Dragon fruit residue polysaccharide as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of biochemistry, and particularly discloses dragon fruit residue polysaccharide as well as a preparation method and application thereof. The main structure of the pitaya residue polysaccharide is a repetitive unit composed of galactose and lactone galactose; in the monosaccharide composition of the pitaya residue polysaccharide, the content of galactose is 42 wt% or above. The pitaya pomace polysaccharide is prepared by taking pitaya pomace as a raw material and carrying out acidolysis, alcohol precipitation, dialysis and freeze drying on the pitaya pomace powder, and the pitaya pomace polysaccharide has high galactose content. A high-fat diet mouse model is used for testing the intestinal mucoprotein proportion, the oxidation resistance, the blood fat content and the like of the pitaya residue polysaccharide, and the result proves that the pitaya residue polysaccharide is beneficial to reducing blood fat, improving the oxidation resistance of the liver and maintaining the stability of mucus, has better protection and repair effects on intestinal barrier injury, and can be used for preparing the health-care food. The compound can be used for preparing medicines with the effects of reducing blood sugar, protecting liver, repairing intestinal barriers and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of biochemistry, and in particular relates to pitaya pomace polysaccharide and a preparation method and application thereof. Background Art

[0002] The global emission of pitaya pomace is high every year. The conventional treatment method of pitaya pomace is to dry it and press it into feed. This application has low added value, huge energy consumption and low economic benefits. The pitaya pomace used for extracting juice is rich in active ingredients such as flavonoids, polyphenols and polysaccharides. Therefore, exploring the high added value utilization of pitaya pomace and its active ingredients has significant social value and potential economic benefits.

[0003] Polysaccharides are widely present in plants and play the role of supporting tissues or storing nutrients. On the one hand, because plant polysaccharides have multiple biological activities and are safe and non-toxic, they have been gradually developed and applied in the pharmaceutical, health food and other industries; on the other hand, the use of polysaccharides is of great significance for maintaining mucus stability and protecting and repairing intestinal barrier damage. Polysaccharides play a role in lowering blood sugar and blood lipids, mainly relying on improving insulin sensitivity, regulating intestinal flora and regulating lipid metabolism. The type and content of monosaccharides in polysaccharides affect the biological activity of polysaccharides. For example, the galactose content is considered to be related to the physicochemical properties and activity of polysaccharides, and different extraction methods affect the composition of polysaccharide products. At present, there are no reports on the extraction method and application of pitaya pomace polysaccharides based on galactose content as an indicator.

[0004] Therefore, it is urgent to develop a drug with small side effects, reasonable price, derived from natural products, and capable of anti-oxidation, maintaining mucus stability, and protecting and repairing intestinal barrier damage. As one of my country's major agricultural products, pitaya produces a large amount of waste during processing, causing environmental pollution and waste of resources. Pitaya residue is rich in active ingredients such as flavonoids, polyphenols, and polysaccharides, and has biological activities such as anti-tumor, antioxidant, and immunomodulatory. Therefore, it is of great significance to further understand the relevant biological activities of pitaya residue, promote the development of food and pharmaceutical processing industries related to pitaya residue, and maintain human health. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a pitaya pomace polysaccharide and a preparation method and application thereof, aiming to further increase the content of galactose in pitaya pomace polysaccharide and promote the application of pitaya pomace polysaccharide in the preparation of drugs for lowering blood lipids, protecting liver, and repairing intestinal barrier.

[0006] To solve the above technical problems, the first aspect of the present invention provides a pitaya pomace polysaccharide, the structure of which includes repeating units consisting of galactose and ether galactose; in the monosaccharide composition of the pitaya pomace polysaccharide, the content of galactose is above 42wt%.

[0007] Specifically, the structure of the pitaya residue polysaccharide of the present invention is mainly composed of repeating units of lactose and ether galactose, and the content of galactose in the monosaccharide composition is as high as 42.84% or more. The high galactose content is beneficial to improving the biological activity of the pitaya residue polysaccharide, and has a good effect on lowering blood lipids, improving the antioxidant effect of the liver, and protecting and repairing intestinal barrier damage.

