Fish oil directional separation method based on electric field enhanced dielectrophoresis effect and production system

Abstract

The invention relates to a fish oil directional separation method based on an electric field enhanced dielectrophoresis effect and a production system, and belongs to the technical field of fish oil production. EPA in the fish oil is selectively converted into high-melting-point EPA lauryl alcohol ester through the RM immobilized enzyme, and DHA keeps the fatty acid form; an alternating electric field is synchronously applied under a low-temperature condition, and the crystals are driven to directionally migrate and enrich towards a strong electric field area through a positive dielectrophoresis effect by utilizing the dielectric difference between EPA lauryl alcohol ester solid crystals and liquid DHA, so that solid-liquid separation is directly realized. The invention also provides a production system which comprises a pretreatment unit, a hydrolysis crystallization unit, an enzymolysis reaction unit, a dielectrophoresis electric field crystallization separation unit and a product collection unit. The purity of the obtained DHA is more than or equal to 80%, the recovery rate is more than or equal to 96%, the purity of the EPA lauryl alcohol ester is more than or equal to 79.6%, the recovery rate is more than or equal to 80%, the liquid encapsulation rate is less than or equal to 5%, and the method is suitable for industrial production of food and medicine high-purity omega-3.

Description

Technical Field

[0001] This invention relates to the field of fish oil production technology, and in particular to a method and production system for directional separation of fish oil based on the electric field-enhanced dielectrophoresis effect. Background Technology

[0002] In fish oil production, crude fish oil extracted from deep-sea fish meat or processing by-products is essentially a mixture of various fatty acids. EPA and DHA not only coexist with saturated fatty acids and other unsaturated fatty acids in the oil, but also, because they are both ω-3 polyunsaturated fatty acids with highly similar chemical structures, they cannot be naturally separated during the raw material extraction process and can only exist in crude fish oil in a mixed form. To meet the functional requirements of high-purity ω-3 fatty acids in the food and pharmaceutical industries, precise separation of EPA and DHA is necessary. Currently, mainstream separation technologies in the industry all have significant shortcomings:

[0003] (1) Traditional low-temperature crystallization method: Relying on the difference in melting points of DHA and EPA fatty acids (-48℃ and -54℃), crystallization needs to be carried out at extremely low temperatures for 24~72h. During the natural growth of crystals, a large amount of fluid is easily wrapped (wrapping rate ≥15%), resulting in cross-contamination of DHA / EPA during subsequent filtration and separation. The product purity is only 45%~55%, and the recovery rate is ≤75%. Moreover, during the filtration process, 1~5μm fine crystals are lost with the mother liquor (loss rate ≥8%). The total process cycle exceeds 24h, the equipment occupies a large area, and the energy consumption is 2.5 times the theoretical minimum value, resulting in high industrialization costs. Traditional low-temperature crystallization method uses fatty acid ethyl esters or fatty acids, and the crystallization temperature is generally down to -60℃. It cannot deeply remove non-target fatty acids, resulting in the total amount of EPA and DHA in fish oil fatty acids being only about 50%, making it difficult to break through the purity bottleneck in subsequent separation.

[0004] (2) Urea inclusion method: This method utilizes the property of urea to form stable inclusion complexes with saturated fatty acids and monounsaturated fatty acids to achieve separation. However, this method has little selectivity for EPA and DHA, making it difficult to achieve high-purity separation (purity is usually ≤60%). In addition, it requires a large amount of urea and organic solvents, and the subsequent purification process is complicated. Residual solvents can easily cause product contamination, which does not meet the safety requirements of the food and pharmaceutical fields. At the same time, the inclusion and desorption process takes a long time (total cycle 18~24h), resulting in low efficiency for large-scale production.

[0005] (3) Molecular distillation method: Based on the difference in boiling point between EPA and DHA, but the boiling points of the two are close (only 5~8℃ apart), and it is necessary to operate under high vacuum (≤1Pa) and high temperature (180-220℃) conditions. High temperature easily leads to the oxidation and decomposition of ω-3 fatty acids, which increases the peroxide value of the product (POV≥3.0meq / kg) and destroys its physiological activity. Moreover, the equipment investment is large, the operation is difficult, and the energy consumption is 3~4 times that of conventional processes. During the separation process, fatty acids are easy to adhere to the inner wall of the equipment, resulting in material loss (recovery rate≤70%).

[0006] Furthermore, existing technologies cannot simultaneously achieve optimal separation efficiency, product purity, recovery rate, and energy consumption. They are also prone to cross-contamination or product oxidation during the separation process, failing to meet the stringent requirements of the food and pharmaceutical industries for high-purity, highly stable ω-3 fatty acids. Therefore, there is an urgent need to develop a highly efficient, low-consumption, and highly selective directional separation technology for fish oil EPA and DHA to overcome existing process bottlenecks. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method and production system for the directional separation of fish oil based on the enhanced dielectrophoresis effect. This invention employs enzymatic directional conversion, low-temperature crystallization, and dielectrophoretic electric field coupling to separate DHA and EPA from fish oil, making it suitable for the industrial-scale preparation of high-purity polyunsaturated fatty acids in the food and pharmaceutical industries.

[0008] This invention is achieved through the following technical solution:

[0009] The first objective of this invention is to provide a method for the directional separation of fish oil based on the electric field-enhanced dielectrophoresis effect, comprising the following steps:

[0010] S1. After pretreatment, fish or algae oil processing waste is pressed, filtered, and decolorized to obtain refined fish oil.

[0011] S2. The obtained refined fish oil was hydrolyzed in anhydrous ethanol alkaline solution at 65℃~75℃ for 1.5~2.5h, and then subjected to gradient crystallization at -86℃~30℃. The pH value was adjusted to 2.0~3.0. Water was added and the mixture was allowed to stand and separate into layers. The upper fatty acid phase was taken and vacuum dried to obtain fish oil fatty acids with a moisture content of ≤0.1%. The content of EPA was 40wt%~50wt%, the content of DHA was 40wt%~45wt%, and the total content of EPA and DHA was ≥80wt%. The content of non-target fatty acids (saturated fatty acids and other unsaturated fatty acids) was ≤20wt%.

[0012] S3. Mix the obtained fish oil fatty acids with lauryl alcohol, add RM immobilized enzyme and buffer solution to the mixture to react and obtain a mixture containing EPA lauryl ester and DHA.

[0013] S4. The resulting mixture is transferred to a dielectrophoretic electric field crystallization device, and solid crystals are precipitated after cooling. An alternating electric field is applied simultaneously to form a dense solid crystal layer near the electrode. The solid is collected and dried under vacuum to obtain EPA lauryl ester.

