Method for extracting stachyose and catalpol from fresh rehmannia

Abstract

The invention belongs to the technical field of sugar alcohol preparation, and relates to a method for extracting stachyose and catalpol from fresh rehmannia glutinosa, which comprises the following steps: selecting fresh rehmannia glutinosa, cleaning, peeling, cutting into small pieces, putting the small pieces of fresh rehmannia glutinosa into a stirrer, stirring, and homogenizing to obtain slurry to be extracted; and adding distilled water into the to-be-extracted slurry according to a solid-liquid ratio of 1: 10, putting the to-be-extracted slurry into a constant-temperature oscillation water bath for dissolving treatment at the rotating speed of 100 rpm, the temperature of 60 DEG C and the time of 60 minutes, and carrying out suction filtration treatment to respectively obtain a stachyose extracting solution and radix rehmanniae residues. And extracting stachyose from the stachyose extracting solution, and extracting catalpol from catalpol residues. The stachyose and the catalpol in the fresh rehmannia are extracted by adopting a water extraction method, the use amount of an organic solvent is effectively reduced, the stachyose and the catalpol are extracted by adopting heating oscillation, the contact area of feed liquid can be increased, the extraction yield is improved, the stachyose is purified by adopting the activated carbon, and the catalpol is purified by adopting the macroporous resin and the silica gel, so that the extraction efficiency is improved. The purity of stachyose and catalpol is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sugar alcohol preparation, and particularly relates to a method for extracting stachyose and catalpol from fresh rehmannia root. Background Art

[0002] Rehmannia glutinosa is a commonly used tonic Chinese medicine. It is the fresh rhizome or dried root of Rehmannia glutinosa Libosch, a plant of the Scrophulariaceae family. It is widely used in clinical practice and has certain effects on immunity, blood, endocrine, cardiovascular and cerebrovascular, nervous system, antibacterial and anti-inflammatory aspects. Modern pharmacological experiments have found that its main active components are rehmannia sugars and iridoid glycosides. Stachyose is one of the main effective active ingredients of Rehmannia glutinosa. It has the effects of moistening the intestines and relieving constipation, improving the intestinal microenvironment, proliferating bifidobacteria, regulating the balance of intestinal microecology, improving the body's immunity, and regulating endocrine. It is called "super bifidobacterial factor" and "microecological regulator". Catalpol is the iridoid glycoside with the highest content in Rehmannia glutinosa and belongs to the epoxy ether monoterpenoid compound. Stachyose and catalpol are both representative physiologically active substances in Rehmannia glutinosa and have good market prospects. However, as a functional oligosaccharide, stachyose has always been a problem for sugar chemists due to the complexity of its own composition and connection, as well as the difficulty in detection. Therefore, it is difficult to select a suitable method to separate the collected oligosaccharide mixture. Although catalpol has the highest content among iridoid glycosides, its chemical stability is poor, so it is also very difficult to prepare a large amount of catalpol monomer components with a purity of more than 90%.

[0003] At present, the extraction of stachyose from Rehmannia glutinosa is mainly done by water extraction. Water extraction also extracts some water-soluble impurities, such as protein, linalool, linalool, pigment, etc., which makes the water extract very dark in color and must be decolorized. Catalpol is extracted from natural plants and purified by HPLC. There are no reports on the artificial synthesis of catalpol, nor is it commercialized. Only a small amount of standard products (mg) are sold and are expensive. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for extracting stachyose and catalpol from fresh rehmannia root, wherein a water extraction method is adopted to extract stachyose and catalpol from fresh rehmannia root, thereby effectively reducing the usage of organic solvents, and heating and shaking are adopted to extract stachyose and catalpol, thereby increasing the contact area between feed and liquid and improving the extraction yield, and activated carbon is adopted to purify stachyose, and macroporous resin and silica gel are adopted to purify catalpol, thereby effectively improving the purity of stachyose and catalpol.