[0008] In some embodiments of the present invention, the monosaccharide composition of the pitaya pomace polysaccharide includes, by weight percentage: rhamnose 12-18%, arabinose 16-24%, galactose 42-45%, glucose 1-3%, xylose 1-2%, mannose 0.5-2%, galacturonic acid 5-10%, and glucuronic acid 5-10%.

[0009] The second aspect of the present invention provides a method for preparing the above-mentioned pitaya pomace polysaccharide, comprising the following steps:

[0010] (1) filtering the pitaya residue to obtain a filter residue;

[0011] (2) drying, crushing and sieving the filter residue to obtain residue powder;

[0012] (3) subjecting the residue powder to acid extraction, alcohol precipitation, dialysis, and freeze-drying to obtain the dragon fruit residue polysaccharide.

[0013] Specifically, the present invention first filters the pomace after extracting juice from pitaya to obtain filter residue; then dries, crushes and sieves the filter residue to obtain residue powder; then acid hydrolyzes the residue powder, and the product after acid hydrolysis has a polysaccharide structure, but has a higher galactose content than other extraction methods; then alcohol precipitation, dialysis and freeze drying are performed to obtain pitaya pomace polysaccharide. The pitaya pomace polysaccharide prepared by the present invention is beneficial to lowering blood lipids, improving the antioxidant capacity of the liver, maintaining mucus stability, and having a good protective and repairing effect on intestinal barrier damage due to its high content of galactose.

[0014] In some embodiments of the present invention, in step (2), the drying temperature is 50-70° C., and the drying time is 20-28 hours.

[0015] In some embodiments of the present invention, in step (2), the sieve used for sieving has a mesh size of 20-40.

[0016] In some embodiments of the present invention, in step (3), the acid extraction step comprises: adding the slag powder into water to dissolve it, then adding an acid solution, adjusting the pH value, heating, and leaching; and finally concentrating it.

[0017] In some embodiments of the present invention, the mass ratio of the slag powder to water is 1:(12-18).

[0018] In some embodiments of the present invention, the water is distilled water.

[0019] In some embodiments of the present invention, the acid solution is concentrated sulfuric acid.

[0020] In some embodiments of the present invention, the pH value is 1.5-2.5.

[0021] In some embodiments of the present invention, the heating temperature is 80-90°C.

[0022] In some embodiments of the present invention, the extraction time is 1-3 hours.

[0023] In some embodiments of the present invention, the concentration is carried out by rotary evaporation.

[0024] In some embodiments of the present invention, in step (3), the alcohol precipitation step comprises: adding ethanol to the acid-extracted product for alcohol precipitation, then centrifuging, collecting the precipitate, and finally volatilizing the ethanol.

[0025] In some embodiments of the present invention, the volume ratio of the acid-extracted product to ethanol is 1:(4-6).

[0026] In some embodiments of the present invention, the alcohol precipitation time is 12-24 hours.

[0027] In some embodiments of the present invention, the ethanol is 95% ethanol.

[0028] In some embodiments of the present invention, in step (3), the dialysis step comprises: adding the alcohol-precipitated product into water to dissolve it, and then dialyzing it using a dialysis bag for 20-28 hours.

[0029] In some embodiments of the present invention, the dissolving temperature is 40-50°C.

[0030] In some embodiments of the present invention, the purified water is changed 4-6 times during the dialysis process.

[0031] The third aspect of the present invention provides the use of the above-mentioned pitaya pomace polysaccharide in the preparation of a drug, wherein the drug includes any one of a blood sugar lowering drug, a liver protecting drug and an intestinal barrier repairing drug.

