Astragalus polysaccharide as well as preparation method and application thereof in Taihe silky fowl

Abstract

The invention discloses astragalus polysaccharide as well as a preparation method and application thereof in Taihe silky fowl. The astragalus polysaccharide is a homogeneous polysaccharide PAPS, is composed of mannose, ribose, rhamnose, glucuronic acid, glucose, galactose and arabinose in a molar percentage of 0.17%: 0.34%: 0.44%: 0.42%: 98.54%: 0.02%: 0.07%, and is connected by glucosidic bonds, the glucosidic bonds comprise t-Glc (p), 3-Glc (p), 4-Man (p), 6-Glc (p), 4-Glc (p), 3, 4-Glc (p), 2, 4-Glc (p) and 4, 6-Glc (p), and the ratio of 4-Glc (p) is the maximum; the number-average molecular weight Mn of the polysaccharide is 3487Da, the weight-average molecular weight Mw of the polysaccharide is 26369 Da, and the peak molecular weight of the polysaccharide is 13864Da. The preparation method of the homogeneous polysaccharide comprises the steps of polysaccharide extraction, deproteinization, dialysis and freeze-drying. The invention also provides application of the crude polysaccharide APS in Taihe silky fowl. The uniform polysaccharide PAPS is clear in chemical composition, and meanwhile, the crude polysaccharide APS can improve the growth performance and immune function of the Taihe silky fowl and regulate intestinal microorganisms of the Taihe silky fowl.

Description

Technical Field

[0001] The present invention relates to the field of feed additives, and in particular to a polysaccharide of Astragalus membranaceus, and also relates to its preparation method and application. Background Art

[0002] Taihe black-boned chicken is a unique and precious poultry in China, originating from Taihe County, Ji'an City, Jiangxi Province. It is highly regarded for its high nutritional value and its medicinal, edible and ornamental values. However, Taihe black-boned chicken has the disadvantages of a long growth cycle, a small body size and high production costs. Moreover, with the demands of intensive farming and market development, Taihe black-boned chicken is constantly exposed to various external stressors, and is susceptible to infection by bacteria and pathogens, resulting in a decline in growth performance, oxidative stress and intestinal barrier damage, which has an adverse impact on production. In the past few decades, antibiotic growth promoters have usually been used in the intensive poultry industry to control diseases and improve growth performance. However, the abuse of antibiotics has caused bacterial drug resistance and antibiotic residues in animal products. China has implemented a policy of completely banning the use of feed additive antibiotics for growth promotion since July 1, 2020. In view of the high demand for high-quality poultry products, it is very important to develop antibiotic alternatives that can both improve production performance and maintain the health of Taihe black-boned chicken.

[0003] A large number of studies have shown that plant polysaccharides can replace antibiotic growth promoters in poultry production. Astragalus membranaceus is one of the most widely used traditional Chinese herbs and has currently been included in the feed ingredient catalog. Polysaccharide of Astragalus membranaceus is one of the main active components of Astragalus membranaceus and has functions such as regulating blood sugar, anti-cancer, anti-aging, anti-tumor, immune regulation, antioxidant and regulating intestinal microecology. The structure of polysaccharides is closely related to their functions. However, the polysaccharide products of Astragalus membranaceus on the market are complex and diverse, and their structures are unclear. At present, the effects of applying polysaccharide of Astragalus membranaceus in the production of Taihe black-boned chicken have not been evaluated. Summary of the Invention

[0004] In view of the unclear composition on the market, the purpose of the present invention is to provide a polysaccharide of Astragalus membranaceus, its preparation method and its application to Taihe black-boned chicken.

[0005] The technical solution of the present invention:

[0006] A polysaccharide of Astragalus membranaceus PAPS, the polysaccharide of Astragalus membranaceus is a homogeneous polysaccharide PAPS, which is composed of mannose, ribose, rhamnose, glucuronic acid, glucose, galactose and arabinose, and the molar percentages are 0.17%: 0.34%: 0.44%: 0.42%: 98.54%: 0.02%: 0.07% respectively. It is connected by glycosidic bonds, and the glycosidic bond types include t-Glc(p), 3-Glc(p), 4-Man(p), 6-Glc(p), 4-Glc(p), 3,4-Glc(p), 2,4-Glc(p) and 4,6-Glc(p), among which 4-Glc(p) has the largest proportion;

[0007] The number-average molecular weight Mn of the polysaccharide is 3487 Da, the weight-average molecular weight Mw is 26369 Da, and the peak molecular weight is 13864 Da.

