An ultrasonic synergistic biological enzyme method for extracting insect chitin and chitosan

Abstract

The application discloses an ultrasonic and biological enzyme method for extracting insect chitin and chitosan. The ultrasonic and biological enzyme method for extracting insect chitin and chitosan provided by the application uses a double-frequency synchronous ultrasonic (20+28HZ) combined with an intermittent ultrasonic method, and the extraction rate of the extracted chitosan is 3% to 5%, the deacetylation degree of the chitosan is 89.32 to 97.21%, the solubility is 87.54 to 90.3%, and the molecular weight is 3.214*10 4 Da to 3.799*10 4 Da, the crystallinity is 81.11 to 98.93%, and the viscosity is 438.4 to 755.4 mPa.s.The method can improve the product quality and production efficiency, greatly reduce the use amount of harmful chemicals such as acid and alkali, effectively control environmental pollution, and is more suitable for industrial development.

Description

Technical Field

[0001] This invention relates to a method for extracting insect chitin and chitosan using an ultrasound-assisted bioenzymatic method, belonging to the field of insect chitosan preparation technology. Background Technology

[0002] Chitin is a high-molecular-weight compound composed of N-acetyl-2-amino-2-deoxy-D-glucose linked by β-1,4 glycosidic bonds. It is a naturally occurring, nitrogen-containing, homogeneous mucopolysaccharide. Due to the presence of acetyl groups on the chitin molecule and the hydrogen bonds between these acetyl groups, chitin is insoluble in water, dilute acids, dilute alkalis, and most organic solvents. This is the biggest problem encountered in the application of chitin. Chitosan, a derivative of chitin after deacetylation, is the second most abundant organic resource on Earth after cellulose. It is the only naturally occurring alkaline polysaccharide with unique physicochemical properties such as excellent adsorption, film-forming properties, antibacterial properties, and safety and non-toxicity. Therefore, it is widely used in food, medicine, functional materials manufacturing, agriculture, and light textile industries, demonstrating a very promising market prospect.

[0003] Chitosan is mainly derived from the exoskeletons of crustaceans such as shrimp and crabs, insects, as well as the cell walls of fungi and plants. Currently, the raw materials for industrial production of chitin are mainly aquatic products such as shrimp and crab shells, whose main components include protein (about 30%) and inorganic salts (mainly calcium carbonate, about 40%). Compared with shrimp and crabs, insects contain 20%-60% chitin, and their body walls contain only a small amount of inorganic salts, which is more conducive to the separation and extraction of chitin, making them a more ideal chitin resource. Silkworm pupae are a byproduct of the silk industry. my country's silk reeling industry produces about 100,000 tons of silkworm pupae annually. The chitin content in the residue generated during the production of silkworm pupa protein isolate is as high as 36%. Studies have confirmed that silkworm pupa chitosan has some superior properties compared to shrimp and crab chitosan, such as solubility, film-forming properties, and antibacterial properties. As the last stage in the growth and reproduction of mealworms, adult mealworms die after laying eggs. Dead adults are not meaningful for the breeding and reproduction of mealworms. However, adult mealworms have a high chitin content of about 19.55%, making it worthwhile to develop and utilize the dead adults to improve the utilization rate of mealworm byproducts.

[0004] Currently, the mainstream process for producing chitin and chitosan both domestically and internationally is the chemical method. The extraction route is: alkali deproteinization – acid removal of inorganic salts – oxidant decolorization – concentrated alkali deacetylation – chitosan. However, this process uses large amounts of acids, alkalis, and harmful chemical reagents, consuming energy and causing severe environmental pollution. Frequent cleaning and washing waste precious freshwater and reduces the molecular weight and acetylation degree of chitin, thus affecting product quality. Therefore, more and more people are turning to enzymatic hydrolysis and physical methods (ultrasonic extraction). Enzymatic extraction is a newer process with mild and environmentally friendly reaction conditions, but it suffers from long extraction times, low efficiency, and incomplete deproteinization. It also requires the addition of NaOH and treatment under relatively mild conditions to improve the purity and structure of chitin. In recent years, ultrasonic extraction has attracted more attention due to its advantages such as mild extraction conditions, short extraction time, convenient operation, less loss of active ingredients, and high extraction rate. Some studies have also combined enzymatic methods with ultrasonic extraction, using the thermal, cavitation and mechanical effects of ultrasound to accelerate the release, diffusion and dissolution of intracellular effective substances, thereby improving the extraction rate while shortening the extraction time. However, existing methods only use single-frequency ultrasound for extraction, and the degree of deacetylation, molecular weight and viscosity of the extracted chitin and its derivatives are not ideal. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide an ultrasonic-assisted bioenzymatic method for extracting insect chitin and chitosan, which significantly improves the extraction rate, degree of deacetylation, solubility, crystallinity and viscosity of the obtained chitosan.

