Fish oil purification method

Abstract

The invention belongs to the technical field of fish oil refining, and particularly relates to a fish oil purification method. Comprising the following steps: preparing specific free fatty acid adsorption starch; preparing oxygen vacancy carbon composite decolorized hydrotalcite; and refining and purifying the fish oil. The preparation method comprises the following steps: carrying out alkylation treatment on high-amylose corn starch, and subsequently carrying out cross-linking combination on the high-amylose corn starch, template molecule oleic acid of free fatty acid, 3-acrylamido phenylboronic acid, temperature-sensitive N-isopropylacrylamide and pentaerythritol triacrylate, so as to prepare the specific free fatty acid adsorption starch. According to the invention, the starch-lipid mixture can be generated with free fatty acid at a high temperature, the deacidification efficiency is improved, meanwhile, under the modification of an oleic acid specific template, the adsorption amount and adsorption efficiency of the specific free fatty acid adsorption starch on the free fatty acid can be further increased, and the free fatty acid in the fish oil can be efficiently removed; the peroxide value and the acid value of the purified fish oil are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of fish oil refining, and particularly relates to a method for purifying fish oil. Background Art

[0002] Crude fish oil is usually extracted by physical separation methods such as hot pressing or steam boiling, which results in the crude fish oil containing more impurities such as protein, free fatty acids, pigments, mineral salts and hydrocarbons. These components can easily induce hydrolysis, rancidity and oxidation of fish oil, thereby reducing the safety and preservation ability of fish oil. Therefore, crude fish oil needs to undergo a series of refining and purification before it can be used in food or medical fields.

[0003] The procedure for refining and purifying crude fish oil usually includes the steps of degumming, deacidification, decolorization and deodorization. The purpose of degumming is to remove phospholipids, proteins and mineral salt impurities. The commonly used method is acid degumming. The acid reagent is generally phosphoric acid, which has the characteristics of low pollution, easy operation and high removal efficiency. The purpose of deacidification is to remove a large amount of free fatty acids and phospholipids in fish oil. The commonly used method is to add sodium hydroxide aqueous solution to the fish oil, which easily reacts with triglycerides to form saponification products and causes greater pollution to the environment. Decolorization is to improve the sensory quality of fish oil by removing colored substances in the fish oil. It often requires multiple decolorization treatments in combination with multiple decolorizers, and the steps are complicated. Summary of the invention

[0004] In order to solve the above technical defects, the present invention has developed a method for purifying fish oil, which has the characteristics of high purification efficiency and purification quality, simple process and high environmental protection.

[0005] A method for purifying fish oil comprises the following steps: S1: Preparation of starch with specific free fatty acid adsorption High-amylose corn starch is modified by using γ-methacryloxypropyltrimethoxysilane to obtain alkylated high-amylose corn starch, and then the alkylated high-amylose corn starch is placed in a reaction system of oleic acid, acetone-acetonitrile mixed solvent, 3-acrylamidophenylboronic acid, N-isopropylacrylamide and pentaerythritol triacrylate, and reacted under the initiation of azobisisobutyronitrile, filtered, washed and dried to obtain specific free fatty acid adsorbed starch; S2: Preparation of oxygen vacancy carbon composite decolorized hydrotalcite The carbon fiber is arranged in a two - electrode system for charging to obtain an electro - activated carbon cloth. MgCl₂·6H₂O and AlCl₃·6H₂O are dissolved in deionized water to prepare solution A. Sodium hydroxide and sodium carbonate are dissolved in deionized water at a mass ratio of 1:(0.5 - 0.6) to prepare solution B. The electro - activated carbon cloth is immersed in the mixed solution of solution A and solution B, and titanium oxysulfate is added for hydrothermal reaction. Then the product is washed and dried to obtain an oxygen - vacancy carbon - composite decolorizing hydrotalcite; S3: Refining and purification of fish oil The crude fish oil is degummed with phosphoric acid, and then specific free - fatty - acid - adsorbed starch is added. After heating and stirring, it is naturally cooled to room temperature. The precipitate is separated and the filtered oil is collected to obtain deacidified fish oil. Then a composite decolorizing agent prepared by mixing oxygen - vacancy carbon - composite decolorizing hydrotalcite and activated clay is added, and heating and stirring are carried out for decolorization to obtain decolorized fish oil. Then deodorization is carried out to obtain purified fish oil.