[0008] A preparation method of the astragalus polysaccharide described above includes the following steps:

[0009] (1) Crush astragalus, extract with hot water, the solid-liquid ratio is 1:25. After concentration, add anhydrous ethanol for precipitation, stir while adding until the total ethanol concentration reaches 50%, let stand for 10 hours. Wash the sugar-containing precipitate part with anhydrous ethanol, acetone, petroleum ether, and anhydrous ethanol in sequence, and obtain crude polysaccharide (APS) after evaporation to dryness.

[0010] (2) Dissolve the crude polysaccharide in water, repeatedly remove proteins by the Savage method, collect the polysaccharide solution after protein removal and dialyze it in a dialysis bag with a cut-off molecular weight of 10 KDa. Freeze-dry the dialyzed solution to obtain astragalus polysaccharide PAPS.

[0011] An application of the crude polysaccharide APS, when added to the feed of Taihe black-boned chickens at 1000 mg / kg, can improve the growth performance, immunity of Taihe black-boned chickens aged 20 - 90 days and improve the intestinal microbial composition.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] (1) The astragalus polysaccharide of the present invention is a homogeneous polysaccharide extracted from astragalus, and its chemical composition is clear.

[0014] (2) The preparation method of the astragalus polysaccharide of the present invention has the advantages of simple preparation, mild reaction conditions, and the crude polysaccharide has the property of... Description of the Drawings

[0015] Figure 1 It is a route diagram of the preparation method of astragalus polysaccharide in Example 1.

[0016] Figure 2 It is a high performance gel permeation chromatogram of astragalus polysaccharide (PAPS) in Example 2.

[0017] Figure 3 It is a monosaccharide composition map of astragalus polysaccharide (PAPS) in Example 2.

[0018] Figure 4 It is an ultraviolet spectrum scan diagram of astragalus polysaccharide (PAPS) in Example 2.

[0019] Figure 5 It is an infrared spectrum scan diagram of astragalus polysaccharide (PAPS) in Example 2.

[0020] Figure 6The total ion chromatogram and electron impact mass spectrometry (EI-MS) spectra of polysaccharide from Astragalus membranaceus (PAPS) in Example 2.

[0021] Figure 7 The sugar nuclear magnetic resonance spectrum of polysaccharide from Astragalus membranaceus (PAPS) in Example 2.

[0022] Figure 8 The effects of APS on serum immunoglobulins and complements in Taihe black-bone chickens in Example 3 (n = 8).

[0023] Figure 9A The effect diagram of APS on the intestinal microbiota of Taihe black-bone chickens in Example 3 (community heat map at the genus level).

[0024] Figure 9B The effect diagram of APS on the intestinal microbiota of Taihe black-bone chickens in Example 3 (LEfSe Bar). Detailed implementation mode

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0026] Example 1: Preparation of polysaccharide from Astragalus membranaceus

[0027] The route of the preparation method is as Figure 1 shown, and the specific operations are as follows:

[0028] 1. The polysaccharide from Astragalus membranaceus was extracted 3 times by boiling water extraction method. Each time, distilled water was added according to the solid-liquid ratio of 1:25, and the extraction was carried out for 2.5 hours; after 7.5 hours, the supernatant was taken, the liquid was concentrated on a rotary evaporator and then filtered, and ethanol precipitation was carried out while stirring on a magnetic stirrer until the concentration of absolute ethanol was 50%, and after continuing to stir for 1 h, it was left standing overnight.

[0029] 2. The sugar-containing precipitate part was washed successively with absolute ethanol - acetone - petroleum ether - absolute ethanol, and the organic reagents were volatilized to obtain crude polysaccharide (APS).

[0030] 3. Remove the protein inside by Sevage method: After dissolving the obtained crude polysaccharide, a protein precipitant (chloroform: n-butanol = 4:1 (V∶V)) was added according to the volume ratio of 4:1, shaken well and left standing for 30 minutes, centrifuged at 6000 r / min for 5 minutes, and the supernatant was collected. The above steps were repeated until the protein layer in the liquid disappeared.

[0031] 4. Dialysis with a 10Kd dialysis bag: The collected supernatant was loaded into a dialysis bag and dialyzed with distilled water for 24 h, and the water was changed every 2 h.

[0032] 5. Freeze-drying: The polysaccharide in the dialysis bag was placed in a petri dish and frozen in a refrigerator at -80 °C until completely frozen. Then they were transferred to a freeze dryer for drying to obtain the target Astragalus polysaccharide PAPS.