[0006] Technical solution: The present invention provides an ultrasonic-assisted bioenzymatic extraction method for insect chitin and chitosan, comprising the following steps:

[0007] (1) Pre-treat the insects containing chitosan and grind them into powder for later use;

[0008] (2) The insect powder obtained in step (1) is mixed with distilled water to form a suspension. An alkaline solution is added to adjust the pH of the suspension to the optimal pH of the protease. The suspension is pretreated. After adding the protease, the protein is enzymatically hydrolyzed by dual-frequency synchronous ultrasound. The enzyme is inactivated. The supernatant is removed by centrifugation. The precipitate is washed until neutral, filtered, and dried. The conditions for dual-frequency synchronous ultrasound are: ultrasound frequency 20+28HZ, ultrasound power 110-130W, ultrasound temperature 40-50℃, and ultrasound time 0.5-2.5h.

[0009] (3) Add the dried filter residue from step (2) into the acid solution, perform dual-frequency synchronous ultrasonication, filter, wash, and dry to obtain chitin.

[0010] (4) Chitin was subjected to dual-frequency synchronous ultrasonic decolorization treatment;

[0011] (5) Add a low concentration of sodium hydroxide solution to the decolorized chitin, intermittently sonicate, filter, wash, and dry to obtain chitosan.

[0012] The insects mentioned in step (1) include silkworm pupae or adult mealworms.

[0013] The pretreatment operation in step (1) involves soaking the insects in petroleum ether for 1-3 hours and using an electric heating drying oven at a temperature of 50-70°C.

[0014] The optimal pH in step (1) is 8.5-10.5.

[0015] In step (2), the alkaline solution is sodium hydroxide or potassium hydroxide; the protease is one or more of papain, alkaline protease, and trypsin, with an enzyme activity unit of 100,000 to 200,000 u / g.

[0016] The centrifugation conditions described in step (2) are 3000-6000 r / min and the centrifugation time is 5-10 min.

[0017] The acid solution mentioned in step (3) is one or more of acetic acid, lactic acid, hydrochloric acid, boric acid, and citric acid; the acid concentration is 5%-20%.

[0018] The dual-frequency synchronous ultrasound conditions described in step (3) are: ultrasound frequency 20+28HZ, ultrasound power 120-130W, ultrasound temperature 30-50℃, and ultrasound time 1-1.5h.

[0019] In step (4), the decolorizing agent used is one or more of potassium permanganate, hydrogen peroxide, and sodium hypochlorite, with a concentration of 8%-10%; the dual-frequency synchronous ultrasonic conditions are ultrasonic frequency 20+28HZ, ultrasonic power 110-130W, ultrasonic temperature 30-50℃, and ultrasonic time 0.5-3h.

[0020] In step (5), the concentration of the low-concentration sodium hydroxide solution is 10% to 40%, and the solid-liquid ratio of chitosan to sodium hydroxide solution is 1g:10 to 35ml.

[0021] The ultrasonic conditions for the dual-frequency synchronous ultrasound in step (5) are: ultrasonic frequency 20+28HZ, ultrasonic power 110~130W, ultrasonic temperature 60~80℃, and ultrasonic time 5~7h.

[0022] The specific steps of intermittent ultrasound in step (5) include: first, adding half the amount of sodium hydroxide to the chitin, taking it out when half of the ultrasound time has elapsed, filtering it, adding the other half of the sodium hydroxide to the precipitate, continuing the ultrasound, filtering it after the ultrasound is finished, mixing the two filtrates, adding water, cooling it to obtain a gel-like substance, which is used for subsequent filtration.