[0032] Specifically, this discovery used a high-fat diet mouse model to conduct tests on intestinal mucin percentage, antioxidant capacity, blood lipid content, etc. The results showed that pitaya pomace polysaccharides have beneficial effects on lowering blood lipids and maintaining mucus stability, protecting and repairing intestinal barrier damage, and can be used to prepare drugs with effects such as lowering blood sugar, protecting the liver and repairing the intestinal barrier.

[0033] Compared with the prior art, the above technical solution of the present invention has at least the following technical effects or advantages:

[0034] The present invention uses pitaya pomace as raw material, and obtains pitaya pomace polysaccharide by acid hydrolysis, alcohol precipitation, dialysis and freeze drying of pitaya pomace powder, and the pitaya pomace polysaccharide has a high galactose content. The present invention uses a high-fat diet mouse model to test the pitaya pomace polysaccharide for intestinal mucin ratio, antioxidant capacity, blood lipid content, etc. The results show that pitaya pomace polysaccharide is beneficial for lowering blood lipids, improving the antioxidant capacity of the liver, maintaining mucus stability, and having a good protective and repairing effect on intestinal barrier damage. It can be used to prepare drugs with the effects of lowering blood sugar, protecting the liver and repairing the intestinal barrier. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a physical picture of the pitaya pomace polysaccharide prepared in Example 1;

[0036] Figure 2 This is the Fourier transform infrared spectrum of the pitaya pomace polysaccharide prepared in Example 1;

[0037] Figure 3 This is a flowchart of the mouse experiment;

[0038] Figure 4 This is the weight change trend of mice in different treatment groups in the high-fat diet-induced obese mice experiment within 10 weeks;

[0039] Figure 5 The morphology of animals in each treatment group in the high-fat diet-induced obese mouse experiment;

[0040] Figure 6 is the percentage of epididymal fat mass in each treatment group of the high-fat diet-induced obese mouse experiment;

[0041] Figure 7 This is a graph showing blood lipid levels in mice induced by high-fat diet;

[0042] Figure 8 This is an example of the experimental oxidative capacity of high-fat diet-induced obese mice;

[0043] Fig. 9 These are examples of HE-stained tissue pathological sections of each treatment group in the high-fat diet-induced obese mouse experiment. DETAILED DESCRIPTION

[0044] The present invention is described in detail below in conjunction with the examples, so that the technical personnel of the relevant technical field can understand the present invention. It is necessary to point out here that the examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. The non-essential improvements and adjustments made to the present invention by the skilled person in the relevant field according to the above invention content should still belong to the scope of protection of the present invention. At the same time, the raw materials mentioned below that are not described in detail are all commercially available products; the process steps or preparation methods that are not mentioned in detail are all process steps or preparation methods known to those skilled in the art.

[0045] Example 1

[0046] A method for preparing pitaya pomace polysaccharide comprises the following steps:

[0047] (1) adding pitaya residue to distilled water (the mass ratio of pitaya residue to distilled water is 1:4), stirring and filtering at room temperature, and collecting the residue;

[0048] (2) placing the filter residue collected in step (1) in an oven and drying it at 60° C. for 24 hours, then crushing the dried filter residue and passing it through a 20-mesh sieve to obtain residue powder;

[0049] (3) adding the residue powder obtained in step (2) to distilled water (the mass ratio of the residue powder to the distilled water is 1:15), then adding concentrated sulfuric acid to adjust the pH to 2.0, extracting at 90° C. for 2 hours, and concentrating by rotary evaporation; adding the concentrated solution to 95% ethanol (the volume ratio of the concentrated solution to the ethanol is 1:5) for alcohol precipitation for 24 hours, centrifuging, taking the precipitate, and evaporating the ethanol in the precipitate; dissolving the precipitate from which the ethanol has been evaporated with distilled water at 45° C., placing it in a dialysis bag, changing the distilled water 5 times during the process, and dialysis for 24 hours; freeze-drying the dialyzed sample to obtain the dragon fruit residue polysaccharide of this embodiment, as shown in the physical diagram Figure 1 shown.