[0006] Further, the preparation of the specific free - fatty - acid - adsorbed starch in step S1 includes the following steps: S1.1: Place 2 - 5 parts by weight of high - amylose corn starch in a container, add 10 - 12 parts by weight of methanol and 2 - 3 parts by weight of γ - methacryloxypropyltrimethoxysilane, and then stir and react at 40 - 45 °C and 300 - 400 rpm for 4 - 5 hours. Then filter to obtain the filter residue, wash it 2 - 3 times with distilled water, and then place it in an oven and dry it to constant weight at 60 - 65 °C to obtain alkylated high - amylose corn starch; S1.2: Place 0.2 - 0.3 parts by weight of oleic acid in a container, add 2 - 3 parts by weight of acetone - acetonitrile mixed solvent and stir for 15 - 20 minutes. Then add 0.4 - 0.6 parts by weight of 3 - acrylamidophenylboronic acid and 0.3 - 0.4 parts by weight of N - isopropylacrylamide, and stir at a stirring speed of 250 - 300 rpm for 2 - 3 hours to obtain a pre - reaction solution; S1.3: Add 2 - 4 parts by weight of pentaerythritol triacrylate, 0.6 - 0.8 parts by weight of azobisisobutyronitrile and 15 - 20 parts by weight of alkylated high - amylose corn starch to the pre - reaction solution prepared in step S1.2, transfer it to an ultrasonic cleaner and process it at an ultrasonic frequency of 25 - 30 kHz for 15 - 20 minutes, and then react at 55 - 60 °C for 20 - 24 hours. Filter to obtain the filtrate, wash it 3 - 4 times with a tetrahydrofuran - deionized water mixed solution, and then vacuum - dry it to constant weight at 45 - 50 °C to obtain specific free - fatty - acid - adsorbed starch.

[0007] Further, the preparation of the oxygen - vacancy carbon - composite decolorizing hydrotalcite in step S2 includes the following steps: S2.1: Place a carbon fiber cloth with a length and width of 2 cm × 1 cm as the working electrode in a two-electrode system, a platinum sheet as the counter electrode, and a H2SO4 solution with a concentration of 0.1 - 0.2 mol / L as the electrolyte. Use a DC power supply with constant voltage and constant current to charge the carbon cloth for 4 - 5 minutes to obtain an electro-activated carbon cloth; S2.2: Dissolve MgCl2·6H2O and AlCl3·6H2O in deionized water to prepare solution A. The concentration of Mg 2+ in solution A is 0.6 - 0.7 mol / L, and the concentration of Al 3+ is 0.3 - 0.35 mol / L. Dissolve sodium hydroxide and sodium carbonate in deionized water at a mass ratio of 1:(0.5 - 0.6) to prepare solution B. The concentration of OH - in solution B is 1 - 1.2 mol / L. Place the electro-activated carbon cloth in a hydrothermal reactor, then add solution A and solution B to the hydrothermal reactor according to a volume ratio of 1:(1 - 1.2) to completely immerse the electro-activated carbon cloth. Then add titanium oxysulfate and stir evenly. Control the concentration of titanium oxysulfate at 0.1 - 0.2 mol / L. React at 115 - 120 °C for 10 - 12 hours. After taking out the product, rinse it clean with deionized water and place it in an oven to dry at a temperature of 65 - 70 °C to constant weight to obtain oxygen vacancy carbon composite decolorized hydrotalcite.

[0008] Furthermore, the refined purification of fish oil in step S3 includes the following steps: S3.1: Under the condition of water bath oscillation at 65 - 70 °C and 140 - 150 rpm, gradually add phosphoric acid with a volume fraction of 75 - 80% dropwise to the crude fish oil at a mass ratio of 1:(100 - 120). Then keep it warm at a water bath temperature of 65 - 70 °C for 1.5 - 2 minutes. Then place it in a centrifuge while it is hot and centrifuge at a speed of 10000 - 12000 rpm for 10 - 15 minutes. Then collect the upper layer of grease to obtain degummed fish oil; S3.2: Add 4 - 4.5 wt% of specific free fatty acid adsorption starch to the degummed fish oil, then stir at 65 - 70 °C and 250 - 300 rpm for 60 - 80 minutes. Then naturally cool to room temperature, filter and separate the precipitate, and collect the filtered oil to obtain deacidified fish oil. Mix the oxygen vacancy carbon composite decolorized hydrotalcite and activated clay evenly at a mass ratio of 1:(2 - 3) to obtain a composite decolorant. Add 2 - 5 wt% of the composite decolorant to the deacidified fish oil and stir evenly. Decolorize at a decolorization temperature of 55 - 70 °C for 40 - 60 minutes. Then filter and collect the filtered oil to obtain decolorized fish oil. Then transfer it to a deodorization tower for deodorization treatment to obtain purified fish oil.

[0009] Furthermore, the amylose content of the high amylose corn starch in step S1.1 is 55 - 60%.

[0010] Further, the acetone-acetonitrile mixed solvent in step S1.2 is composed of acetone and acetonitrile at a volume ratio of 1:(2 - 2.5).

[0011] Further, the tetrahydrofuran-deionized water mixed solution in step S1.3 is composed of tetrahydrofuran and deionized water at a volume ratio of 1:(0.25 - 0.3).

