Nanoscale asparagus microcrystalline cellulose, and preparation method and application thereof

Abstract

The application provides a kind of nano asparagus microcrystalline cellulose and its preparation method and application, belong to food processing technical field.The old stem of asparagus or asparagus straw is microwave heat pump dried in the application, and after rehydration, the coarse fiber is obtained by steam explosion treatment;After the coarse fiber is subjected to alkali hydrolysis, acid hydrolysis and decolorization treatment, a hydrolysate is obtained, the hydrolysate is mixed with cellulase, and the extraction liquid is obtained by magnetic induction electric field assisted extraction;After the extraction liquid is subjected to acid hydrolysis treatment, the solid hydrolysis product is obtained by filtration, the solid hydrolysis product is washed, and the nano asparagus microcrystalline cellulose is obtained by drying.The by-product of asparagus (asparagus straw or old stem) is used as raw material in the application, the yield and purity of the nano asparagus microcrystalline cellulose prepared after extracting dietary fiber are high, and the quality is good, the prepared microcrystalline cellulose is added to milk tea, which can significantly improve its stability.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, and in particular relates to a nano-asparagus microcrystalline cellulose, its preparation method and application. Background Technology

[0002] Asparagus, a perennial herb belonging to the Asparagaceae family and the Asparagus genus, is also known as stone asparagus, dragon's beard vegetable, and green asparagus. As a rare vegetable used for both medicinal and culinary purposes, it is not only delicious but also possesses various unique nutritional and therapeutic effects, earning it the title of "King of Vegetables" in the international market. Asparagus stalks or old stems are byproducts generated during asparagus harvesting, packaging, and quick-freezing. These stalks and old stems are still rich in polysaccharides, dietary fiber, and other bioactive components. However, due to a lack of effective comprehensive utilization methods, this high-quality byproduct resource has long been discarded, with only a very small portion used as animal feed. This not only results in a huge waste of resources but also seriously pollutes the environment.

[0003] Microcrystalline cellulose (MCC) is a linear polysaccharide primarily composed of β-1,4-glucosidic bonds. It is a white, odorless, and tasteless crystalline powder consisting of extremely fine, free-flowing, short rod-shaped or powdery porous particles, formed by the hydrolysis of natural cellulose to its limiting degree of polymerization (LODP) using dilute acid. The particle size is generally 20–80 μm, with a LODP ranging from 15 to 375. It is non-fibrous but extremely free-flowing. It is insoluble in water, dilute acids, organic solvents, and oils, but partially dissolves and swells in dilute alkaline solutions. It exhibits high reactivity during carboxymethylation, acetylation, and esterification processes. Due to its low degree of polymerization and large specific surface area, microcrystalline cellulose is widely used in the pharmaceutical, food, and cosmetic industries.

[0004] However, existing methods for preparing microcrystalline cellulose from asparagus have problems such as low yield, poor quality, and low purity. Therefore, there is an urgent need to provide a new method for preparing nano-asparagus microcrystalline cellulose to improve the resource utilization efficiency of asparagus waste. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide nano-asparagus microcrystalline cellulose, its preparation method and application, so as to overcome the problems of low yield, poor quality and low purity of microcrystalline cellulose in existing methods.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing nano-asparagus microcrystalline cellulose, comprising the following steps:

[0008] 1) Dry the old asparagus stems or asparagus stalks with microwave heat pump, rehydrate them, and then perform steam explosion treatment to obtain crude fiber;

[0009] 2) After the crude fiber is subjected to alkaline hydrolysis, acid hydrolysis and decolorization, a hydrolysate is obtained. The hydrolysate is mixed with cellulase and extracted with magnetic induction electric field to obtain an extract.

[0010] 3) After acid hydrolysis of the extract, the solid hydrolysate was filtered to obtain the solid hydrolysate. The solid hydrolysate was washed and dried to obtain nano-asparagus microcrystalline cellulose.

[0011] Preferably, the power of the microwave heat pump drying in step 1) is 300-400W, and the temperature of the microwave heat pump drying is 55-65℃.

