Astragaloside-rich astragalus polysaccharide powder and preparation method thereof

Abstract

The invention belongs to the technical field of plant extraction, and particularly relates to astragalus polysaccharide powder rich in astragaloside and a preparation method of the astragalus polysaccharide powder. The preparation method comprises the following steps: soaking a radix astragali medicinal material in 2-3 times of water for 1-2 hours, freezing in an ultralow temperature environment for 3-4 hours, carrying out primary grinding, standing for 30-40 minutes, filtering, freezing filter residues in an ultralow temperature environment again for 3-4 hours, carrying out secondary grinding, adding water, carrying out pressurized soaking for 3-4 hours, filtering, and merging filtrate to obtain filtrate A and filter residues for later use; and performing subcritical alkaline water extraction and filtration on the obtained filter residues to obtain a filtrate B and filter residues, continuously introducing carbon dioxide into the filtrate B for 1-2 hours, performing filtration to obtain a filtrate C, combining the filtrate A and the filtrate C, performing membrane filtration, concentrating the filtrate into thick paste, adding maltodextrin, and performing centrifugal spray drying to obtain astragalus polysaccharide powder. According to the preparation method, the extraction process is simple and feasible, the wastewater component is single, the pollution to the environment is reduced, and the obtained astragalus polysaccharide powder is good in water solubility, high in astragaloside content and strong in biological pesticide effect.

Description

Technical Field

[0001] The invention belongs to the technical field of plant extraction, and particularly relates to astragaloside-rich astragaloside polysaccharide powder and a preparation method thereof. Background Art

[0002] Astragaloside is a water-soluble heteropolysaccharide extracted, concentrated and purified from the dried roots of Astragalus mongolica or Astragalus membranaceus, a leguminous plant. It is light yellow, fine powder, uniform and free of impurities, and has hygroscopic properties. Astragaloside is composed of hexuronic acid, glucose, fructose, rhamnose, arabinose, galacturonic acid and glucuronic acid, etc. It can be used as an immunostimulant or regulator, and has antiviral, anti-tumor, anti-aging, anti-radiation, anti-stress and antioxidant effects. Astragaloside IV, also known as astragaloside IV or astragaloside IV (AS-IV), is a representative component of astragalol-type saponins in Astragalus. It belongs to the tetracyclic triterpenoid saponin. Its structure contains two glucose sugars, and the aglycone is cycloastragenol. The efficacy of astragaloside IV is more than twice that of conventional astragaloside, and its antiviral effect is 30 times that of astragaloside. Due to its low content and good effect, it is known as "super astragaloside". Astragaloside Ⅳ has a significant promoting effect on the body's immune system and antiviral ability, can specifically and non-specifically eliminate foreign matter that invades the body, and improve the body's disease resistance. The presence of astragaloside Ⅳ in astragalus polysaccharide powder can further enhance its effect. The current common astragaloside extraction method uses calcium oxide aqueous solution for extraction, and then treats with water and alcohol to obtain an astragaloside powder with an astragaloside Ⅳ content of about 0.1%, and an astragaloside Ⅳ extraction yield of less than 50%, which wastes a lot of useful resources, has a complicated and cumbersome production process, and is difficult to treat the wastewater produced. Therefore, it is necessary to develop an extraction method for astragaloside powder that is simple in process and rich in astragaloside Ⅳ. Summary of the invention

[0003] In view of the shortcomings of the prior art, the purpose of the present invention is to provide an astragaloside-rich astragaloside powder and a preparation method thereof. The preparation method has a simple and feasible extraction process, a single wastewater component, and reduced pollution to the environment. The obtained astragaloside powder has good water solubility, a high astragaloside content, and strong biological efficacy, and has promotional significance.

[0004] In order to solve the technical problem proposed by the present invention, the present invention provides a method for preparing astragalus polysaccharide powder rich in astragaloside IV, comprising the following steps: (1) Soak the Astragalus membranaceus in 2-3 times the amount of water for 1-2 hours, freeze it in an ultra-low temperature environment for 3-4 hours, grind it once, let it stand for 30-40 minutes, filter it, freeze the residue in an ultra-low temperature environment for 3-4 hours, grind it again, soak it in water under pressure for 3-4 hours, filter it, combine the filtrate to obtain filtrate A, and set the residue aside; (2) extracting the filter residue obtained in step (1) with subcritical alkaline water, filtering, and obtaining filtrate B and filter residue; (3) Continuously introduce carbon dioxide into filtrate B for 1-2 hours, and obtain filtrate C after filtration; (4) Filtrate A and filtrate C are combined, filtered through a membrane, and the filtrate is concentrated to a thick paste. Maltodextrin is added and centrifugal spray drying is performed to obtain astragalus polysaccharide powder.