[0012] Further, the voltage for power charging in step S2.1 is 5V and the current is 0.5A.

[0013] Further, the deodorization temperature for the deodorization treatment in step S3.2 is 180 - 220 °C and the time is 20 - 30 minutes.

[0014] The beneficial effects are as follows: 1. The present invention uses high amylose corn starch with a linear chain content of 55 - 60%, alkylates it, and then cross-links and combines it with template molecules of free fatty acids such as oleic acid, 3-acrylamidophenylboronic acid, thermosensitive N-isopropylacrylamide, and pentaerythritol triacrylate in subsequent steps to prepare specific free fatty acid adsorbing starch. Amylose can form a starch-lipid mixture with free fatty acids at high temperatures, and the formed starch-lipid mixture can also promote the uniform dispersion of starch in fish oil, improving the deacidification efficiency. At the same time, under the modification of the specific oleic acid template, it can further adsorb free fatty acids with a structure similar to oleic acid, increasing the adsorption amount and adsorption efficiency of specific free fatty acid adsorbing starch for free fatty acids, and can efficiently remove free fatty acids in fish oil, reducing the peroxide value and acid value of the purified fish oil.

[0015] 2. The present invention first charges the carbon fiber cloth and then places it in the hydrothermal reaction system for preparing Mg-Al-Ti hydrotalcite, enabling Mg-Al-Ti hydrotalcite to adhere to the carbon fiber cloth and forming a large number of oxygen vacancies, resulting in an oxygen vacancy carbon composite decolorizing hydrotalcite with a honeycomb structure of the carbon fiber cloth, a nanosheet structure of Mg-Al-Ti hydrotalcite, and an oxygen vacancy structure. When compounded with activated clay in subsequent steps to form a composite decolorizing agent, it can effectively remove colored substances in the deacidified fish oil, and has the characteristics of low oil absorption rate and high decolorization efficiency.

[0016] 3. The present invention can avoid using complex processes while ensuring the purification efficiency and quality of fish oil, and does not require the use of a large amount of chemical reagents during the fish oil purification process, having the characteristics of high environmental protection and simple operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the method for purifying fish oil adopted in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0019] Embodiment 1

[0020] A method for purifying fish oil, as Figure 1 shown, includes the following steps: S1: Preparation of specific free fatty acid adsorbing starch S1.1: Place 2 parts by weight of high amylose corn starch with a straight-chain content of 55% in a container, add 10 parts by weight of methanol and 2 parts by weight of γ-methacryloxypropyltrimethoxysilane, and then stir and react at 40°C and 300 rpm for 4 hours. Then filter to obtain the filter residue, wash it twice with distilled water, and then place it in an oven and dry it to constant weight at 60°C to obtain alkylated high amylose corn starch; S1.2: Place 0.2 parts by weight of oleic acid in a container, add 2 parts by weight of acetone-acetonitrile mixed solvent and stir for 15 minutes. The acetone-acetonitrile mixed solvent is composed of acetone and acetonitrile in a volume ratio of 1:2. Then add 0.4 parts by weight of 3-acrylamidophenylboronic acid and 0.3 parts by weight of N-isopropylacrylamide, and stir at a stirring speed of 250 rpm for 2 hours to obtain a pre-reaction solution; S1.3: Add 2 parts by weight of pentaerythritol triacrylate, 0.6 parts by weight of azobisisobutyronitrile and 15 parts by weight of alkylated high amylose corn starch to the pre-reaction solution prepared in step S1.2, transfer it to an ultrasonic cleaner and treat it at an ultrasonic frequency of 25 kHz for 15 minutes, and then react at 55°C for 20 hours. Filter to obtain the filtrate, wash it three times with a tetrahydrofuran-deionized water mixed solution. The tetrahydrofuran-deionized water mixed solution is composed of tetrahydrofuran and deionized water in a volume ratio of 1:0.25, and then vacuum dry it to constant weight at 45°C to obtain specific free fatty acid adsorbing starch.

[0021] S2: Preparation of oxygen vacancy carbon composite decolorizing hydrotalcite S2.1: Use a carbon fiber cloth with a length and width of 2 cm × 1 cm as the working electrode in a two-electrode system, a platinum sheet as the counter electrode, and a H2SO4 solution with a concentration of 0.1 mol / L as the electrolyte. Charge the carbon cloth for 4 minutes using a DC power supply with constant voltage and constant current. The charging voltage of the power supply is 5 V and the current is 0.5 A to obtain electro-activated carbon cloth; S2.2: Dissolve MgCl2·6H2O and AlCl3·6H2O in deionized water to prepare solution A. In solution A, Mg2+ With a concentration of 0.6 mol / L, Al 3+ With a concentration of 0.3 mol / L, sodium hydroxide and sodium carbonate are dissolved in deionized water at a mass ratio of 1:0.5 to prepare solution B. The concentration of OH - in solution B is 1 mol / L. Electrically activated carbon cloth is placed in a hydrothermal autoclave, and then solution A and solution B are added to the hydrothermal autoclave at a volume ratio of 1:1 to completely immerse the electrically activated carbon cloth. Then titanium oxysulfate is added and stirred evenly. The concentration of titanium oxysulfate is controlled at 0.1 mol / L, and the reaction is carried out at 115 °C for 10 hours. After the product is taken out, it is rinsed clean with deionized water and placed in an oven to be dried at 65 °C to constant weight to obtain oxygen vacancy carbon composite decolorizing hydrotalcite.

