Method for improving DHA / DPA proportion in grease by optimizing schizochytrium limacinum fermentation process through chemical regulator and application

Abstract

The invention belongs to the technical field of microbial fermentation, and discloses a method for optimizing the fermentation process of schizochytrium limacinum through chemical regulators to increase the proportion of DHA / DPA in grease and application of the method. In the fermentation process of schizochytrium limacinum, one or more chemical regulators are added into fermentation liquor, and the proportion of DHA / DPA in grease is increased; the chemical regulator is selected from one or more of melatonin, ethanolamine, betaine and inositol so as to improve the proportion of DHA / DPA in the grease. According to the present invention, by adding the specific chemical regulator, the DHA content can be increased or the accumulation of DPA can be reduced so as to achieve the specific optimization of the DHA / DPA ratio. Compared with gene engineering, the method does not need complex gene operation, and can achieve the target only by adding a chemical regulator in the fermentation process. The method is simple to operate, low in cost and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of microbial fermentation, and relates to microbial fermentation and oil production, in particular to a method and application for optimizing the fermentation process of Schizochytrium sp. to increase the DHA / DPA ratio in oil by using chemical regulators. Background Art

[0002] Schizochytrium sp. is an important industrial microorganism that can efficiently synthesize polyunsaturated fatty acids (PUFAs), especially docosahexaenoic acid (DHA, C22:6 ω-3) and docosapentaenoic acid (DPA, C22:5 ω-3). These two ω-3 fatty acids have wide application values in the fields of food, health products, medicine, etc. Among them, due to its important role in nervous system development, retinal function and cardiovascular health, the market demand for DHA is significantly higher than that for DPA.

[0003] In the Schizochytrium sp. HX-308 strain used in the present invention, both the synthesis abilities of DHA and DPA are relatively strong, and the DHA content has reached a relatively high level. However, the accumulation amount of DPA is also relatively high, resulting in the DHA / DPA ratio not reaching the optimal value (there is no specific most suitable value for the DHA / DPA ratio, but in view of the current situation of this strain, the higher the DHA / DPA ratio, the better, and it is generally about 2.6 in this strain). This ratio limits the application potential of the fermentation product in high-value-added fields (such as infant formula milk powder and high-purity DHA preparations). Therefore, how to further optimize the DHA / DPA ratio without significantly reducing the DHA yield has become the core objective of the present invention.

[0004] Specifically, the following defects exist in the prior art:

[0005] 1. The synthesis processes of DHA and DPA in Schizochytrium sp. involve multiple enzymatic reactions and complex metabolic pathways, and it is difficult to accurately regulate the activities of key enzymes in the metabolic pathways.

[0006] 2. There are few exogenous regulatory factors for regulating the DHA / DPA ratio, and the effects of these factors are often not significant or stable enough.

[0007] 3. The methods for increasing the DHA yield by optimizing the fermentation conditions are already relatively mature, but they have limited effects in adjusting the DHA / DPA ratio. Summary of the Invention

[0008] The purpose of the present invention is to overcome the deficiencies in the prior art, and provide a method and application for optimizing the fermentation process of Schizochytrium sp. to increase the DHA / DPA ratio in oil by using chemical regulators.

[0009] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0010] A method for optimizing the fermentation process of Schizochytrium sp. to increase the DHA / DPA ratio in oil by using chemical regulators. During the fermentation process of Schizochytrium sp., one or more chemical regulators are added to the fermentation broth. The chemical regulators are selected from one or several of melatonin (MT), ethanolamine (ETA), betaine (Bet), and inositol, so as to increase the DHA / DPA ratio in the oil.

[0011] Further, the addition amount of the chemical regulator is 1 mM to 200 mM, preferably 1 mM to 100 mM.

[0012] Alternatively, the chemical regulator is added to the fermentation medium during 0 - 36 h of fermentation production;

[0013] Alternatively, the temperature of the fermentation production is 25 - 29 °C, the rotation speed is 150 - 200 rpm, and the total fermentation time is 72 - 120 h.