[0005] Furthermore, in step (1), the ultra-low temperature environment temperature is -40~-20°C; the first grinding time is 1-2h; and the second grinding time is 2-3h.

[0006] Furthermore, in step (1), the mass of water added after secondary grinding is 6-8 times the mass of the astragalus medicinal material, the particle size after grinding is 100-120 mesh, the pressure during immersion is 1-2MPa, and the temperature is 25-30°C. In this technical solution, the astragalus material after absorbing water is rapidly frozen in an ultra-low temperature environment, which can effectively destroy its cell tissue. At the same time, the grinding technology can further release the effective components in the cells, and then the material after secondary freezing and grinding is subjected to pressure immersion treatment, which greatly improves the release of components such as astragalus polysaccharides.

[0007] Furthermore, in step (2), the temperature of subcritical alkaline water extraction is 105-120°C, the time is 40-60min, the pressure is 9-10MPa, and the solid-liquid ratio is 1:3-5. Subcritical alkaline water extraction is a medium-temperature and high-pressure alkaline extraction environment, which can effectively protect the extract from damage, has high extraction efficiency, and can also promote the conversion of astragaloside to astragaloside IV, thereby increasing the content of astragaloside IV.

[0008] Furthermore, in step (2), the alkaline water used for extraction is alkaline water with a pH value of 9-10 added with calcium hydroxide.

[0009] Furthermore, in step (3), carbon dioxide is introduced into the filtration process to maintain the liquid temperature at 40-50°C.

[0010] Furthermore, in step (4), the pore size of the filter membrane is 0.45 μm; and the concentration is performed by vacuum concentration with a vacuum degree of -0.08 MPa and a temperature of 60-80° C., and the concentration is performed to 1 / 4-1 / 3 of the original volume.

[0011] Furthermore, in step (4), the amount of maltodextrin added is 30-40% of the astragalus polysaccharide powder.

[0012] Furthermore, in step (4), the centrifugal spray drying inlet temperature is 180-200°C, the outlet temperature is 80-90°C, the material flow rate is 2-4L / min, and the rotation speed is 8000-10000r / min. The centrifugal spray drying solution is atomized in the spray tower, and the droplets are quickly contacted and dried with the hot air during the falling process, with small particle size, good uniformity, and fast drying speed, which can effectively prevent the drug from being destroyed.

[0013] The present invention also provides an astragaloside powder prepared by the above-mentioned preparation method, wherein the content of astragaloside Ⅳ in the astragaloside powder is 0.2-0.4%.

[0014] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The invention changes the extraction method, firstly soaks the astragalus medicinal material with a small amount of water, then puts it in an ultra-low temperature environment and quickly freezes it, and then grinds it. The freezing treatment is not only conducive to subsequent grinding, but also the water in the cells of the astragalus medicinal material expands rapidly to destroy the cell wall, cell membrane, fiber, etc., so as to facilitate the extraction of effective components. After two freezing treatments, the cells of the astragalus medicinal material are basically destroyed, and most of the water-soluble components such as polysaccharides can be extracted by water extraction; then, the medicinal residues are subjected to subcritical alkaline water extraction to further extract the polysaccharides and astragaloside IV in the medicinal residues. At the same time, since the alkaline water extraction is adopted, the conversion of astragaloside into astragaloside IV can be promoted to a certain extent, and the content of astragaloside IV can be increased; then, the calcium for adjusting pH in the filtrate is removed by the method of introducing carbon dioxide, so as to improve the purity of the product; finally, all the filtrates are combined, filtered and concentrated by membrane, and then maltodextrin is added to carry out centrifugal spray drying, the drying speed is fast, the entire medicinal component is not destroyed, and the spray product is fine and uniform without agglomeration.