[0033] Example 2: Determination of the physicochemical properties of Astragalus polysaccharide PAPS

[0034] 1. Chemical composition

[0035] The total sugar content was determined by the phenol-sulfuric acid method, the uronic acid content was determined by the sulfuric acid-carbazole method, and the protein content in Astragalus polysaccharide PAPS was detected using the BCA Protein Assay Kit from Beyotime. The results showed that the total sugar content of PAPS was 96.15%, the uronic acid content was 1.61%, and the protein content was below the detection limit.

[0036] 2. Molecular weight determination

[0037] High performance gel permeation chromatography (HPGFC): A Waters 1525 high performance liquid chromatograph (equipped with a 2410 refractive index detector and an Empower workstation) was used to determine the molecular weight of the polysaccharide. The chromatographic conditions were as follows: The chromatographic column was ULtrahydrogel TM Linea (300 mm × 7.8 mm id × 2); the column temperature was 25 °C, the flow rate was 0.8 mL / min, and the mobile phase was 0.1 N sodium nitrate. The standard sample was a dextran standard with a known molecular weight. 50 mg of each was taken and placed in a 10 mL volumetric flask, dissolved with the mobile phase, made up to the mark, and then subjected to HPGFC detection. The injection volume was 20 μL. The sample was prepared into a solution with a concentration of 5 mg / mL, filtered through a 0.22 μm filter membrane, and then detected on the chromatograph. The molecular weight of PAPS was obtained from the standard curve based on the retention time.

[0038] The results Figure 2 showed a single, sharp, and symmetrical peak at 15 - 20 min, indicating that PAPS is a homogeneous polysaccharide. Its number average molecular weight Mn was 3487 Da, the weight average molecular weight Mw was 26369 Da, and the peak molecular weight was 13864 Da.

[0039] 3. Monosaccharide composition analysis

[0040] Pre-column high performance liquid chromatography (HPLC) with 1-phenyl-3-methyl-5-pyrazolone (PMP) was used to analyze the monosaccharide composition of Astragalus polysaccharide PAPS.

[0041] (1) Derivatization of the mixed standard sample: Prepare a mixed monosaccharide standard solution with a mass concentration of 36 mg / mL for each monosaccharide. Take the mixed monosaccharide standard solution and mix it with 0.6 mol / L NaOH solution in a ratio of 1:1 to prepare 200 μL of the mixed solution, which is placed in a 1 mL stoppered test tube and mixed well. Then take 50 μL of the mixed solution and put it into an ampoule, add an equal volume of 0.5 mol / L PMP methanol solution, and mix well. Place it in an oven at 70 °C for 100 min, then cool to room temperature. Add 50 μL of 0.3 mol / L HCl, then add water to 1 mL, and then add 1 mL of chloroform. Shake well, let it stand, discard the lower chloroform phase, and extract until the chloroform phase is colorless. Filter the aqueous phase through a 0.45 μm microporous filter membrane and then perform HPLC analysis.

[0042] (2) Derivatization of the sample: Prepare the sample to be tested into a 5 g / L sugar solution. Take 100 μL and put it into an ampoule, add an equal volume of 4 mol / L trifluoroacetic acid (TFA), seal the tube with N 2 and hydrolyze it in an oven at 110 °C; after cooling, open the lid, add 200 μL of methanol, and then blow dry with N 2 repeating 3 times to remove TFA; add 50 μL of 0.3 mol / L NaOH solution to fully dissolve the precipitate. The subsequent steps are the same as (1) for PMP derivatization and HPLC analysis. The liquid chromatography conditions are as follows: the chromatographic column is ZORBAX Eclipse XDB-C18 (4.6×250 mm / 5 μm); the column temperature is 30 °C; the mobile phase is acetonitrile and 1 mol / L potassium dihydrogen phosphate aqueous solution (pH = 6.7, volume ratio is 17:83); the flow rate is 1 mL / min; the sample injection volume is 20 μL, and the detection wavelength is 245 nm. Calculate the molar ratio of the monosaccharide composition through the standard curve.

[0043] The results are as Figure 3 shown. PAPS is composed of mannose, ribose, rhamnose, glucuronic acid, glucose, galactose, and arabinose, and its molar percentages are 0.17%: 0.34%: 0.44%: 0.42%: 98.54%: 0.02%: 0.07%. The main component is glucose.

