A method for extracting arachidonic acid peanut oil by ultrasonic-assisted aqueous enzymatic method combined with hydrothermal liquefaction process

Abstract

This invention discloses a method for extracting crude arachidonic acid oil using an ultrasound-assisted aqueous enzymatic method combined with hydrothermal liquefaction, comprising: S1. Selecting *Morchella esculenta* mycelium, pulverizing it, and adding water to prepare a slurry; S2. Adjusting the pH of the slurry to 4.0-5.5, heating to 45-60℃; adding 1.5-3 wt% of a compound enzyme preparation, and hydrolyzing under ultrasound at 200-400 W for 3-5 hours; centrifuging and collecting the upper crude oil layer; S3. Mixing the middle aqueous phase with the lower residue, adding 0.05-0.15 wt% of an oil-soluble antioxidant, introducing a protective gas, and maintaining a pressure of 1.2-2.5 MPa; heating to 170-220℃ and reacting for 25-50 minutes; cooling and centrifuging to separate the upper oil layer; S4. Mixing the obtained oil, adding 4-6% anhydrous sodium sulfate, filtering and dehydrating, and then reacting at 55-65℃ under a vacuum of ≤-0.095 MPa. Arachidonic acid crude oil is obtained by rotary evaporation for 25-35 minutes under the specified conditions. The method provided by this invention enhances enzymatic hydrolysis efficiency through ultrasonic cavitation and combines it with medium-temperature hydrothermal liquefaction for deep degreasing, thereby reducing energy consumption while improving extraction rate and product safety.

Description

Technical Field

[0001] This invention relates to the field of vegetable oil extraction technology, specifically to a method for extracting crude arachidonic acid oil using an ultrasound-assisted hydro-enzyme method combined with hydrothermal liquefaction. Background Technology

[0002] Arachidonic acid (ARA) is an essential omega-6 polyunsaturated fatty acid for the human body, playing a vital role in infant brain development, immune regulation, and the maintenance of nervous system function. It is widely used in infant formula, health supplements, and pharmaceuticals. Currently, the industrial production of ARA mainly relies on microbial fermentation, and its extraction process directly affects product quality and production costs.

[0003] Traditional methods for extracting crude ARA oil mainly include organic solvent extraction, pressing, and single-aqueous enzymatic extraction. While organic solvent extraction offers high extraction rates, it carries the risk of solvent residue (such as hexane and ethanol), affecting product safety. Furthermore, solvent recovery is energy-intensive and environmentally polluting. Pressing is suitable for high-oil-content raw materials, but its extraction rate is low (typically ≤65%) for low-oil-content raw materials such as microbial mycelia, and it easily leads to ARA oxidation. Single-aqueous enzymatic extraction releases oil by breaking down cell walls through enzymatic hydrolysis. Although it leaves no solvent residue, its enzymatic efficiency is limited. For raw materials with dense cell wall structures, the hydrolysis time needs to be extended (typically ≥6 hours), and some oil remains trapped in the residue, making it difficult to achieve an extraction rate exceeding 80%.

[0004] To address the aforementioned issues with oils, existing technologies are exploring the combined use of various extraction techniques. For instance, Chinese patent CN105482890A proposes a microwave-ultrasound-assisted aqueous enzymatic extraction method for flaxseed oil. This method significantly shortens the enzymatic hydrolysis time by using microwave-ultrasound-assisted enzymatic hydrolysis. However, microwaves can easily lead to excessively high local temperatures, causing oxidation of unsaturated fatty acids. Therefore, there is an urgent need to develop a low-energy-consumption, high-extraction-rate, and solvent-free ARA crude oil extraction method. Summary of the Invention

