Extraction method and application of insoluble dietary fibers in Yuan River asparagus processing by-products

Abstract

The invention discloses a method for extracting insoluble dietary fibers from Yuan River asparagus processing by-products and application of the insoluble dietary fibers. According to the method, a sodium citrate solution is added into asparagus shell powder for constant-temperature extraction, and ultrasonic temperature-controlled extraction is carried out. And adding cellulase, saccharifying enzyme and neutral protease for enzymolysis, heating for enzyme deactivation, centrifuging, washing and dehydrating the precipitate with ethanol, drying and crushing to obtain the insoluble dietary fiber. The insoluble dietary fiber has relatively strong water-holding capacity and oil-holding capacity, has relatively strong adsorption capacity on cholesterol, sodium cholate and glucose, and has relatively strong scavenging capacity on DPPH, ABTS and hydroxyl free radicals. According to the method, the used raw materials are byproducts in the processing process of the Yuan River asparagus, the cost of the raw materials is low, the asparagus shells are turned into wealth, the pollution of the processing waste to the environment is reduced, and the extracted insoluble dietary fibers have good functional characteristics, can be used for developing functional products for reducing blood fat and the like, and have good application prospects. The potential market prospect is realized.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, and more specifically to an extraction method and application of insoluble dietary fiber in byproducts of Yuanjiang asparagus processing. Background Art

[0002] Yuanjiang City is located in the hinterland of Dongting Lake. It is known as the "land of fish and rice" and the "land of reeds". The city has a reed area of ​​450,000 mu and an annual output of 370,000 tons of reeds, accounting for more than 50% of the total reed production in the Dongting Lake area. Its large output and excellent quality are well-known in the province and even the country. More than 90% of the reeds in Yuanjiang belong to the Nandi population. Asparagus is the seedling of Nandi, rich in flavonoids, dietary fiber, organic selenium, calcium, magnesium, zinc and other trace elements. It has obvious characteristics of high potassium and low sodium. It is a natural, healthy, green and environmentally friendly rare food. Yuanjiang asparagus has a large biomass, high dietary fiber content, low ash content, strong stress resistance, and low production and management costs. It is a pure natural and pollution-free health wild plant resource. It has a good development and utilization value as a medicinal and edible raw material plant resource and has attracted much attention in recent years.

[0003] Dietary fiber is a polysaccharide, known as the "seventh nutrient", mainly found in coarse grains, vegetables and fruits. It can neither be digested nor provide energy for the human body. Depending on whether it is soluble in water, it can be divided into soluble dietary fiber (SDF) and insoluble dietary fiber (IDF). Both types of dietary fiber have unique functions, which can improve the structure of intestinal flora, reduce the intestinal absorption of glucose and lipids, lower blood sugar, blood lipids and cholesterol indicators, and reduce the risk of cardiovascular and cerebrovascular diseases, diabetes and certain cancers.

[0004] In the invention patent "Method for preparing functional dietary fiber by enzymatic hydrolysis of discarded bamboo shoots", the inventor used bamboo shoots discarded after bamboo shoot processing as raw materials, added cellulose decomposing enzyme solution for enzymatic hydrolysis. The invention method is simple and reasonable, effectively utilized the fiber resources in bamboo shoots, and increased the soluble dietary fiber content in bamboo shoots. In the invention patent "A method for extracting and preparing bamboo shoot dietary fiber from bamboo shoots waste", the inventor used microwave-ultrasonic combined assisted extraction method to extract soluble and insoluble bamboo shoot dietary fiber from bamboo shoots waste. The preparation method has high extraction efficiency and high dietary fiber yield. In the invention patent "A kind of Lei bamboo shoot dietary fiber and its preparation method", the inventor used bamboo shoot residue after juicing as raw materials, and adopted chemical extraction combined with fungal fermentation to prepare dietary fiber. The prepared dietary fiber has better water holding capacity, swelling capacity and water binding capacity than the chemical method and fermentation method alone. This method effectively reduces production costs and solves the environmental pollution problem caused by the waste of bamboo shoot residue. In the invention patent "A method for preparing insoluble dietary fiber from rice bran", the inventor used defatted rice bran as raw material, added high-temperature amylase for enzymatic hydrolysis, and then used high-pressure microfluidization for treatment. The yield of insoluble dietary fiber obtained reached 38.5% and the purity reached more than 80%.