[0050] Figure 2 This is the Fourier infrared spectrum of the dragon fruit residue polysaccharide prepared in Example 1, wherein the abscissa Wavenumbers represents the wave number, and the ordinate Transmittance represents the transmittance. Figure 2 It can be seen that at 3366cm -1 The strong absorption peak at 2936cm is the stretching absorption peak of the hydroxyl group -OH in the oligosaccharide molecule. -1 The peak at 1617cm is the stretching vibration peak of alkyl-CH. -1 The 1479cm -1 The weak absorption peak at 1192cm is due to the stretching vibration of the sulfate group. -1 The peak that appears near (specifically 1252cm-1 1061cm -1 The absorption peak of the pyranose ring is at 861cm -1 The characteristic absorption peak of galactose can be found at 773 cm -1 The weak absorption peak near the pyranose ring may be caused by the symmetrical stretching vibration. The results show that the structure of the dragon fruit residue polysaccharide is mainly composed of galactose and ether galactose repeating units.

[0051] The monosaccharide components of the pitaya pomace polysaccharide prepared in this embodiment include, by weight percentage, 16.38% rhamnose, 19.76% arabinose, 42.84% galactose, 2.02% glucose, 1.05% xylose, 0.78% mannose, 8.84% galacturonic acid, and 8.32% glucuronic acid.

[0052] Example 2

[0053] A method for preparing pitaya pomace polysaccharide comprises the following steps:

[0054] (1) adding pitaya residue to distilled water (the mass ratio of pitaya residue to distilled water is 1:5), stirring and filtering at room temperature, and collecting the residue;

[0055] (2) placing the filter residue collected in step (1) in an oven and drying it at 80° C. for 18 hours, then crushing the dried filter residue and passing it through a 20-mesh sieve to obtain residue powder;

[0056] (3) adding the residue powder obtained in step (2) to distilled water (the mass ratio of the residue powder to the distilled water is 1:10), then adding concentrated sulfuric acid to adjust the pH to 2.5, extracting at 80° C. for 2 hours, and concentrating by rotary evaporation; adding the concentrated solution to 95% ethanol (the volume ratio of the concentrated solution to the ethanol is 1:3) for alcohol precipitation for 24 hours, centrifuging, taking the precipitate, and evaporating the ethanol in the precipitate; dissolving the precipitate from which the ethanol has been evaporated with distilled water at 55° C., placing it in a dialysis bag, changing the distilled water 5 times during the process, and dialysis for 24 hours; freeze-drying the dialyzed sample to obtain the dragon fruit residue polysaccharide of this embodiment.

[0057] Example 3

[0058] A method for preparing pitaya pomace polysaccharide comprises the following steps:

[0059] (1) adding pitaya residue to distilled water (the mass ratio of pitaya residue to distilled water is 1:6), stirring and filtering at room temperature, and collecting the residue;

[0060] (2) placing the filter residue collected in step (1) in an oven and drying it at 80° C. for 12 hours, then crushing the dried filter residue and passing it through a 20-mesh sieve to obtain residue powder;

[0061] (3) adding the residue powder obtained in step (2) to distilled water (the mass ratio of the residue powder to the distilled water is 1:12), then adding concentrated sulfuric acid to adjust the pH to 2.0, extracting at 80°C for 3 hours, and concentrating by rotary evaporation; adding the concentrated solution to 95% ethanol (the volume ratio of the concentrated solution to the ethanol is 1:4) for alcohol precipitation for 24 hours, centrifuging, taking the precipitate, and evaporating the ethanol in the precipitate; dissolving the precipitate from which the ethanol has been evaporated with distilled water at 65°C, placing it in a dialysis bag, changing the distilled water 5 times, and dialysis for 48 hours; freeze-drying the dialyzed sample to obtain the dragon fruit residue polysaccharide of this embodiment.