[0044] 4. Ultraviolet spectrum detection

[0045] Prepare the sample to be tested into a 0.05% polysaccharide solution and measure the ultraviolet absorption spectrum in the wavelength range of 200 - 400 nm on a UV spectrophotometer.

[0046] The results are as Figure 4 shown. PAPS has no absorption peaks at 260 nm and 280 nm, indicating that the sample does not contain nucleic acids and proteins.

[0047] 5. Infrared spectrum detection (FT-IR)

[0048] Weigh 2 g of the polysaccharide powder, mix it with 200 mg of KBr, grind it into a powder, press it into a tablet, and perform infrared spectroscopy scanning in the range of 4000 - 400 cm -1 , and the number of scans is 32 times.

[0049] The results are as Figure 5 shown. The FT-IR spectrum of PAPS shows a typical polysaccharide absorption spectrum in the range of 4000 - 400 cm -1 . The broad and strong band at 3425 cm -1 corresponds to the stretching vibration of the hydroxyl O-H, and the 2930 cm -1 corresponds to the asymmetric stretching vibration peak of the methylene C-H; the 1160 - 1020 cm -1 is related to the C-O-C stretching vibration of the pyranose; the 1648 cm -1 corresponds to the characteristic stretching vibration representing the C=O bond. The 1424 cm -1 corresponds to the outer and inner ring C-O stretching bands. The 930 cm -1 is generated by the asymmetric ring stretching vibration of D-pyranose, and the 854 cm -1 indicates the presence of an α-glycosidic bond. At 615 cm -1 and 580 cm -1 correspond to the backbone of the pyranose ring.

[0050] 6. Methylation analysis

[0051] The glycosidic bonds of PAPS were determined by methylation analysis using gas chromatography - mass spectrometry (GC-MS). Briefly, the process is divided into three steps: methylation, acetylation, and GC-MS detection of permethylated alditol acetates (PMAAs). First, dissolve 3 mg of freeze-dried PAPS in 500 μL of DMSO and 1 mg of NaOH and incubate for 30 minutes, then add 50 μL of methyl iodide solution to ensure complete methylation. After 1 hour, stop the reaction using water (1 mL) and dichloromethane (2 mL), then vortex, mix, and centrifuge the reaction solution, and discard the aqueous phase in sequence. After 3 times, collect the lower dichloromethane phase, dry it with nitrogen to obtain the methylated product. Second, hydrolyze the methylated polysaccharide with 2 mol / L TFA (100 μL) at 121 °C for 90 minutes and evaporate to dryness at 30 °C. NaBD 4And acetic anhydride were used to convert polysaccharides into partially methylated alditol acetates (PMAAs). Finally, the PMAA was analyzed using an Agilent 6890A-5977B GC-MS system. The analysis conditions of GC-MS were as follows: the chromatographic column was BPX70 (30 m × 0.25 mm × 0.25 μm); the injection volume was 1 μL, and the split ratio was 10:1; the carrier gas was high-purity helium; the flow rate was 1.5 mL / min; the initial column temperature was 140 °C, held for 2 min, and then the temperature was raised to 230 °C at a rate of 3 °C / min for 3 min; electron impact: 70 eV, ion source temperature: 300 °C.

[0052] GC-MS analyzed the sugar chain information of PAPS, and the total ion chromatogram and the spectrum of electron impact mass spectrometry (EI-MS) were respectively as Figure 6 (Part A) and Figure 6 (Part B-I) shown. The EI-MS spectrum was compared with the Complex Carbohydrate Research Center (CCRC) spectral database for verification, and the detailed information of sugar residues is shown in Table 1. The results showed that there were 8 kinds of sugar residues in PAPS: t-Glc(p), 3-Glc(p), 4-Man(p), 6-Glc(p), 4-Glc(p), 3,4-Glc(p), 2,4-Glc(p), and 4,6-Glc(p), and their molar percentages were 6.07%: 0.19%: 0.67%: 0.54%: 87.51%: 0.55%: 0.38%: 4.10%. Among them, 4-Glc(p) had the largest proportion, indicating that it might be the main backbone of PAPS.