[0005] In December 2015, Yuanjiang asparagus registered the "National Geographical Indication Certification Trademark" with the State Administration for Industry and Commerce. In August 2017, it obtained the "Registration of Agricultural Product Geographical Indication". In July 2018, Yuanjiang asparagus was rated as the "one county, one specialty" leading characteristic industry in Yuanjiang City by Hunan Province. Up to now, there are 16 asparagus production and sales enterprises in Yuanjiang City, including 4 provincial leading enterprises and 7 municipal leading enterprises. The total fixed asset investment has reached 500 million yuan, the asparagus output has reached about 30,000 tons, and the comprehensive output value has reached 3 billion yuan. However, the picking period of Yuanjiang asparagus is short. It is concentrated in March every year for picking and processing. After the processing procedures such as killing, shelling, pickling, desalting and trimming, only about 30% of the edible part remains, and 70% of the asparagus shells are discarded, causing great environmental pollution. Therefore, the comprehensive utilization of the by-products of Yuanjiang asparagus processing can not only turn waste into treasure and increase the added value of products, but also solve the environmental pollution problem in the asparagus processing process. Summary of the invention

[0006] Aiming at the blank of comprehensive utilization of by-products in the processing of Yuanjiang asparagus, the present invention provides an extraction method and application of insoluble dietary fiber in the by-products of Yuanjiang asparagus processing.

[0007] In order to achieve the above object, the technical solution provided by the present invention is: The method for extracting insoluble dietary fiber from the byproduct of Yuanjiang asparagus processing comprises the following steps: (1) Mixing asparagus shell powder and sodium citrate solution at a mass volume ratio of 1:100 to 1:200, and extracting at a constant temperature of 60°C for 4 to 6 hours, preferably 4 hours, to obtain a sample solution; the unit of the mass volume ratio is g / mL; (2) subjecting the sample solution obtained in step (1) to ultrasonic treatment; (3) adding cellulase, saccharifying enzyme and neutral protease to the sample solution treated in step (2), wherein the mass percentage contents of cellulose, saccharifying enzyme and neutral protease in the sample solution are 1.5-3%, 0.1-0.2% and 0.4% respectively, stirring and mixing, performing enzymolysis in a constant temperature water bath and then boiling to inactivate the enzyme, obtaining the sample solution after enzyme treatment, and then centrifuging to obtain the precipitate; (4) The precipitate in step (3) is washed with water, dehydrated with ethanol, and then dried, crushed and sieved to obtain insoluble dietary fiber.

[0008] Preferably, the asparagus shells used in step (1) are the shells peeled off when the fresh asparagus is withered during the traditional processing of Yuanjiang asparagus and the shells peeled off when the asparagus is trimmed after pickling.

[0009] Preferably, the concentration of sodium citrate in the sodium citrate solution in step (1) is 0.1 mol / L, and the mass volume ratio of the asparagus shell powder to the sodium citrate solution is 1:150.

[0010] Preferably, the ultrasonic treatment time in step (2) is 20-30 min, preferably 20 min, the ultrasonic temperature is 20-60° C., preferably 40° C., and the ultrasonic power is 100-250 W, preferably 150 W.

[0011] Preferably, the enzymatic activities of the cellulase, saccharifying enzyme and neutral protease in step (3) are 3000 U / g, 50000 U / g and 50000 U / g, respectively.

[0012] Preferably, in step (3), the mass percentage contents of cellulase, saccharifying enzyme and neutral protease in the sample solution are 2%, 0.2% and 0.4% respectively, the enzymolysis time is 1-3 h, and the enzymolysis temperature is 40-60°C.

[0013] Preferably, the boiling and enzyme inactivation time in step (3) is 10-15 min, and the centrifugation condition is 6000-12000 rpm for 5-10 min.

[0014] Preferably, the precipitate in step (4) is rinsed with 30-50 mL, preferably 30 mL, of 80% ethanol, and the drying temperature is 40-60° C., preferably 60° C., and the drying time is 8-12 h, preferably 10 h.