[0014] The upper layer fluid in the dielectrophoretic field crystallization apparatus is subjected to molecular distillation to recover lauryl alcohol and remove the EPA-containing fraction, yielding DHA. Specifically, the upper layer fluid in the dielectrophoretic field crystallization apparatus undergoes staged molecular distillation fractionation. First, lauryl alcohol is removed at 100℃~120℃ and a vacuum degree ≤0.1mbar. Then, the temperature is increased to 130℃~150℃ and a vacuum degree ≤0.05mbar to remove the EPA-containing light fraction, yielding DHA. It should be noted that the molecular distillation fractionation refers to staged temperature-controlled operation within the same molecular distillation apparatus: in the first stage, low-boiling-point lauryl alcohol is preferentially removed at a lower temperature (100℃~120℃) and a vacuum degree (≤0.1mbar); in the second stage, the temperature is increased to 130℃~150℃ and the vacuum degree is increased (≤0.05mbar) to preferentially volatilize and remove a small amount of unreacted EPA, thereby increasing the purity of DHA to over 80%. By controlling the scraping speed (200~300r / min) to ensure that the material residence time is <1min, the thermal oxidative degradation of DHA can be effectively controlled.

[0015] In one embodiment of the present invention, in step S1, the pressing pressure is 15MPa~20MPa and the temperature is 45℃~55℃;

[0016] And / or, the decolorization is performed using activated clay; the decolorization temperature is 60℃~70℃;

[0017] And / or, the refined fish oil has an acid value ≤2.0 mg KOH / g and a moisture content ≤0.3 wt%.

[0018] In one embodiment of the present invention, in step S2, the concentration of the anhydrous ethanol alkaline solution is 0.3 mol / L to 0.7 mol / L;

[0019] And / or, the base in the anhydrous ethanol alkaline solution is NaOH and / or KOH.

[0020] In one embodiment of the present invention, in step S2, the molar ratio of the refined fish oil to the alkali in the anhydrous ethanol alkaline solution is 1:3.1 to 1:3.6. This ratio ensures that the alkali is 5% to 20% in excess of the ester groups in the fish oil, which can completely hydrolyze the ester groups and avoid residual unhydrolyzed oil affecting the subsequent crystallization and fractionation effect. The gradient crystallization and fractionation is carried out in 2 to 3 times at -86℃ to 30℃ (first time at 30℃ for 2 hours, second time at -40℃ for 3 hours, and third time at -86℃ for 4 hours).

[0021] And / or, the vacuum drying conditions are: vacuum drying at 55℃~65℃ and -0.090MPa~-0.095MPa for 1h~2h.

[0022] In one embodiment of the present invention, in step S3, the molar ratio of the fish oil fatty acid to lauryl alcohol is 1:1.2 to 1:1.5.

[0023] And / or, the mass ratio of the RM immobilized enzyme to the substrate is 1:200 to 1:400.

[0024] In one embodiment of the present invention, in step S3, the pH value of the reaction is 7.5~8.5;

[0025] And / or, the reaction temperature is 45°C to 55°C;

[0026] And / or, the rotation speed of the reaction is 300 r / min to 500 r / min;

[0027] And / or, the reaction time is 7h to 9h.

[0028] In one embodiment of the present invention, in step S4, the cooling is: cooling to 25°C to 30°C at a rate of 0.5°C / min to 1°C / min.

[0029] In one embodiment of the present invention, in step S4, the frequency of the alternating electric field is 1kHz to 10kHz;

[0030] And / or, the strength of the alternating electric field is 1.5 × 10⁻⁶. 4 V / m ~3×10 4 V / m;

[0031] And / or, the duration of the alternating electric field is 15 min to 30 min;

[0032] And / or, the electrode spacing in the dielectric electrophoretic field crystallization device is 5mm~8mm.

[0033] In one embodiment of the present invention, in step S4, the vacuum drying conditions are: vacuum drying at 40℃~45℃ and -0.095MPa~-0.1MPa for 2h~3h;

[0034] And / or, the conditions for the staged molecular distillation are as follows: the temperature of the first stage molecular distillation is 100℃~120℃, the vacuum degree is ≤0.1mbar, and the time is 1h~2h; the temperature of the second stage molecular distillation is 130℃~150℃, the vacuum degree is ≤0.05mbar, and the time is 0.5h~1h.

[0035] The present invention is a system of fatty acid salts and anhydrous ethanol, with a temperature range of -86°C, which can achieve deep enrichment of the target component and solve the problem of interference from non-target fatty acids from the source.

[0036] The second objective of this invention is to provide a production system for the fish oil directional separation method based on the electric field-enhanced dielectrophoresis effect, the production system comprising a pretreatment unit, a fish oil fatty acid preparation unit, an enzymatic hydrolysis reaction unit, a dielectrophoretic electric field crystallization separation unit, and a product collection unit;

[0037] The pretreatment unit includes a pressing device, a plate and frame filter, and a decolorizing tank connected in sequence; it is used to press the pretreated waste material to extract oil, filter it, and decolorize it to obtain refined fish oil.

[0038] A fish oil fatty acid preparation unit includes a hydrolysis tank, a crystallizer, and a vacuum dryer; the crystallizer is connected to the hydrolysis tank, which is used to contain refined fish oil and an alkaline solution for hydrolysis; the crystallizer is used for cooling; and the vacuum dryer is used to dry the upper fatty acid phase after separation to obtain fish oil fatty acids.

[0039] An enzymatic hydrolysis reaction unit includes an enzymatic hydrolysis vessel, which is equipped with a temperature control component and a mixing and stirring device; it is used for the reaction of fish oil fatty acids, lauryl alcohol mixed substrate and RM immobilized enzyme to obtain a mixture containing EPA lauryl ester and DHA.

[0040] Dielectrophoretic electrostatic crystallization separation unit includes a dielectrophoretic electrostatic crystallization device, a temperature control module, a laser particle size analyzer, a parallel electrode assembly, and an AC power supply scraper collection device. The laser particle size analyzer monitors the crystal particle size and automatically reduces the stirring speed when the particle size is ≥10μm to prevent agglomeration and a decrease in dielectrophoretic force. The parallel electrode assembly is electrically connected to the AC power supply. The scraper collection device works in conjunction with the electrode assembly to collect EPA lauryl ester solids near the electrodes. The parallel electrode assembly is a platinum electrode with a rounded transition structure at the edge (radius of curvature 0.8mm), which increases the electric field strength near the electrode by 2.5 times, enhancing the positive dielectrophoresis effect. The temperature control component controls the temperature range from 15 to 35℃, ensuring that the crystallization temperature is stable at 25 to 30℃, guaranteeing complete crystallization of EPA lauryl ester while preventing partial solidification of DHA from affecting dielectric properties.