[0022] S3: Refining and purification of fish oil S3.1: Under the conditions of a water bath oscillation at 65 °C and 140 rpm, phosphoric acid with a volume fraction of 75% is added dropwise to crude fish oil at a mass ratio of 1:100, and then kept warm at a water bath temperature of 65 °C for 1.5 minutes. Then it is placed in a centrifuge while it is still hot and centrifuged at a centrifugal speed of 10000 rpm for 10 minutes. Then the upper layer of oil is collected to obtain degummed fish oil; S3.2: 4 wt% of specific free fatty acid adsorbing starch is added to the degummed fish oil, and then stirred at 65 °C and 250 rpm for 60 minutes. Then it is naturally cooled to room temperature, the precipitate is filtered and separated, and the filtered oil is collected to obtain deacidified fish oil. The oxygen vacancy carbon composite decolorizing hydrotalcite and activated clay are mixed evenly at a mass ratio of 1:2 to obtain a composite decolorizing agent. 2 wt% of the composite decolorizing agent is added to the deacidified fish oil and stirred evenly. It is decolorized at a decolorizing temperature of 55 °C for 40 minutes, and then the filtered oil is collected by filtration to obtain decolorized fish oil. Then it is transferred to a deodorizing tower for deodorization treatment. The deodorizing temperature of the deodorization treatment is 180 °C and the time is 20 minutes to obtain purified fish oil.

[0023] Example 2

[0024] A method for purifying fish oil, as Figure 1 shown, includes the following steps: S1: Preparation of specific free fatty acid adsorbing starch S1.1: Place 5 parts by weight of high amylose corn starch with a straight-chain content of 55% in a container, add 12 parts by weight of methanol and 3 parts by weight of γ-methacryloxypropyltrimethoxysilane, and then stir and react at 40 °C and 300 rpm for 4 hours. Then filter to obtain the filter residue, wash it 2 times with distilled water, and then place it in an oven to be dried at 60 °C to constant weight to obtain alkylated high amylose corn starch; S1.2: Place 0.3 parts by weight of oleic acid in a container, add 3 parts by weight of an acetone - acetonitrile mixed solvent, and stir for 15 minutes. The acetone - acetonitrile mixed solvent is composed of acetone and acetonitrile in a volume ratio of 1:2. Then add 0.6 parts by weight of 3 - acrylamidophenylboronic acid and 0.4 parts by weight of N - isopropylacrylamide, and stir at a stirring speed of 250 rpm for 2 hours to obtain a pre - reaction solution; S1.3: Add 4 parts by weight of pentaerythritol triacrylate, 0.8 parts by weight of azobisisobutyronitrile, and 20 parts by weight of alkylated high - amylose corn starch to the pre - reaction solution prepared in step S1.2. Transfer it to an ultrasonic cleaner and treat it at an ultrasonic frequency of 25 kHz for 15 minutes. Then react at 55 °C for 20 hours. Filter and wash the filtrate 3 times with a tetrahydrofuran - deionized water mixed solution. The tetrahydrofuran - deionized water mixed solution is composed of tetrahydrofuran and deionized water in a volume ratio of 1:0.25. Then dry it to a constant weight under vacuum at 45 °C to obtain specific free - fatty - acid - adsorbed starch.

[0025] S2: Preparation of oxygen - vacancy carbon - composite decolorizing hydrotalcite S2.1: Use a carbon fiber cloth with a length and width of 2 cm×1 cm as a working electrode and place it in a two - electrode system. Use a platinum sheet as a counter electrode and a 0.1 mol / L H2SO4 solution as an electrolyte. Charge the carbon cloth with a DC power supply under constant voltage and constant current for 4 minutes. The charging voltage of the power supply is 5 V and the current is 0.5 A to obtain an electro - activated carbon cloth; S2.2: Dissolve MgCl2·6H2O and AlCl3·6H2O in deionized water to prepare solution A. In solution A, the concentration of Mg 2+ is 0.7 mol / L, and the concentration of Al 3+ is 0.35 mol / L. Dissolve sodium hydroxide and sodium carbonate in deionized water in a mass ratio of 1:0.6 to prepare solution B. In solution B, the concentration of OH - is 1.2 mol / L. Place the electro - activated carbon cloth in a hydrothermal autoclave, then add solution A and solution B to the hydrothermal autoclave in a volume ratio of 1:1.2 to completely immerse the electro - activated carbon cloth. Then add titanium oxysulfate and stir evenly. Control the concentration of titanium oxysulfate at 0.2 mol / L and react at 115 °C for 10 hours. After taking out the product, rinse it with deionized water and place it in an oven to dry to a constant weight at 65 °C to obtain oxygen - vacancy carbon - composite decolorizing hydrotalcite.