[0015] The insoluble dietary fiber obtained by the method of the present invention has strong water-holding capacity and oil-holding capacity, has strong adsorption capacity for cholesterol, sodium cholate and glucose, and has strong scavenging capacity for DPPH, ABTS and hydroxyl free radicals. The raw materials used in the method are by-products in the processing of Yuanjiang asparagus, and the raw material cost is low. The method not only realizes the transformation of asparagus shells into treasure, but also reduces the pollution of processing waste to the environment. The extracted insoluble dietary fiber has good functional characteristics, indicating that it can be used in the development of functional products such as lowering blood lipids, and has potential market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a graph showing the effect of the IDF of Yuanjiang asparagus shell on cholesterol adsorption capacity; Figure 2 This is a graph showing the effect of different concentrations of Yuanjiang asparagus shell IDF on the scavenging rate of DPPH free radicals; Figure 3 is the scavenging rate of hydroxyl free radicals by different concentrations of Yuanjiang asparagus shell IDF of the present invention; Figure 4 It is the scavenging rate of ABTS free radicals by the Yuanjiang asparagus shell IDF of different concentrations of the present invention. DETAILED DESCRIPTION

[0017] The Yuanjiang asparagus shells are selected, cleaned, dried, crushed, sieved through a 60-mesh sieve, packed in bags, sealed, and stored in a desiccator for later use.

[0018] Asparagus shell powder was weighed and added with 0.1 M sodium citrate solution at a solid-liquid ratio of 1:200 (g / mL) for constant temperature extraction at 60 ℃ for 4 h, the pH value was adjusted to neutral with buffer, and ultrasonic temperature control (40 ℃, 150 W) was used for 20 min. Cellulase, saccharifying enzyme, and neutral protease (3000 U / g, 50000 U / g, and 50000 U / g) were added, and enzymolysis was carried out at 50 ℃ for 3 h, enzyme inactivation was carried out for 10 min, and the sample after enzyme inactivation was centrifuged at 8000 rpm for 10 min, and the precipitate was washed and dehydrated with 30 mL of 80% ethanol, and then dried at 60 ℃ for 10 h. After crushing and sieving, insoluble dietary fiber (IDF) was obtained.

[0019] The monosaccharide composition of IDF of Yuanjiang asparagus shell was analyzed by PMP pre-column derivatization HPLC. The chromatographic separation conditions were as follows: sodium phosphate buffer (0.05 mol / L, pH 6.85)-acetonitrile (87∶17, V∶V) as the mobile phase, flow rate 1 mL / min, isocratic elution for 60 min, and UV detection wavelength of 250 nm.

[0020] As shown in Table 1, 8 monosaccharides including xylose, glucose, arabinose, galactose, mannose, rhamnose, galacturonic acid and glucuronic acid were detected in the insoluble dietary fiber of Yuanjiang River, which was mainly composed of xylose, galactose and arabinose, and the total content could reach 92.56%, indicating that the hemicellulose content in the insoluble dietary fiber of Yuanjiang River asparagus shell was high. The content of galacturonic acid was low, and the soluble pectin substances were relatively small.

[0021] Monosaccharides content / % Xylose 59.10 glucose 5.41 Galactose 18.14 Arabinose 15.32 Mannose 0.65 Rhamnose 0.15 Galacturonic acid 1.06 Glucuronic acid 0.37

[0022] (1) Water holding capacity determination Weigh 0.5 g of insoluble dietary fiber sample, mix it with 15 mL of distilled water and add it to a 50 mL centrifuge tube. Shake it at room temperature for 24 h and then centrifuge it (4000 rpm, 10 min). Take out the precipitate and weigh it, dry it in an oven at 105°C and weigh it, and calculate the water holding capacity of the sample according to the following formula.

[0023]

[0024] Where: m1 is the wet weight of the sample after absorbing water (g); m2 is the weight of the sample after drying after absorbing water (g).

[0025] (2) Expansion force measurement Add 0.2 g of dietary fiber sample to a 25 mL measuring cylinder, then add 10 mL of distilled water and let stand at room temperature for 18 hours. Read the volume of the sample before and after 18 hours, and calculate the water absorption expansion capacity of the sample according to the following formula.

[0026]

[0027] Where: V1 is the volume of the sample after water absorption and expansion (mL); V0 is the volume of the sample before water absorption and expansion (mL); m is the mass of the sample before water absorption and expansion (g).

[0028] (3) Oil holding capacity measurement Weigh 0.2 g of dietary fiber sample and place it in a 50 mL centrifuge tube. Add 5 mL of soybean oil and mix well. Let it stand at room temperature for 1 h and then centrifuge (4000 rpm, 10 min). Remove the upper layer of oil sample, collect and weigh the precipitate, and calculate the oil holding capacity of the sample according to the following formula.