[0062] Comparative Example 1

[0063] A method for preparing pitaya pomace polysaccharide comprises the following steps:

[0064] (1) adding pitaya residue to distilled water (the mass ratio of pitaya residue to distilled water is 1:4), stirring and filtering at room temperature, and collecting the residue;

[0065] (2) placing the filter residue collected in step (1) in an oven and drying it at 60° C. for 24 hours, then crushing the dried filter residue and passing it through a 20-mesh sieve to obtain residue powder;

[0066] (3) adding the residue powder obtained in step (2) to distilled water (the mass ratio of the residue powder to the distilled water is 1:15), then adding ammonia water to adjust the pH to 8.0-10.0, extracting at 90° C. for 4 hours, adjusting the pH to 7 with hydrochloric acid, and concentrating by rotary evaporation; adding the concentrated solution to 95% ethanol (the volume ratio of the concentrated solution to the ethanol is 1:5) for alcohol precipitation for 24 hours, centrifuging, taking the precipitate, and evaporating the ethanol in the precipitate; dissolving the precipitate from which the ethanol has been evaporated with distilled water at 45° C., placing it in a dialysis bag, changing the distilled water 5 times, and dialyzing for 24 hours; freeze-drying the dialyzed sample to obtain the dragon fruit residue polysaccharide of this comparative example.

[0067] The monosaccharide components of the pitaya dregs polysaccharide prepared in Comparative Example 1 include, by weight percentage: 25.66% rhamnose, 16.17% arabinose, 25.94% galactose, 3.00% glucose, 1.19% xylose, 1.49% mannose, 15.14% galacturonic acid, and 1.41% glucuronic acid. It can be seen that the content of galactose in the monosaccharide components of the pitaya dregs polysaccharide prepared in Comparative Example 1 using the alkali extraction method is significantly reduced compared with Example 1 using the acid extraction method. Under the premise that the structures of the two are similar, the activity of the pitaya dregs polysaccharide will also decrease accordingly, thereby proving that the extraction process of the pitaya dregs polysaccharide is closely related to its performance.

[0068] Application Example 1: Establishment of a high-fat diet-induced obese mouse model

[0069] Inbred mice (C57BL / 6) were selected for animal experiments to construct a high-fat diet mouse model. Figure 3 As shown, the animals were randomly divided into four groups (there was no significant difference in body weight among the groups): the conventional diet group (NC) consumed ordinary feed and was gavaged with 200 mg / kg normal saline; the HFD group consumed 60% high-fat feed; the pitaya residue polysaccharide group (HFD+PDPS 200 ), consuming 60% high-fat diet and gavage-fed 200 mg / kg PDPS; positive control group (HFD+PC 200 , 60% high-fat diet and 200 mg / kg dimethylformamide hydrochloride were gavaged, and the number of mice in each group was 12. The mice were adapted to normal diet and drinking water in the first week, and their body weight was recorded once a week. The experimental time was 10 weeks.

[0070] Figure 4 and Figure 5 The following are the weight change trends of mice in different treatment groups and the animal morphology of each treatment group in the 10-week experiment of high-fat diet-induced obese mice. Figure 4 and Figure 5 It can be seen that at the beginning of the experiment (week 0), there was no difference in body weight among the four groups of mice; after 10 weeks of feeding, the body weight of the high-fat diet group (HFD group) was significantly (p<0.0001) higher than that of the normal feed group (NC group); and the intervention of PDPS and PC effectively inhibited the rapid weight gain induced by HFD.

[0071] Throughout the experiment, as described above, the mice were observed weekly for 77 days for body weight, diet, and mental state. After the last feeding, the mice were fasted for 24 hours and then sacrificed. The colon, colon contents, liver, epididymal fat, and serum were collected for later use.