[0005] The present invention is achieved by providing a method for extracting stachyose and catalpol from fresh Rehmannia root, comprising the following steps: Step 1: Select fresh Rehmannia root, wash it, peel it and cut it into small pieces, put the small pieces of Rehmannia root into a blender, and blend it to obtain a slurry to be extracted; Step 2: Add distilled water to the slurry to be extracted, with a solid-liquid ratio of 1:10, and place it in a constant temperature oscillating water bath for dissolution treatment. The speed of the constant temperature water bath is 100 rpm, the temperature is 60° C., and the time is 60 min. Filter and obtain stachyose extract and Rehmannia glutinosa residue respectively; Step 3, subjecting the stachyose extract obtained in step 2 to a first evaporation concentration process to obtain a stachyose concentrate; Step 4: Add anhydrous ethanol to the stachyose concentrate until the ethanol concentration of the solution is 85%, and stand at 4°C for 24 hours to remove the supernatant to obtain a stachyose crystal product. The crystal product is volatilized and placed in a ventilated place until there is no alcohol smell, thereby obtaining a stachyose crude product; Step 5, re-dissolving the crude stachyose product with distilled water, decolorizing and purifying it with activated carbon, removing the activated carbon by centrifugation, and subjecting the centrifugal filtrate to a first vacuum freeze-drying treatment to obtain a stachyose powder product; Step 6: Add 60% ethanol to the Rehmannia root residue obtained in step 2, with a solid-liquid ratio of 1:5, and place it in a constant temperature oscillating water bath for dissolution treatment. The speed of the constant temperature water bath is 100 rpm, the temperature is 60° C., and the time is 120 min. Then, filter and obtain the catalpol extract, and remove the filter residue; Step 7, subjecting the catalpol extract to a second evaporation concentration treatment until there is no alcohol smell, to obtain a catalpol concentrate, and subjecting the catalpol concentrate to a second vacuum freeze-drying treatment, to obtain a catalpol crude extract powder; Step 8, re-dissolve the catalpol crude powder with distilled water, take 40 mL and add it to a chromatography column filled with H103 resin, the resin filling does not exceed 2 / 3 of the column length, fully adsorb for 2 hours, the flow rate is 2 mL / min; elute with water until the color is light, then elute with 10% ethanol until the color is light, and then elute with 20% ethanol; combine the fractions containing catalpol, and perform vacuum freeze-drying on the fractions containing catalpol to obtain a crude catalpol powder; Step nine, add methanol to dissolve the crude catalpol powder, add it to the silica gel column with a plastic dropper, use a mixed solution of ethyl acetate: methanol = 3:1 by volume as the eluent, perform isocratic elution, the flow rate is 2.0 mL / min, and the collected effluent is subjected to rotary evaporation to remove the solvent, the sediment is then dissolved with deionized water, and the membrane filtrate is obtained by passing through a 0.22 μm membrane, and the membrane filtrate is subjected to vacuum freeze-drying to obtain a finished catalpol powder.

[0006] Furthermore, in step three, the first evaporation concentration treatment refers to evaporating the stachyose extract at 55° C. and -0.1 MPa for 2 hours.

[0007] Furthermore, in step five, the decolorization and purification using activated carbon refers to mixing the reconstituted solution with 0.32 g / 100 mL of activated carbon, and decolorizing and purifying the solution at a temperature of 40° C. and a time of 1.5 h.

[0008] Furthermore, in step five, the first vacuum freeze-drying treatment refers to freeze-drying the centrifugal filtrate at a vacuum degree of about 10 Pa and a temperature of -45°C for 48 hours.

[0009] Furthermore, in step seven, the second evaporation concentration treatment refers to evaporating the catalpol extract at 55° C. and −0.1 MPa.

[0010] Furthermore, in step seven, the second vacuum freeze-drying treatment refers to freeze-drying the catalpol concentrate at a vacuum degree of about 10 Pa and a temperature of -45°C for 48 hours.

[0011] Compared with the prior art, the method for extracting stachyose and catalpol from fresh Rehmannia root of the present invention has the following characteristics: 1. Environmental protection: The method of the present invention does not require the use of a large amount of organic solvents, which greatly reduces the pollution to the environment and is in line with the current development trend of green chemistry.