[0029]

[0030] Where: m1 is the dry weight of the sample (g); m2 is the wet weight of the sample (g). As shown in Table 2, the water holding capacity and swelling capacity of the insoluble dietary fiber in Yuanjiang asparagus shell are higher than those in ordinary bamboo shoot shells, and are better than the commonly used bran dietary fiber standards (water holding capacity 4.00 g / g, swelling capacity 4.00 mL / g). High water holding capacity and swelling capacity can absorb a large amount of water in the human intestine, increase the volume and speed of human defecation, thereby shortening the time that food residues and toxic substances stay in the intestine, reducing the accumulation of excessive fat in the body, and reducing the potential risk of disease. The oil holding capacity of the insoluble dietary fiber in Yuanjiang asparagus shell is (5.32±0.02) g / g, which is also higher than that of the insoluble dietary fiber in ordinary bamboo shoot shells. It can better reduce the accumulation of saturated fatty acids in the human body and has a positive effect on the prevention and treatment of cardiovascular diseases and hyperlipidemia.

[0031] (1) Cholesterol adsorption capacity determination The cholesterol standard curve was drawn with reference to the method of GB5009.128-2016 and slightly modified. The specific operation is as follows: 0.00 mL, 0.50 mL, 1.00 mL, 1.50 mL, 2.00 mL, 2.50 mL, and 3 mL of cholesterol standard solution were respectively placed in 10 mL test tubes, glacial acetic acid was added to each tube to make the total volume reach 4 mL, 2 mL of iron alum colorimetric solution was slowly added along the wall of the test tube, mixed evenly, and colorimetric analysis was performed at 560-575 nm after 20 min. The standard curve was drawn with cholesterol content as the horizontal axis X and absorbance value OD as the vertical axis Y.

[0032] Take the egg yolk of commercially available fresh eggs, dilute it with 9 times distilled water, and stir it thoroughly to form an emulsion. In a 200 mL dry conical flask, first add 0.5 g of dietary fiber sample and record it as a, then measure 30 mL of egg yolk emulsion and add it, shake it thoroughly, mix it evenly, adjust the pH value of the system to 2.0 and 7.0 respectively, place it in a shaker, oscillate at 37℃ for 2 hours, centrifuge it at 4000 r / min for 20 minutes, take 4 mL of supernatant, measure its absorbance value at a wavelength of 550 nm, calculate the amount of cholesterol in the sample before adsorption, record it as b, and the amount of cholesterol after adsorption, record it as c, and calculate it according to the following formula.

[0033]

[0034] Where: b is the amount of cholesterol before sample adsorption (μg / g); c is the amount of cholesterol after sample adsorption (μg / g); a is the sample weight (g).

[0035] (2) Determination of sodium cholate binding capacity Preparation of sodium cholate content standard curve: Pipette 0.00 mL, 0.20 mL, 0.40 mL, 0.60 mL, 0.80 mL and 1.00 mL of sodium cholate standard solution into capped test tubes, and add 1.00 mL of distilled water. Add 6 mL of 45% hydrochloric acid and 1 mL of 0.3% furfural solution, mix and shake well. Heat the reaction in a 65℃ water bath for 0.5 h. Place the container containing the reaction solution in a water pool, and after the reaction solution cools to room temperature, detect its absorbance at 620 nm in a UV spectrophotometer.

[0036] Accurately weigh 0.2 g of insoluble dietary fiber sample into two conical bottles, add 100 mL of 15 mmol / L sodium chloride solution containing 0.3 g and 0.6 g sodium cholate adjusted to pH 7 in advance, stir evenly, shake at a constant temperature of 37°C in a shaker for 2 h, centrifuge (4200 rpm, 20 min), and take the supernatant to determine the sodium cholate concentration. Calculate the sodium cholate binding capacity according to the following formula.

[0037]

[0038] Where: mL is the content of sodium cholate before sample adsorption (mg); m2 is the content of sodium cholate in the supernatant after sample adsorption (mg); m is the sample weight (g). The functional properties of insoluble dietary fiber from Yuanjiang asparagus shell are shown in Table 3. As can be seen from the table, the cholesterol adsorption capacity of insoluble dietary fiber from Yuanjiang asparagus shell at pH=7 is stronger than that at pH=2, indicating that the ability of insoluble dietary fiber to bind cholesterol in the small intestine is better than that in gastric acid. Because in an acidic environment, hydrogen ions make both IDF and cholesterol positively charged, and the electrostatic repulsion between the two reduces the binding force, and the cholesterol adsorption capacity decreases.