[0072] Figure 6 is the percentage of epididymal fat mass in each treatment group of high-fat diet-induced obese mice (Epididymalfat index), Figure 6 It can be seen that the epididymal fat mass in the HFD-fed mice was significantly increased compared with the NC group; while the experimental group supplemented with PDPS (HFD+PDPS 200 group), the epididymal fat content showed a lower trend than that of the HFD group.

[0073] Application Example 2: Determination of blood lipid content

[0074] The blood of mice (about 1 mL) was collected by removing the eyeballs. The collected blood was allowed to stand at room temperature for 2 hours, then centrifuged at 4°C (5000 rpm, 10 minutes), and the supernatant was collected in a new centrifuge tube and stored in a -80°C refrigerator. After thawing the -80°C frozen serum, 70 μL was taken and diluted 3 times with 0.9% saline. The Nanjing Jiancheng kit was used to measure triglycerides (TG), total cholesterol (T-CHO), high-density lipoprotein cholesterol (HLD-C), and low-density lipoprotein cholesterol (LDL-C) in serum. The principle of the detection is that the detection target (triglycerides, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol) is treated with a specific enzyme to generate a color substance, and the depth of the color is proportional to the content of the detection target.

[0075] Figure 7 This is a graph showing blood lipid levels in mice induced by a high-fat diet. Figure 7 It can be seen that the blood biochemical indicators of each group of mice correspond to the effects of pitaya pomace polysaccharide on body weight, and pitaya pomace polysaccharide can improve HFD-induced dyslipidemia. 200 TG in mouse serum ( Figure 7 A) T-CHO( Figure 7 B) LDL-C ( Figure 7 C) and HDL-C ( Figure 7 D) content decreased significantly.

[0076] Application Example 3: Determination of liver antioxidant capacity

[0077] Take 50 mg of mouse liver tissue frozen at -80℃, add PBS buffer solution at a ratio of 1:9, and crush it with a tissue crusher to obtain a tissue homogenate. Centrifuge at 45000rpm for 10 minutes at 4℃, take the supernatant and use Nanjing Jiancheng kit to determine the content of superoxide dismutase (SOD) and reduced glutathione (GSH) in liver tissue. Use BCA kit (Biyuntian) to determine the content of protein in the liver. The results are as follows: Figure 8 shown.

[0078] Depend on Figure 8 It can be seen that PDPS can increase the level of GSH ( Figure 8 A) and SOD levels ( Figure 8 B), it helps to improve the antioxidant capacity of the liver. This polysaccharide can be used in antioxidant aspects, and dragon fruit pomace and its dragon fruit pomace polysaccharide can be used with high added value.

[0079] Application example 4: Intestinal tissue morphology observation

[0080] 1. HE staining of colon tissue

[0081] (1) Fixation: The freshly dissected colon tissue was placed in 4% paraformaldehyde solution for 24 hours;

[0082] (2) Dehydration: Remove the fixed tissue, rinse the excess fixative on the surface with distilled water, and then use 60%, 70%, 80%, 90%, 95% and 100% ethanol for dehydration.

[0083] (3) Transparency: Place the dehydrated tissue in xylene I and xylene II solutions in turn to make the intestinal tissue transparent.

[0084] (4) Wax immersion and embedding: The transparent tissue is transferred to molten paraffin for 2-3 times, and the paraffin block is cut into 4 μm thick slices using a microtome.

[0085] (5) Dewaxing: Treat the paraffin sections with xylene I and xylene II for 20 minutes each, then treat with xylene-anhydrous ethanol (V:V = 1:1) solution for 5 minutes; then treat the sections with ethanol solutions of decreasing concentrations for 3-5 minutes each, and finally immerse the sections in distilled water for 10 minutes.

[0086] (6) H&E staining: After dewaxing, the sections were stained with hematoxylin for 8 minutes, washed with water, immersed in 1% hydrochloric acid for 30 seconds, and then washed with water. They were treated with eosin stain for 1 minute, and then treated with 70%, 80%, 90%, 95%, and 100% ethanol and xylene for 10 minutes to remove moisture. Finally, the sections were sealed with neutral gum and observed under a microscope. The results were as follows: Fig. 9 shown.