[0014] Further, the chemical regulator is inositol, and its addition concentration in the fermentation broth is 50 mM;

[0015] Alternatively, the chemical regulators are inositol and betaine. The addition concentration of inositol in the fermentation broth is 50 mM, and the addition concentration of betaine in the fermentation broth is 75 mM.

[0016] Further, the fermentation medium used during fermentation contains glucose, ammonium sulfate, and phosphate.

[0017] Further, by regulating the addition time and concentration of the chemical regulator, the DHA / DPA ratio in the oil of Schizochytrium sp. can be significantly increased, and the increase range is 40% - 95%.

[0018] Further, the Schizochytrium sp. is Schizochytrium sp. HX - 308.

[0019] Further, after inoculating Schizochytrium sp. into the seed medium for activation, the fermentation strain is obtained; the fermentation strain is inoculated into the fermentation medium for fermentation culture, and after fermentation ends, the thalli are collected to extract oil.

[0020] Further, the OD value of the fermentation strain is 8 - 10; the inoculation amount of the fermentation strain is 0.8% - 1.5% of the volume of the fermentation medium.

[0021] Further, the specific steps are as follows:

[0022] Inoculate Schizochytrium sp. HX-308 into the seed medium and culture it at 28 °C for 24 h to obtain the primary seeds; take the primary seeds and inoculate them into the seed medium at an inoculation amount of 10% of the volume of the seed medium, and culture them again at 28 °C for 24 h to obtain the secondary seeds; take the secondary seeds and inoculate them into the seed medium at an inoculation amount of 10% of the volume of the seed medium, and culture them again at 28 °C for 24 h. Through the above activation process, the fermentation strain is obtained; take the fermentation strain with an OD600 value of 8-10 and inoculate it into the fermentation medium at an inoculation amount of 1%, and ferment and culture it for 120 h under the conditions of a temperature of 25 °C and a rotation speed of 170 rpm.

[0023] Furthermore, the components of the seed medium are: glucose 45 g / L, yeast powder 2 g / L, sodium glutamate 15 g / L, MgCl 2 ·7H 2 O 4 g / L, Na 2 SO 4 15 g / L, KCl 1 g / L, NaCl 1 g / L, MgSO 4 ·7H 2 O 5 g / L, KH 2 PO 4 3 g / L, and the solvent is water;

[0024] The components of the fermentation medium are: glucose 90 g / L, yeast powder 4 g / L, sodium glutamate 15 g / L, MgCl 2 ·7H 2 O 4 g / L, Na 2 SO 4 15 g / L, KCl 1 g / L, NaCl 1 g / L, MgSO 4 ·7H 2 O 5 g / L, KH 2 PO 4 3 g / L and (NH 4 ) 2 SO 4 4 g / L, and the solvent is water.

[0025] Application of the method as described above in improving the DHA / DPA ratio in the fermented oil of Schizochytrium sp.

[0026] The advantages and positive effects achieved by the present invention are:

[0027] 1. By adding specific chemical regulators, the present invention can increase the DHA content or reduce the accumulation of DPA, thereby achieving the specific optimization of the DHA / DPA ratio. Compared with genetic engineering, the present invention does not require complex gene operations and only needs to add chemical regulators during the fermentation process to achieve the goal. This method is simple to operate, low in cost, and suitable for large-scale industrial production.

[0028] 2. While optimizing the DHA / DPA ratio, the present invention does not have a significant negative impact on the growth performance and fermentation efficiency of Schizochytrium sp. The strain can still maintain a high DHA yield and fermentation stability, ensuring the feasibility of industrial production.

[0029] 3. The method of the present invention shows good stability and repeatability under different fermentation batches and production conditions.

[0030] 4. The chemical regulators melatonin (MT), betaine (Bet), and inositol used in the present invention are substances with good biocompatibility and environmental friendliness and will not cause pollution to the environment.

