Method for improving glutamic acid fermentation efficiency

Abstract

The invention belongs to the technical field of biological production, and discloses a method for improving glutamic acid fermentation efficiency, which comprises the following steps: glutamic acid is produced by fermentation of glutamic acid producing strains, and a surfactant is added in the fermentation process. The method adopts the surfactant to regulate the fermentation mode, improves the yield of glutamic acid, and is environment-friendly and low in cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of biological production, and particularly relates to a method for improving the efficiency of glutamic acid fermentation. Background Art

[0002] L-Glutamic acid is an acidic amino acid with the chemical name α-aminoglutaric acid and the chemical formula C5H9NO4. L-Glutamic acid is a non-essential acidic amino acid and one of the most abundant amino acids in the human body, discovered by the German scientist Ritthausen in 1856. The structure of glutamic acid is linear, with two carboxyl groups and a negative charge. L-Glutamic acid is a specific precursor of amino acids (arginine and proline), bioactive molecules (γ-aminobutyric acid (GABA)), and biomolecules (glutathione, adrenaline, and acetylcholine). GABA has various biological functions, including antihypertensive, antidiabetic, and inhibitory effects on sympathetic nerve transmission, while glutathione plays an important role in protecting the mucosa from peroxide damage and dietary toxins. L-Glutamic acid is one of the main excitatory neurotransmitters in the brain, which can enhance brain function, mental activity, and detoxify the brain from ammonia by binding to nitrogen atoms. L-Glutamic acid is a multifunctional amino acid that participates in taste perception, intermediate metabolism, cell processes, energy production, and cell wall synthesis. The highest concentration of L-glutamic acid is in the brain and muscles, which is crucial for life activities. L-Glutamic acid mainly exists in the form of its sodium salt, monosodium glutamate. Glutamine is a derivative of glutamic acid and is catalyzed by glutamine synthetase from glutamic acid and ammonia in the body, and has anti-cancer activity. Therefore, glutamic acid is called an anti-cancer agent. On the other hand, L-glutamic acid receptors are present on immune cells, indicating that L-glutamic acid plays a role in the innate and adaptive immune systems. L-Glutamic acid has received extensive attention due to its medicinal and food applications and is commercially produced as an important industrial amino acid due to its growing demand. There are various methods for producing L-glutamic acid, but mainly through microbial fermentation because this method is economical and environmentally friendly. Corynebacterium glutamicum (Brevibacterium flavum) strains are used as industrial strains for producing L-glutamic acid.

[0003] The L-glutamic acid synthesis pathway involves the glycolysis pathway, pentose phosphate pathway, carbon dioxide fixation reaction, TCA cycle, and glyoxylate cycle. Amino acid fermentation conditions determine the direction of carbon flow in the synthesis pathway and the activity levels of key enzymes, thus determining the yield of glutamic acid. However, the optimization of fermentation conditions is a complex process involving a large number of experimental studies and is a time-consuming, laborious, and costly process.

[0004] In the prior art, a large amount of research has been done on fermentation culture conditions.

[0005] For example, Chinese Patent CN110846352 discloses a method for preparing a glutamic acid fermentation medium, which uses a proteolytic extract of bacteria to replace yeast extract, significantly reducing the cost and increasing the added value of bacterial protein and the acid production efficiency.

[0006] Chinese Patent CN105296561A discloses a glutamic acid fermentation medium, comprising the following components in weight percentage: corn steep liquor 2 - 10%, glucose 4 - 10%, phosphoric acid 0.2 - 0.4%, magnesium sulfate 0.1 - 0.2%, potassium chloride 0.3 - 0.5%, yeast culture waste liquid 0.35 - 0.5%, lysine 0.05 - 0.1%, and the balance being water. It uses yeast culture waste liquid, which is a waste generated in yeast production and contains a large amount of short peptides, soluble proteins, vitamins and other rich nitrogen sources. By replacing the soybean meal hydrolysate with this, it provides a reliable and sufficient nitrogen source for the glutamic acid fermentation medium, reduces the cost of glutamic acid fermentation, and solves the problem of difficult treatment of yeast production waste.