[0012] 2. High efficiency: The method of the present invention can obtain high-yield and high-purity stachyose and catalpol, especially the stachyose preparation process, which only requires water extraction-alcohol crystallization-decolorization to obtain a sample with a purity of more than 90%, thereby improving the utilization rate of resources.

[0013] 3. Convenience: The preparation method of stachyose of the present invention is simple to operate, short in time, low in cost, conducive to large-scale production, and meets the needs of industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the effect of different extraction solvents on the extraction yield of stachyose; Figure 2 Schematic diagram of the purity and yield of stachyose powder at each stage; Figure 3 Schematic diagram of the effect of different extraction methods on catalpol extraction yield; Figure 4 Schematic diagram of the powder purity of catalpol at each stage. DETAILED DESCRIPTION

[0015] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0016] A preferred embodiment of the method for extracting stachyose and catalpol from fresh Rehmannia glutinosa of the present invention comprises the following steps: Step 1: Select fresh Rehmannia root, wash it, peel it and cut it into small pieces. Put the small pieces of Rehmannia root into a blender and blend it to obtain the slurry to be extracted.

[0017] Step 2: Add distilled water to the slurry to be extracted, with a solid-liquid ratio of 1:10, and put it into a constant temperature oscillating water bath for dissolution. The speed of the constant temperature water bath is 100 rpm, the temperature is 60°C, and the time is 60 min. Filter and obtain stachyose extract and Rehmannia glutinosa residue respectively.

[0018] Step 3: subjecting the stachyose extract obtained in step 2 to a first evaporation concentration treatment to obtain a stachyose concentrate.

[0019] Step 4: Add anhydrous ethanol to the stachyose concentrate until the ethanol concentration of the solution is 85%, and stand at 4°C for 24 hours. Remove the supernatant to obtain a crystalline product of stachyose. The crystalline product is volatilized and placed in a ventilated place until there is no alcohol taste, thereby obtaining a crude stachyose product.

[0020] Step 5: re-dissolve the crude stachyose with distilled water, decolorize and purify it with activated carbon, remove the activated carbon by centrifugation, and perform a first vacuum freeze-drying treatment on the centrifugal filtrate to obtain a stachyose powder product.

[0021] Step 6: Add 60% ethanol to the Rehmannia glutinosa residue obtained in step 2 at a solid-liquid ratio of 1:5, and place it in a constant temperature oscillating water bath for dissolution. The speed of the constant temperature water bath is 100 rpm, the temperature is 60°C, and the time is 120 min. Then, filter it to obtain the catalpol extract and remove the filter residue.

[0022] Step 7: subjecting the catalpol extract to a second evaporation concentration treatment until there is no alcohol smell, to obtain a catalpol concentrate (500 mL / 1 h); subjecting the catalpol concentrate to a second vacuum freeze-drying treatment, to obtain a catalpol crude extract powder.

[0023] Step 8. Dissolve the crude catalpol powder with distilled water, take 40 mL and add it to a chromatography column filled with H103 resin. The resin filling should not exceed 2 / 3 of the column length. Fully adsorb for 2 hours at a flow rate of 2 mL / min; elute with water until the color is light, then elute with 10% ethanol until the color is light, collect in sections, collect 500 mL each, and then elute with 20% ethanol; combine the catalpol-containing fractions, and perform vacuum freeze-drying on the catalpol-containing fractions to obtain a crude catalpol powder.

[0024] Step nine, add methanol to dissolve the crude catalpol powder, add it to the silica gel column (glass column) with a plastic dropper, use a mixed solution of ethyl acetate: methanol = 3:1 (v / v) as the eluent, perform isocratic elution, the flow rate is 2.0 mL / min, collect the effluent (50 mL / tube), perform rotary evaporation to remove the solvent, dissolve the sediment with deionized water, pass through a 0.22 μm membrane to obtain a membrane filtrate, and perform vacuum freeze-drying on the membrane filtrate to obtain a finished catalpol powder.

[0025] Specifically, in step three, the first evaporation concentration treatment refers to evaporating the stachyose extract at 55° C. and -0.1 MPa for 2 hours.