[0023] Beneficial Effects: Compared with the prior art, the present invention has the following significant advantages: The ultrasonic-assisted bio-enzymatic extraction method of the present invention for extracting insect chitin and chitosan utilizes dual-frequency synchronous ultrasound (20+28Hz) combined with intermittent ultrasound, resulting in a chitin extraction rate of 3%–5%, a chitosan deacetylation degree of 89.32–97.21%, a solubility of 87.54–90.3%, and a molecular weight of 3.214 × 10⁻⁶. 4 Da ~ 3.799 × 10 4 Da has a crystallinity of 81.11%–98.93% and a viscosity of 438.4–755.4 mPa·s. This method improves product quality and production efficiency while significantly reducing the use of harmful chemicals such as acids and alkalis, effectively controlling environmental pollution, and is more suitable for industrial development. Detailed Implementation

[0024] The technical solution of the present invention will be further described below.

[0025] Example 1

[0026] (1) Remove the internal organs of the silkworm pupae (purchased from Shandong Huimin Specialty Store) and clean them. Soak the silkworm pupae skin in petroleum ether for 1 hour at room temperature, then wash with distilled water, dry in an oven at 60°C to a constant weight, and then process with a pulverizer to obtain silkworm pupae skin powder.

[0027] (2) Weigh 10g of silkworm pupa skin powder and put it into a beaker. Add 150ml of distilled water at a material-to-liquid ratio of 1g:15ml. Mix well to make a suspension. Use 0.5mol / L The pH of the suspension was adjusted to 9 with NaOH, and the temperature was raised to 45℃. To ensure uniform mixing and prevent precipitation, the suspension was pretreated with ultrasound for 30 min (under the conditions of dual-frequency ultrasound 20+28 Hz, power 120 W, 45℃). After the treatment, the pH was measured and adjusted to 9. 8% alkaline protease with an enzyme activity of 200,000 u / g was added, and the container was sealed with plastic wrap. The enzyme was enzymatically hydrolyzed with ultrasound at frequencies of 20, 28, 40, 20+28, and 20+40 Hz, with ultrasonic powers of 90, 100, 110, 120, and 130 W, and ultrasonic temperatures of 40, 45, 50, 55, and 60℃ for 0.5, 1, 1.5, 2, and 2.5 h, respectively. After the treatment, the enzyme was inactivated by heating in a 100℃ water bath for 5 min. The enzyme was then centrifuged at 4000 r / min for 5 min. After centrifugation, the enzyme was filtered, and the resulting residue was rinsed with deionized water until neutral and then dried. The effect of various ultrasonic conditions on deproteinization was investigated using the nitrogen content of the extract as an indicator. The specific ultrasonic conditions and nitrogen content results are shown in Table 1.

[0028] Table 1

[0029] Experiment 1 20 90 40 0.5 9.07％ Experiment 2 20 100 45 1 6.98％ Experiment 3 20 110 50 1.5 4.18％ Experiment 4 20 120 55 2 3.29％ Experiment 5 20 130 60 2.5 3.56％ Experiment 6 28 90 45 1.5 9.09％ Experiment 7 28 100 50 2 6.99％ Experiment 8 28 110 55 2.5 5.57％ Experiment 9 28 120 60 0.5 3.42％ Experiment 10 28 130 40 1 3.67％ Experiment 11 40 90 50 2.5 11.51％ Experiment 12 40 100 55 0.5 10.77％ Experiment 13 40 110 60 1 10.03％ Experiment 14 40 120 40 1.5 9.81％ Experiment 15 40 130 45 2 10.66％ Experiment 16 20+28 90 55 1 3.49％ Experiment 17 20+28 100 60 1.5 2.13％ Experiment 18 20+28 110 40 2 1.41％ Experiment 19 20+28 120 45 2.5 1.05％ Experiment 20 20+28 130 50 0.5 1.39％ Experiment 21 20+40 90 60 2 6.95％ Experiment 22 20+40 100 40 2.5 4.79％ Experiment 23 20+40 110 45 0.5 3.45％ Experiment 24 20+40 120 50 1 3.37％ Experiment 25 20+40 130 55 1.5 3.05％

[0030] The results show that the nitrogen content was lowest, ranging from 1.05% to 1.41%, when the ultrasonic frequency was 20 ± 28 Hz, the ultrasonic power was 110–130 W, the ultrasonic temperature was 40–50 °C, and the ultrasonic time was 0.5–2.5 h. The lowest nitrogen content of 1.05% was taken as the optimal ultrasonic conditions, i.e., ultrasonic frequency 20 ± 28 Hz, ultrasonic power 120 W, ultrasonic temperature 45 °C, and ultrasonic time 2.5 h, for subsequent experiments.