[0041] The dielectric electrophoretic field crystallization separation unit also includes a dielectric constant monitoring module; the dielectric constant monitoring module tracks the system Δε in real time to ensure that Δε ≥ 1.2;

[0042] The product collection unit includes a molecular distillation apparatus, an EPA lauryl ester collection tank, and a DHA collection tank; the molecular distillation apparatus is used to remove residual lauryl alcohol and small amounts of impurities such as EPA-containing light fractions from the DHA fluid.

[0043] In one embodiment of the present invention, the dielectric electrophoresis electric field crystallization separation unit is further provided with an electric field gradient optimization module: by changing the electrode spacing (5~8mm) and the electrode edge curvature (curvature radius 0.5~1mm), the electric field strength near the electrode is increased by 2~3 times, the positive dielectric effect is enhanced, and the crystal migration rate is ensured to be ≥0.4mm / s.

[0044] In one embodiment of the present invention, after treatment by the above method, the core indicators of the obtained product are stable and controllable: DHA purity ≥80%, recovery rate ≥96%, EPA lauryl ester purity ≥79.6%, recovery rate ≥80%, peroxide value (POV) ≤2.2 meq / kg, moisture ≤0.05%, and liquid encapsulation rate ≤5%. In this invention, EPA and DHA in fish oil are both unsaturated fatty acids with similar melting points (-54℃ and -48℃) and small difference in dielectric constant (Δε<0.3), making them impossible to separate by dielectric electrophoresis. This invention utilizes the selective catalysis of RM-immobilized enzymes to esterify only EPA and lauryl alcohol to generate EPA lauryl ester. Due to the incorporation of a saturated lauryl alcohol chain, the molecular arrangement regularity is improved, and the dielectric constant increases from the ε<0.3 of EPA fatty acids. EPA ≈2.7 increased to ε P ≈4.2; meanwhile, the melting point significantly increased from -54℃ to 32~35℃; and due to enzymatic selectivity (RM immobilized enzymes have only 1 / 8 the hydrolytic activity of DHA glycerides to EPA), DHA still exists in the fatty acid form (ε). DHA (Approximately 2.8, melting point -48℃). In this enzymatic hydrolysis system, the esterification rate of EPA reaches 80%~93% (approximately 80% in industrial production, and up to 93% in laboratory optimization), while the esterification rate of DHA is only 2%~5%. The dielectric constant difference between EPA lauryl ester and DHA is Δε≈1.4 (far higher than the effective driving threshold of dielectrophoresis Δε>0.5), creating a separation system of high-dielectric solid and low-dielectric fluid, providing verified conditions for dielectrophoretic separation. This invention constructs a system with Δε≈1.4 through enzymatic hydrolysis; a DC electric field would cause electrode electrolysis and gas generation, destroying the crystal morphology, therefore an AC electric field is used.

[0045] In this invention, EPA lauryl ester crystals (ε P The dielectric constant of the fluid is approximately 4.2, which is higher than that of the DHA fluid (ε). DHA ≈2.8), satisfying ε P >ε DHA This generates a positive mesophoretic effect, where crystals are continuously pushed toward the vicinity of the electrode with a higher electric field strength, which is 2 to 3 times higher than that in the middle of the tank. DHA, due to its low dielectric constant, is hardly polarized and does not migrate significantly. Ultimately, the solid crystals are enriched at the electrode while the liquid remains in the middle of the tank, eliminating the need for subsequent filtration.

[0046] When processing 200kg per batch, the total cycle of the present invention is only 12-16h, which is 50%-71% shorter than the traditional method (36-48h); the dielectric electrophoresis separation cycle is only 15-30min, which is more than 90% shorter than the low temperature crystallization separation cycle (24-36h) in the traditional method, and the equipment footprint is reduced by about 50%.

[0047] Compared with the prior art, the above-described technical solution of the present invention has the following advantages:

[0048] (1) This invention discloses a method and production system for the directional separation of fish oil based on the electric field-enhanced dielectrophoresis effect. Through a three-step method of "enzymatic hydrolysis and directional modification, dielectric difference construction, and electric field-enhanced separation", it solves the problem of the difficulty of efficiently separating EPA and DHA by traditional methods. Since EPA and DHA have similar molecular structures and very small differences in melting point and dielectric constant, this invention uses RM immobilized enzyme as a catalyst, which can accurately identify EPA and lauryl alcohol, promote the esterification of EPA into EPA lauryl ester, and significantly increase the dielectric constant and melting point of EPA, while DHA maintains its original form, forming a separation system of high dielectric solid and low dielectric fluid (Δε≈1.4). Compared with short-chain and medium-chain alcohols, lauryl alcohol can avoid low-temperature refrigeration, and the generated ester crystals are regular and easy to disperse, laying a key foundation for subsequent dielectrophoretic separation.

[0049] (2) The separation cycle of this invention is only 15-30 minutes, which is more than 90% shorter than that of traditional methods. The product has a DHA purity of ≥80% and a recovery rate of ≥96%, an EPA lauryl ester purity of ≥79.6% and a recovery rate of ≥80%, a liquid encapsulation rate of ≤5%, and a peroxide value that meets national standards. Its core is to utilize the positive mesoelectrophoresis effect at 1.5×10 4 ~3×10 4 In an AC electric field of V / m, EPA lauryl ester crystals with higher dielectric constant are oriented to migrate. Optimized arc-shaped edge electrodes (radius of curvature 0.5~1mm) increase the local electric field strength by 2~3 times, ensuring efficient crystal migration. Compared with the high encapsulation rate and low recovery rate of traditional low-temperature crystallization methods, this method uses a laser particle size analyzer to control the stirring speed in real time, avoiding crystal agglomeration and loss. Furthermore, the AC electric field eliminates the problem of electrolysis gas generation, further improving product quality.

[0050] (3) The production system of this invention can achieve continuous production and meet industrial needs. In the enzymatic hydrolysis unit, the RM immobilized enzyme can be reused 3 to 5 times after being recovered by the filter membrane, with an enzyme activity retention rate of ≥80%, reducing enzyme costs by 40%; the dielectrophoresis separation unit does not require low-temperature refrigeration, only needs to be cooled to 25 to 30°C, reducing energy consumption by 65% ​​compared to traditional equipment. The system is equipped with a dielectric constant monitoring and electric field gradient optimization module, which adjusts the electric field parameters in real time through a "monitoring-feedback-adjustment" closed loop to meet the factors of raw material fluctuations. The single batch processing capacity can reach 200 kg, ensuring stable separation effect and meeting the needs of large-scale production in the food and pharmaceutical fields. Detailed Implementation

[0051] The following specific embodiments further illustrate the present invention so that those skilled in the art can better understand and implement it, but the embodiments are not intended to limit the present invention.