[0007] Chinese Patent CN105296562A uses betaine phosphate instead of betaine hydrochloride in the glutamic acid fermentation medium. By using betaine phosphate to replace betaine hydrochloride in the original medium, the chelation reaction between phosphoric acid and betaine hydrochloride is avoided, and the problems of damage to the fermenter caused by the precipitation of chelates and difficulty in cleaning are avoided.

[0008] Chinese Patent CN110878325A discloses an optimized glutamic acid fermentation medium, which comprises fermentation medium A and fermentation medium B. Fermentation medium A is added first, and then fermentation medium B is added after an interval of more than 12 hours. The fermentation medium of the present invention consists of two parts. Fermentation medium A focuses on enhancing the proliferation of strains, and fermentation medium B focuses on the synthesis and secretion of glutamic acid. The two fermentations cooperate with each other to increase the glutamic acid yield.

[0009] Chinese Patent CN103088081A discloses a fermentation method for producing glutamic acid by supplementing biotin, and the steps include: using a biotin - defective strain as the production strain, controlling the initial biotin content in the fermentation medium, and supplementing penicillin and biotin during the fermentation process. Adding biotin in the middle and late stages of the fermentation process can overcome the problem of biotin deficiency in the late stage of the "sub - optimal amount" process, ensure that the medium contains sufficient biotin to provide for the growth and metabolism of bacteria, greatly increase the synthesis rate of glutamic acid by bacteria, shorten the fermentation cycle, and reduce the production cost. Summary of the Invention

[0010] On the basis of the prior art, the applicant regulates multiple factors involved in the transport and secretion of glutamic acid according to the characteristics of microbial fermentation, thereby affecting the production of glutamic acid.

[0011] The present invention is achieved through the following technical solutions.

[0012] A method for improving the efficiency of glutamic acid fermentation, which comprises the following steps: Using a glutamic acid-producing strain to ferment and produce glutamic acid, and during the fermentation process, adding 0.25 - 1 g / L of a surfactant.

[0013] Preferably, during the fermentation process, direct current is passed through.

[0014] Preferably, the surfactant is sucrose laurate.

[0015] Preferably, the current intensity of the direct current is 5 - 10 mA.

[0016] More preferably, the addition amount of the sucrose laurate is 0.5 g / L.

[0017] More preferably, the addition timing of the surfactant is in the middle and late stages of fermentation.

[0018] Preferably, the time for passing the direct current is in the middle and late stages of fermentation.

[0019] Most preferably, the method comprises: Inoculating the seed liquid of Brevibacterium flavum producing glutamic acid into a 10 L small fermenter containing 6 L of fermentation medium at an inoculation amount of 5 - 15% for fermentation culture for 36 h; then adding 0.5 g / L of sucrose laurate to the fermenter and passing direct current with a current intensity of 10 mA, and continuing fermentation for 12 h, and collecting the fermentation broth.

[0020] Furthermore, the preparation method of the fermentation medium is as follows: taking the raw materials of the fermentation medium and preparing them according to the following concentrations: glucose 80 g / L, corn steep liquor dry powder 20 g / L, ammonium chloride 5 g / L, K2HPO4 2 g / L, MgSO4·7H2O 50 mg / L, MnSO4·H2O 10 mg / L, FeSO4·7H2O 10 mg / L, VB1 5 mg / L, biotin 10 μg / L; after stirring the raw materials evenly, sterilizing at 121 °C for 15 min and naturally cooling to obtain.

[0021] Furthermore, during the fermentation process, controlling the fermentation temperature at 36 °C, the ventilation ratio at 1:0.7, the stirring speed at 200 r / min, and maintaining the dissolved oxygen at 25%; feeding a glucose solution to maintain the residual sugar not less than 1.0%, feeding an antifoaming agent to defoam, and simultaneously feeding ammonia water to control the pH value of the fermentation broth to 7.0.