[0026] Specifically, in step five, the decolorization and purification using activated carbon refers to mixing the reconstituted solution with 0.32 g / 100 mL of activated carbon, and decolorizing and purifying the mixture at a temperature of 40° C. and a time of 1.5 h.

[0027] Specifically, in step five, the first vacuum freeze-drying treatment refers to freeze-drying the centrifugal filtrate at a vacuum degree of about 10 Pa and a temperature of -45°C for 48 hours.

[0028] Specifically, in step seven, the second evaporation concentration treatment refers to evaporating the catalpol extract at 55° C. and −0.1 MPa.

[0029] Specifically, in step seven, the second vacuum freeze-drying treatment refers to freeze-drying the catalpol concentrate at a vacuum degree of about 10 Pa and a temperature of -45°C for 48 hours.

[0030] The method for extracting stachyose and catalpol from fresh Rehmannia root of the present invention is further illustrated by specific examples and comparative examples below.

[0031] Example 1

[0032] The first embodiment of the method for extracting stachyose and catalpol from fresh Rehmannia glutinosa of the present invention comprises the following steps: Step 11: Select 50 g of fresh Rehmannia root, wash it, peel it and cut it into small pieces. Put the small pieces of fresh Rehmannia root into a blender and blend it to obtain a slurry to be extracted.

[0033] Step 12: add 50 g of fresh Rehmannia root slurry to be extracted into distilled water at a solid-liquid ratio of 1:10, and place the mixture into a constant temperature oscillating water bath for dissolution. The speed of the constant temperature water bath is 100 rpm, the temperature is 60° C., and the time is 60 min. Filter the mixture to obtain stachyose extract and Rehmannia root residue, respectively. The Rehmannia root residue is set aside.

[0034] Step 13, filtering the stachyose extract through a 0.22 μm membrane to obtain a first membrane filtrate.

[0035] The average extraction rate of stachyose in the first membrane filtrate of this embodiment was determined by HPLC to be 16.46%, and the average extraction rate was 91.90%.

[0036] Comparative Example 1 The only difference between this comparative example and Example 1 is that 20% ethanol is used instead of distilled water. The other steps and conditions are the same as those of Example 1.

[0037] The average extraction rate of stachyose in the first membrane filtrate of this comparative example was determined by HPLC to be 13.18%, and the average extraction rate was 73.59%.

[0038] Comparative Example 2 The only difference between this comparative example and Example 1 is that 40% ethanol is used instead of distilled water. The other steps and conditions are the same as those of Example 1.

[0039] The average extraction rate of stachyose in the first membrane filtrate of this comparative example was determined by HPLC to be 10.82%, and the average extraction rate was 60.41%.

[0040] Comparative Example 3 The only difference between this comparative example and Example 1 is that 0.26 mol / L hydrochloric acid is used instead of distilled water. The other steps and conditions are the same as those of Example 1.

[0041] The average extraction rate of stachyose in the first membrane filtrate of this comparative example was determined by HPLC to be 9.96%, and the average extraction rate was 55.61%.

[0042] The average extraction yield and average extraction rate of stachyose tested in Example 1 and Comparative Examples 1 to 3 were sorted out as follows: Figure 1 The comparison chart shown shows the effect of different extraction solvents on the extraction yield of stachyose. Figure 1 It can be clearly seen that compared with Comparative Examples 1 to 3, the average extraction yield and average extraction rate of stachyose obtained by the extraction solvent distilled water and method of Example 1 are the highest, and the effect is the best.

[0043] Among them, the average extraction rate and average extraction rate of stachyose were calculated based on the average of three sets of parallel experimental data on stachyose extraction rate and stachyose extraction yield.

[0044] The extraction rate (%) and yield (%) of stachyose were calculated by the following formula:

[0045] In formulas (1) and (2), Extracted stachyose content (g / 100g): The stachyose content of the sample detected by HPLC, Total stachyose content (g / 100g): total stachyose content in the sample (total mass detected by repeated extraction), Mass of Rehmannia powder (g): mass of raw material powder used to extract stachyose.

[0046] Example 2

[0047] A second embodiment of the method for extracting stachyose and catalpol from fresh Rehmannia glutinosa of the present invention comprises the following steps: Step 21: subject the stachyose extract obtained in step 12 of Example 1 to a first evaporation concentration treatment, evaporating for 2 hours at 55° C. and −0.1 MPa to obtain a stachyose concentrate.