[0053] Table 1. Methylation analysis of PAPS

[0054]

[0055] 6. Nuclear magnetic resonance analysis (NMR)

[0056] PAPS was dissolved in 99.8% D 2 O to prepare homogeneous solutions of 20 mg / mL and 50 mg / mL respectively for measuring the H and C carbon spectra. 1D and 2D NMR experiments were carried out at 298 K using a nuclear magnetic resonance spectrometer. For 1 H spectral analysis, the external magnetic field frequency was 500 MHz, and the number of scans was 16 times; for 13 C spectral analysis, the external magnetic field frequency was 125 MHz, and the number of scans was 5120 times. The recorded 1D and 2D NMR spectra included 1 H NMR, 13 C NMR, 1 H- 1 H COSY,1 H- 13 C HSQC, 1 H- 13 CHMBC. The spectra were analyzed using MestReNova 14 software.

[0057] The 1 H and 13 C NMR spectra of PAPS are as Figure 7 shown. An anomeric proton shift of δ > 5.0 ppm indicates the α configuration, and conversely, a shift less than 5.0 ppm indicates the β configuration. The anomeric proton signal of PAPS extends from 3.3 ppm to 5.7 ppm, indicating the simultaneous presence of α and β configurations in PAPS ( Figure 7 part A). The anomeric hydrogen signals at δ 5.41, 4.98, and 4.65 ppm ( Figure 7 A) and the anomeric carbon signals at δ 99.7, 99.5, 98.6, and 95.7 ppm ( Figure 7 part B) suggest that PAPS may contain four types of monosaccharide residues; this finding is consistent with the results of our methylation and GC-MS analyses. This result is consistent with Fourier transform infrared spectroscopy. As 1 H- 1 H COSY ( Figure 7 part C) and HSQC ( Figure 7 part D) spectra show that the anomeric proton / carbon signals at δ 5.41 / 99.5 ppm (A), 5.41 / 99.7 ppm (B), 4.98 / 98.6 ppm (C), and 4.65 / 95.7 ppm (D) were identified as 1,4-α-D-Glcp, 1,4,6-α-D-Glcp, anomeric α-D-Glcp, and anomeric β-D-Glcp, respectively. Based on the HMBC spectrum, the linkage sequence of PAPS was determined ( Figure 7 part E). Cross-peaks from A1 (δH 5.41) to A4 (δC 77.1) and from A4 (δH 3.69) to A1 (δC 99.5) indicate that. Cross-peaks of B1 / A4 (δH / C 5.41 / 77.1) and B4 / A1 (δH / C 3.67 / 99.5) indicate that both C-1 and C-4 of 1,4,6-α-D-Glcp are linked to 1,4-α-D-Glc. In summary, it can be speculated that the backbone of the PAPS structure is 1,4-α-D-Glcp, where some of the O-6 of 1,4-α-D-Glcp is linked to t-α / β-D-Glcp. The corresponding spectral interpretations are shown in Table 2. The content of other monosaccharides is relatively low, and NMR signals cannot be detected. The predicted structure of PAPS is as Figure 7 shown in part F.

[0058] Table 2. 1 H NMR and13 13C NMR Chemical Bond Assignment (ppm)

[0059]

[0060] The structure of polysaccharide from Astragalus membranaceus is different from the structural characteristics reported in current studies, which may be due to the differences in raw materials and purification processes. PAPS was determined to have a backbone of 1,4-α-D-Glcp, with a terminal α / β-D-Glcp ( Figure 7 F part) linked to the 6-position of every 21 residues, and the same structure has not been reported yet. Some studies have reported that polysaccharides similar to those isolated from Dictyophora echinovolvata, Polygonum multiflorum, Cordyceps sinensis, and Ganoderma lucidum, which are composed of α-(1→4)-glucan, have immunomodulatory activities. Considering the actual production applications, the crude polysaccharide APS, the precursor of PAPS, will be used as the research object next to explore its application effects when added to feed.

[0061] Example 3: Study on the Application Effect of Polysaccharide from Astragalus membranaceus in Taihe Black-Boned Chickens

[0062] 1. Experimental Materials: The crude polysaccharide APS from Astragalus membranaceus in Example 1, 20-day-old female Taihe black-boned chickens

[0063] 2. Experimental Methods: A total of 960 20-day-old female Taihe black-boned chickens were randomly assigned to 4 dietary treatments, with 6 replicates in each group and 40 broilers in each replicate. The 4 dietary treatments were as follows: 1) Control group (basal diet); 2) APS_L group (basal diet supplemented with 500 mg / kg APS); 3) APS_M group (basal diet supplemented with 1000 mg / kg APS), and 4) APS_H group (basal diet supplemented with 1500 mg / kg APS). The experimental period was 70 days, including 2 phases, namely the 20th to 56th day and the 56th to 90th day phases. During the experiment, all experimental chickens had free access to food and water. The temperature in the chicken house was 32 °C.