[0012] Preferably, the pressure of the steam explosion treatment in step 1) is 1.2 to 1.5 MPa, and the time of the steam explosion treatment is 1 to 3 minutes.

[0013] Preferably, the amount of cellulase used in step 2) is 0.06 to 0.08% of the mass of the hydrolysate;

[0014] The excitation voltage of the magnetic induction electric field is 300-500V, and the frequency of the magnetic induction electric field is 500-700Hz.

[0015] Preferably, in step 2), the alkaline hydrolysis uses a sodium hydroxide solution with a mass concentration of 2-4%, the alkaline hydrolysis temperature is 80-120℃, the time is 1.0-1.5h, the weight ratio of the asparagus stalks to the sodium hydroxide solution is 1:0.5-1.5, or the weight ratio of the asparagus stalks to the sodium hydroxide solution is 1:0.5-1.5.

[0016] Preferably, in step 2), the acid hydrolysis is performed using a hydrochloric acid solution with a mass concentration of 4-6%, at 80-100°C for 0.5-1.5 hours. The weight ratio of the asparagus stalks to the hydrochloric acid solution is 1:4-8, or the weight ratio of the asparagus stalks to the hydrochloric acid solution is 1:9-11.

[0017] Preferably, the decolorization treatment in step 2) is as follows: first, decolorize with a 1.5-2.5% H2O2 solution at 55-65℃ for 0.5-1.5 hours, then rinse with a 1.5-2.5% sodium sulfite solution until neutral, and wash with water 1-3 times; the weight ratio of the asparagus stem to the H2O2 solution is 1:4-6, or the weight ratio of the asparagus stalk to the H2O2 solution is 1:4-6.

[0018] Preferably, the acid hydrolysis treatment in step 3) uses a hydrochloric acid solution with a mass concentration of 6-9% and hydrolyzes at 80-100℃ for 0.5-1.5 hours.

[0019] The present invention also provides nano-asparagus microcrystalline cellulose prepared by the preparation method described above.

[0020] This invention also provides the application of the aforementioned nano-asparagus microcrystalline cellulose in improving the emulsification stability of milk tea.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention uses asparagus by-products (asparagus stalks or old stems) as raw materials, extracts dietary fiber, and prepares nano-asparagus microcrystalline cellulose. Milk tea has a high solids content during production; adding the prepared microcrystalline cellulose to milk tea can significantly improve its stability.

[0023] This invention utilizes microwave heat pump drying to maximize the removal of moisture from asparagus stalks or old stems. It employs steam explosion grading to convert long fibers into short fibers, thereby reducing the difficulty of subsequent enzymatic hydrolysis. Alkaline hydrolysis removes proteins and fatty acids from the raw materials, while acid hydrolysis removes sugars, starches, and pectins. Decolorization removes pigments. The enzymatic extraction process is conducted in a magnetic induction electric field reaction device, with different voltages and frequencies set to improve the extraction rate of dietary fiber. Finally, acid hydrolysis and freeze-spray drying yield high-yield, high-purity, and high-quality nano-asparagus microcrystalline cellulose. Detailed Implementation

[0024] This invention provides a method for preparing nano-asparagus microcrystalline cellulose, comprising the following steps:

[0025] 1) Dry the old asparagus stems or asparagus stalks with microwave heat pump, rehydrate them, and then perform steam explosion treatment to obtain crude fiber;

[0026] 2) After the crude fiber is subjected to alkaline hydrolysis, acid hydrolysis and decolorization, a hydrolysate is obtained. The hydrolysate is mixed with cellulase and extracted with magnetic induction electric field to obtain an extract.

[0027] 3) After acid hydrolysis of the extract, the solid hydrolysate was filtered to obtain the solid hydrolysate. The solid hydrolysate was washed and dried to obtain nano-asparagus microcrystalline cellulose.