[0031] 5. During the fermentation process of Schizochytrium sp., one or more chemical regulators are added to the culture medium, and the fermentation process of Schizochytrium sp. is optimized by the chemical regulators to increase the DHA / DPA ratio. The present invention is directed to the Schizochytrium sp. HX-308 strain, and by adding specific chemical regulators, its metabolic pathway is precisely regulated. By increasing the DHA content or reducing the accumulation of DPA, the DHA / DPA ratio is significantly increased. In the fermentation medium of Schizochytrium sp., chemical regulators are added, and the chemical regulators include melatonin (MT), ethanolamine (ETA), betaine (Bet), and inositol. When inositol (50 mM) is added, the DHA / DPA ratio is increased by 51.15%. When chemical regulators are used in combination, more significant effects are achieved. For example, when inositol (50 mM) + betaine (75 mM) is added, the DHA / DPA ratio is increased by 93.92%. The present invention increases the DHA / DPA ratio and has the advantages of simple operation, low cost, and suitability for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a diagram showing the effect of adding chemical regulators on the DHA / DPA ratio in oil in Example 1 of the present invention;

[0033] Figure 2 It is a diagram showing the effect of different concentrations of inositol on the DHA / DPA ratio in oil in Example 2 of the present invention;

[0034] Figure 3 This is the graph showing the effect of different concentrations of betaine on the DHA / DPA ratio in oil in Example 3 of the present invention;

[0035] Figure 4 This is the graph showing the effect of the combined use of different chemical regulators on the DHA / DPA ratio in oil in Example 4 of the present invention;

[0036] Figure 5 This is the gas chromatogram without the regulation of chemical regulators in the present invention;

[0037] Figure 6 This is the gas chromatogram after fermentation regulation by adding 50 mM inositol + 75 mM betaine in the present invention. Detailed implementation manners

[0038] The present invention will be further described below in conjunction with embodiments. The following embodiments are narrative and not restrictive, and the protection scope of the present invention cannot be limited by the following embodiments.

[0039] All kinds of experimental operations involved in the specific embodiments are conventional techniques in the art. For the parts not specifically noted in this article, those of ordinary skill in the art can implement them with reference to various commonly used reference books, scientific and technological literatures, or relevant specifications and manuals before the filing date of the present invention application.

[0040] A method for optimizing the fermentation process of Schizochytrium sp. by chemical regulators to increase the DHA / DPA ratio in oil. During the fermentation process of Schizochytrium sp., one or more chemical regulators are added to the fermentation broth. The chemical regulators are selected from one or several of melatonin (MT), ethanolamine (ETA), betaine (Bet), and inositol to increase the DHA / DPA ratio in oil.

[0041] Preferably, the addition amount of the chemical regulator is 1 mM to 200 mM, and preferably 1 mM to 100 mM.

[0042] Alternatively, during the fermentation production for 0 - 36 h, the chemical regulator is added to the fermentation medium;

[0043] Alternatively, the temperature of the fermentation production is 25 - 29 °C, the rotation speed is 150 - 200 rpm, and the total fermentation time is 72 - 120 h.

[0044] Preferably, the chemical regulator is inositol, and its addition concentration in the fermentation broth is 50 mM;

[0045] Alternatively, the chemical regulator is inositol and betaine, and the addition concentration of inositol in the fermentation broth is 50 mM, and the addition concentration of betaine in the fermentation broth is 75 mM.

[0046] Preferably, the fermentation medium used in fermentation contains glucose, ammonium sulfate, and phosphate.

[0047] Preferably, by regulating the addition time and concentration of the chemical regulator, the ratio of DHA / DPA in the oil of Schizochytrium can be significantly increased, and the increase range of the ratio is 40%-95%.

[0048] Preferably, the Schizochytrium is Schizochytrium sp. HX-308.