[0064] 3. Sample Collection and Index Detection: At 20, 55, and 90 days of age, the body weights and feed intakes of chickens in each replicate were recorded, and the average daily gain (ADG), average daily feed intake (ADFI), and feed to gain ratio (F / G) of each group were calculated. The mortality of chickens was recorded every day, and then the calculations of the above indexes were corrected. At 90 days of age, 8 Taihe black-boned chickens with similar body weights were randomly selected from each group, killed by cervical dislocation and bled, and blood samples were collected. Serum samples obtained by centrifugation (3000 rpm / min, 4 °C, 15 min) were stored at -20 °C for analysis. After dissection, cecal contents were collected and stored in a -80 °C refrigerator for subsequent microbial analysis.

[0065] 4. Experimental results: The results showed that adding 1000 mg / kg APS to the diet of Taihe silky fowl could significantly reduce the feed-to-gain ratio (P<0.05) (Table 3); however, it had no significant effect on ADG and ADFI (P>0.05). It significantly increased the contents of IgA, IgY, C3 and C4 in the serum of Taihe silky fowl (P<0.05), improving the immunity of Taihe silky fowl( Figure 8 ). It increased the abundances of intestinal beneficial bacteria such as Alistipes, Faecalibacterium, Ruminococcus_torques_group, unclassified_f__Lachnospiraceae, norank_f__Eubacterium_coprostanoligenes_group( Figure 9A , Figure 9B ).

[0066] Table 3. Effects of adding APS on the growth performance of Taihe silky fowl (n = 240).

[0067]

[0068] Data are presented as means and S.E.M (n = 240). Different letters (a–c) above the means indicate significant differences (P<0.05). ADG, average daily gain; ADFI, average daily feed intake; F / G, feed-to-gain ratio. A: ANONA; L: linear; Q: quadratic.

[0069] In the present invention, crude polysaccharide APS and relatively high-purity homogeneous polysaccharide PAPS were obtained from Astragalus membranaceus by water extraction and alcohol precipitation separation and purification. The structural characteristics of PAPS were comprehensively analyzed by techniques such as chromatography, spectroscopy and spectrometry. On this basis, the application effects of Astragalus polysaccharide on Taihe silky fowl were further explored.

[0070] The above-described embodiments merely represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, all of which belong to the protection scope of the present invention. The protection scope of the present invention is given by the appended claims and any equivalent technical solutions thereof.

Claims

1. An astragalus polysaccharide PAPS, characterized in that: The astragalus polysaccharide is a homogeneous polysaccharide PAPS, which is composed of mannose, ribose, rhamnose, glucuronic acid, glucose, galactose, and arabinose, with molar percentages of 0.17%: 0.34%: 0.44%: 0.42%: 98.54%: 0.02%: 0.07%, respectively, connected by glycosidic bonds, and the glycosidic bond types include t-Glc(p), 3-Glc(p), 4-Man(p), 6-Glc(p), 4-Glc(p), 3,4-Glc(p), 2,4-Glc(p) and 4,6-Glc(p), among which 4-Glc(p) accounts for the largest proportion; The number average molecular weight Mn of the polysaccharide is 3487 Da, the weight average molecular weight Mw is 26369 Da, and the peak molecular weight is 13864 Da.

2. A method for preparing astragalus polysaccharide according to claim 1, characterized in that: The following steps are involved: (1) Grind the astragalus root, extract it with hot water, and the solid-liquid ratio is 1:

25. After concentration, add anhydrous ethanol to precipitate, stirring while adding until the total ethanol concentration reaches 50%. Let it stand for 10 hours, wash the sugar-containing precipitate with anhydrous ethanol, acetone, petroleum ether, and anhydrous ethanol in sequence, and evaporate to dryness to obtain crude polysaccharide (APS); (2) Add water to dissolve the crude polysaccharide, and repeatedly remove the protein using the Savage method. Collect the polysaccharide solution after removing the protein and dialyze it in a dialysis bag with a molecular weight cutoff of 10KDa. After dialysis, the solution is freeze-dried to obtain Astragalus polysaccharide PAPS.

3. An application of the crude polysaccharide APS prepared according to claim 2, characterized in that: Adding 1000mg / kg to Taihe black-bone chicken feed can improve the growth performance, immunity and intestinal microbial composition of Taihe black-bone chickens aged 20-90 days.

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