[0028] In this invention, asparagus stems or stalks are dried using a microwave heat pump, rehydrated, and then subjected to a steam explosion treatment to obtain coarse fibers. The power of the microwave heat pump drying is preferably 300-400W, more preferably 320-380W; the temperature of the microwave heat pump drying is preferably 55-65℃, more preferably 58-62℃; a refining treatment is performed before rehydration, and the length of the asparagus stems or stalks after the refining treatment is preferably 3-5cm, more preferably 3.5-4.5cm; the moisture content of the asparagus stems or stalks after rehydration treatment is preferably 40-50wt%, more preferably 42-48wt%; the pressure of the steam explosion treatment is preferably 1.2-1.5MPa, more preferably 1.3-1.4MPa; and the time of the steam explosion treatment is preferably 1-3min, more preferably 1.5-2.5min.

[0029] In this invention, crude fiber is subjected to alkaline hydrolysis, acid hydrolysis, and decolorization to obtain a hydrolysate. The hydrolysate is mixed with cellulase, and an extract is obtained by extraction assisted by a magnetic induction electric field. The alkaline hydrolysis preferably uses a sodium hydroxide solution with a mass concentration of 2-4%, and the mass concentration of the sodium hydroxide solution is preferably 2.5-3.5%. The alkaline hydrolysis temperature is preferably 80-120℃, more preferably 90-110℃; the time is preferably 1.0-1.5 h, more preferably 1.2-1.4 h; the weight ratio of asparagus stalks to sodium hydroxide solution is preferably 1:0.5-1.5, more preferably 1:0.7-1.4; or the weight ratio of asparagus stalks to sodium hydroxide solution is preferably 1:0.5-1.5, more preferably 1:0.7-1.4. The acid hydrolysis preferably uses a hydrochloric acid solution with a mass concentration of 4-6%, wherein the mass concentration of the hydrochloric acid solution is 4.5-5.5%; the hydrolysis is carried out at 80-100℃ for 0.5-1.5 hours, wherein the hydrolysis temperature is preferably 85-95℃, and the hydrolysis time is preferably 0.7-1.4 hours; the weight ratio of the asparagus stalks to the hydrochloric acid solution is preferably 1:4-8, more preferably 1:5-7; or the weight ratio of the asparagus stalks to the hydrochloric acid solution is preferably 1:9-11, more preferably 1:9.5-10.5. The decolorization process is as follows: first, decolorize with a 1.5–2.5% (w / w) H₂O₂ solution at 55–65°C for 0.5–1.5 h, wherein the H₂O₂ solution has a preferred (w / w) concentration of 1.8–2.2%; the decolorization temperature is preferably 58–62°C; and the decolorization time is preferably 0.7–1.4 h. Then, rinse with a 1.5–2.5% (w / w) sodium sulfite solution until neutral, wherein the sodium sulfite solution has a preferred (w / w) concentration of 1.8–2.2%; wash with water 1–3 times. The weight ratio of the asparagus stalks to the H₂O₂ solution is preferably 1:4–6, more preferably 1:4.5–5.5; or the weight ratio of the asparagus stalks to the H₂O₂ solution is preferably 1:4–6, more preferably 1:4.5–5.5. The amount of cellulase used is preferably 0.06-0.08% of the mass of the hydrolysate, more preferably 0.065-0.075%; the excitation voltage of the magnetic induction electric field is preferably 300-500V, more preferably 350-450V; the frequency of the magnetic induction electric field is preferably 500-700Hz, more preferably 550-650Hz.

[0030] In this invention, the extract is acid-hydrolyzed and then filtered to obtain a solid hydrolysate. The solid hydrolysate is washed and freeze-spray dried to obtain microcrystalline cellulose. The acid-hydrolyzation treatment preferably uses a 6-9% hydrochloric acid solution at 80-100°C for 0.5-1.5 hours; the hydrochloric acid solution preferably has a weight concentration of 7-8%; the hydrolysis temperature is preferably 85-95°C; the weight ratio of the extract to the hydrochloric acid solution is preferably 1:3-5, more preferably 1:3.5-4.5; the hydrolysis time is preferably 0.7-1.4 hours; and the washing process uses water at 90-100°C to wash the solid hydrolysate until neutral.