[0049] Preferably, after inoculating Schizochytrium into the seed medium for activation, the fermentation strain is obtained; the fermentation strain is inoculated into the fermentation medium for fermentation culture, and after fermentation, the thallus is collected to extract oil.

[0050] Preferably, the OD value of the fermentation strain is 8-10; the inoculation amount of the fermentation strain is 0.8-1.5% of the volume of the fermentation medium.

[0051] Preferably, the specific steps are as follows:

[0052] Inoculate Schizochytrium sp. HX-308 into the seed medium and culture it at 28°C for 24 h to obtain the first-stage seeds; take the first-stage seeds and inoculate them into the seed medium at an inoculation amount of 10% of the volume of the seed medium, and culture them at 28°C for 24 h again to obtain the second-stage seeds; take the second-stage seeds and inoculate them into the seed medium at an inoculation amount of 10% of the volume of the seed medium, and culture them at 28°C for 24 h again. After the above activation process, the fermentation strain is obtained; take the fermentation strain with an OD600 value of 8-10 and inoculate it into the fermentation medium at an inoculation amount of 1%, and ferment and culture it at a temperature of 25°C and a rotation speed of 170 rpm for 120 h.

[0053] Preferably, the composition of the seed medium is: 45 g / L of glucose, 2 g / L of yeast powder, 15 g / L of sodium glutamate, MgCl 2 ·7H 2 O 4 g / L, Na 2 SO 4 15 g / L, KCl 1 g / L, NaCl 1 g / L, MgSO 4 ·7H 2 O 5 g / L, KH 2 PO 4 3 g / L, and the solvent is water;

[0054] The components of the fermentation medium are: 90 g / L of glucose, 4 g / L of yeast powder, 15 g / L of sodium glutamate, MgCl 2 ·7H 2 O 4 g / L, Na 2 SO 4 15 g / L, 1 g / L of KCl, 1 g / L of NaCl, MgSO 4 ·7H 2 O 5 g / L, KH 2 PO 4 3 g / L and (NH 4 ) 2 SO 4 4 g / L, and the solvent is water.

[0055] Specifically, the related preparation and detection are as follows:

[0056] The components of the culture medium used in each example are as follows:

[0057] The components of the seed culture medium are: 45 g / L of glucose, 2 g / L of yeast powder, 15 g / L of sodium glutamate, MgCl 2 ·7H 2 O 4 g / L, Na 2 SO 4 15 g / L, 1 g / L of KCl, 1 g / L of NaCl, MgSO 4 ·7H 2 O 5 g / L, KH 2 PO 4 3 g / L, and the solvent is water.

[0058] The components of the fermentation medium are: 90 g / L of glucose, 4 g / L of yeast powder, 15 g / L of sodium glutamate, MgCl 2 ·7H 2 O 4 g / L, Na 2 SO 4 15 g / L, 1 g / L of KCl, 1 g / L of NaCl, MgSO 4 ·7H 2 O 5 g / L, KH 2 PO 4 3 g / L and (NH 4 ) 2 SO 4 4 g / L, and the solvent is water.

[0059] Specific fermentation method:

[0060] Inoculate Schizochytrium sp. into the seed medium and culture it at 28°C for 24 h to obtain the primary seeds. Take the primary seeds and inoculate them into the seed medium at an inoculation amount of 10% of the volume of the seed medium, and culture them again at 28°C for 24 h to obtain the secondary seeds. Take the secondary seeds and inoculate them into the seed medium at an inoculation amount of 10% of the volume of the seed medium, and culture them again at 28°C for 24 h. Through the above activation process, the strain for fermentation is obtained.

[0061] Take 0.5 L of the strain for fermentation with an OD600 value of 8 - 10 and inoculate it into 50 L of the fermentation medium. Ferment and culture it for 120 h under the conditions of a temperature of 25°C and a rotation speed of 170 rpm.