[0031] (3) Take the dried filter residue from step (2) and place it in a beaker. Add 10% citric acid solution at a solid-liquid ratio of 1g:10ml. Use the preferred ultrasonic frequencies of 28, 20+28, and 20+40Hz and ultrasonic power of 110, 120, and 120W from step (2) and ultrasonic temperatures of 30, 40, and 50℃ for 1, 1.5, and 2 hours respectively. After the reaction, filter the residue and wash it repeatedly with deionized water until neutral. Dry it in an oven at 60℃ to a constant weight to obtain the product chitin. Detect the ash content of the obtained chitin, as shown in Table 2.

[0032] Table 2

[0033] Experiment 1 28 110 30 1 1.82％ Experiment 2 28 120 40 1.5 1.39％ Experiment 3 28 130 50 2 1.56％ Experiment 4 20+28 110 40 2 1.37％ Experiment 5 20+28 120 50 1 0.24％ Experiment 6 20+28 130 30 1.5 0.77％ Experiment 7 20+40 110 50 1.5 1.44％ Experiment 8 20+40 120 30 2 1.67％ Experiment 9 20+40 130 40 1 1.09％

[0034] The results show that the lowest ash content, ranging from 0.24% to 0.77%, was achieved when the ultrasonic frequency was 20 ± 28 Hz, the ultrasonic power was 120–130 W, the ultrasonic temperature was 30–50 °C, and the ultrasonic time was 1–1.5 h. The lowest ash content of 0.24% was taken as the optimal ultrasonic conditions, i.e., ultrasonic frequency 20 ± 28 Hz, ultrasonic power 120 W, ultrasonic temperature 50 °C, and ultrasonic time 1 h, for subsequent experiments.

[0035] (4) In order to make the color of the obtained chitin meet the national requirements for food-grade chitosan, the chitin powder with ash content of 0.24% obtained in step (2) was mixed with 8% H2O2 at a material-to-liquid ratio of 1g:10ml, and ultrasonicated at the optimal ultrasonic frequency of 20+28HZ and ultrasonic power of 120W for 30min at an ultrasonic temperature of 40℃. After the reaction was completed, the mixture was filtered, and the resulting filter residue was washed with deionized water until neutral. It was then dried in an oven at 60℃ to a constant weight to obtain the decolorized chitin.

[0036] (5) The chitin obtained in step (4) is subjected to deacetylation treatment. Usually, concentrated alkali is used for deacetylation. While a high deacetylation rate is obtained, the main chain of chitin is severely degraded, thereby reducing the molecular weight of chitosan and affecting product quality. This invention uses a low-concentration dilute alkali and removes acetyl groups through intermittent ultrasonic alkali treatment. While obtaining a high degree of deacetylation, it reduces the degradation of the chitin main chain and ensures the quality of chitosan products.

[0037] The specific operation is as follows: Take 5g of chitin powder, add half of the required amount of 20% NaOH at a material-to-liquid ratio of 1g:20ml, and sonicate for 5, 6, and 7 hours at optimal ultrasonic frequencies of 28, 20+28, and 20+40Hz, ultrasonic powers of 110, 120, and 130W, and ultrasonic temperatures of 60, 70, and 80℃. When the reaction time is halfway complete, remove the mixture after it has cooled slightly, filter off the alkaline solution (the filtrate is recovered for chitosan separation), and then add the remaining alkaline solution back into the ultrasonic reactor to continue deacetylation. After the reaction is complete, filter the mixture. The filtrates obtained from both reactions are diluted with water and cooled to reveal a gel-like substance—chitosan. Filter the mixture using a Buchner funnel and repeatedly wash the gel-like substance with water until it is neutral. Then, dry the gel-like substance in an oven at 60℃ to obtain chitosan. Calculate the chitosan extraction rate (%) = G1 / G0 × 100%, where G0 is the mass of silkworm pupa skin powder (g) and G1 is the mass of chitosan (g). The degree of deacetylation, solubility, and molecular weight of the obtained chitosan were measured, and the results are shown in Table 3.

[0038] Detection method:

[0039] Deacetylation: Weigh 0.2–0.3 g of sample into an Erlenmeyer flask, add 30 ml of standard hydrochloric acid solution, and stir at 20–25 °C until the sample is completely dissolved. Then add 2–3 drops of methyl orange-aniline blue indicator. Add standard sodium hydroxide solution to the solution to titrate excess hydrochloric acid.