[0031] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0032] Example 1

[0033] Asparagus stems were dried using a microwave heat pump at 350W and 60℃. The dried asparagus stems were then cut into 4cm lengths and rehydrated to a moisture content of 45wt%. The rehydrated asparagus stems were then placed in a steam explosion reactor for steam explosion treatment at a pressure of 1.4MPa for 2 minutes to obtain coarse fibers.

[0034] The crude fiber was subjected to alkaline hydrolysis in a sodium hydroxide solution with a sodium hydroxide alkaline solution concentration of 3% by weight, a temperature of 100℃, and a time of 1.3 hours. The weight ratio of asparagus stems to sodium hydroxide solution was 1:1. After alkaline hydrolysis, a 5% hydrochloric acid solution was added, and hydrolysis was carried out at 90℃ for 1 hour. The weight ratio of asparagus stems to hydrochloric acid solution was 1:6. After acid hydrolysis, the asparagus was first treated with a 2% H2O2 solution at 60℃ for 1 hour for decolorization. The weight ratio of asparagus stems to H2O2 solution was 1:5. Then, the asparagus was rinsed with a 2% sodium sulfite solution until neutral, and washed twice with water to obtain a hydrolysate. The hydrolysate was mixed with 0.07% (by weight) of cellulase and fed into a magnetic induction electric field reactor at a flow rate of 0.5 L / min to assist extraction and obtain an extract. The excitation voltage of the magnetic induction electric field reactor was 400V, and the frequency of the magnetic induction electric field was 600Hz.

[0035] The extract and an 8% hydrochloric acid solution were mixed at a weight ratio of 1:4 and hydrolyzed at 90°C for 1 hour. The hydrolysate was rapidly cooled, filtered through a sintered glass funnel, and thoroughly washed with 1 L of 95°C hot water until neutral. The solid hydrolysate was collected and dried to obtain nano-asparagus microcrystalline cellulose.

[0036] Example 2

[0037] Asparagus stems were dried using a microwave heat pump at 300W and 55°C. The dried asparagus stems were then cut into 3cm lengths and rehydrated to a moisture content of 40wt%. The rehydrated asparagus stems were then placed in a steam explosion reactor for steam explosion treatment at a pressure of 1.2MPa for 1 minute to obtain coarse fibers.

[0038] The crude fiber was subjected to alkaline hydrolysis in a sodium hydroxide solution with a sodium hydroxide alkaline solution concentration of 2% by weight, a temperature of 80℃, and a time of 1.0 h. The weight ratio of asparagus stems to sodium hydroxide solution was 1:0.5. After alkaline hydrolysis, a 4% hydrochloric acid solution was added, and hydrolysis was carried out at 80℃ for 0.5 h. The weight ratio of asparagus stems to hydrochloric acid solution was 1:4. After acid hydrolysis, the asparagus was first treated with a 1.5% H2O2 solution at 55℃ for 0.5 h for decolorization. The weight ratio of asparagus stems to H2O2 solution was 1:4. Then, the asparagus was rinsed with a 1.5% sodium sulfite solution until neutral, and washed once with water to obtain a hydrolysate. The hydrolysate was mixed with 0.06% (by weight) of cellulase and fed into a magnetic induction electric field reactor at a flow rate of 0.5 L / min to assist extraction and obtain an extract. The excitation voltage of the magnetic induction electric field reactor was 300 V, and the frequency of the magnetic induction electric field was 500 Hz.

[0039] The extract and a 6% hydrochloric acid solution were mixed at a weight ratio of 1:3 and hydrolyzed at 80°C for 0.5 h. The hydrolysate was rapidly cooled, filtered through a sintered glass funnel, and thoroughly washed with 1 L of 90°C hot water until neutral. The solid hydrolysate was collected and dried to obtain nano-asparagus microcrystalline cellulose.