[0005] To address the problems of solvent residue, low extraction rate, high energy consumption, and easy product oxidation in existing ARA crude oil extraction methods, this invention provides an extraction method combining ultrasound-assisted hydro-enzyme method and hydrothermal liquefaction. By enhancing enzymatic hydrolysis efficiency through the ultrasonic cavitation effect and combining it with medium-temperature hydrothermal liquefaction for deep degreasing, this method improves extraction rate and product safety while reducing energy consumption.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a method for extracting crude arachidonic acid oil using an ultrasound-assisted aqueous enzymatic method combined with hydrothermal liquefaction, comprising the following steps: S1. Select alpine var. mycelium ( Mortierella alpina), crush into powder, add water and mix into a paste to make a slurry; S2. Adjust the pH of the slurry to 4.0~5.5 and raise the temperature to 45~60℃; add 1.5~3wt% of the raw material mass of the compound enzyme preparation, and enzymatically hydrolyze it at 120~180r / min for 3~5h with the assistance of 200~400W ultrasound; then centrifuge, collect the upper crude oil, and retain the middle aqueous phase and the lower residue. S3. Mix the middle aqueous phase with the lower residue, add 0.05~0.15wt% of oil-soluble antioxidant by weight of raw materials, introduce protective gas and maintain the pressure at 1.2~2.5MPa; heat to 170~220℃ and react for 25~50min; after cooling, centrifuge to separate the upper oil layer. S4. Mix the oils obtained in steps S2 and S3, add 4-6% anhydrous sodium sulfate by weight of the oils, stir, filter and dehydrate, and then rotary evaporate at 55-65℃ and vacuum degree ≤-0.095MPa for 25-35 minutes to obtain crude arachidonic acid oil.

[0007] In this invention, raw materials rich in ARA are used as the target. First, the cell walls of the raw materials are rapidly destroyed by ultrasound-assisted hydro-enzyme method to initially release the oil. Then, hydrothermal liquefaction is used to treat the enzymatic hydrolysis residue and the aqueous phase to further break down the stubborn structure and polymerize and disperse the oil, thereby achieving deep extraction. Finally, high-quality crude ARA oil is obtained through purification.

[0008] Preferably, in step S1, before pulverizing into powder, the mycelium of *Morchella alpina* is dried to a moisture content of ≤10%; and impurities are removed, with the impurity content controlled to ≤2%. Then, after being crushed at 8000~12000 r / min for 2~4 min, it is passed through an 80~100 mesh sieve to obtain uniform powder.

[0009] Preferably, in step S1, the ratio of powder to water is 1:4 to 1:6 (g:mL). The homogenization is carried out in a homogenizer under the following conditions: homogenization at 10000 to 15000 r / min for 1 to 3 min to produce a homogeneous slurry and avoid particle agglomeration.

[0010] Preferably, in step S2, the pH of the raw material slurry is adjusted to 4.0~5.5 using 1 mol / L citric acid or NaOH. After heating to 45~60℃, it is preferably kept at this temperature for 10 minutes.

[0011] Preferably, in step S2, the compound enzyme preparation is composed of cellulase, pectinase and protease in a ratio of 1.5~2.5:1:1~1.5, with an enzyme activity ≥5000U / g.

[0012] Preferably, in step S2, the ultrasound is intermittent ultrasound, with a 3-5 second interval between each operation and a 2-3 second interval.

[0013] In step S2 of this invention, the ultrasonic cavitation effect can generate microbubbles. When the bubbles burst, they release shock waves, which destroy the cell wall structure of the raw materials, increase the contact area between the enzyme and the substrate, and shorten the enzymatic hydrolysis time. Intermittent ultrasound can avoid excessively high local temperatures and prevent ARA oxidation.

[0014] Preferably, in step S2, the centrifugation conditions are: centrifugation at 7000~9000 r / min for 12~18 min.

[0015] In step S2 of this invention, after centrifugation, the system is divided into an upper layer of crude oil, a middle layer of aqueous phase, and a lower layer of residue; the upper layer of crude oil is collected, while the middle layer of aqueous phase and the lower layer of residue are retained for further processing.

[0016] Preferably, in step S3, the oil-soluble antioxidant includes at least one of vitamin E, phospholipids, ascorbate palmitate, and rosemary extract, with vitamin E being the most preferred. During the hydrothermal liquefaction deep degreasing process, due to the high temperature, adding a certain amount of oil-soluble antioxidant can effectively prevent ARA oxidation.

[0017] Preferably, in step S3, the protective gas is nitrogen, which is introduced into the reactor to replace the air inside the reactor and control the pressure inside the reactor.

[0018] In step S3 of this invention, the medium-temperature hydrothermal environment (170~220℃) can further break down the cell wall residues that are not completely enzymatically hydrolyzed, and at the same time, it can polymerize the emulsified oil dispersed in the aqueous phase to form separable oil droplets, thereby improving the oil recovery rate.