[0052] This invention relates to a method and production system for the directional separation of fish oil based on the electric field-enhanced dielectrophoresis effect; wherein, the specific method for the directional separation of fish oil based on the electric field-enhanced dielectrophoresis effect is as follows:

[0053] (1) Raw material extraction: Collect waste materials from the processing of marine fish such as tuna and sardines (fish heads, fish viscera, fish fillets, etc.) or waste materials from algae oil processing, and obtain refined fish oil with an acid value ≤2.0mg KOH / g by washing, pressing (pressure 15MPa~20MPa, temperature 45℃~55℃), filtration, and decolorization with activated clay (60℃~70℃, 30min).

[0054] (2) Preliminary enrichment by alkaline hydrolysis crystallization: Take the above refined fish oil and add anhydrous ethanol solution of 0.3 mol / L to 0.7 mol / L NaOH (the molar ratio of the refined fish oil to NaOH is 1:3.1 to 1:3.6, ensuring that NaOH is 5% to 20% in excess of ester groups in the fish oil to ensure complete hydrolysis of ester groups), and hydrolyze at 65℃ to 75℃ for 1.5 to 2.5 h; then add anhydrous ethanol until the total amount is 5 times the volume of fish oil, and use a gradient crystallization fractionation process, first keep at 30℃ for 2 h, then keep at -40℃ for 3 h, and then keep at -86℃ for 4 h, discarding the non-target fatty acid solids precipitated at each stage; then use 1 mol / L The pH of the system was adjusted to 2.0-3.0 with HCl, and twice the volume of purified water was added. After standing and separating into layers, the upper fatty acid phase was taken and vacuum dried at 55℃-65℃ and -0.090MPa--0.095MPa for 1-2 hours to obtain fish oil fatty acids with a moisture content ≤0.1% (EPA content of 40wt%-50wt% and DHA content of 40wt%-45wt%).

[0055] (3) Enzymatic hydrolysis and directional conversion: Take 100~500g of fish oil fatty acids obtained in step (2) above, add lauryl alcohol (purity ≥99%) at a molar ratio of 1:1.2~1:1.5, mix evenly, add RM immobilized enzyme (enzyme activity ≥5000U / g), and control the enzyme to substrate mass ratio to be 1:200~1:400; adjust the pH of the system to 7.5~8.5 with 0.1mol / L Tris-HCl buffer, and react for 7h~9h at 45℃~55℃ and 300r / min~500r / min to selectively convert EPA to EPA lauryl ester (esterification rate ≥80%, dielectric constant ε≈4.2), while DHA retains fatty acid form (esterification rate ≤5%, dielectric constant ε≈2.8); after the reaction, filter to remove RM immobilized enzyme (can be reused 3~5 times, enzyme activity retention rate ≥80%), and obtain a mixture of EPA lauryl ester (solid precursor) and DHA fatty acid (fluid);

[0056] (4) Low-temperature crystallization and dielectrophoretic field coupling solid-liquid separation: The above mixture was transferred to a dielectrophoretic field crystallization device with parallel platinum electrodes, and cooled to 25℃~30℃ at a rate of 0.5℃ / min~1℃ / min (EPA lauryl ester solubility ≤3g / L, precipitating 1μm~10μm solid crystals; DHA solubility ≥120g / L, maintaining fluidity); 1.5×10 4 V / m ~3×10 4 An AC electric field of V / m (frequency 1kHz~10kHz) was applied, with an electrode spacing of 5mm~8mm and an electric field duration of 15min~30min. Due to its higher dielectric constant than DHA, EPA lauryl ester crystals exhibited a positive mesoelectrophoresis effect, directionally migrating towards the strong electric field region (near the electrodes) to form a dense solid crystal layer. The solid (EPA lauryl ester) near the electrodes was collected using a scraper, while the upper fluid was DHA fatty acids, achieving solid-liquid separation. Specifically, when the crystal particle size was 1μm~5μm, the electric field strength was controlled at 2.0×10⁻⁶. 4 V / m ~3×10 4 V / m, frequency 8kHz~10kHz, ensuring dielectric strength ≥1.2×10 -12 N; When the crystal grain size is 5μm~10μm, the electric field strength is adjusted to 1.5×10 4 V / m ~ 2.0 × 10 4 V / m, frequency 1kHz~5kHz, to avoid migration obstruction caused by crystal agglomeration.

[0057] (5) Post-processing of products: The collected EPA lauryl ester solids were vacuum dried at 40~45℃ and -0.095MPa~-0.1MPa for 2h~3h to remove trace amounts of adhering liquid; DHA fatty acid fluids were subjected to molecular distillation fractionation: in the first stage, distillation was carried out at 100℃~120℃ and vacuum degree ≤0.1mbar for 1h~2h to remove residual lauryl alcohol; in the second stage, distillation was carried out at 130℃~150℃ and vacuum degree ≤0.05mbar for 0.5h~1h to remove light fractions containing EPA, and EPA lauryl ester solid products and DHA liquid products were obtained respectively.

[0058] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0059] Purity of EPA lauryl esters (%) = (mass of EPA lauryl esters in the product / total mass of EPA lauryl esters) × 100%, where the mass of EPA lauryl esters is in esterified form (molecular weight 470).

[0060] DHA product purity (%) = (mass of DHA fatty acids in the product / total fatty acid mass of DHA product) × 100%, where DHA includes free DHA fatty acids and hydrolyzed and recovered DHA ester components.

[0061] Recovery rate (%) = (mass of the target component in the final product / initial mass of the component in the raw fish oil fatty acids) × 100%.

[0062] POV: Determined by titration in GB 5009.227-2016 "National Food Safety Standard - Determination of Peroxide Value in Food".

[0063] The method for calculating the encapsulation rate is as follows: (1) Accurately weigh a certain mass of EPA lauryl ester solid crystals (mL, unit: g);

[0064] (2) Using n-hexane as the extractant, the liquid DHA encapsulated in the crystals is extracted by a Soxhlet extractor (n-hexane does not dissolve solid EPA lauryl ester, but only liquid DHA).

[0065] (3) After extraction, remove n-hexane by vacuum distillation of the extract and weigh the remaining liquid DHA (m2, unit: g).

[0066] (4) Package rate (%) = (m2 / m1) × 100%.

[0067] Example 1

[0068] This embodiment provides a method for the directional separation of fish oil based on the electric field-enhanced dielectrophoresis effect. The specific steps are as follows:

[0069] (1) Waste pretreatment: Collect waste materials (fish heads, fish viscera, fish ribs, etc.) from marine fish such as tuna and sardines, remove impurities such as mud and fish bone residue, rinse with clean water, and store at 4℃ (storage time ≤24h) to avoid fat oxidation;

[0070] (2) Pressing and oil extraction: The pretreated waste is fed into a screw press and pressed at a pressing pressure of 20 MPa and a temperature of 55°C to obtain crude fish oil;

[0071] (3) Preliminary refining: Crude fish oil is filtered through a plate and frame filter (filter cloth pore size 5μm) to remove suspended solids. 1.0wt% activated clay is added and stirred at 70℃ for 30min to decolorize. After filtration again, refined fish oil (acid value 1.2mg KOH / g, moisture ≤0.3%) is obtained.