[0015] The invention optimizes the extraction production process, does not need to use ethanol and calcium oxide, is simpler and more convenient to process, does not generate wastewater, and has less pollution. The obtained astragalus polysaccharide powder has good water solubility, high astragaloside IV content, stronger biological efficacy, and good product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a comparison chart of the weight changes of mice in each group; Figure 2 This is a comparison chart of the changes in peripheral blood interferon-γ in each group of mice; Figure 3 This is a comparison chart of the changes in peripheral blood IgG content of mice in each group; Figure 4 This is a comparison chart of the changes in spleen index of mice in each group. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. When the concentrations involved in the present invention are not specified, they are all mass concentrations. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0018] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0019] The Astragalus membranaceus medicinal material is from the same batch of Mongolian Astragalus membranaceus, in which the content of astragaloside I is 0.07% and the moisture content is 5%.

[0020] Example 1 A method for preparing astragaloside-rich astragaloside polysaccharide powder comprises the following steps: (1) Soak 10 kg of Astragalus membranaceus in 2 times the amount of water for 2 hours, freeze it in an ultra-low temperature environment of -40~-20℃ for 3 hours, grind it once for 2 hours, let it stand for 30 minutes, filter it, freeze the residue in an ultra-low temperature environment for 4 hours, grind it again for 2 hours until the particle size is 100-120 mesh, add 8 times the amount of water, soak it under pressure at a pressure of 2MPa and a temperature of 30℃ for 4 hours, filter it, combine the filtrate to obtain filtrate A, and set the residue aside; (2) extracting the residue obtained in step (1) with subcritical alkaline water at an extraction pressure of 9 MPa, a solid-liquid ratio of 1:5, an aqueous solution of calcium hydroxide with a pH of 9-10, a temperature of 120° C., a time of 50 min, and filtering to obtain filtrate B and residue; (3) Keep filtrate B at 50°C and continue to introduce carbon dioxide for 2 hours, then filter to obtain filtrate C; (4) Filtrate A and filtrate C were combined and filtered through a membrane (pore size 0.45 μm). The filtrate was concentrated to 1 / 4 of its original volume under a vacuum degree of -0.08 MPa and a temperature of 80°C. 0.6 kg of maltodextrin was added and centrifugal spray drying was performed at an inlet temperature of 180°C, an outlet temperature of 80°C, a material flow rate of 2 L / min, and a rotation speed of 8000 r / min to obtain 2.0 kg of astragalus polysaccharide powder.

[0021] Example 2 A method for preparing astragaloside-rich astragaloside polysaccharide powder comprises the following steps: (1) Soak 10 kg of Astragalus membranaceus in 3 times the amount of water for 1 hour, freeze it in an ultra-low temperature environment of -40~-20℃ for 4 hours, grind it once for 1 hour, let it stand for 40 minutes, filter it, freeze the residue in an ultra-low temperature environment for 3 hours again, grind it again for 3 hours until the particle size is 100-120 mesh, add 6 times the amount of water, soak it under pressure at a pressure of 1MPa and a temperature of 25℃ for 4 hours, filter it, combine the filtrate to obtain filtrate A, and set the residue aside; (2) extracting the residue obtained in step (1) with subcritical alkaline water at an extraction pressure of 10 MPa, a solid-liquid ratio of 1:3, an aqueous solution of calcium hydroxide with a pH of 9-10, a temperature of 105° C., a time of 60 min, and filtering to obtain filtrate B and residue; (3) Keep filtrate B at 40°C and continue to introduce carbon dioxide for 1 hour, then filter to obtain filtrate C; (4) Filtrate A and filtrate C were combined and filtered through a membrane (pore size 0.45 μm). The filtrate was concentrated to 1 / 3 of its original volume under a vacuum degree of -0.08 MPa and a temperature of 70°C. 0.9 kg of maltodextrin was added and centrifugal spray drying was performed at an inlet temperature of 200°C, an outlet temperature of 90°C, a material flow rate of 4 L / min, and a rotation speed of 9000 r / min to obtain 2.3 kg of astragalus polysaccharide powder.