[0019] Preferably, in step S3, after the reaction is complete, the mixture is allowed to cool naturally to room temperature, and the pressure is slowly released to atmospheric pressure to collect the material. The material is then transferred to a centrifuge for centrifugation. The centrifugation conditions are: centrifugation at 9000~11000 r / min for 18~25 min. The separated upper layer of oil has higher purity, and the ARA content is 5~8% higher than that of the initially extracted oil.

[0020] Preferably, in step S3, before adding the oil-soluble antioxidant, 0.01~0.03% by weight of hydroxyapatite (HAP) nanocatalyst is added, and then stirred to allow the catalyst to adsorb onto the surface of the residue. The preferred particle size of the hydroxyapatite nanocatalyst is 50~100nm. It is resistant to hydrothermal environments of 170~220℃, and its surface hydroxyl and phosphate groups can adsorb oil molecules, promoting oil droplet polymerization. It is also non-toxic and easy to separate.

[0021] Preferably, in step S3, a gradient pressure regime is adopted during the reaction: the initial pressure is maintained at 1.2~1.4MPa, the temperature is increased to 170~190℃ at 4~6℃ / min, and the reaction is held at this temperature for 15~20min; then the pressure is increased to 2.3~2.5MPa at a rate of 0.1~0.3MPa / min, and the temperature is simultaneously increased to 190~220℃ at 4~6℃ / min, and the reaction is held at this temperature for 10~30min.

[0022] In the above process, during the low-pressure stage (1.2~1.4MPa), the low-pressure hydrothermal environment, combined with the hydroxyl adsorption of the HAP catalyst, destroys the incompletely enzymatically hydrolyzed cell wall cellulose structure and releases the encapsulated oil. During the high-pressure stage (2.3~2.5MPa), the high-pressure environment enhances the polymerization catalytic effect of the HAP catalyst on the aqueous emulsion oil, causing tiny oil droplets to polymerize into separable oil droplets with a particle size ≥5μm, improving centrifugal separation efficiency and thus increasing the extraction rate of ARA.

[0023] Preferably, step S4 includes dehydration treatment and vacuum removal of light components. The dehydration treatment is as follows: anhydrous sodium sulfate is added to the oil, stirred at 25~35℃ for 25~35 min, allowed to stand for 1 h, and then filtered to remove water from the oil, controlling the water content in the oil to ≤0.5%.

[0024] Preferably, in step S4, the vacuum removal of light components is carried out in a vacuum rotary evaporator to remove volatile impurities (such as small molecule organic acids and low-boiling-point alcohols).

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. High extraction rate: Ultrasonic assistance significantly shortens the enzymatic hydrolysis time (from 6-8 hours in the traditional water-enzyme method to 3-5 hours), and combined with hydrothermal liquefaction for deep defatting, the ARA extraction rate is ≥88%, which is 8-12% higher than that of the single water-enzyme method.

[0026] 2. High product safety: No organic solvents are used throughout the process, avoiding solvent residue; intermittent ultrasound and vitamin E addition can effectively prevent ARA oxidation, with ARA content in crude oil ≥30%, moisture ≤0.5%, and volatile impurities ≤0.1%.

[0027] 3. Low energy consumption: The hydrothermal liquefaction temperature is controlled at 170~220℃ (lower than the traditional hydrothermal method of 230~250℃). The synergistic effect of ultrasound and oscillation reduces the amount of enzyme used (20~30% less than the traditional water-enzyme method), and the overall energy consumption is reduced by 15~20%.

[0028] 4. Wide applicability: It is suitable for different raw materials such as microbial mycelium and plant seeds, and the process parameters are controllable, making it easy to scale up industrial production. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] Unless otherwise specified, the experimental methods used in the following examples and comparative examples are conventional methods, and the materials and reagents used are commercially available.

[0032] Example 1

[0033] This embodiment provides a method for extracting crude arachidonic acid oil using an ultrasound-assisted aqueous enzymatic method combined with hydrothermal liquefaction, comprising the following steps: 1. Alpine spore mycelium ( Mortierella alpina Raw material pretreatment: Take dried alpine spore mycelium (8% moisture, 1.5% impurities, initial ARA content 38%), crush it at 10000 r / min for 3 min, and pass it through a 90 mesh sieve; mix the raw material powder with deionized water at a ratio of 1:5, homogenize it at 12000 r / min for 2 min to make a slurry.