[0048] Step 22, subjecting the stachyose concentrate to alcohol crystallization, adding anhydrous ethanol until the ethanol concentration of the solution is 85%, standing for crystallization at 4°C for 24 hours, removing the supernatant to obtain a stachyose crystal product, and placing the crystal product in a ventilated place for volatilization until there is no alcohol smell, thereby obtaining a crude stachyose product.

[0049] Step 23: In order to remove some pigments and impurities in the crude stachyose, the crude stachyose obtained in step 22 is further processed and optimized, and activated carbon is added for decolorization and purification. The crude stachyose is redissolved in distilled water and decolorized and purified using activated carbon. Under the conditions of 0.32 g / 100 mL of activated carbon, 40° C., and 1.5 h, the decolorization rate of activated carbon is more than 90%.

[0050] Step 24, centrifugation to remove the activated carbon, the centrifugal filtrate is subjected to a first vacuum freeze-drying treatment, at a vacuum degree of about 10 Pa, a temperature of -45°C, and a freeze-drying time of 48 hours to obtain a stachyose powder product.

[0051] The stachyose extract obtained in step 12 of Example 1 and the stachyose crude product obtained in step 22 are subjected to vacuum freeze-drying treatment according to the method of step 24 to obtain extract powder and alcohol crystal powder, respectively.

[0052] The purity and yield of the extract powder, alcohol crystal powder and stachyose powder were measured respectively, and the average purity was 49.47%, 74.79% and 92.97%, and the average yield was 16.64%, 11.88% and 9.81%, respectively. Figure 2 Attached Figure 2 The purity and yield of stachyose powder at each stage are shown. Figure 2 It can be seen that after the crude stachyose was decolorized and purified, the purity of the stachyose increased by 18.18% and reached more than 90%, and the purity of the stachyose was significantly improved.

[0053] The stachyose yield formula refers to formula (2) in Example 1, and the stachyose purity % is calculated by the following formula:

[0054] In formula (3), the mass of stachyose (g) is: the mass of stachyose detected by HPLC in the freeze-dried powder, Lyophilized powder mass (g): the mass of powder obtained by freeze drying.

[0055] Example 3

[0056] A third embodiment of the method for extracting stachyose and catalpol from fresh Rehmannia glutinosa of the present invention comprises the following steps: Step 31. Add 60% ethanol to 25 g of the Rehmannia glutinosa residue obtained in step 12 of Example 1, with a solid-liquid ratio of 1:5, and put it into a constant temperature oscillating water bath for dissolution treatment. The speed of the constant temperature water bath is 100 rpm, the temperature is 60°C, and the time is 120 min. Then, filter it to obtain the catalpol extract and remove the filter residue.

[0057] Step 32, filtering the catalpol extract through a 0.22 μm membrane to obtain a second membrane filtrate.

[0058] The average extraction rate of catalpol in the second membrane filtrate of this embodiment was determined by HPLC to be 2.53%, and the average extraction rate was 93.68%.

[0059] Comparative Example 4 The only difference between this comparative example and Example 3 is that the ethanol solution of Rehmannia glutinosa residue is soaked at room temperature for 3 hours to extract catalpol instead of being placed in a constant temperature oscillating water bath for dissolution. The other steps and conditions are the same as those in Example 3.

[0060] The average extraction rate of catalpol in the second membrane filtrate of this comparative example was determined by HPLC to be 1.80%, and the average extraction rate was 66.91%.

[0061] Comparative Example 5 The only difference between this comparative example and Example 3 is that the catalpol is extracted by ultrasonic treatment at room temperature for 30 minutes instead of being dissolved in a constant temperature oscillating water bath. The other steps and conditions are the same as those in Example 3.

[0062] The average extraction rate of catalpol in the second membrane filtrate of this comparative example was determined by HPLC to be 2.58%, and the average extraction rate was 96.04%.