[0040] Example 3

[0041] Asparagus stems were dried using a microwave heat pump at 400W and 65°C. The dried asparagus stems were then cut into 5cm lengths and rehydrated to a moisture content of 50wt%. The rehydrated asparagus stems were then placed in a steam explosion reactor for steam explosion treatment at a pressure of 1.5MPa for 3 minutes to obtain coarse fibers.

[0042] The crude fiber was subjected to alkaline hydrolysis in a sodium hydroxide solution with a sodium hydroxide alkaline solution concentration of 4% by weight, a temperature of 120℃, and a time of 1.5 h. The weight ratio of asparagus stems to sodium hydroxide solution was 1:1.5. After alkaline hydrolysis, a 6% hydrochloric acid solution was added, and hydrolysis was carried out at 100℃ for 1.5 h. The weight ratio of asparagus stems to hydrochloric acid solution was 1:8. After acid hydrolysis, the asparagus was first treated with a 2.5% H2O2 solution at 65℃ for 1.5 h for decolorization. The weight ratio of asparagus stems to H2O2 solution was 1:6. Then, the asparagus was rinsed with a 2.5% sodium sulfite solution until neutral, and washed three times with water to obtain a hydrolysate. The hydrolysate was mixed with 0.08% (by weight) of cellulase and fed into a magnetic induction electric field reactor at a flow rate of 0.5 L / min to assist extraction and obtain an extract. The excitation voltage of the magnetic induction electric field reactor was 500 V, and the frequency of the magnetic induction electric field was 700 Hz.

[0043] The extract and a 9% hydrochloric acid solution were mixed at a weight ratio of 1:5 and hydrolyzed at 100°C for 1.5 h. The hydrolysate was rapidly cooled, filtered through a sintered glass funnel, and thoroughly washed with 1 L of 100°C hot water until neutral. The solid hydrolysate was collected and dried to obtain nano-asparagus microcrystalline cellulose.

[0044] Experimental Example 1

[0045] Effects of different drying methods on the dehydration rate of asparagus stems

[0046] The specific process is as follows:

[0047] Eight groups (A, B, C, D, E, F, G, and H) were set up. Asparagus stems were dried to constant weight using different drying methods, and their moisture content was measured using a moisture analyzer. The dehydration rate was calculated as 1 - moisture content. Group A was dried according to the method in Example 1; Group B was dried according to the method in Example 2; Group C was dried according to the method in Example 3; Group D underwent microwave vacuum drying at 600W, followed by hot air drying at 80°C; Group E underwent microwave heat pump drying at 250W and 60°C; Group F underwent microwave heat pump drying at 450W and 60°C; Group G underwent microwave heat pump drying at 350W and 50°C; and Group H underwent microwave heat pump drying at 350W and 70°C.

[0048] Experimental results are shown in Table 1.

[0049] Table 1. Effects of different drying methods on the dehydration rate of asparagus stems.

[0050] deal with Dehydration rate % A 95.16 B 94.65 C 95.01 D 89.34 E 73.24 F 78.67 G 69.76 H 75.19

[0051] As shown in Table 1, microwave heat pump drying is more suitable for dehydrating and drying old asparagus stems than microwave hot air drying. When using microwave heat pump drying, excessively high or low microwave power and temperature will result in poor dehydration efficiency, which will be detrimental to subsequent steam explosion treatment.

[0052] Experimental Example 2

[0053] Effects of different magnetic induction electric field reaction conditions on the extraction of insoluble dietary fiber from old asparagus stems

[0054] Seven groups (A, B, C, D, E, F, and G) were set up. Asparagus stems were extracted under different magnetic induction electric field conditions. The resulting extracts were dried at 105°C to constant weight, pulverized, and weighed to obtain insoluble dietary fiber. The insoluble dietary fiber extraction rate (%) was calculated as: insoluble dietary fiber (g) / dry weight of asparagus stems (g). Specifically, group A was extracted according to the method in Example 1; group B according to the method in Example 2; group C according to the method in Example 3; group D had the excitation voltage of the magnetic induction electric field in Example 1 changed to 250V; group E had the excitation voltage of the magnetic induction electric field in Example 1 changed to 550V; group F had the frequency of the magnetic induction electric field in Example 1 changed to 450Hz; and group G had the frequency of the magnetic induction electric field in Example 1 changed to 550Hz.