[0022] Example 3 A method for preparing astragaloside-rich astragaloside polysaccharide powder comprises the following steps: (1) Soak 10 kg of Astragalus membranaceus in 2 times the amount of water for 1.5 hours, place it in an ultra-low temperature environment of -40~-20℃ and freeze it for 3 hours, grind it for 1.5 hours, let it stand for 35 minutes, filter it, freeze the residue in an ultra-low temperature environment again for 4 hours, grind it for a second time for 2.5 hours until the particle size is 100-120 mesh, add 7 times the amount of water, and soak it under pressure at a pressure of 1.5 MPa and a temperature of 30℃ for 3 hours, filter it, combine the filtrate to obtain filtrate A, and set the residue aside; (2) extracting the residue obtained in step (1) with subcritical alkaline water at an extraction pressure of 10 MPa, a solid-liquid ratio of 1:4, an aqueous solution of calcium hydroxide with a pH of 9-10, a temperature of 110° C., a time of 40 min, and filtering to obtain filtrate B and residue; (3) Keep filtrate B at 45°C and continue to introduce carbon dioxide for 1.5 hours, then filter to obtain filtrate C; (4) Filtrate A and filtrate C were combined and filtered through a membrane (pore size 0.45 μm). The filtrate was concentrated to 1 / 4 of its original volume under a vacuum degree of -0.08 MPa and a temperature of 60°C. 0.75 kg of maltodextrin was added and centrifugal spray drying was performed at an inlet temperature of 190°C, an outlet temperature of 85°C, a material flow rate of 3 L / min, and a rotation speed of 10,000 r / min to obtain 2.15 kg of astragalus polysaccharide powder.

[0023] Comparative Example 1 A method for preparing astragalus polysaccharide powder, which differs from Example 1 in that step (1) comprises: soaking 10 kg of astragalus medicinal materials in 8 times the amount of water for 2 hours, freezing them in an ultra-low temperature environment of -40 to -20°C for 3 hours, grinding them once for 2 hours, standing them for 30 minutes, filtering them to obtain filtrate A, and using the filter residue for later use. Finally, 1.94 kg of astragalus polysaccharide powder is obtained.

[0024] Comparative Example 2 A method for preparing astragalus polysaccharide powder, which differs from Example 1 in that step (1) comprises: soaking 10 kg of astragalus medicinal material in 1 times of water for 2 hours, freezing it in an ultra-low temperature environment of -40 to -20°C for 3 hours, grinding it once for 2 hours, letting it stand for 30 minutes, filtering, freezing the filter residue in an ultra-low temperature environment for 4 hours again, grinding it again for 2 hours to a particle size of 100-120 mesh, adding 8 times of water and soaking it at a temperature of 30°C for 4 hours, filtering, combining the filtrate to obtain filtrate A, and using the filter residue for later use. Finally, 1.95 kg of astragalus polysaccharide powder is obtained.

[0025] Comparative Example 3 A method for preparing astragalus polysaccharide powder, which differs from Example 1 in that step (1) is as follows: 10 kg of astragalus medicinal materials are soaked in 8 times water for 6 hours and then filtered to obtain filtrate A, and the filter residue is set aside. Finally, 1.92 kg of astragalus polysaccharide powder is obtained.

[0026] Comparative Example 4 A method for preparing astragalus polysaccharide powder, which differs from Example 1 in that step (2) comprises: extracting the filter residue obtained in step (1) with subcritical water at an extraction pressure of 9 MPa, a material-water ratio of 1:5, a temperature of 120° C., and a time of 50 min, filtering to obtain filtrate B and filter residue. Finally, 1.99 kg of astragalus polysaccharide powder is obtained.

[0027] Comparative Example 5 A method for preparing astragalus polysaccharide powder, which differs from Example 1 in that step (2) comprises: adding water to the filter residue obtained in step (1), wherein the material-water ratio is 1:5, soaking at a temperature of 120° C. for 50 minutes, filtering to obtain filtrate B and filter residue. Finally, 1.97 kg of astragalus polysaccharide powder is obtained.

[0028] Comparative Example 6 A method for preparing astragalus polysaccharide powder, which differs from Example 1 in that step (4) comprises: combining filtrate A and filtrate C, filtering through a membrane (pore size 0.45 μm), concentrating the filtrate to 1 / 4 of the original volume at a vacuum degree of -0.08 MPa and a temperature of 60°C, adding 0.6 kg of maltodextrin, mixing well, and drying at 105°C for 5 hours to obtain 1.98 kg of astragalus polysaccharide powder.

[0029] Test Example 1 1. The moisture content, appearance, solubility and stability of the astragalus polysaccharide powder obtained in Examples 1-3 and Comparative Examples 1-6 were tested. The results are shown in Table 1.

