid solution, loads the obtained black mulberry leaf extract solution onto a cation exchange resin adsorption column, and elutes the column using a triethylamine aqueous solution as an eluent to obtain 1-deoxynojirimycin.

[0032] The present invention mixes the black mulberry leaf extract with an acid solution to obtain a black mulberry leaf extract solution. In the present invention, the acid solution is preferably a hydrochloric acid or acetic acid aqueous solution; the mass fraction of the acid solution is preferably 10% to 15%, more preferably 10% to 12%. The solid-liquid ratio of the black mulberry leaf extract to the acid solution is preferably 1g:10 to 12mL, more preferably 1g:10mL.

[0033] In the present invention, the cation exchange resin in the cation exchange resin adsorption column is preferably a 001×7 strong acid styrene cation exchange resin. In the present invention, the cation exchange resin is preferably subjected to a first acid treatment, an alkali treatment and a second acid treatment in sequence before use. Before the first acid treatment, the present invention preferably rinses the cation exchange resin with water, and soaks the rinsed cation exchange resin in water overnight to obtain an expanded resin. After obtaining the expanded resin, the present invention preferably subjects the expanded resin to a first acid treatment. In the present invention, the reagent used for the first acid treatment is preferably hydrochloric acid; the mass fraction of the hydrochloric acid is preferably 3% to 5%, more preferably 4%; the volume ratio of the cation exchange resin to the hydrochloric acid is preferably 1:1 to 3, more preferably 1:2; the time of the first acid treatment is preferably 3 to 5h, more preferably 3h. After the first acid treatment, the present invention preferably washes the obtained first acid-treated resin with water until the pH value of the water washing liquid is 4, and then subjects the first acid-treated resin to an alkali treatment. In the present invention, the reagent used for the alkali treatment is preferably an aqueous sodium hydroxide solution; the mass fraction of the aqueous sodium hydroxide solution is preferably 2% to 4%, specifically 2%, 3% or 4%; the time of the alkali treatment is preferably 3 to 5 hours, more preferably 3 hours. After the alkali treatment, the present invention preferably washes the obtained alkali-treated resin with water until the pH value of the water washing liquid is 7.35 to 7.45, and then performs a second acid treatment on the alkali-treated resin. In the present invention, the reagent used for the second acid treatment is preferably hydrochloric acid; the mass fraction of the hydrochloric acid is preferably 3% to 5%, preferably 4%; the time of the second acid treatment is preferably 2 to 3 hours, more preferably 3 hours. After the second acid treatment, the present invention preferably washes the obtained second acid-treated resin with water until the pH value of the water washing liquid is 4, and then uses a wet column to obtain a cation exchange resin adsorption column.

[0034] After obtaining the black mulberry leaf extract solution and the cation exchange resin adsorption column, the present invention loads the black mulberry leaf extract solution onto the cation exchange resin adsorption column, elutes with triethylamine aqueous solution as an eluent, and collects the eluent, wherein the eluent contains 1-deoxynojirimycin. In the present invention, the flow rate of the black mulberry leaf extract solution is preferably 10 to 15 mL / min, more preferably 10 to 12 mL / min. After loading the black mulberry leaf extract solution onto the cation exchange resin adsorption column, the present invention preferably washes the cation exchange resin adsorption column with water until the pH value is neutral. After the water washing, the present invention preferably elutes with triethylamine aqueous solution as an eluent. In the present invention, the mass fraction of the triethylamine aqueous solution is preferably 2% to 4%, specifically 2%, 3% or 4%. The amount of the triethylamine aqueous solution used in the present invention is preferably 8 to 12 column volumes, more preferably 10 column volumes.

[0035] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The particle size of the quartz sand used in the embodiment is 60 mesh;

[0037] The room temperature conditions in the examples are all 25-30°C;

[0038] The instrument used for vacuum drying is a Shanghai Yiheng vacuum drying oven, model 133PA, and the vector temperature of the heating system is (105°C, 100°C).

[0039] Example 1

[0040] 10.00 g of black mulberry leaves (wherein the mass fraction of 1-DNJ is 0.341%) were placed in a mortar, quartz sand was added, and the ground black mulberry leaves were ground at room temperature. The ground black mulberry leaves were sieved through a 100-mesh sieve to obtain a ground material.

[0041] The milled material was placed in a round-bottom flask and soaked in deionized water at room temperature for 30 min.

[0042] After the soaking, the round-bottom flask containing the ground material and deionized water was placed in a water bath, and the extraction was continuously boiled and extracted three times under water bath conditions. The material-liquid ratios of the three decoctions were 1g:17mL, 1g:11mL and 1g:11mL, respectively. The three decoctions and extractions were all 1.6h long, and the water bath temperature was 96°C. After the third decoction, a total of 180mL of black mulberry leaf extract containing 1-deoxynojirimycin (1-DNJ) was obtained.

[0043] The black mulberry leaf extract was filtered through three layers of qualitative filter paper to remove the residue, and the obtained extract was vacuum dried and concentrated under the following conditions: the feed temperature was 40°C, the feed rate was 15 mL·min -1 , conveyor belt speed is 4mm·min -1 , time is 25min; after vacuum drying and concentration, black mulberry leaf extract is obtained.