[0040] Degree of deacetylation (DD) = 203 × (C1V1 - C2V2) / 42 × (C1V1 - C2V2) + m(1 - W) × 100%

[0041] Wherein, C1 is the concentration of hydrochloric acid standard solution (mol / L); C2 is the concentration of sodium hydroxide standard solution (mol / L); V1 is the volume of hydrochloric acid standard solution added (ml); V2 is the volume of sodium hydroxide standard solution consumed in the titration (ml); m is the mass of the sample (mg); W is the moisture content in the sample (%); 203 is the molecular weight of chitin; and 42 is the molecular weight of acetyl.

[0042] Solubility: Place 0.1 g of chitosan into a weighed centrifuge tube and dissolve the chitosan in 10 mL of 1% acetic acid aqueous solution at 30°C. Stir continuously for 1 hour and centrifuge. Remove the supernatant and dry the particles at 60°C overnight.

[0043] Solubility (%) = (M1-M2) / (M1-M0)×100

[0044] Where M0 is the initial weight of the centrifuge tube, and M1 and M2 are the initial weight of the centrifuge tube plus the sample and the final weight of the centrifuge tube plus the sample, respectively.

[0045] Molecular weight: 0.1 g of chitosan was dissolved in 10 ml of a mixed buffer solution of 0.5 M acetic acid and 0.5 M sodium acetate, and the intrinsic viscosity [η] of the sample was measured at 25 °C.

[0046] [η]=K[M v ] a

[0047] K = 0.119, a = 0.59. Both "K" and "a" depend on the properties of the solute and solvent, as well as the temperature used.

[0048] Crystallinity: Crystallization index (CrI): CrI (%) = [(I 110 -I am ) / I 110 ]×100

[0049] I 110 I represents the maximum diffraction intensity at 20°. am The maximum diffraction intensity is at 16°.

[0050] Viscosity: Dissolve 1.5g LiCl in 30ml dimethylacetamide solution to completely dissolve the LiCl solid. Weigh 1-1.2g chitosan using weighing paper and dissolve it in dimethylacetamide solution to completely dissolve the solid. Keep the room temperature at 25℃ and stir until completely dissolved. After standing until the bubbles disappear, use a digital viscometer to test its viscosity value.

[0051] Table 3

[0052]

[0053] The results above show that the optimal ultrasonic conditions are as follows: ultrasonic frequency 20 ± 28 Hz, ultrasonic power 120 W, ultrasonic temperature 80 ℃, and ultrasonic time 5 h. The extraction rate of chitosan reaches over 5%, the degree of acetylation is 97.21%, the solubility is 90.3%, the molecular weight is 3.799 × 10⁴ Da, the crystallinity is 98.93%, the viscosity is 438.4 mPa·s, and the extraction rate is 5.106%.

[0054] Comparative Example 1

[0055] (1) Pretreatment of silkworm pupae: Remove the internal organs of the silkworm pupae and clean them. Soak the silkworm pupae skin in petroleum ether for 1-2 hours at room temperature, then wash with distilled water, dry in an electric hot air drying oven at 50-60℃ to a constant weight, and then use a pulverizer to make silkworm pupae powder.

[0056] (2) Enzymatic hydrolysis of protein: Weigh a certain amount of silkworm pupa powder and mix it evenly with distilled water to prepare a suspension. Adjust the pH of the suspension to 8.5-10.5 with 0.5 mol / L NaOH. Add 8% alkaline protease with an enzyme activity of 200,000 u / g and hydrolyze in a water bath at 55℃ for 6-7 hours. After hydrolysis, inactivate the enzyme by boiling in a water bath. Then, centrifuge to remove the supernatant, wash with deionized water until neutral, vacuum filter, and dry.

[0057] (3) Chitin extraction: Take the dried filter residue, add 10% citric acid solution at a solid-liquid ratio of 1g:10ml, react at 40℃ for 1-3h and then filter. Wash the obtained filter residue with deionized water until neutral, dry and obtain chitin.

[0058] (4) Chitosan extraction: The chitin obtained in step (3) is deacetylated and 45% NaOH solution is added at a solid-liquid ratio of 1g:10ml. The reaction is carried out at 90℃ for 9h. After the reaction is completed, the mixture is filtered by a Buchner funnel and repeatedly washed with distilled water until neutral. Then it is dried in an oven at 60℃ to obtain chitosan.

[0059] The chitosan extraction rate, degree of deacetylation, solubility, nitrogen content, ash content, molecular weight, crystallinity, and viscosity were tested. The results are shown in Table 4.