[0062] Gas chromatography analysis: Take the fermentation broth after the end of fermentation and adjust the pH to 10 with NaOH. Add lysing enzyme at 0.3‰ of the mass of the fermentation broth, enzymolyze it at 55°C for 1 h, then add n - hexane for extraction, let it stand for layering, take the upper yellow organic - phase liquid, repeat the extraction until the upper layer color becomes colorless, combine the organic - phase liquids, evaporate the solvent to obtain the total oil. Add 2 ml of a 15% NaOH solution by mass and 5.5 ml of an aqueous solution with a methanol content of 70% to the total oil. React in a water bath at 65°C for 1.5 h; cool to room temperature, add 2 ml of n - hexane (chromatographic grade) for extraction, collect the upper organic phase; pass the upper organic phase through a micro - membrane pore to remove impurities, and then analyze it by gas chromatography.

[0063] Example 1 Screening of chemical regulators

[0064] In order to increase the oil production and EPA content during the fermentation of Schizochytrium sp. HX - 308, the most suitable chemical regulator is screened from four chemical regulators: melatonin (MT), ethanolamine (ETA), betaine (Bet), and myo - inositol (MI). By comparing the addition of each regulator, the regulator with the best performance in fermentation is screened out.

[0065] According to the above - mentioned specific fermentation method, at the 24th hour of the fermentation process, add melatonin, ethanolamine, betaine, and myo - inositol to the fermenter respectively, and the addition concentration is 50 mM.

[0066] Fermentation ends at the 120th h. Through the above - mentioned method, extract the oil and detect the DHA content and DPA content in the oil by gas chromatography, and then calculate the DHA / DPA ratio.

[0067] During the screening process, the effects of melatonin, ethanolamine, betaine, and myo - inositol on the DHA / DPA ratio in the oil fermented by Schizochytrium sp. were tested respectively. The screening results are shown in Table 1 below.

[0068] Table 1

[0069]

[0070] Figure 1 The effects of different chemical regulators (melatonin, ethanolamine, betaine, inositol) on the DHA / DPA ratio in the fermented oil of Schizochytrium sp. at a concentration of 50 mM were shown. The experimental results showed that compared with the control group without adding chemical regulators, all four chemical regulators could significantly increase the DHA / DPA ratio. Among them, inositol showed the best effect, and the DHA / DPA ratio increased from 2.62 in the control group to 3.93, with an increase of 50.00%. In addition, melatonin, ethanolamine, and betaine also increased the DHA / DPA ratio by 40.83%, 41.22%, and 47.33%, respectively. This indicates that chemical regulators can optimize the DHA / DPA ratio by regulating the metabolic pathway of Schizochytrium sp., reducing the accumulation of DPA or increasing the content of DHA.

[0071] Example 2 Optimization of inositol concentration

[0072] In order to further increase the DHA / DPA ratio in the fermented oil of Schizochytrium sp., the concentration of inositol, which showed the best effect in Example 1, was optimized in this example to determine the most suitable inositol concentration to increase the DHA / DPA ratio.

[0073] The specific fermentation method was basically the same as that in Example 1, except that in this example, at the 24th hour of fermentation, different concentrations of inositol were added to the fermentation tank group, and the concentration range was set as 1 mM, 10 mM, 25 mM, 50 mM, 75 mM, and 100 mM. When the fermentation reached the 120th hour, the fermentation broth was collected, the oil was extracted, and the DHA content and DPA content in the oil were detected. The results are shown in Table 2.

[0074] Table 2

[0075]

[0076] Figure 2 The effects of different concentrations of inositol (1 mM, 10 mM, 25 mM, 50 mM, 75 mM, 100 mM) on the DHA / DPA ratio were analyzed. The results showed that inositol had the most significant effect on increasing the DHA / DPA ratio at a concentration of 50 mM, and the ratio reached 3.93, which was 51.15% higher than that of the control group. When the inositol concentration exceeded 50 mM, the DHA / DPA ratio began to decline, indicating that too high an inositol concentration might have an inhibitory effect on metabolic regulation. This further verified that 50 mM was the optimal concentration of inositol for maximizing the increase in the DHA / DPA ratio.