[0026] S3: Refining and purification of fish oil S3.1: Under the conditions of water bath oscillation at 65 °C and 140 rpm, phosphoric acid with a volume fraction of 75% was added dropwise to crude fish oil at a mass ratio of 1:120. Then, it was kept warm at a water bath temperature of 65 °C for 1.5 minutes, and then placed in a centrifuge while it was still hot and centrifuged at a speed of 10,000 rpm for 10 minutes. Then, the upper-layer oil was collected to obtain degummed fish oil. S3.2: 4.5 wt% of specific free fatty acid adsorbing starch was added to the degummed fish oil, and then stirred at 65 °C and 250 rpm for 60 minutes. Then, it was naturally cooled to room temperature, and the precipitate was separated by filtration. The filtered oil was collected to obtain deacidified fish oil. The oxygen vacancy carbon composite decolorizing hydrotalcite and activated clay were mixed evenly at a mass ratio of 1:3 to obtain a composite decolorizing agent. 5 wt% of the composite decolorizing agent was added to the deacidified fish oil and stirred evenly, and decolorized at a decolorizing temperature of 55 °C for 40 minutes. Then, the filtered oil was collected by filtration to obtain decolorized fish oil, which was then transferred to a deodorization tower for deodorization treatment. The deodorization temperature of the deodorization treatment was 180 °C and the time was 20 minutes to obtain purified fish oil.

[0027] Example 3

[0028] A method for purifying fish oil, as Figure 1 shown, includes the following steps: S1: Preparation of specific free fatty acid adsorbing starch S1.1: 2 parts by weight of high amylose corn starch with a straight-chain content of 60% was placed in a container, 10 parts by weight of methanol and 2 parts by weight of γ-methacryloxypropyltrimethoxysilane were added, and then stirred and reacted at 45 °C and 400 rpm for 5 hours. Then, the filter residue was filtered and washed 3 times with distilled water, and then placed in an oven and dried to constant weight at 65 °C to obtain alkylated high amylose corn starch. S1.2: 0.2 part by weight of oleic acid was placed in a container, 2 parts by weight of acetone-acetonitrile mixed solvent was added and stirred for 20 minutes. The acetone-acetonitrile mixed solvent was composed of acetone and acetonitrile at a volume ratio of 1:2.5. Then, 0.4 part by weight of 3-acrylamidophenylboronic acid and 0.3 part by weight of N-isopropylacrylamide were added, and stirred at a stirring speed of 300 rpm for 3 hours to obtain a pre-reaction solution. S1.3: 2 parts by weight of pentaerythritol triacrylate, 0.6 part by weight of azobisisobutyronitrile and 15 parts by weight of alkylated high amylose corn starch were added to the pre-reaction solution prepared in step S1.2, transferred to an ultrasonic cleaner and treated at an ultrasonic frequency of 30 kHz for 20 minutes, and then reacted at 60 °C for 24 hours. The filtrate was filtered and the filter cake was washed 4 times with a tetrahydrofuran-deionized water mixed solution. The tetrahydrofuran-deionized water mixed solution was composed of tetrahydrofuran and deionized water at a volume ratio of 1:0.3, and then vacuum dried to constant weight at 50 °C to obtain specific free fatty acid adsorbing starch.

[0029] S2: Preparation of Oxygen Vacancy Carbon Composite Decolorizing Hydrotalcite S2.1: A carbon fiber cloth with a length of 2 cm and a width of 1 cm was used as the working electrode and placed in a two - electrode system. A platinum sheet was used as the counter electrode, and a 0.2 mol / L H2SO4 solution was used as the electrolyte. A DC power supply with constant voltage and constant current was used to charge the carbon cloth for 5 minutes. The charging voltage of the power supply was 5 V and the current was 0.5 A to obtain electro - activated carbon cloth; S2.2: MgCl2·6H2O and AlCl3·6H2O were dissolved in deionized water to prepare solution A. In solution A, the concentration of Mg 2+ was 0.6 mol / L, and the concentration of Al 3+ was 0.3 mol / L. Sodium hydroxide and sodium carbonate were dissolved in deionized water at a mass ratio of 1:0.5 to prepare solution B. The concentration of OH - in solution B was 1 mol / L. The electro - activated carbon cloth was placed in a hydrothermal reactor, and then solution A and solution B were added to the hydrothermal reactor at a volume ratio of 1:1 to completely immerse the electro - activated carbon cloth. Then, titanium oxysulfate was added and stirred evenly. The concentration of titanium oxysulfate was controlled at 0.1 mol / L, and the reaction was carried out at 120 °C for 12 hours. After the product was taken out, it was rinsed clean with deionized water and placed in an oven to be dried at 70 °C to constant weight to obtain oxygen vacancy carbon composite decolorizing hydrotalcite.