[0044] Place the cation exchange resin (001×7 strong acid styrene cation exchange resin) in a clean beaker and rinse with clean water until the washing liquid is clear. Soak the cation exchange resin in water overnight to fully expand it; then soak the cation exchange resin in 4wt% hydrochloric acid, which is twice the volume of the cation exchange resin, for 3 hours, and stir it from time to time; then wash the cation exchange resin with water until the pH value of the washing liquid is 4, and then soak it in 4wt% sodium hydroxide aqueous solution for 3 hours; then wash it with water until the washing liquid is slightly alkaline (pH value is 7.35-7.45), and soak it in 4wt% hydrochloric acid again for 3 hours, at which time the cation exchange resin is in hydrogen form; finally wash it with water until the pH value of the washing liquid is 4, use wet column packing to obtain the pretreated cation exchange resin adsorption column for standby use.

[0045] Accurately weigh 1.000 g of black mulberry leaf extract in a beaker, add 10 mL of 10 wt% hydrochloric acid and stir to dissolve, to obtain a black mulberry leaf extract solution; load the black mulberry leaf extract solution onto a pretreated cation exchange resin adsorption column at a flow rate of 10 mL / min, wash with water until the pH value is neutral; then elute with 3 wt% triethylamine aqueous solution for 10 column volumes to obtain an eluate.

[0046] Test Example 1

[0047] 20 μL of the eluate obtained in Example 1 was diluted to 2 mL with deionized water, and the resulting mixed solution was filtered through a 0.45 μm microporous filter membrane (to prevent bubbles and impurities in the liquid on the machine) to obtain a test solution.

[0048] The test solution was subjected to liquid chromatography-tandem mass spectrometry (LC-MS / MS) detection, and the results were as follows: Figure 1 As shown, Figure 1 (a) is the LC-MS / MS chromatogram of the 1-DNJ compound reference substance (1.08 min), and (b) is the LC-MS / MS chromatogram of the eluate obtained in Example 1. Figure 1 It can be seen that the eluate obtained in Example 1 contains 1-DNJ.

[0049] The results showed that the 1-DNJ content in the black mulberry leaf extract obtained in Example 1 was 4.25 mg / g (here g is the weight of the black mulberry leaf), and the 1-DNJ content in the eluate was 78.07 mg / g (here g is the weight of the black mulberry leaf extract). The 1-DNJ content in the eluate was 18.37 times higher than that in the black mulberry leaf extract.

[0050] Comparative Example 1

[0051] A group of samples (10.00g black mulberry leaf, wherein the mass fraction of 1-DNJ is 0.341%) was mixed with 100mL of 90% ethanol aqueous solution by volume, and the obtained liquid was placed on an electric heating mantle, and refluxed and extracted twice continuously at 80°C, each time for 2h. After the second ethanol aqueous solution extraction, the extract (recorded as #1 extract) and the residue (recorded as #1 residue) were collected respectively. The #1 residue was mixed with 100mL of water, and the obtained liquid was placed on an electric heating mantle, and refluxed and extracted twice continuously at 80°C, each time for 2h. After the second water extraction, the extract (recorded as #2 extract) was collected. The #1 extract and the #2 extract were respectively decompressed to recover the solvent, and then the solvent was evaporated, and the remaining liquid was concentrated to obtain #1 black mulberry leaf extract (ethanol extract) and #2 black mulberry leaf extract (water extract). Each group of samples was extracted three times in parallel.

[0052] Weigh 0.1000g #1 black mulberry leaf extract and 0.1000g #2 black mulberry leaf extract respectively, add 3mL of methanol to the #1 black mulberry leaf extract to dissolve it, and obtain #1 solution; add 3mL of 80% methanol aqueous solution to the #2 black mulberry leaf extract to dissolve it, and obtain #2 solution; combine the #1 solution and the #2 solution, centrifuge at 10000r / min for 5min, and collect the supernatant.

[0053] Comparative test example 1

[0054] 50 μL of the supernatant obtained in Comparative Example 1 was taken with a pipette, and the volume was made up to 10 mL with methanol. The obtained mixed solution was filtered through a 0.22 μm filter membrane to obtain a test solution.

[0055] The results showed that the 1-DNJ content in the black mulberry leaf extract obtained by the ethanol heating reflux method was 1.89 mg / g (here g is the mass of the black mulberry leaf), which was much lower than the 1-DNJ content obtained by the water decoction extraction-cation exchange resin purification method in Example 1.

[0056] Comparative Example 2

[0057] 10.00 g of black mulberry leaves (wherein the mass fraction of 1-DNJ is 0.341%) were placed in a mortar, quartz sand was added, and the ground black mulberry leaves were ground at room temperature. The ground black mulberry leaves were sieved through a 100-mesh sieve to obtain a ground material.

[0058] The milled material was placed in a round-bottom flask and soaked in deionized water at room temperature for 30 min.