[0055] Experimental results are shown in Table 2.

[0056] Table 2. Extraction rate of insoluble dietary fiber from old asparagus stems under different magnetic induction electric fields.

[0057] deal with Extraction rate % A 69.89 B 69.76 C 69.81 D 48.13 E 45.62 F 50.04 G 49.13

[0058] As shown in Table 2, appropriately increasing the excitation voltage and frequency of the magnetic induction electric field can greatly improve the extraction rate of insoluble dietary fiber, but excessively high excitation voltage and frequency will inhibit the enzymatic hydrolysis of cellulose.

[0059] Experimental Example 3

[0060] Performance determination of nano-asparagus microcrystalline cellulose prepared in Examples 1-3

[0061] 1. Calculate the yield of nano-asparagus microcrystalline cellulose.

[0062] Nano-asparagus microcrystalline cellulose yield / % = microcrystalline cellulose mass / insoluble dietary fiber mass in old asparagus stems × 100%.

[0063] 2. Determination of the degree of polymerization (DP) of nano-asparagus microcrystalline cellulose

[0064] Weigh 0.900g of water-free nano-asparagus microcrystalline cellulose sample, accurate to 0.5mg, and place it in a 30mL dissolving bottle. Add 15mL of distilled water and 7 copper plates, tighten the stopper, and shake vigorously to disperse the sample. Then, measure 15mL of copper ethylenediamine solution into the bottle and remove air by adding glass beads. Tighten the stopper and place the bottle in a reciprocating shaker for about 15 minutes. After the sample is completely dissolved, place the dissolving bottle in a viscometer to test the solution outflow time. Calculate the intrinsic viscosity value using the calculated relative viscosity and then calculate the average degree of polymerization according to Formula I.

[0065] DP 0.905 =0.75[η] (Formula I)

[0066] In Equation I: DP - average degree of polymerization;

[0067] [η] - Intrinsic viscosity value.

[0068] 3. Determination of carbohydrates in nano-asparagus microcrystalline cellulose

[0069] Accurately weigh approximately 100 mg of nano-asparagus microcrystalline cellulose sample and completely transfer it to a 250 mL Erlenmeyer flask using 20 mL of distilled water. Add 50 mL of 0.5 mol / L potassium dichromate solution, shake well, and slowly add 100 mL of concentrated sulfuric acid along the wall. Heat to a gentle boil, and after cooling to room temperature, transfer to a 250 mL volumetric flask. Dilute to volume with water and mix well. Pipette 5 mL of the treated solution, add 1 drop of o-phenanthroline-ferrous indicator solution, and titrate with a standardized ferrous ammonium sulfate standard solution (0.1 mol / L). Record the volume consumed. Titrate the blank simultaneously. Calculate the carbohydrate content in the nano-asparagus microcrystalline cellulose using Formula II.

[0070]

[0071] In Formula II: ω represents the carbohydrate content (%) in nano-asparagus microcrystalline cellulose;

[0072] V1 - Volume of ferrous ammonium sulfate consumed during blank titration, mL

[0073] V2 - Volume of ferrous ammonium sulfate consumed during titration of the sample solution, mL

[0074] Concentration of c-ferrous ammonium sulfate standard solution, mol / L

[0075] Mass of m-microcrystalline cellulose sample, g

[0076] 4. X-ray diffraction analysis of microcrystalline cellulose

[0077] Instrument parameters: copper target X-ray tube, LynxEye array detector, tube power: 2.2kW, scanning mode: goniometer, angle accuracy: 0.001°, angle range: 10~90°. The prepared nano-asparagus microcrystalline cellulose was placed in a circular sample cell, flattened with a glass slide, and then placed into the instrument for testing.

[0078] Calculate the crystallinity index using the formula.

[0079]

[0080] In Formula III: ICr represents the crystallinity index.

[0081] I 002 This represents the maximum diffraction intensity of plane 002.