[0030] S3: Refining and Purification of Fish Oil S3.1: Under the conditions of a water bath oscillation at 70 °C and 150 rpm, phosphoric acid with a volume fraction of 75% was added dropwise to crude fish oil at a mass ratio of 1:100. Then, it was kept warm at a water bath temperature of 70 °C for 2 minutes, and then quickly placed in a centrifuge and centrifuged at a centrifugal speed of 10000 rpm for 15 minutes. Then, the upper - layer grease was collected to obtain degummed fish oil; S3.2: 4 wt% of specific free fatty acid - adsorbing starch was added to the degummed fish oil, and then stirred at 70 °C and 300 rpm for 80 minutes. Then, it was naturally cooled to room temperature, the precipitate was filtered and separated, and the filtered oil was collected to obtain deacidified fish oil. The oxygen vacancy carbon composite decolorizing hydrotalcite and activated clay were mixed evenly at a mass ratio of 1:2 to obtain a composite decolorizing agent. 2 - 5 wt% of the composite decolorizing agent was added to the deacidified fish oil and stirred evenly. The decolorization was carried out at a decolorization temperature of 70 °C for 60 minutes, and then the filtered oil was collected by filtration to obtain decolorized fish oil. Then, it was transferred to a deodorization tower for deodorization treatment. The deodorization temperature of the deodorization treatment was 220 °C and the time was 30 minutes to obtain purified fish oil.

[0031] Comparative Example 1 Compared with Example 1, the difference is that in Comparative Example 1, step S1 was removed, and specific free fatty acid-adsorbing starch was not added in step S3.2. The remaining steps are the same as those in Example 1.

[0032] Comparative Example 2 Compared with Example 1, the difference is that in Comparative Example 2, steps S1.2 and S1.3 were removed, and the subsequent specific free fatty acid-adsorbing starch was replaced with an equal mass of alkylated high amylose corn starch. The remaining steps are the same as those in Example 1.

[0033] Comparative Example 3 Compared with Example 1, the difference is that in Comparative Example 3, step S2 was removed, and the subsequent oxygen vacancy carbon composite decolorized hydrotalcite was replaced with an equal mass of activated clay. The remaining steps are the same as those in Example 1.

[0034] Experiment 1: Take equal masses of the purified fish oils prepared in Examples 1-3 and Comparative Examples 1-2, and respectively conduct tests on the peroxide value, acid value, and free fatty acid recovery rate. The peroxide value was determined with reference to GB5009.227-2023, and the acid value was determined with reference to GB5009.229-2016. Each group was tested three times, and the data were averaged. The test results are shown in Table 1.

[0035] Table 1: Peroxide value, acid value, and free fatty acid recovery rate of purified fish oil Peroxide value (mmol / kg) Acid value (mgKOH / g) Recovery rate of free fatty acids / % Example 1 2.32 0.21 97.72 Example 2 2.28 0.19 97.93 Example 3 2.26 0.18 97.98 Comparative example 1 8.85 4.46 —— Comparative example 2 5.64 2.01 66.71 As can be seen from the data of Examples 1-3 and Comparative Example 1 in Table 1, by preparing specific free fatty acid-adsorbing starch to deacidify and purify degummed fish oil, the present invention can adsorb a large amount of free fatty acids, thereby reducing the peroxide value and acid value. And from the data of Comparative Example 2, it can be known that by crosslinking and binding high amylose corn starch with the template molecules of free fatty acids, oleic acid, 3-acrylamidophenylboronic acid, thermosensitive N-isopropylacrylamide, and pentaerythritol triacrylate, the adsorption capacity for free fatty acids can be synergistically enhanced with high amylose corn starch, further reducing the peroxide value and acid value of the purified fish oil.

[0036] Experiment 2: Take 12 equal weight portions of crude fish oil, divide it into 4 groups, with each group being 3 weight portions. Each group was purified using the specific implementation manners of Examples 1-3 and Comparative Example 3 respectively. Then, the deacidified fish oil and decolorized fish oil obtained were subjected to a full scan in the wavelength range of 190-1100 nm to screen out the wavelength band with the best absorption peak. At the wavelength of the best absorption peak, the absorbance of the fish oil before and after decolorization was measured. The absorbance of the deacidified fish oil at the best wavelength was denoted as A, and the absorbance of the decolorized fish oil at the best wavelength was denoted as A1. The decolorization rate was calculated as (A - A1) / A × 100%. The test results are shown in Table 2.