[0060] Table 4

[0061]

[0062] The present invention discloses an ultrasonic-assisted bio-enzymatic method for extracting insect chitin and chitosan. The chitosan extraction rate is 3%–5%, the degree of deacetylation of chitosan is 89.32–97.21%, the solubility is 87.54–90.3%, and the molecular weight is 3.214 × 10⁻⁶. 4 Da ~ 3.799 × 10 4 The crystallinity of Da ranges from 81.11% to 98.93%, and the viscosity ranges from 438.4% to 755.4 mPa·s, both of which show significant improvements. It possesses the advantages of high chitin / chitosan purity, stable product quality, short extraction time, and high application value. It focuses on leveraging the role of ultrasonic extraction, including ultrasonic frequency, ultrasonic power, ultrasonic temperature, and ultrasonic time, to achieve the best ultrasonic extraction effect. This solves the drawbacks of current bio-enzymatic methods, while effectively controlling energy consumption and environmental pollution, and has extremely high application value and market prospects.

Claims

1. A method for extracting insect chitin and chitosan using an ultrasound-assisted bioenzymatic method, characterized in that, Includes the following steps: (1) Pre-treat the silkworm pupae and grind them into powder for later use; (2) The insect powder obtained in step (1) is mixed with distilled water to form a suspension. An alkaline solution is added to adjust the pH of the suspension to the optimal pH for alkaline protease. The suspension is pretreated. After adding alkaline protease, the protein is enzymatically hydrolyzed by dual-frequency synchronous ultrasound. The enzyme is inactivated. The supernatant is removed by centrifugation. The precipitate is washed until neutral, filtered, and dried. The conditions for dual-frequency synchronous ultrasound are: ultrasound frequency 20+28HZ, ultrasound power 110~130W, ultrasound temperature 40~50℃, and ultrasound time 0.5~2.5 h. (3) Add the dried filter residue from step (2) into an acid solution, perform dual-frequency synchronous ultrasonication, filter, wash, and dry to obtain chitin; (4) Chitosan was subjected to dual-frequency synchronous ultrasonic decolorization treatment; (5) Add a low concentration of sodium hydroxide solution to the decolorized chitin, intermittently sonicate, filter, wash, and dry to obtain chitosan.

2. The extraction method according to claim 1, characterized in that, The alkaline solution mentioned in step (2) is sodium hydroxide or potassium hydroxide; the enzyme activity unit of alkaline protease is 100,000-200,000 u / g.

3. The extraction method according to claim 1, characterized in that, The centrifugation conditions described in step (2) are 3000-6000 r / min and the centrifugation time is 5-10 min.

4. The extraction method according to claim 1, characterized in that, The acid solution mentioned in step (3) is one or more of acetic acid, lactic acid, hydrochloric acid, boric acid, and citric acid; the acid concentration is 5%-20%.

5. The extraction method according to claim 1, characterized in that, The dual-frequency synchronous ultrasound conditions described in step (3) are: ultrasound frequency 20+28HZ, ultrasound power 120~130W, ultrasound temperature 30~50℃, and ultrasound time 1~1.5 h.

6. The extraction method according to claim 1, characterized in that, The decolorizing agent used in step (4) is one or more of potassium permanganate, hydrogen peroxide, and sodium hypochlorite, with a concentration of 8%-10%; the dual-frequency synchronous ultrasonic conditions are ultrasonic frequency 20+28HZ, ultrasonic power 110~130W, ultrasonic temperature 30~50℃, and ultrasonic time 0.5~3 h.

7. The extraction method according to claim 1, characterized in that, The concentration of the low-concentration sodium hydroxide solution mentioned in step (5) is 10%~40%, and the solid-liquid ratio of chitosan to sodium hydroxide solution is 1g:10~35ml.

8. The extraction method according to claim 1, characterized in that, The ultrasonic conditions for the dual-frequency synchronous ultrasound described in step (5) are: ultrasonic frequency 20+28HZ, ultrasonic power 110~130W, ultrasonic temperature 60~80℃, and ultrasonic time 5~7 h.

9. The extraction method according to claim 1, characterized in that, The specific steps of intermittent ultrasound in step (5) include: first, adding half the amount of sodium hydroxide to the chitin, taking it out when half of the ultrasound time has elapsed, filtering it, adding the other half of the sodium hydroxide to the precipitate, continuing the ultrasound, filtering it after the ultrasound is finished, mixing the two filtrates, adding water, cooling it to obtain a gel-like substance, which is used for subsequent filtration.

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