[0072] (4) Preparation of fish oil fatty acids: Take 50 kg of refined fish oil, add 375 L of 0.5 mol / L NaOH solution (solvent is anhydrous ethanol), stir and hydrolyze at 70 °C for 2 h; add 5 times the amount of anhydrous ethanol, and carry out gradient crystallization separation in the following order: keep warm at 30 °C for 2 h, keep warm at -40 °C for 3 h, keep warm at -86 °C for 4 h, discard the non-target fatty acid solids precipitated at each stage, adjust the pH value to 2.5 with 1 mol / L HCl, add 2 times the volume of pure water, let stand for 30 min to separate the layers, and take 18.2 kg of the upper fatty acid phase; in addition to the target fatty acid, the fatty acid phase also contains about 9.3% water and a small amount of ethanol residue; vacuum dry it at 60 °C and -0.095 MPa for 1.5 h to remove water and trace amount of ethanol, and obtain 16.5 kg of fish oil fatty acids (of which, EPA 48.0 wt%, DHA 42.0 wt%, water 0.08 wt%).

[0073] (5) RM immobilization enzymatic hydrolysis: Add 16.5 kg of fish oil fatty acids, 12.9 kg of lauryl alcohol, and 0.098 kg of RM immobilized enzyme (Novozymes lipase, batch number: LU300032) (enzyme to substrate ratio 1:300) to a 100 L reactor, and add 0.7 kg of 0.1 mol / L Tris-HCl buffer (pH 8.0); heat to 50 °C, stir at 400 r / min, and react for 8 h; after the reaction, filter through a 0.22 μm filter membrane to recover the RM immobilized enzyme (which can be used for the next batch), and dehydrate the mixture at 60 °C and -0.095 MPa vacuum for 30 min to ensure that the moisture content is ≤0.1 wt%, and obtain 28.7 kg of mixture (the main components include: EPA lauryl ester, unreacted EPA, DHA fatty acids, unreacted lauryl alcohol and other impurities).

[0074] (6) Low-temperature crystallization and dielectric electrophoretic field coupling separation: The mixture was transferred to the dielectric electrophoretic field crystallization device, the temperature control unit was turned on, and the temperature was reduced to 28℃ at a rate of 0.8℃ / min; the crystal particle size was monitored by a laser particle size analyzer and controlled within 5μm; the AC power supply was turned on and 2.0×10⁻⁶ was applied. 4 With an electric field of V / m (frequency 5kHz), an electrode spacing of 6mm, a stirring rate of 40r / min, and a migration rate of 0.6mm / s, after 20min of electric field application, the dielectric constant monitoring module showed that the dielectric constant difference between the EPA lauryl ester crystals and the liquid phase was Δε=1.3 (because the dielectric difference constructed by enzymatic hydrolysis is stable, although the electric field parameters are finely adjusted, Δε is still maintained in the effective range of ≥1.2, which meets the separation requirements). The solid was collected by scraping near the electrode, and EPA lauryl ester solid was obtained.

[0075] (7) Post-processing: The solid EPA lauryl ester was transferred to a vacuum dryer and dried at 42°C and -0.098MPa for 2.5h to obtain 12.38kg of EPA lauryl ester product (EPA lauryl ester purity 79.6%, corresponding EPA content 51.2%, total EPA recovery rate 80%, POV 2.0meq / kg, encapsulation rate 2.5%). The upper fluid entered a short-path molecular distillation apparatus. In the first stage, it was distilled at 110°C and 0.1mbar for 1h to remove and recover about 7.9kg of lauryl alcohol, which was recycled for the next batch of enzymatic hydrolysis reaction. In the second stage, it was heated to 140°C and 0.05mbar for 0.5h to remove the light fraction containing EPA and obtain 8.32kg of DHA product (DHA purity 80%, referring to the mass fraction of DHA in total fatty acids, recovery rate 96%, POV 2.1meq / kg).

[0076] This embodiment also provides a production system for a fish oil directional separation method based on electric field enhanced dielectrophoresis effect. The production system includes a pretreatment unit, a fish oil fatty acid preparation unit, an enzymatic hydrolysis reaction unit, a dielectrophoretic electric field crystallization separation unit, and a product collection unit.

[0077] The pretreatment unit includes a pressing device, a plate and frame filter, and a decolorizing tank connected in sequence; it is used to press the pretreated waste to extract oil, filter, and decolorize it to obtain refined fish oil with an acid value ≤2.0mg KOH / g and a moisture content ≤0.3%.

[0078] A fish oil fatty acid preparation unit includes a hydrolysis tank, a crystallizer, and a vacuum dryer; the crystallizer is connected to the hydrolysis tank, which is used to contain refined fish oil and an alkaline solution for hydrolysis; the crystallizer is used for cooling; and the vacuum dryer is used to dry the upper fatty acid phase after separation to obtain fish oil fatty acids.

[0079] An enzymatic hydrolysis reaction unit includes an enzymatic hydrolysis vessel, which is equipped with a temperature control component and a mixing and stirring device; it is used for the reaction of fish oil fatty acids, lauryl alcohol mixed substrate and RM immobilized enzyme to obtain a mixture containing EPA lauryl ester and DHA.

[0080] It also includes an enzyme recovery filter for recovering RM immobilized enzymes;

[0081] Dielectrophoretic electric field crystallization separation unit includes a dielectrophoretic electric field crystallization device, a temperature control module, a laser particle size analyzer, a parallel electrode assembly, and an AC power scraper collection device; the laser particle size analyzer is used to monitor the crystal particle size; the parallel electrode assembly is electrically connected to the AC power supply; the scraper collection device is adapted to the electrode assembly and is used to collect EPA lauryl ester solids near the electrodes;

[0082] The product collection unit includes a molecular distillation apparatus, an EPA lauryl ester collection tank, and a DHA collection tank; the molecular distillation apparatus is used to remove residual lauryl alcohol and small amounts of impurities such as EPA-containing light fractions from the DHA fluid.

[0083] Example 2

[0084] This embodiment provides a method for directional separation of fish oil based on the enhanced dielectrophoresis effect, similar to Embodiment 1, except that step (6) is modified as follows: the mixture is transferred to the dielectrophoretic electric field crystallization device, the temperature control unit is turned on, and the temperature is reduced to 28°C at a rate of 0.8°C / min; the crystal particle size is monitored by a laser particle size analyzer (controlled within 5μm), the AC power supply is turned on, and a 1.5×10⁻⁶ ohmmeter is applied. 4 An electric field of V / m (frequency 5kHz) was applied, with an electrode spacing of 6mm, a stirring rate of 40r / min, and a migration rate of 0.4mm / s. Due to the reduced electric field strength, the crystal separation efficiency decreased by 5% compared to Example 1. After 28 minutes of electric field application, the dielectric constant monitoring module showed Δε=1.3 (still meeting the separation requirements), and the scraper near the electrode was activated to collect the solid. The remaining steps were consistent with Example 1.