[0030] Table 1 Performance of Astragalus Polysaccharide Powder

[0031] 2. The content of astragaloside IV in astragalus polysaccharide powder was detected by high performance liquid chromatography, and the results are shown in Table 2. Extraction rate % = (mass of astragaloside IV in astragalus polysaccharide powder) * 100 / mass of astragaloside IV in astragalus medicinal materials.

[0032] Table 2 Content and extraction rate of astragaloside Ⅳ in astragalus polysaccharide powder

[0033] From the results in Table 1, it can be seen that the astragalus polysaccharide powder prepared by the extraction method of the present invention has uniform color, is fine and uniform, and is loose. It has good solubility in warm water at 25°C, does not deteriorate or change color when stored in a high temperature and high humidity environment, and has good stability.

[0034] It can be seen from the results in Table 2 that the astragaloside content of the astragaloside polysaccharide powder of the present invention is as high as 3.2%, and the extraction rate is above 90%, the resource extraction rate is high, and there is no waste.

[0035] Test Example 2 The astragalus polysaccharide powder obtained in Example 1 and commercially available common astragalus polysaccharide powder were subjected to a mouse immunological test. The method is as follows: 48 young mice were randomly divided into 4 groups: negative control group, model control group, astragalus polysaccharide powder administration group of Example 1, and commercially available common astragalus polysaccharide powder administration group (astragaloside IV content is less than 0.1%), with 12 mice in each group, half male and half female. The negative control group was fed with water; the mice in the model control group were intraperitoneally injected with cyclophosphamide at a dose of 80 mg / kg per day, and injected continuously for 3 days, and then reinforced once after 9d, 10d, 11d, 19d, 20d, and 21d, that is, intraperitoneally injected with cyclophosphamide at a dose of 80 mg / kg per day. The astragalus polysaccharide powder administration group was made into an astragalus polysaccharide powder suspension with water as the solvent, and was gavaged to mice (mice after continuous injection of cyclophosphamide for 3 days) once a day for 30 consecutive days, and the dosage was fed at 200 mg / kg per day. The mice were weighed once a week, and the dosage was adjusted according to the weight change. During the experiment in each group, the mice ate and drank normally, had no abnormal defecation, and no abnormal death.

[0036] result: 1. Effect on the weight of mice: Observe the weight changes of mice during the whole experiment. Figure 1 As shown, from Figure 1It can be seen that the weight gain of mice in the model control group showed a downward trend, and the difference was significant compared with the negative control group; the drug-treated group could improve the weight gain of mice, and the trend was consistent with that of the negative control group, indicating that the astragalus polysaccharide powder could improve the weight of mice, and the difference of the astragalus polysaccharide powder in Example 1 of the present invention was smaller, indicating that the astragalus polysaccharide powder in Example 1 of the present invention had better efficacy.

[0037] 2. Effect on γ-interferon in peripheral blood of mice: γ-interferon is secreted by T cells and natural killer cells after being stimulated and activated by tumors, antigens and mitotic factors. It has biological functions such as antiviral, immune regulation and anti-tumor properties. This experiment uses ELISA to detect γ-interferon in peripheral blood of mice after treatment. The results are as follows: Figure 2 As shown. Figure 2 The results show that the γ-interferon content of mice in the model control group is significantly lower than that in the negative control group, indicating that cyclophosphamide can effectively reduce the γ-interferon level of mice and inhibit the immune function of mice, and the model is successful. After consuming the astragalus polysaccharide powder, the γ-interferon level can be significantly improved, especially after consuming the astragalus polysaccharide powder of the present invention, the difference with the negative control group is the smallest, which is basically the same, indicating that the astragalus polysaccharide powder can increase the γ-interferon level in mice and improve the immune function, and the astragalus polysaccharide powder of the present invention has a stronger efficacy.