[0039] (3) Determination of glucose adsorption Preparation of glucose standard curve: Pipette 0.00 mL, 0.20 mL, 0.40 mL, 0.60 mL, 0.80 mL and 1 mL of glucose standard solution into test tubes, add water to 1 mL, add 0.5 mL of 6% phenol and 2.5 mL of concentrated sulfuric acid, shake quickly to mix, let stand for 30 min, and then detect the absorbance at 490 nm with a UV spectrophotometer. Draw a standard curve with glucose content as the horizontal axis X and absorbance value OD as the vertical axis Y.

[0040] Figure 1The figure shows the adsorption capacity of insoluble dietary fiber from Yuanjiang asparagus shell for glucose. As can be seen from the figure, with the increase of glucose concentration gradient, the adsorption capacity of insoluble dietary fiber from Yuanjiang asparagus shell for glucose is greatly improved, especially when the glucose concentration is 10 mmol / L to 50 mmol / L, the increase is most obvious, from 0.84~3.40 mmol / g·L. The increase in concentration increases the contact area between dietary fiber and glucose, and the binding force on glucose will be enhanced. The function of dietary fiber in lowering blood sugar mainly comes from its ability to effectively absorb glucose, which can hinder the diffusion and absorption of glucose in the human body, thereby reducing the concentration of glucose and maintaining normal blood sugar levels after meals.

[0041] (1) Determination of DPPH free radical scavenging ability Dietary fiber was prepared into concentrations of 0.1, 0.25, 0.5, 0.75, 1, and 2 mg / mL for later use. The prepared concentration was 2×10 -4 mol / L DPPH-ethanol solution, store in dark for later use, and dilute with anhydrous ethanol to an absorbance of 0.600±0.02 at 517 nm by spectrophotometer before use. Add 2 mL of sample solution with different concentration gradients to the test tube, add 2 mL DPPH solution, mix well and react in dark for 30 min, measure the absorbance at 517 nm and record it as A1; at the same time, measure the absorbance of 2 mL anhydrous ethanol and sample solution with different concentration gradients and record it as A2, and 2 mL DPPH solution plus 2 mL distilled water as blank, and its absorbance is recorded as A0; Vc is used as the positive control group. Calculate the free radical scavenging rate of each sample for DPPH according to the following formula.

[0042]

[0043] Where: A1——the absorbance of DPPH plus the sample to be tested; A2——the absorbance of anhydrous ethanol plus the sample to be tested; A0——The absorbance of DPPH plus distilled water.

[0044] from Figure 2 It can be seen that within the mass concentration range of 0.1~2 mg / mL, with the increase of mass concentration, the scavenging rate of insoluble dietary fiber on DPPH free radicals also gradually increased, ranging from 10.5% to 82.7%. Compared with Vc, due to the strong antioxidant activity of Vc, the antioxidant activity of insoluble dietary fiber from Yuanjiang asparagus shell is not as good as that of Vc at low mass concentrations. As the mass concentration increases, the scavenging effect on DPPH gradually approaches that of Vc. This shows that Yuanjiang asparagus shell IDF has antioxidant activity and has a good effect on scavenging DPPH free radicals, and its effect is closely related to its concentration.

[0045] (2) Determination of hydroxyl radical scavenging ability Dietary fiber was prepared into concentrations of 0.1, 0.25, 0.5, 0.75, 1, and 2 mg / mL for later use. 0.2 mL of sample solution of different concentrations was mixed with 0.2 mL of 5 mmol / L FeSO4 solution, and then 0.2 mL of 1% (v / v) H2O2 was added. After reacting at room temperature for 60 min, 1 mL of deionized water was added and the absorbance was detected at 536 nm. Deionized water was used as the blank group and Vc was used as the positive control group. The free radical scavenging rate was calculated using the following formula.

[0046]

[0047] In the formula: A0 is the absorbance of the sample to be tested; A1 is the absorbance of the blank group; A2 is the absorbance of the control group.

[0048] from Figure 3 It can be seen that the scavenging ability of insoluble dietary fiber from Yuanjiang asparagus shell on hydroxyl free radicals increases with the increase of mass concentration, and the scavenging rate is between 2.13% and 25.13%, with significant differences.