[0077] Example 3 Optimization of Betaine Concentration

[0078] In Example 1, the chemical regulator with the best effect on increasing the DHA / DPA ratio was inositol. In addition, betaine also has a significant effect on increasing the DHA / DPA ratio. Therefore, in the present invention, the optimal concentration of betaine used was explored to further increase the DHA / DPA ratio in the oil fermented by Schizochytrium.

[0079] The specific fermentation method was basically the same as that in Example 1, except that: in this example, at the 24th hour of fermentation, betaine at different concentrations was added to the fermentation tank group, and the concentration range was set to 1 mM, 10 mM, 25 mM, 50 mM, 75 mM, 100 mM. When the fermentation reached 120 h, the fermentation broth was collected, the oil was extracted, and the DHA content and DPA content in the oil were detected. The results are shown in Table 3.

[0080] Table 3

[0081]

[0082] Figure 3 Shows the effects of different concentrations of betaine (1 mM, 10 mM, 25 mM, 50 mM, 75 mM, 100 mM) on the DHA / DPA ratio. The experimental results show that betaine has the best effect on increasing the DHA / DPA ratio at a concentration of 75 mM, and the ratio reaches 3.92, which is 49.05% higher than that of the control group. However, when the betaine concentration exceeds 75 mM, the DHA / DPA ratio decreases slightly, indicating that the metabolic regulation effect of betaine reaches the optimum at 75 mM, and too high a concentration may lead to an increase in metabolic burden.

[0083] Example 4 Combined Use of Chemical Regulators

[0084] It can be seen from the foregoing examples that the use of chemical regulators has a significant effect on increasing the DHA / DPA ratio in the oil fermented by Schizochytrium, and among them, the effects of the chemical regulators betaine and inositol are the most significant. Therefore, in this example, it was explored whether the combined use of multiple chemical regulators could have a better effect. The results are shown in Table 4.

[0085] Table 4

[0086]

[0087] Figures 4 to 6It shows the regulatory effects of adding no chemical regulator and adding different chemical regulators in combination on the DHA / DPA ratio in the oil fermented by Schizochytrium sp.. The experimental results show that, compared with the control group without adding chemical regulator (DHA / DPA ratio is 2.63), the combined use of inositol (50 mM) and betaine (75 mM) shows a significant synergistic effect, and the DHA / DPA ratio increases to 5.10, with an increase amplitude of 93.92%. When inositol (50 mM) or betaine (75 mM) is used alone, the DHA / DPA ratios are 3.93 (an increase of 49.43%) and 3.92 (an increase of 49.05%) respectively. In addition, when inositol is used in combination with melatonin (50 mM), the ratio is 4.37 (an increase of 66.16%), and when inositol is used in combination with ethanolamine (50 mM), the ratio is 4.09 (an increase of 55.51%). It shows that the combination strategy of chemical regulators can act synergistically, thus significantly enhancing the optimization effect of the DHA / DPA ratio.

[0088] Comparative example: Comparison of the DHA / DPA ratio in the oil of Schizochytrium sp. fermentation optimized with chemical regulators and Schizochytrium sp. fermentation without adding chemical regulators

[0089] Compare the DHA / DPA ratio in the oil of Schizochytrium sp. fermentation optimized with chemical regulators and Schizochytrium sp. fermentation without adding chemical regulators. As described in Example 1, the DHA / DPA ratio in the control group oil of Schizochytrium sp. fermentation without adding chemical regulator is 2.60, while the DHA / DPA ratio in the oil of Schizochytrium sp. fermentation with added chemical regulator has increased to varying degrees. The DHA / DPA ratios in the oil of Schizochytrium sp. fermentation with added melatonin (50 mM), ethanolamine (50 mM), betaine (75 mM), and inositol (50 mM) are 3.69, 3.70, 3.93, and 3.92 respectively, with the ratios increasing by 41.92%, 42.31%, 51.15%, and 50.77% respectively.