[0038] 3. Effect on peripheral blood IgG of mice: Immunoglobulin G (IgG) is synthesized in the spleen and lymph nodes, with the highest content in serum and a long half-life in serum. It is mainly distributed in serum and tissue fluid. It is the main component of antibacterial, antitoxin and antiviral antibodies, and is also an important material basis for the body's anti-infection immunity. This experiment uses the ELISA method to detect the IgG content in the peripheral blood of mice after the treatment. The results are as follows: Figure 3 As shown. Figure 3 The results show that the IgG content of mice in the model control group is significantly lower than that in the negative control group, indicating that cyclophosphamide can effectively reduce the IgG level of mice and inhibit the immune function of mice. After consuming the astragalus polysaccharide powder, the IgG content can be significantly increased, especially after consuming the astragalus polysaccharide powder of the present invention, the difference with the negative control group is the smallest, indicating that the astragalus polysaccharide powder can increase the IgG content in mice and improve the immune function, and the astragalus polysaccharide powder of the present invention has a stronger efficacy.

[0039] 4. Effect on the spleen of mice: The spleen coefficient of each group of mice was measured in this experiment. The results are as follows: Figure 4 As shown. Figure 4It can be seen that the spleen index of mice in the model control group increased significantly compared with the negative control group, indicating that cyclophosphamide can effectively change the spleen index of mice. After consuming the astragalus polysaccharide powder, the spleen index can be significantly reduced, especially after consuming the astragalus polysaccharide powder of the present invention, the difference with the negative control group is the smallest, indicating that the astragalus polysaccharide powder can reduce the spleen index, thereby repairing damaged immune organs, and the astragalus polysaccharide powder of the present invention has better efficacy.

[0040] In summary, the present invention optimizes the extraction production process to obtain astragalus polysaccharide powder that is fine, uniform, loose, has good water solubility and stability, high astragaloside content, stronger biological efficacy, good product quality, and has broad application prospects.

[0041] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for preparing astragaloside-rich astragaloside polysaccharide powder, characterized in that: The following steps are involved: (1) Soak the Astragalus membranaceus in 2-3 times the amount of water for 1-2 hours, freeze it in an ultra-low temperature environment for 3-4 hours, grind it once, let it stand for 30-40 minutes, filter it, freeze the residue in an ultra-low temperature environment for 3-4 hours, grind it again, soak it in water under pressure for 3-4 hours, filter it, combine the filtrate to obtain filtrate A, and set the residue aside; (2) extracting the filter residue obtained in step (1) with subcritical alkaline water, filtering, and obtaining filtrate B and filter residue; (3) Continuously introduce carbon dioxide into filtrate B for 1-2 hours, and obtain filtrate C after filtration; (4) Filtrate A and filtrate C are combined, filtered through a membrane, and the filtrate is concentrated to a thick paste. Maltodextrin is added and centrifugal spray drying is performed to obtain astragalus polysaccharide powder.

2. The preparation method according to claim 1, characterized in that: In step (1), the ultra-low temperature environment temperature is -40~-20°C; the first grinding time is 1-2h; and the second grinding time is 2-3h.

3. The preparation method according to claim 1, characterized in that: In step (1), the mass of water added after the secondary grinding is 6-8 times the mass of the Astragalus medicinal material, the particle size after grinding is 100-120 mesh, the pressure during soaking is 1-2 MPa, and the temperature is 25-30°C.

4. The preparation method according to claim 1, characterized in that: In step (2), the temperature of subcritical alkaline water extraction is 105-120°C, the time is 40-60 min, the pressure is 9-10 MPa, and the solid-liquid ratio is 1:3-5.

5. The preparation method according to claim 1, characterized in that: In step (2), the alkaline water used for extraction is alkaline water with a pH value of 9-10 added with calcium hydroxide.

6. The preparation method according to claim 1, characterized in that: In step (3), carbon dioxide is introduced into the filtration process to maintain the liquid temperature at 40-50°C.

7. The preparation method according to claim 1, characterized in that: In step (4), the pore size of the filter membrane is 0.45 μm; the concentration is performed by vacuum concentration with a vacuum degree of -0.08 MPa and a temperature of 60-80°C, and the concentration is performed to 1 / 4-1 / 3 of the original volume.

8. The preparation method according to claim 1, characterized in that: In step (4), the amount of maltodextrin added is 30-40% of the astragalus polysaccharide powder.

9. The preparation method according to claim 1, characterized in that: In step (4), the centrifugal spray drying inlet temperature is 180-200°C, the outlet temperature is 80-90°C, the material flow rate is 2-4L / min, and the rotation speed is 8000-10000r / min.

10. An astragalus polysaccharide powder prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The content of astragaloside Ⅳ in the astragalus polysaccharide powder is 0.2-0.4%.

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