[0059] After the soaking, the round-bottom flask containing the ground material and deionized water was placed in a water bath, and the extraction was continuously boiled and extracted three times under water bath conditions. The material-liquid ratios of the three decoctions were 1g:17mL, 1g:11mL and 1g:11mL, respectively. The three decoctions and extractions were all 1.6h long, and the water bath temperature was 96°C. After the third decoction, a total of 180mL of black mulberry leaf extract containing 1-deoxynojirimycin (1-DNJ) was obtained.

[0060] The black mulberry leaf extract was filtered through three layers of qualitative filter paper to remove the residue, and the obtained extract was vacuum dried and concentrated under the following conditions: the feed temperature was 40°C, the feed rate was 15 mL·min -1 , conveyor belt speed is 4mm·min -1 , time is 25min; after vacuum drying and concentration, black mulberry leaf extract is obtained.

[0061] The polyamide resin of 30-60 mesh is soaked in an ethanol aqueous solution with a volume fraction of 95%, and is continuously stirred to remove bubbles and then loaded into a chromatography column; then eluted with 95% ethanol with a volume fraction of 4 times the volume of the polyamide resin until the eluent is transparent and there is no residue after evaporation; then eluted with a NaOH aqueous solution with a mass fraction of 5% with a volume fraction of 2 times the volume of the polyamide resin, water with a volume fraction of 1 times the volume of the polyamide resin, and an acetic acid aqueous solution with a mass fraction of 10% with a volume fraction of 2 times the volume of the polyamide resin; finally, eluted with water until the pH value of the water washing solution is neutral, and a wet column is used to obtain a pretreated polyamide resin column (50 mL) for standby use.

[0062] Wash 3 volumes of polyamide resin column with hydrochloric acid with pH value of 3. Accurately weigh 10.00g of black mulberry leaf extract, add 100mL of water to dissolve, adjust the flow rate to 10mL / min and load it on the polyamide resin column. Then slowly wash with 4 volumes of hydrochloric acid with pH value of 3 of polyamide resin column, and collect the eluate.

[0063] Comparative test example 2

[0064] 40 μL of the eluate obtained in Comparative Example 2 was taken, and the volume was fixed to 2 mL with methanol. The obtained mixed solution was filtered through a 0.22 μm microporous filter membrane to obtain a test solution.

[0065] The results showed that the 1-DNJ content in the eluate obtained by the water decoction extraction and then purification with polyamide adsorption resin was 54.63 mg / g (here g is the mass of black mulberry leaf extract), which was lower than the 1-DNJ content obtained by water decoction extraction-cation exchange resin purification in Example 1.

[0066] Therefore, the method provided by the present invention is simple and efficient, and the 1-deoxynojirimycin obtained thereby has high purity, and can improve the yield of 1-deoxynojirimycin, and has a high recovery rate.

[0067] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for extracting and purifying 1-deoxynojirimycin from black mulberry leaves, comprising the following steps: The black mulberry leaf is sequentially soaked and boiled in water to obtain a black mulberry leaf extract containing 1-deoxynojirimycin; Concentrating the black mulberry leaf extract to obtain a black mulberry leaf extract; The black mulberry leaf extract is mixed with an acid solution, the obtained black mulberry leaf extract solution is loaded onto a cation exchange resin adsorption column, and eluted with a triethylamine aqueous solution as an eluent to obtain 1-deoxynojirimycin.

2. The method according to claim 1, characterized in that The soaking temperature is 20-35° C. and the soaking time is 20-30 minutes.

3. The method according to claim 2, characterized in that The decoction extraction includes a first extraction, a second extraction and a third extraction performed in sequence; the solid-liquid ratio of the first extraction is 1g:15-17mL, the solid-liquid ratio of the second extraction is 1g:10-13mL, and the solid-liquid ratio of the third extraction is 1g:10-13mL.

4. The method according to claim 3, characterized in that The temperatures of the first extraction, the second extraction and the third extraction are independently 96-98° C., and the times are independently 1.3-1.6 h.

5. The method according to claim 1, characterized in that The acid solution is hydrochloric acid or acetic acid aqueous solution; the mass fraction of the acid solution is 10% to 15%; the solid-liquid ratio of the black mulberry leaf extract to the acid solution is 1g:10 to 12mL.

6. The method according to claim 1, characterized in that The cation exchange resin in the cation exchange resin adsorption column is 001×7 strong acid styrene cation exchange resin.

7. The method according to claim 1, characterized in that The mass fraction of the triethylamine aqueous solution is 2% to 4%.

8. The method according to claim 1 or 2, characterized in that: The method comprises grinding the black mulberry leaves before soaking to obtain a grinding material; the particle size of the grinding material is ≤100 meshes.

9. The method according to claim 6, characterized in that The cation exchange resin is sequentially subjected to a first acid treatment, an alkali treatment and a second acid treatment before use; the reagents used in the first acid treatment and the second acid treatment are hydrochloric acid, and the reagent used in the alkali treatment is a sodium hydroxide aqueous solution.

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