[0090] The present invention provides a reference for subsequent metabolic engineering transformation by adding chemical regulators to the fermentation medium of Schizochytrium sp. to increase the DHA / DPA ratio in the oil.

[0091] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art can understand that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the content disclosed in the embodiments.

Claims

1. A method for optimizing the Schizochytrium fermentation process by chemical regulators to increase the DHA / DPA ratio in oils and fats, characterized in that: During the fermentation process of Schizochytrium, one or more chemical regulators are added to the fermentation broth, wherein the chemical regulators are selected from one or more of melatonin, ethanolamine, betaine, and inositol to increase the ratio of DHA / DPA in the oil; The chemical regulator is one of melatonin, ethanolamine and inositol, and the concentration of the chemical regulator added to the fermentation broth is 50 mM; Alternatively, the chemical regulators are inositol and betaine, the concentration of inositol added to the fermentation broth is 50 mM, and the concentration of betaine added to the fermentation broth is 75 mM.

2. The method according to claim 1, characterized in that: Adding the chemical regulator to the fermentation medium at 0-36h of fermentation production; Alternatively, the fermentation production temperature is 25-29° C., the rotation speed is 150-200 rpm, and the total fermentation time is 72-120 h.

3. The method according to claim 1, characterized in that: The fermentation medium used during fermentation contains glucose, ammonium sulfate and phosphate.

4. The method according to claim 1, characterized in that: The schizochytrium is Schizochytrium sp. HX-308.

5. The method according to claim 1, characterized in that: The Schizochytrium is inoculated into a seed culture medium for activation to obtain a strain for fermentation; the strain for fermentation is inoculated into a fermentation culture medium for fermentation culture, and after the fermentation is completed, the strain is collected to extract oil.

6. The method according to claim 5, characterized in that: The OD value of the fermentation bacteria is 8-10; the inoculation amount of the fermentation bacteria is 0.8-1.5% of the volume of the fermentation medium.

7. The method according to any one of claims 1 to 6, characterized in that: The specific steps are as follows: Schizochytrium sp. HX-308 is inoculated into a seed culture medium, and cultured at a temperature of 28°C for 24 hours to obtain primary seeds; the primary seeds are inoculated into a seed culture medium at an inoculation amount of 10% of the volume of the seed culture medium, and cultured again at a temperature of 28°C for 24 hours to obtain secondary seeds; the secondary seeds are inoculated into a seed culture medium at an inoculation amount of 10% of the volume of the seed culture medium, and cultured again at a temperature of 28°C for 24 hours, and fermentation strains are obtained through the above activation process; the fermentation strain with an OD600 value of 8-10 is inoculated into a fermentation culture medium at an inoculation amount of 1%, and fermentation culture is carried out for 120 hours at a temperature of 25°C and a rotation speed of 170rpm.

8. The method according to claim 7, characterized in that: The components of the seed culture medium are: glucose 45g / L, yeast powder 2g / L, sodium glutamate 15g / L, MgCl2·7H2O 4g / L, Na2SO4 15g / L, KCl 1g / L, NaCl 1g / L, MgSO4·7H2O 5g / L, KH2PO4 3g / L, and the solvent is water; The components of the fermentation medium were: glucose 90 g / L, yeast powder 4 g / L, sodium glutamate 15 g / L, MgCl2·7H2O 4 g / L, Na2SO4 15 g / L, KCl 1 g / L, NaCl 1 g / L, MgSO4·7H2O 5 g / L, KH2PO4 3 g / L and (NH4)2SO4 4 g / L, and the solvent was water.

9. Use of the method according to any one of claims 1 to 8 in increasing the DHA / DPA ratio in oils fermented by Schizochytrium.

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