[0034] 2. Ultrasonic-assisted enzymatic lipid extraction: Adjust the pH of the slurry to 4.8, raise the temperature to 52℃, add 2% of the raw material mass of compound enzyme (cellulase: pectinase: protease = 2:1:1.2, enzyme activity 5500U / g), turn on the ultrasound (power 300W, working for 4s, intermittent for 2.5s), and enzymatically hydrolyze at 150r / min for 4h; after enzymatic hydrolysis, centrifuge at 8000r / min for 15min, and collect the upper crude oil (ARA content 45%).

[0035] 3. Hydrothermal liquefaction deep degreasing: Transfer the middle aqueous phase and the lower residue to a high-pressure reactor, add 0.1% vitamin E by weight of the raw material, purge with nitrogen to maintain a pressure of 1.8 MPa, heat to 190°C at 5°C / min, and react for 35 min; after cooling, centrifuge at 10000 r / min for 20 min and collect the upper oil layer.

[0036] 4. Crude oil purification: Mix the two layers of oil, add 5% anhydrous sodium sulfate by weight of the oil, stir at 30℃ for 30 min, filter and dehydrate; rotary evaporate at 60℃ and -0.096MPa vacuum for 30 min to obtain ARA crude oil.

[0037] Tests showed that the crude oil contained 51.3% ARA, with an extraction rate of 90.6%, 0.42% moisture, and no solvent residue.

[0038] Example 2

[0039] This embodiment provides a method for extracting crude arachidonic acid oil using an ultrasound-assisted aqueous enzymatic method combined with hydrothermal liquefaction, comprising the following steps: 1. Raw material pretreatment: Take dried alpine spore mycelium (8% moisture, 1.5% impurities, initial ARA content 38%), crush at 11000 r / min for 2.5 min, and pass through an 80 mesh sieve; mix powder and water at a ratio of 1:4 (g:mL), homogenize at 13000 r / min for 1.5 min to prepare a slurry.

[0040] 2. Ultrasonic-assisted water-enzymatic lipid extraction: Adjust pH to 4.5, heat to 55℃, add 2.5% of the raw material mass of compound enzyme (cellulase: pectinase: protease = 2.2:1:1.3, enzyme activity 6000U / g), turn on ultrasound (350W, 3s operation, 2s interval), and oscillate at 160r / min for 3.5h; centrifuge at 8500r / min for 12min and collect the upper crude oil.

[0041] 3. Hydrothermal liquefaction deep degreasing: Transfer the middle aqueous phase and residue to a reactor, add 0.12% ascorbate palmitate by weight of the raw material, and purge with nitrogen to maintain a pressure of 2.0 MPa. Heat to 180℃ at 5℃ / min and hold for 35 min; after cooling, centrifuge at 10500 r / min for 22 min and collect the upper oil layer.

[0042] 4. Crude oil purification: Mix the oils and add 6% anhydrous sodium sulfate, stir at 32℃ for 25 min, filter and dehydrate; evaporate under vacuum at 62℃ and -0.097MPa for 28 min to obtain ARA crude oil.

[0043] Tests showed that the crude oil contained 50.8% ARA, had an extraction rate of 88.0%, 0.35% moisture, and no solvent residue.

[0044] Example 3

[0045] This embodiment provides a method for extracting crude arachidonic acid oil using an ultrasound-assisted aqueous enzymatic method combined with hydrothermal liquefaction, comprising the following steps: 1. Raw material pretreatment: Take dried alpine spore mycelium (8% moisture, 1.5% impurities, initial ARA content 38%), crush at 9000 r / min for 3.5 min, and pass through a 100 mesh sieve; mix powder and water at a ratio of 1:6 (g:mL), homogenize at 14000 r / min for 2.5 min to make a slurry.

[0046] 2. Ultrasonic-assisted enzymatic lipid extraction: Adjust pH to 5.2, heat to 48℃, add 1.8% of the raw material mass of compound enzyme (cellulase: pectinase: protease = 1.8:1:1.1, enzyme activity 5200U / g), turn on ultrasound (250W, 5s operation, 3s interval), and oscillate at 140r / min for 4.5h; centrifuge at 7500r / min for 16min and collect the upper crude oil.