[0037] Table 2: Decolorization Rates of the Composite Decolorizer Composed of Oxygen Vacancy Carbon Composite Decolorizing Hydrotalcite and Activated Clay Decolorization rate / % First part by weight Second part by weight Third part by weight Example 1 95.37 95.34 95.38 Example 2 95.41 95.42 95.39 Example 3 95.51 95.53 95.51 Comparative example 3 70.35 70.33 70.36 It can be seen from the data of Examples 1 - 3 in Table 2 that the composite decolorizer prepared in the examples of this application has a high decolorization rate. And from the data of Comparative Example 3, it can be known that when the oxygen vacancy carbon composite decolorizing hydrotalcite is replaced with activated clay, the decolorization rate drops significantly. It can be proved that the oxygen vacancy carbon composite decolorizing hydrotalcite prepared in this application can effectively remove the colored substances in the deacidified fish oil in cooperation with activated clay, and has a high decolorization efficiency.

[0038] The above examples are only illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above examples without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for purifying fish oil, characterized in that, It includes the following steps: S1: Preparation of specific free fatty acid adsorption starch Modify and modify high amylose corn starch with γ-methacryloxypropyltrimethoxysilane to obtain alkylated high amylose corn starch, and then place the alkylated high amylose corn starch in a reaction system of oleic acid, acetone-acetonitrile mixed solvent, 3-acrylamidophenylboronic acid, N-isopropylacrylamide and pentaerythritol triacrylate, and react under the initiation of azobisisobutyronitrile. After filtration, washing and drying, specific free fatty acid adsorption starch is prepared; S2: Preparation of oxygen vacancy carbon composite decolorizing hydrotalcite Arrange carbon fiber cloth in a double electrode system for charging to obtain electro-activated carbon cloth. Dissolve MgCl2·6H2O and AlCl3·6H2O in deionized water to prepare solution A. Dissolve sodium hydroxide and sodium carbonate in deionized water at a mass ratio of 1:(0.5-0.6) to prepare solution B. Immerse the electro-activated carbon cloth in the mixed solution of solution A and solution B, add titanium oxysulfate for hydrothermal reaction, and then wash and dry the product to obtain oxygen vacancy carbon composite decolorizing hydrotalcite; S3: Refining and purification of fish oil Use phosphoric acid to degum the crude fish oil, then add specific free fatty acid adsorption starch, heat and stir, and then naturally cool to room temperature. Separate the precipitate and collect the filtered oil to obtain deacidified fish oil. Then add a composite decolorizing agent prepared by mixing oxygen vacancy carbon composite decolorizing hydrotalcite and activated clay, heat and stir for decolorization to obtain decolorized fish oil, and then deodorize to obtain purified fish oil.

2. The purification method of a fish oil according to claim 1, wherein The preparation of the specific free fatty acid adsorption starch in step S1 includes the following steps: S1.1: Place 2-5 parts by weight of high amylose corn starch in a container, add 10-12 parts by weight of methanol and 2-3 parts by weight of γ-methacryloxypropyltrimethoxysilane, and then stir and react at 40-45°C and 300-400 rpm for 4-5 hours. Then filter and take the filter residue, wash it 2-3 times with distilled water, and then place it in an oven and dry it to constant weight at 60-65°C to obtain alkylated high amylose corn starch; S1.2: Place 0.2-0.3 parts by weight of oleic acid in a container, add 2-3 parts by weight of acetone-acetonitrile mixed solvent and stir for 15-20 minutes, then add 0.4-0.6 parts by weight of 3-acrylamidophenylboronic acid and 0.3-0.4 parts by weight of N-isopropylacrylamide, and stir at a stirring speed of 250-300 rpm for 2-3 hours to obtain a pre-reaction solution; S1.3: Add 2-4 parts by weight of pentaerythritol triacrylate, 0.6-0.8 parts by weight of azobisisobutyronitrile and 15-20 parts by weight of alkylated high amylose corn starch to the pre-reaction solution prepared in step S1.2, transfer it to an ultrasonic cleaner and treat it at an ultrasonic frequency of 25-30 kHz for 15-20 minutes, and then react at 55-60°C for 20-24 hours. Filter and take the filtrate, wash it 3-4 times with a tetrahydrofuran-deionized water mixed solution, and then vacuum dry it to constant weight at 45-50°C to obtain specific free fatty acid adsorption starch.