[0063] The average extraction yield and average extraction rate of catalpol tested in Example 3 and Comparative Examples 4-5 were sorted out to obtain the following: Figure 3 The comparison chart shown shows the effect of different extraction methods on the extraction rate of catalpol. Figure 3It can be clearly seen that, compared with Comparative Examples 4-5, the average extraction yield and average extraction rate of catalpol in Example 3 are higher than those in Comparative Example 4, and close to those in Comparative Example 5. It is relatively simple that Example 3 adopts a constant temperature oscillating water bath for dissolution treatment, the operation process is simple, and the equipment cost is relatively low, which is suitable for large-scale or conventional laboratory operations. Comparative Example 5 adopts an ultrasonic treatment device, which usually has a higher cost, and the parameters such as ultrasonic frequency, processing time, temperature, etc. need to be accurately controlled during the operation, requiring a higher technical level, and is not suitable for large-scale industrial production. Therefore, the method of Example 3 is better.

[0064] The average extraction rate of catalpol and the average extraction rate were calculated based on the average values ​​of three sets of parallel experimental data of catalpol extraction rate and catalpol extraction rate, respectively.

[0065] The catalpol extraction rate (%) and extraction yield (%) were calculated by the following formula:

[0066] In formulas (4) and (5), Extracted catalpol content (mg): Catalpol content of the sample detected by HPLC, Total catalpol content (mg): total catalpol content in the sample (total mass detected by repeated extraction), Mass of Rehmannia glutinosa residue powder (mg): mass of raw material powder used to extract catalpol.

[0067] Example 4

[0068] A fourth embodiment of the method for extracting stachyose and catalpol from fresh Rehmannia glutinosa of the present invention comprises the following steps: Step 41: To meet the needs of industrialization, the catalpol extract is subjected to a second evaporation concentration treatment until there is no alcohol taste, and rotary evaporation and concentration are performed at 60° C. and -0.1 MPa for 1 h / 500 mL to obtain a catalpol concentrate.

[0069] Step 42: subjecting the catalpol concentrate to a second vacuum freeze-drying treatment at a vacuum degree of about 10 Pa, a temperature of -45° C., and a freeze-drying time of 48 h to obtain a catalpol crude powder.

[0070] Step 43, re-dissolve the catalpol crude powder with distilled water, take 40 mL of the re-solution and add it to a chromatography column filled with H103 perforated resin, the resin filling does not exceed 2 / 3 of the column length, fully adsorb for 2 hours, and the flow rate is 2 mL / min. Elute with water until the color is light, then elute with 10% ethanol until the color is light, collect in sections, collect 500 mL each, and then elute with 20% ethanol; combine the catalpol-containing fractions, and perform vacuum freeze-drying on the catalpol-containing fractions to obtain a catalpol crude powder.

[0071] Step 44, add methanol to dissolve the crude catalpol powder, add it to the silica gel column with a plastic dropper, use a mixed solution of ethyl acetate: methanol = 3:1 (v / v) as the eluent, perform isocratic elution, and the flow rate is 2.0 mL / min. The collected effluent (50 mL / tube) is subjected to rotary evaporation to remove the solvent, and the sediment is dissolved in deionized water, passed through a 0.22 μm membrane to obtain a membrane filtrate, and the membrane filtrate is subjected to vacuum freeze-drying to obtain a finished catalpol powder.

[0072] The purity of catalpol crude powder, catalpol crude powder and catalpol powder was measured respectively, and the average purity was 7.83%, 41.07% and 78.35% respectively. Figure 4 Attached Figure 4 The purity of catalpol powder at each stage is shown. Figure 4 It can be seen that after the crude catalpol is decolorized and purified and purified by silica gel column, the purity of catalpol is further improved, which meets the expected requirements.