[0047] 3. Hydrothermal liquefaction deep degreasing: Transfer the middle aqueous phase and residue to the reactor, add 0.08% of rosemary extract by weight of raw material, purge with nitrogen to maintain pressure of 1.5 MPa, heat to 175℃ at 4℃ / min, and react for 40 min; after cooling, centrifuge at 9500 r / min for 24 min and collect the upper oil layer.

[0048] 4. Crude oil purification: Mix the oils and add 4.5% anhydrous sodium sulfate, stir at 28℃ for 32 min, filter and dehydrate; evaporate under vacuum at 58℃ and -0.095MPa for 32 min to obtain ARA crude oil.

[0049] Tests showed that the crude oil contained 51.5% ARA, had an extraction rate of 89.8%, 0.42% moisture, and no solvent residue.

[0050] Example 4

[0051] Using the same *Morchella syringae* mycelium as in Example 1, the difference was that in the hydrothermal liquefaction deep degreasing process, after transferring the middle aqueous phase and residue to the reactor, 0.02% (by weight of the raw material) of hydroxyapatite nanocatalyst (70 nm particle size) was added, and the mixture was stirred and adsorbed for 10 min; then 0.1% (by weight of the raw material) of vitamin E was added, and nitrogen gas was introduced. A gradient pressure was used: an initial pressure of 1.3 MPa, a temperature increase of 5 °C / min to 180 °C, and a holding time of 18 min; subsequently, the pressure was increased to 2.4 MPa at 0.2 MPa / min, and the temperature was simultaneously increased to 210 °C at 5 °C / min, and a holding time of 20 min. After cooling, the mixture was centrifuged at 10000 r / min for 20 min, and the upper oil layer was collected.

[0052] Tests showed that the crude oil contained 53.6% ARA, with an extraction rate of 95.2%, 0.38% moisture, and no solvent residue.

[0053] Comparative Example 1: Traditional single-aqueous enzymatic method Using the same alpine spore mycelium as in Example 1, the difference from Example 1 is that after pretreatment of the raw material, the pH was adjusted to 4.8 and the temperature was 52°C. The same compound enzyme (2% of the raw material mass) was added, and the enzyme was shaken and hydrolyzed for 6 hours. After centrifugation, the material was directly purified.

[0054] The crude oil contained 43.1% ARA, with an extraction rate of 78.7%, and the enzymatic hydrolysis time was extended by 50% compared to Example 1.

[0055] Comparative Example 2 Using the same alpine mollusc mycelium as in Example 1, the difference from Example 1 is that: no hydrothermal liquefaction deep degreasing step is performed, and the collected upper crude oil is directly purified.

[0056] The crude oil contained 44.5% ARA, with an extraction rate of 82.6%.

[0057] Comparative Example 3 Using the same alpine spore mycelium as in Example 1, the difference from Example 1 is that constant ultrasound with a power of 300W is used in the ultrasonic-assisted hydroenzymatic fat extraction process; and no vitamin E is added in the hydrothermal liquefaction deep degreasing process.

[0058] Tests showed that the crude oil contained 46.1% ARA, with an extraction rate of 85.5%, 0.51% moisture, and no solvent residue.

[0059] Table 1 ARA content in crude oil Extraction rate Example 1 51.3% 90.6% Example 2 50.8% 88.0% Example 3 51.5% 89.8% Example 4 53.6% 95.2% Comparative Example 1 43.1% 78.7% Comparative Example 2 44.5% 82.6% Comparative Example 3 46.1% 85.5% In summary, the ultrasound-assisted hydro-enzyme extraction method combined with hydrothermal liquefaction provided by this invention enhances enzymatic hydrolysis efficiency through the ultrasonic cavitation effect and combines it with medium-temperature hydrothermal liquefaction for deep degreasing, thereby reducing energy consumption while improving the extraction rate and product safety of ARA.