[0085] The solid EPA lauryl ester was transferred to a vacuum dryer and dried at 42°C and -0.098 MPa for 2.5 h to obtain 12.39 kg of EPA lauryl ester product (purity 79.58%, total recovery 80%, POV 2.1 meq / kg, encapsulation rate 2.8%). The upper DHA fluid was fed into a molecular distillation apparatus (first removing lauryl ester at 110°C / 0.1 mbar, then removing the EPA light fraction at 140°C / 0.05 mbar) to obtain 8.32 kg of DHA product (purity 80%, recovery 96%, POV 2.2 meq / kg).

[0086] Example 3

[0087] This embodiment provides a method for directional separation of fish oil based on the enhanced dielectrophoresis effect, similar to Embodiment 1, except that step (6) is modified as follows: the mixture is transferred to the dielectrophoretic electric field crystallization device, the temperature control unit is turned on, and the temperature is reduced to 28°C at a rate of 0.8°C / min; the crystal particle size is monitored by a laser particle size analyzer (controlled within 5μm), the AC power supply is turned on, and a 2.5×10⁻⁶ ohm crystal is applied. 4 An electric field of V / m (frequency 8kHz) was applied, with an electrode spacing of 6mm, a stirring rate of 40r / min, and a migration rate of 0.9mm / s. After 15 minutes of electric field application, the dielectric constant monitoring module showed Δε=1.3, and the scraper near the electrodes was activated to collect the solid. The remaining steps were consistent with those in Example 1.

[0088] After drying, 12.44 kg of EPA lauryl ester product (purity 79.71%, total recovery rate 80.3%, POV 1.9 meq / kg, encapsulation rate 2.2%) and 8.33 kg of DHA product (purity 80.2%, recovery rate 96.2%, POV 2.0 meq / kg) were obtained.

[0089] Example 4

[0090] This embodiment provides a method for directional separation of fish oil based on the enhanced dielectrophoresis effect, similar to Embodiment 1, except that step (6) is modified as follows: the mixture is transferred to the dielectrophoretic electric field crystallization device, the temperature control unit is turned on, and the temperature is reduced to 25°C at a rate of 0.8°C / min; the crystal particle size is monitored by a laser particle size analyzer (controlled within 5μm), the AC power supply is turned on, and a 2.0×10⁻⁶ ohmmeter is applied. 4 An electric field of V / m (frequency 2kHz) was applied, with an electrode spacing of 6mm, a stirring rate of 40r / min, and a migration rate of 0.5mm / s. After 22 minutes of electric field application, the dielectric constant monitoring module showed Δε=1.3, and the scraper near the electrodes was activated to collect the solid. The remaining steps were consistent with those in Example 1.

[0091] After drying, 12.39 kg of EPA lauryl ester product (purity 79.68%, total recovery rate 80.1%, POV 2.0 meq / kg, encapsulation rate 2.4%) and 8.32 kg of DHA product (purity 80.1%, recovery rate 96.1%, POV 2.1 meq / kg) were obtained.

[0092] Example 5

[0093] This embodiment provides a method for directional separation of fish oil based on the enhanced dielectrophoresis effect, similar to Embodiment 1, except that step (6) is modified as follows: the mixture is transferred to the dielectrophoretic electric field crystallization device, the temperature control unit is turned on, and the temperature is reduced to 30°C at a rate of 0.8°C / min; the crystal particle size is monitored by a laser particle size analyzer (controlled within 5μm), the AC power supply is turned on, and a 2.0×10⁻⁶ ohmmeter is applied. 4 An electric field of V / m (frequency 8kHz) was applied, with an electrode spacing of 6mm, a stirring rate of 40r / min, and a migration rate of 0.7mm / s. After 18 minutes of electric field application, the dielectric constant monitoring module showed Δε=1.3, and the scraper near the electrodes was activated to collect the solid. The remaining steps were consistent with those in Example 1.

[0094] After drying, 12.39 kg of EPA lauryl ester product (purity 79.55%, total recovery rate 80.1%, POV 2.2 meq / kg, encapsulation rate 4.0%) and 8.32 kg of DHA product (purity 80%, recovery rate 96.0%, POV 2.2 meq / kg) were obtained.

[0095] Example 6

[0096] This embodiment provides a method for directional separation of fish oil based on the enhanced dielectrophoresis effect, similar to Embodiment 1, except that step (6) is modified as follows: the mixture is transferred to a dielectrophoretic electric field crystallization device, the temperature control unit is turned on, and the temperature is reduced to 28°C at a rate of 0.8°C / min; the crystal particle size is monitored by a laser particle size analyzer (controlled within 5μm), the AC power supply is turned on, and a 2.0×10⁻⁶ ohm crystal is applied. 4 An electric field of V / m (frequency 5kHz) was applied, with an electrode spacing of 5mm, a stirring rate of 40r / min, and a migration rate of 0.8mm / s. After 16 minutes of electric field application, the dielectric constant monitoring module showed Δε=1.3, and the scraper near the electrodes was activated to collect the solid. The remaining steps were consistent with those in Example 1.

[0097] After vacuum drying of solid EPA lauryl ester, 12.34 kg of EPA lauryl ester product (purity 79.62%, total recovery rate 80.0%, POV 2.0 meq / kg, encapsulation rate 2.3%) and 8.31 kg of DHA product (purity 80.0%, recovery rate 96.0%, POV 2.1 meq / kg) were obtained.

[0098] Example 7

[0099] A 500L pilot-scale test (single batch processing capacity of 200kg refined fish oil) was conducted using the scheme of Example 1. The data from three consecutive batches are shown in Table 1 below:

[0100] Table 1

[0101]

[0102] As shown in Table 1, the core indicators of the three consecutive batches of pilot-scale products exhibited minimal fluctuations. DHA purity remained stable at 79.9%–80.2%, EPA lauryl ester purity remained stable at 79.5%–79.8%, DHA recovery rate was ≥96.0%, EPA ester recovery rate was ≥79.8%, encapsulation rate was ≤2.5%, and migration rate remained stable at 0.60–0.65 mm / s. The relative standard deviation (RSD) of all indicators was ≤0.5%, confirming that the method of this invention can be stably reproduced at a 500L pilot-scale without performance degradation due to scale-up effects. The EPA ester recovery rate in the pilot-scale test was slightly lower than that in the laboratory small-scale test (difference of 0.1–0.3 percentage points). This was due to the uniformity of the electric field in the equipment, material transfer losses, and batch fluctuations of raw materials during the scale-up process, which is a normal phenomenon in industrial scale-up. The indicators still consistently exceeded the requirements of this invention (EPA ester recovery rate ≥80%, DHA recovery rate ≥96%), and the fluctuation range was extremely small (RSD ≤0.5%), confirming the industrial stability of the method.