[0073] The purity of catalpol (%) was calculated by the following formula:

[0074] In formula (6), catalpol mass (mg): catalpol mass determined by HPLC in freeze-dried powder, Lyophilized powder mass (mg): the mass of powder obtained by freeze drying.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for extracting stachyose and catalpol from fresh Rehmannia root, characterized in that: The steps include: Step 1: Select fresh Rehmannia root, wash it, peel it and cut it into small pieces, put the small pieces of Rehmannia root into a blender, and blend it to obtain a slurry to be extracted; Step 2: Add distilled water to the slurry to be extracted, with a solid-liquid ratio of 1:10, and place it in a constant temperature oscillating water bath for dissolution treatment. The speed of the constant temperature water bath is 100 rpm, the temperature is 60° C., and the time is 60 min. Filter and obtain stachyose extract and Rehmannia glutinosa residue respectively; Step 3, subjecting the stachyose extract obtained in step 2 to a first evaporation concentration process to obtain a stachyose concentrate; Step 4: Add anhydrous ethanol to the stachyose concentrate until the ethanol concentration of the solution is 85%, and stand at 4°C for 24 hours to remove the supernatant to obtain a stachyose crystal product. The crystal product is volatilized and placed in a ventilated place until there is no alcohol smell, thereby obtaining a stachyose crude product; Step 5, re-dissolving the crude stachyose product with distilled water, decolorizing and purifying it with activated carbon, removing the activated carbon by centrifugation, and subjecting the centrifugal filtrate to a first vacuum freeze-drying treatment to obtain a stachyose powder product; Step 6: Add 60% ethanol to the Rehmannia glutinosa residue obtained in step 2, with a solid-liquid ratio of 1:5, and place it in a constant temperature oscillating water bath for dissolution treatment. The speed of the constant temperature water bath is 100 rpm, the temperature is 60° C., and the time is 120 min. Then, filter and obtain a catalpol extract; Step 7, subjecting the catalpol extract to a second evaporation concentration treatment until there is no alcohol smell, to obtain a catalpol concentrate, and subjecting the catalpol concentrate to a second vacuum freeze-drying treatment, to obtain a catalpol crude extract powder; Step 8, re-dissolve the catalpol crude powder with distilled water, take 40 mL and add it to a chromatography column filled with H103 resin, the resin filling does not exceed 2 / 3 of the column length, fully adsorb for 2 hours, the flow rate is 2 mL / min; elute with water until the color is light, then elute with 10% ethanol until the color is light, and then elute with 20% ethanol; combine the fractions containing catalpol, and perform vacuum freeze-drying on the fractions containing catalpol to obtain a crude catalpol powder; Step nine, add methanol to dissolve the crude catalpol powder, add it to the silica gel column with a plastic dropper, use a mixed solution of ethyl acetate: methanol = 3:1 by volume as the eluent, perform isocratic elution, the flow rate is 2.0 mL / min, and the collected effluent is subjected to rotary evaporation to remove the solvent, the sediment is then dissolved with deionized water, and the membrane filtrate is obtained by passing through a 0.22 μm membrane, and the membrane filtrate is subjected to vacuum freeze-drying to obtain a finished catalpol powder.

2. The method for extracting stachyose and catalpol from fresh Rehmannia root as claimed in claim 1, characterized in that: In step three, the first evaporation concentration treatment refers to evaporating the stachyose extract at 55° C. and −0.1 MPa for 2 hours.

3. The method for extracting stachyose and catalpol from fresh Rehmannia root as claimed in claim 1, characterized in that: In step five, the decolorization and purification using activated carbon refers to mixing the reconstituted solution with 0.32 g / 100 mL of activated carbon, and decolorizing and purifying the mixture at a temperature of 40° C. and a time of 1.5 h.

4. The method for extracting stachyose and catalpol from fresh Rehmannia root as claimed in claim 1, characterized in that: In step five, the first vacuum freeze-drying treatment refers to freeze-drying the centrifugal filtrate at a vacuum degree of about 10 Pa and a temperature of -45°C for 48 hours.

5. The method for extracting stachyose and catalpol from fresh Rehmannia root as claimed in claim 1, characterized in that: In step seven, the second evaporation concentration treatment refers to evaporating the catalpol extract at 55° C. and −0.1 MPa.

6. The method for extracting stachyose and catalpol from fresh Rehmannia root as claimed in claim 1, characterized in that: In step seven, the second vacuum freeze-drying treatment refers to freeze-drying the catalpol concentrate at a vacuum degree of about 10 Pa and a temperature of -45°C for 48 hours.

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