[0060] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for extracting crude arachidonic acid oil using an ultrasound-assisted aqueous enzymatic method combined with hydrothermal liquefaction, characterized in that, Includes the following steps: S1. Select alpine spore mycelium, crush it into powder, add water and mix well to make a slurry; S2. Adjust the pH of the slurry to 4.0~5.5 and raise the temperature to 45~60℃; add 1.5~3wt% of the raw material mass of the compound enzyme preparation, and enzymatically hydrolyze it at 120~180r / min for 3~5h with the assistance of 200~400W ultrasound; then centrifuge, collect the upper crude oil, and retain the middle aqueous phase and the lower residue. S3. Mix the middle aqueous phase with the lower residue, add 0.05~0.15wt% of oil-soluble antioxidant by weight of raw materials, introduce protective gas and maintain the pressure at 1.2~2.5MPa; heat to 170~220℃ and react for 25~50min; after cooling, centrifuge to separate the upper oil layer. S4. Mix the oils obtained in steps S2 and S3, add 4-6% anhydrous sodium sulfate by weight of the oils, stir, filter and dehydrate, and then rotary evaporate at 55-65℃ and vacuum degree ≤-0.095MPa for 25-35 minutes to obtain crude arachidonic acid oil.

2. The method for extracting crude arachidonic acid oil using ultrasound-assisted hydro-enzyme method combined with hydrothermal liquefaction process according to claim 1, characterized in that, In step S1, before being pulverized into powder, the mycelium of *Morchella alpina* is dried to a moisture content of ≤10% and the impurity content is controlled to ≤2%. Then, it is crushed at 8000~12000r / min for 2~4min and passed through an 80~100 mesh sieve.

3. The method for extracting crude arachidonic acid oil using ultrasound-assisted hydro-enzyme method combined with hydrothermal liquefaction process according to claim 2, characterized in that, In step S1, the ratio of the powder to water is 1:4 to 1:6 (g:mL). The homogenization conditions are as follows: homogenize at 10000~15000 r / min for 1~3 min.

4. The method for extracting crude arachidonic acid oil using ultrasound-assisted hydro-enzyme method combined with hydrothermal liquefaction process according to claim 1, characterized in that, In step S2, the compound enzyme preparation is composed of cellulase, pectinase and protease in a ratio of 1.5~2.5:1:1~1.5, with an enzyme activity ≥5000U / g.

5. The method for extracting crude arachidonic acid oil using ultrasound-assisted hydro-enzyme method combined with hydrothermal liquefaction process according to claim 1, characterized in that, In step S2, the ultrasound is intermittent ultrasound, with a 3-5 second interval between each operation and a 2-3 second interval.

6. The method for extracting crude arachidonic acid oil using ultrasound-assisted hydro-enzyme method combined with hydrothermal liquefaction process according to claim 1, characterized in that, In step S2, the centrifugation conditions are: centrifugation at 7000~9000 r / min for 12~18 min.

7. The method for extracting crude arachidonic acid oil using ultrasound-assisted hydro-enzyme method combined with hydrothermal liquefaction process according to claim 1, characterized in that, In step S3, the oil-soluble antioxidant includes at least one of vitamin E, phospholipids, ascorbyl palmitate, and rosemary extract.

8. The method for extracting crude arachidonic acid oil using ultrasound-assisted hydro-enzyme method combined with hydrothermal liquefaction process according to claim 1, characterized in that, In step S3, the centrifugation conditions are: centrifugation at 9000~11000 r / min for 18~25 min.

9. The method for extracting crude arachidonic acid oil using ultrasound-assisted hydro-enzyme method combined with hydrothermal liquefaction process according to claim 1, characterized in that, In step S3, before adding the oil-soluble antioxidant, 0.01~0.03% of the raw material mass of hydroxyapatite nanocatalyst is added first, and then the mixture is stirred to allow the catalyst to be adsorbed onto the surface of the residue.

10. The method for extracting crude arachidonic acid oil using ultrasound-assisted hydro-enzyme method combined with hydrothermal liquefaction process according to claim 1, characterized in that, In step S3, a gradient pressure regime is adopted during the reaction: the initial pressure is maintained at 1.2~1.4MPa, the temperature is increased to 170~190℃ at 4~6℃ / min, and the reaction is held at this temperature for 15~20min; then the pressure is increased to 2.3~2.5MPa at a rate of 0.1~0.3MPa / min, and the temperature is simultaneously increased to 190~220℃ at 4~6℃ / min, and the reaction is held at this temperature for 10~30min.