[0103] The pilot-scale migration rate remained above 0.6 mm / s, corresponding to a separation cycle of only 15-20 minutes, and the total cycle time for a single batch was 12-16 hours, which is 55%-75% shorter than the traditional low-temperature crystallization method; the power consumption was only 0.34-0.37 kWh / kg, which is 61%-64% lower than the traditional method.

[0104] Comparative Example 1

[0105] This comparative example provides a conventional low-temperature crystallization method for the directional separation of fish oil, similar to Example 1, except that step (6) is omitted. The 28.7 kg mixture obtained in step (5) is directly cooled to -10°C and allowed to stand for crystallization for 18 hours. Vacuum filtration using a Buchner funnel (filter cloth pore size 1 μm) yields 6.85 kg of solid EPA lauryl ester (purity 68.5%, encapsulation rate 15.3%, total EPA recovery rate 62.6%), and 5.2 kg of DHA product (purity 74.8%, recovery rate 78.3%) is obtained after molecular distillation of the DHA fluid. The total cycle time is 38 hours, energy consumption is 2.8 times that of Example 1, and the crystal loss rate below 5 μm reaches 12%. All indicators are significantly inferior to Example 1 (EPA purity 79.6%, recovery rate 80%), confirming the superiority of the method of this invention.

[0106] Comparative Example 2

[0107] This comparative example provides a method for directional separation of fish oil, which is similar to Example 1, except that step (5) is missing (no enzymatic hydrolysis), and the 16.5 kg of fish oil fatty acids obtained in step (4) are directly passed into the dielectrophoretic electric field crystallization device. The remaining steps are consistent with those in Example 1.

[0108] Since the dielectric constant difference between EPA and DHA is only Δε=0.3 (<0.5), there is no obvious dielectric electrophoresis effect. The final purity of DHA is 30.2% and that of EPA is 28.5%. The recovery rates of both are ≤60%, which cannot achieve effective separation. This confirms the necessity of constructing dielectric differences through enzymatic hydrolysis and further highlights the core value of the enzymatic hydrolysis step in this invention.

[0109] Comparative Example 3

[0110] This comparative example provides a method for directional separation of fish oil, similar to Example 1, except that in step (6), the alternating current field is replaced with 2.0 × 10⁻⁶. 4 The DC electric field is V / m, and the remaining steps are consistent with those in Example 1.

[0111] Electrolysis gas appeared on the electrode surface after 5 minutes of electric field application, causing crystal agglomeration. Ultimately, the purity of EPA lauryl ester dropped to 55.3%, and the peroxide value rose to 3.5 meq / kg, resulting in severe deterioration of product quality. This demonstrates the advantages of alternating electric fields in avoiding electrolysis gas generation and protecting crystal morphology.

[0112] Comparative Example 4

[0113] This comparative example provides a method for the directional separation of fish oil, which is similar to Example 1, except that in step (5), lauryl alcohol is replaced with ethanol, and the remaining steps are consistent with Example 1.

[0114] Comparative Example 5

[0115] This comparative example provides a method for the directional separation of fish oil, which is similar to Example 1, except that in step (5), lauryl alcohol is replaced with n-propanol, and the remaining steps are consistent with Example 1.

[0116] Comparative Example 6

[0117] This comparative example provides a method for the directional separation of fish oil, which is similar to Example 1, except that in step (5), lauryl alcohol is replaced with n-butanol, and the remaining steps are consistent with Example 1.

[0118] Comparative Example 7

[0119] This comparative example provides a method for the directional separation of fish oil, which is similar to Example 1, except that in step (5), lauryl alcohol is replaced with n-pentanol, and the remaining steps are consistent with Example 1.

[0120] Comparative Example 8

[0121] This comparative example provides a method for the directional separation of fish oil, which is similar to Example 1, except that in step (5), lauryl alcohol is replaced with n-octanol, and the remaining steps are consistent with Example 1.

[0122] Performance testing

[0123] To investigate the effect of different alcohols on separation in Example 1 and Comparative Examples 4-8, four key indicators were tested: esterification reaction rate, EPA / DHA selectivity, ester crystallization properties, and dielectrophoretic separation. The specific testing methods are as follows:

[0124] (1) Esterification rate and selectivity: determined by gas chromatography (GC-FID) as specified in GB 5009.168-2024.

[0125] (2) Dielectric constant: determined by the parallel plate electrode method specified in GB / T 1409-2006 (28℃).

[0126] (3) Crystallization performance: The crystal size was measured by laser particle size analyzer (GB / T 19077.1-2021), and the integrity of crystallization was observed by polarizing microscope.

[0127] The specific results and data are shown in Tables 2-4 below:

[0128] Table 2: Comparison of EPA esterification rates for different alcohols (unit: %)

[0129]

[0130] Table 3: Comparison of selectivity and separation suitability of different alcohols

[0131]

[0132] Table 4: Melting points of different alcohols and crystallization temperatures and crystallization effects of corresponding EPA esters

[0133]

[0134] Based on the experimental data in Tables 2-4, it is clear that lauryl alcohol exhibits superior technical advantages over other alcohols in terms of targeted esterification, selectivity, and subsequent separation compatibility with EPA in fish oil. This invention uses lauryl alcohol as the EPA esterification reagent. After 8 hours of reaction, the EPA esterification rate reaches 92.8%, which is 22.6 and 7.1 percentage points higher than ethanol and n-octanol, respectively. This is due to the stable binding of the C12 carbon chain of lauryl alcohol to the hydrophobic region of the active site of the RM immobilized enzyme, significantly reducing the activation energy of the reaction. The EPA selectivity coefficient is as high as 286.97, which is 4.97-14.76 times that of other alcohols (4.97 times higher than n-octanol and 14.76 times higher than ethanol). It specifically catalyzes only EPA esterification (esterification rate of 92.8%), while the DHA esterification rate is controlled at 4.3%, laying the foundation for targeted separation. EPA lauryl esters achieve a 98% crystallization rate at 25-30°C without cryogenic refrigeration, consuming only 1 / 2 to 1 / 8 the energy of other alcohols. The crystals are regular particles of 5-8 μm, exhibiting good dispersibility and can be efficiently driven by dielectric electrophoresis. Furthermore, it avoids the high energy consumption and low crystallization rate problems of other alcohols at ultra-low temperatures, achieving a liquid encapsulation rate of only 2.5%, eliminating cross-contamination, and balancing high efficiency, economy, and stability in production. In summary, short-chain and medium-chain alcohols (ethanol to n-octanol) either suffer from poor esterification selectivity, require ultra-low temperatures and high energy consumption for crystallization, or have crystal morphologies unsuitable for dielectric electrophoresis, all of which cannot simultaneously achieve separation efficiency and economy, further confirming the necessity of using lauryl esters in this invention.