3. The purification method of fish oil according to claim 2, characterized in that, Step S2 Preparation of oxygen vacancy carbon composite decolorized hydrotalcite, including the following steps: S2.1: Use a carbon fiber cloth with a length and width of 2 cm × 1 cm as the working electrode in a two-electrode system, a platinum sheet as the counter electrode, and a H2SO4 solution with a concentration of 0.1 - 0.2 mol / L as the electrolyte. Charge the carbon cloth with a DC power supply under constant voltage and constant current for 4 - 5 minutes to obtain an electro-activated carbon cloth; S2.2: Dissolve MgCl2·6H2O and AlCl3·6H2O in deionized water to prepare solution A. The concentration of Mg in solution A is 0.6 - 0.7 mol / L, and the concentration of Al is 0.3 - 0.35 mol / L. Dissolve sodium hydroxide and sodium carbonate in deionized water at a mass ratio of 1:(0.5 - 0.6) to prepare solution B. The concentration of OH in solution B is 1 - 1.2 mol / L. Place the electro-activated carbon cloth in a hydrothermal reactor, then add solution A and solution B to the hydrothermal reactor at a volume ratio of 1:(1 - 1.2) to completely immerse the electro-activated carbon cloth. Then add titanium oxysulfate and stir evenly. Control the concentration of titanium oxysulfate at 0.1 - 0.2 mol / L. React at 115 - 120 °C for 10 - 12 hours. After taking out the product, rinse it clean with deionized water and place it in an oven to dry at 65 - 70 °C until constant weight to obtain oxygen vacancy carbon composite decolorizing hydrotalcite. 2+ The concentration is 0.6 - 0.7 mol / L, and the concentration of Al 3+ is 0.3 - 0.35 mol / L. Dissolve sodium hydroxide and sodium carbonate in deionized water at a mass ratio of 1:(0.5 - 0.6) to prepare solution B. The concentration of OH - in solution B is 1 - 1.2 mol / L. Place the electro-activated carbon cloth in a hydrothermal reactor, then add solution A and solution B to the hydrothermal reactor at a volume ratio of 1:(1 - 1.2) to completely immerse the electro-activated carbon cloth. Then add titanium oxysulfate and stir evenly. Control the concentration of titanium oxysulfate at 0.1 - 0.2 mol / L. React at 115 - 120 °C for 10 - 12 hours. After taking out the product, rinse it clean with deionized water and place it in an oven to dry at 65 - 70 °C until constant weight to obtain oxygen vacancy carbon composite decolorizing hydrotalcite.

4. A method for purifying fish oil according to claim 3, characterized in that, Step S3 Refining and purification of fish oil, including the following steps: S3.1: Under the conditions of water bath oscillation at 65 - 70 °C and 140 - 150 rpm, add phosphoric acid with a volume fraction of 75 - 80% dropwise to crude fish oil at a mass ratio of 1:(100 - 120), then keep it warm at a water bath temperature of 65 - 70 °C for 1.5 - 2 minutes, and then place it in a centrifuge while it is still hot and centrifuge at a centrifugal speed of 10000 - 12000 rpm for 10 - 15 minutes. Then collect the upper layer of grease to obtain degummed fish oil; S3.2: Add 4 - 4.5 wt% of specific free fatty acid adsorption starch to the degummed fish oil, then stir at 65 - 70 °C and 250 - 300 rpm for 60 - 80 minutes, then naturally cool to room temperature, filter and separate the precipitate, collect the filtered oil to obtain deacidified fish oil. Mix the oxygen vacancy carbon composite decolorized hydrotalcite and activated clay evenly at a mass ratio of 1:(2 - 3) to obtain a composite decolorizing agent. Add 2 - 5 wt% of the composite decolorizing agent to the deacidified fish oil and stir evenly, decolorize at a decolorizing temperature of 55 - 70 °C for 40 - 60 minutes, then filter and collect the filtered oil to obtain decolorized fish oil, and then transfer it to a deodorization tower for deodorization treatment to obtain purified fish oil.

5. The purification method of a fish oil according to claim 2, characterized in that, In step S1.1, the amylose content of the high amylose corn starch is 55 - 60%.

6. The purification method of a fish oil according to claim 2, wherein The acetone - acetonitrile mixed solvent in step S1.2 is composed of acetone and acetonitrile at a volume ratio of 1:(2 - 2.5).

7. A method for purifying fish oil according to claim 2, characterized in that, The tetrahydrofuran - deionized water mixed solution in step S1.3 is composed of tetrahydrofuran and deionized water at a volume ratio of 1:(0.25 - 0.3).

8. A method for purifying fish oil according to claim 3, characterized in that, In step S2.1, the voltage of the power supply charging is 5 V and the current is 0.5 A.

9. A method for purifying fish oil according to claim 4, characterized in that, In step S3.2, the deodorization temperature of the deodorization treatment is 180 - 220 °C and the time is 20 - 30 minutes.

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