[0087] Among them: (NC) is the blank control group, (HFD) is the model group, (HFD+PC 200 ) is the positive control, (HFD+PDPS 200 ) was the intervention group. Fig. 9 It can be seen that the colon morphology of mice in the NC group was normal and the structure was intact; the colon mucosa of mice in the HFD group was thickened and the crypt length was shorter, and the number of goblet cells was significantly reduced compared with the NC group; the colon morphology of mice in the positive control group and intervention group was not significantly different from that of the NC group, and the mucosal thickness and crypt length were not significantly different from those of the NC group; among them, the colon mucosal thickness and crypt length of mice in the intervention group and positive control group were closest to those in the NC group, and the improvement effect on the colon changes caused by the high-fat diet was better.

[0088] For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, without having to go through creative labor. Therefore, simple improvements made to the present invention by those skilled in the art based on the disclosure of the present invention should be within the protection scope of the present invention. The above embodiments are preferred embodiments of the present invention, and all processes similar to the present invention and equivalent changes made should belong to the protection scope of the present invention.

Claims

1. A pitaya pomace polysaccharide, characterized in that: The structure of the pitaya pomace polysaccharide comprises repeating units composed of galactose and ether galactose; in the monosaccharide composition of the pitaya pomace polysaccharide, the content of galactose is above 42wt%.

2. The pitaya pomace polysaccharide according to claim 1, characterized in that The monosaccharide composition of the pitaya pomace polysaccharide comprises, by weight percentage, 12-18% rhamnose, 16-24% arabinose, 42-45% galactose, 1-3% glucose, 1-2% xylose, 0.5-2% mannose, 5-10% galacturonic acid and 5-10% glucuronic acid.

3. A method for preparing dragon fruit pomace polysaccharide according to claim 1 or 2, characterized in that: The following steps are involved: (1) filtering the pitaya residue to obtain a filter residue; (2) drying, crushing and sieving the filter residue to obtain residue powder; (3) subjecting the residue powder to acid extraction, alcohol precipitation, dialysis, and freeze-drying to obtain the dragon fruit residue polysaccharide.

4. The method for preparing pitaya pomace polysaccharide according to claim 3, characterized in that: In step (2), the sieve used for sieving has a mesh size of 20-40.

5. The method for preparing pitaya pomace polysaccharide according to claim 3, characterized in that: In step (3), the acid extraction step includes: adding the slag powder into water to dissolve it, then adding an acid solution, adjusting the pH value, heating, and leaching; and finally concentrating it.

6. The method for preparing pitaya pomace polysaccharide according to claim 5, characterized in that: The acid solution is concentrated sulfuric acid; and / or the pH value is 1.5-2.5; and / or the heating temperature is 80-90° C.; and / or the leaching time is 1-3 hours.

7. The method for preparing dragon fruit residue polysaccharide according to claim 3, characterized in that: In step (3), the alcohol precipitation step comprises: adding ethanol to the acid-extracted product for alcohol precipitation, then centrifuging, taking the precipitate, and finally volatilizing the ethanol.

8. The method for preparing dragon fruit residue polysaccharide according to claim 7, characterized in that: The volume ratio of the acid extraction product to ethanol is 1:(4-6); and / or the alcohol precipitation time is 12-24 hours.

9. The method for preparing dragon fruit pomace polysaccharide according to claim 3, characterized in that: In step (3), the dialysis step comprises: adding the alcohol-precipitated product into water to dissolve it, and then dialyzing it with a dialysis bag for 20-28 hours.

10. A use of the pitaya pomace polysaccharide as claimed in claim 1 or 2 in the preparation of medicines, characterized in that: The drug includes any one of a blood sugar lowering drug, a liver protecting drug and an intestinal barrier repairing drug.

Images