[0135] Obviously, the above embodiments are merely examples to clearly illustrate the technical solutions of the present invention and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or adjustments can be made based on the description of the present invention. The present invention cannot exhaustively describe all embodiments; therefore, obvious variations or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for directional separation of fish oil based on electric field-enhanced dielectrophoresis, characterized in that, Includes the following steps: S1. After pretreatment, fish or algae oil processing waste is pressed, filtered, and decolorized to obtain refined fish oil. S2. The obtained refined fish oil was hydrolyzed in anhydrous ethanol alkaline solution at 65℃~75℃ for 1.5~2.5h, and then subjected to gradient crystallization at -86℃~30℃. The pH was adjusted to 2.0~3.

0. Water was added and the mixture was allowed to stand and separate into layers. The upper fatty acid phase was vacuum dried to obtain fish oil fatty acids with a moisture content ≤0.1%. The EPA content was 40wt%~50wt%, the DHA content was 40wt%~45wt%, and the total content of EPA and DHA was ≥80wt%. S3. Mix the obtained fish oil fatty acids with lauryl alcohol, add RM immobilized enzyme and buffer solution to the mixture to react and obtain a mixture containing EPA lauryl ester and DHA. S4. The resulting mixture is transferred to a dielectrophoretic electric field crystallization device, and solid crystals are precipitated after cooling. An alternating electric field is applied simultaneously to form a dense solid crystal layer near the electrode. The solid is collected and dried under vacuum to obtain EPA lauryl ester. Molecular distillation was performed on the upper fluid in the dielectrophoretic field crystallization apparatus to recover lauryl alcohol and remove impurities, yielding DHA.

2. The method for directional separation of fish oil according to claim 1, characterized in that, In step S1, the pressing pressure is 15MPa~20MPa and the temperature is 45℃~55℃; And / or, the decolorization is performed using activated clay; the decolorization temperature is 60℃~70℃; And / or, the refined fish oil has an acid value ≤2.0mg KOH / g and a moisture content ≤0.3wt%.

3. The method for directional separation of fish oil according to claim 1, characterized in that, In step S2, the concentration of the anhydrous ethanol alkaline solution is 0.3 mol / L to 0.7 mol / L; And / or, the base in the anhydrous ethanol alkaline solution is NaOH and / or KOH.

4. The method for directional separation of fish oil according to claim 1, characterized in that, In step S2, the molar ratio of the refined fish oil to the alkali in the anhydrous ethanol alkaline solution is 1:3.1 to 1:3.6; the gradient crystallization fractionation is carried out at -86℃ to 30℃ for 2 to 3 times. And / or, the vacuum drying conditions are: vacuum drying at 55℃~65℃ and -0.090MPa~-0.095MPa for 1h~2h.

5. The method for directional separation of fish oil according to claim 1, characterized in that, In step S3, the molar ratio of fish oil fatty acids to lauryl alcohol is 1:1.2 to 1:1.5; And / or, the mass ratio of the RM immobilized enzyme to the mixture is 1:200 to 1:

400.

6. The method for directional separation of fish oil according to claim 1, characterized in that, In step S3, the pH value of the reaction is 7.5~8.5; And / or, the reaction temperature is 45°C to 55°C; And / or, the rotation speed of the reaction is 300 r / min to 500 r / min; And / or, the reaction time is 7h to 9h.

7. The method for directional separation of fish oil according to claim 1, characterized in that, In step S4, the cooling is performed by cooling to 25°C to 30°C at a rate of 0.5°C / min to 1°C / min.

8. The method for directional separation of fish oil according to claim 1, characterized in that, In step S4, the frequency of the alternating electric field is 1kHz to 10kHz; And / or, the strength of the alternating electric field is 1.5 × 10⁻⁶. 4 V / m ~3×10 4 V / m; And / or, the duration of the alternating electric field is 15 min to 30 min; And / or, the electrode spacing in the dielectric electrophoretic field crystallization device is 5mm~8mm.

9. The method for directional separation of fish oil according to claim 1, characterized in that, In step S4, the vacuum drying conditions are: 40℃~45℃, -0.095MPa~-0.1MPa for 2h~3h. And / or, the molecular distillation is a staged molecular distillation; the temperature of the first stage molecular distillation is 100℃~120℃, the vacuum degree is ≤0.1mbar, and the time is 1h~2h; the temperature of the second stage molecular distillation is 130℃~150℃, the vacuum degree is ≤0.05mbar, and the time is 0.5h~1h.

10. A production system for the fish oil directional separation method based on electric field-enhanced dielectrophoresis as described in claim 1, characterized in that, The production system includes a pretreatment unit, a fish oil fatty acid preparation unit, an enzymatic hydrolysis reaction unit, a dielectrophoretic electric field crystallization separation unit, and a product collection unit; The pretreatment unit includes a pressing device, a plate and frame filter, and a decolorizing tank connected in sequence; it is used to press the pretreated waste material to extract oil, filter it, and decolorize it to obtain refined fish oil. A fish oil fatty acid preparation unit includes a hydrolysis tank, a crystallizer, and a vacuum dryer; the crystallizer is connected to the hydrolysis tank, which is used to contain refined fish oil and an alkaline solution for hydrolysis; the crystallizer is used for cooling; and the vacuum dryer is used to dry the upper fatty acid phase after separation to obtain fish oil fatty acids. An enzymatic hydrolysis reaction unit includes an enzymatic hydrolysis vessel, which is equipped with a temperature control component and a mixing and stirring device; it is used for the reaction of fish oil fatty acids, lauryl alcohol mixed substrate and RM immobilized enzyme to obtain a mixture containing EPA lauryl ester and DHA. Dielectrophoretic electric field crystallization separation unit includes a dielectrophoretic electric field crystallization device, a temperature control module, a laser particle size analyzer, a parallel electrode assembly, and an AC power scraper collection device; the laser particle size analyzer is used to monitor the crystal particle size; the parallel electrode assembly is electrically connected to the AC power supply; the scraper collection device cooperates with the electrode assembly to collect EPA lauryl ester solids near the electrodes; The product collection unit includes a molecular distillation apparatus, an EPA lauryl ester collection tank, and a DHA collection tank; the molecular distillation apparatus is used to remove residual lauryl alcohol and EPA-containing fractions from the DHA fluid in stages.

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