[0049] (3) Determination of ABTS free radical scavenging ability Dietary fiber was prepared into concentrations of 0.1, 0.25, 0.5, 0.75, 1, and 2 mg / mL, and 0.01 mL of sample solutions of different concentrations were fully mixed with 0.19 mL of ABTS free radical working solution, and the absorbance at 734 mm was measured within 10 min; the extract was used as the blank group, and Vc was used as the positive control group. The ABTS free radical scavenging rate was calculated according to the following formula:

[0050] Where: A0 is the absorbance of the extract solution + ABTS free radical working solution; A1 is the absorbance of the sample solution + ABTS free radical working solution.

[0051] from Figure 3 It can be seen that the scavenging ability of insoluble dietary fiber from Yuanjiang asparagus shell is very low at low concentrations. The clearance rate is only 23.43% at a concentration of 1 mg / mL. When the concentration increases to 2 mg / mL, the clearance rate reaches 37.9%, indicating that with the increase in mass concentration, the scavenging ability of insoluble dietary fiber on ABTS free radicals gradually increases, showing a positive correlation, and it is dose-dependent.

[0052] In summary, the insoluble dietary fiber from Yuanjiang asparagus shell has good water holding capacity, swelling capacity and oil holding capacity, and is significantly better than the insoluble dietary fiber from ordinary bamboo shoot shells. In addition, it has good cholesterol, sodium cholate and glucose adsorption capacity, and is a dietary fiber with high utilization rate. The insoluble dietary fiber from Yuanjiang asparagus shell has a good scavenging effect on free radicals, with obvious dose dependence, and the scavenging effect gradually increases with the increase of mass concentration. In general, the insoluble dietary fiber extracted from Yuanjiang bamboo shoot shell has good hypoglycemic and antioxidant abilities, and can also provide a reference for the reuse of Yuanjiang asparagus shell.

[0053] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0054] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for extracting insoluble dietary fiber from byproducts of Yuanjiang asparagus processing, characterized in that: The method comprises the following steps: (1) Mix asparagus shell powder and sodium citrate solution at a mass-to-volume ratio of 1:100 to 1:200, and extract at a constant temperature of 60°C for 4 to 6 hours to obtain a sample solution; the unit of the mass-to-volume ratio is g / mL; (2) subjecting the sample solution obtained in step (1) to ultrasonic treatment; (3) adding cellulase, saccharifying enzyme and neutral protease to the sample solution treated in step (2), wherein the mass percentage contents of cellulose, saccharifying enzyme and neutral protease in the sample solution are 1.5-3%, 0.1-0.2% and 0.4% respectively, stirring and mixing, performing enzymolysis in a constant temperature water bath and then boiling to inactivate the enzyme, obtaining the sample solution after enzyme treatment, and then centrifuging to obtain the precipitate; (4) The precipitate in step (3) is washed with water, dehydrated with ethanol, and then dried, crushed and sieved to obtain insoluble dietary fiber.

2. The method according to claim 1, characterized in that The asparagus shells used in step (1) are the shells peeled off when the fresh asparagus is withered during the traditional processing of Yuanjiang asparagus and the shells peeled off when the asparagus is trimmed after pickling.

3. The method according to claim 1, characterized in that The concentration of sodium citrate in the sodium citrate solution in step (1) is 0.1 mol / L, and the mass volume ratio of the asparagus shell powder to the sodium citrate solution is 1:

150.

4. The method according to claim 1, characterized in that The ultrasonic treatment time in step (2) is 20-30 min, the ultrasonic temperature is 20-60°C, and the ultrasonic power is 100-250 W.

5. The method according to claim 1, characterized in that The enzymatic activities of the cellulase, saccharifying enzyme and neutral protease in step (3) are 3000 U / g, 50000 U / g and 50000 U / g respectively.

6. The method according to claim 1, characterized in that In step (3), the mass percentage contents of cellulase, saccharifying enzyme and neutral protease in the sample solution are 2%, 0.2% and 0.4% respectively, the enzymolysis time is 1-3 h, and the enzymolysis temperature is 40-60°C.

7. The method according to claim 1, characterized in that The boiling time for inactivating the enzyme in step (3) is 10-15 min, and the centrifugation condition is 6000-12000 rpm for 5-10 min.

8. The method according to claim 1, characterized in that The precipitate in step (4) is rinsed with 30-50 mL of 80% ethanol and dried at a temperature of 40-60° C. for 8-12 h.

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