[0082] I am This represents the diffraction intensity in the amorphous region.

[0083] Experimental results are shown in Table 3.

[0084] Table 3. Performance test results of nano-asparagus microcrystalline cellulose prepared in Examples 1-3

[0085] deal with Yield % Degree of aggregation Carbohydrate content % Crystallinity % Example 1 53.18 86.64 108.91 70.03 Example 2 51.89 84.72 106.33 69.15 Example 3 52.97 85.97 107.45 68.34

[0086] Table 3 shows that the degree of polymerization affects the yield of microcrystalline cellulose products; the lower the degree of polymerization, the greater the probability that the macromolecular cellulose will be degraded into glucose. Carbohydrate content is the main indicator for judging the purity of microcrystalline cellulose. It is evident that the nano-asparagus microcrystalline cellulose prepared in Examples 1-3 has high yield, good quality, and high purity.

[0087] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing nano-asparagus microcrystalline cellulose, characterized in that, Includes the following steps: 1) Dry the old asparagus stems or asparagus stalks with microwave heat pump, rehydrate them, and then perform steam explosion treatment to obtain crude fiber; 2) After the crude fiber is subjected to alkaline hydrolysis, acid hydrolysis and decolorization, a hydrolysate is obtained. The hydrolysate is mixed with cellulase and extracted with magnetic induction electric field to obtain an extract. 3) After acid hydrolysis of the extract, the solid hydrolysate was filtered to obtain the solid hydrolysate. The solid hydrolysate was washed and dried to obtain nano-asparagus microcrystalline cellulose. The excitation voltage of the magnetic induction electric field is 300~500V, and the frequency of the magnetic induction electric field is 500~700Hz.

2. The preparation method according to claim 1, characterized in that, Step 1) The power of the microwave heat pump drying is 300~400W, and the temperature of the microwave heat pump drying is 55~65℃.

3. The preparation method according to claim 1, characterized in that, Step 1) The pressure for the steam explosion treatment is 1.2~1.5 MPa, and the time for the steam explosion treatment is 1~3 min.

4. The preparation method according to claim 1, characterized in that, Step 2) The amount of cellulase used is 0.06~0.08% of the mass of the hydrolysate; The excitation voltage of the magnetic induction electric field is 300~500V, and the frequency of the magnetic induction electric field is 500~700Hz.

5. The preparation method according to claim 1, characterized in that, Step 2) The alkaline hydrolysis uses a sodium hydroxide solution with a mass concentration of 2-4%, the alkaline hydrolysis temperature is 80-120℃, the time is 1.0-1.5h, the weight ratio of the asparagus old stem to the sodium hydroxide solution is 1:0.5-1.5, or the weight ratio of the asparagus stalk to the sodium hydroxide solution is 1:0.5-1.

5.

6. The preparation method according to claim 1, characterized in that, Step 2) The acid hydrolysis is performed using a hydrochloric acid solution with a mass concentration of 4-6% at 80-100℃ for 0.5-1.5 hours. The weight ratio of the asparagus stalks to the hydrochloric acid solution is 1:4-8, or the weight ratio of the asparagus stalks to the hydrochloric acid solution is 1:9-11.

7. The preparation method according to claim 1, characterized in that, Step 2) The decolorization treatment is as follows: first, treat with a 1.5-2.5% H2O2 solution at 55-65℃ for 0.5-1.5 h to decolorize, then rinse with a 1.5-2.5% sodium sulfite solution until neutral, and wash with water 1-3 times; the weight ratio of the asparagus old stem to the H2O2 solution is 1:4-6, or the weight ratio of the asparagus stalk to the H2O2 solution is 1:4-6.

8. The preparation method according to claim 1, characterized in that, Step 3) The acid hydrolysis treatment uses a hydrochloric acid solution with a mass concentration of 6-9% and hydrolyzes at 80-100℃ for 0.5-1.5h.

9. Nano-asparagus microcrystalline cellulose prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the nano-asparagus microcrystalline cellulose according to claim 9 in improving the emulsification stability of milk tea.

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