[0022] The research basis and beneficial effects of the present invention mainly include but are not limited to the following aspects: Sucrose laurate treatment will affect the cell surface membrane structure of the strain and promote the secretion and excretion of glutamate. Sucrose laurate has low toxicity and biodegradability, which can not only reduce pollution to the environment, but also ensure the safety of the product. Sucrose laurate is not used as a nutrient, but as a glutamate secretion promoter. The strain is mainly grown and proliferated in the early stage, and fermentation and acid production are mainly in the middle and late stages. Therefore, a one-time addition method in the middle and late stages of fermentation is selected. Direct current can promote the secretion of glutamate, but the effect of current on cells shows different characteristics with the difference of current intensity. Under the action of strong current, the cell wall will suffer a certain degree of electrical damage, causing electroporation of the cell membrane and even cell death. Appropriate direct current may promote the transport of glutamate by promoting the expression of sensitive channel proteins or changing protein conformation.

[0023] The excretion of glutamate is a complex process involving multiple factors. A single factor may not have a significant effect. The present invention attempts to use a dual-factor regulation method of sucrose laurate and direct current to significantly increase glutamate production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 :Effects of different surfactants on glutamate fermentation; Figure 2 :Effect of direct current on glutamate fermentation yield; Figure 3 : Comparison of glutamate fermentation yields in different groups. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in this application will be clearly and completely described below in conjunction with the specific embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this invention.

[0026] Example 1 A method for improving glutamate fermentation efficiency comprises the following steps: Seed culture: Inoculate the activated Brevibacterium flavum GDK-9 into the seed medium and conduct seed culture until the OD600 reaches 12; the culture conditions are as follows: the temperature is maintained at 33 °C, the dissolved oxygen is controlled at 20%, and the pH is controlled at about 7.0 by ammonia water. The seed medium is as follows: glucose 30 g / L, corn steep liquor dry powder 6 g / L, yeast extract 4 g / L, KH2PO4 1 g / L, K2HPO4 1 g / L, MgSO4·7H2O 0.6 g / L, MnSO4·H2O 5 mg / L, FeSO4·7H2O 5 mg / L, V H 10 mg / L.

[0027] Inoculate the Brevibacterium flavum GDK-9 seed liquid into a 10-L small fermenter containing 6 L of fermentation medium at an inoculation amount of 8% and conduct fermentation culture for 36 h; then add 0.5 g / L of sucrose laurate to the fermenter and apply direct current with a current intensity of 10 mA, and continue fermentation for 12 h to collect the fermentation broth; During the entire fermentation process, control the fermentation temperature at 36 °C, the ventilation ratio at 1:0.7, the stirring speed at 200 r / min, and the dissolved oxygen at 25%; during the entire fermentation process, add glucose with a mass percentage of 50% to maintain the residual sugar not lower than 1.0%, add an antifoaming agent to defoam, and at the same time add ammonia water to control the pH value of the fermentation broth to 7.0; the preparation method of the fermentation medium is as follows: take the raw materials of the fermentation medium and prepare them according to the following concentrations, glucose 80 g / L, corn steep liquor dry powder 20 g / L, ammonium chloride 5 g / L, K2HPO4 2 g / L, MgSO4·7H2O 50 mg / L, MnSO4·H2O 10 mg / L, FeSO4·7H2O 10 mg / L, VB1 5 mg / L, biotin 10 μg / L; after stirring the raw materials evenly, sterilize them at 121 °C for 15 min and cool naturally to obtain the fermentation medium.

[0028] Example 2 A method for improving the fermentation efficiency of glutamic acid, which comprises the following steps: Seed culture: Inoculate the activated Brevibacterium flavum GDK-9 into the seed medium and conduct seed culture until the OD600 reaches 10; the culture conditions are as follows: the temperature is maintained at 33 °C, the dissolved oxygen is controlled at 20%, and the pH is controlled at about 7.0 by ammonia water. The seed medium is as follows: glucose 30 g / L, corn steep liquor dry powder 6 g / L, yeast extract 4 g / L, KH2PO4 1 g / L, K2HPO4 1 g / L, MgSO4·7H2O 0.6 g / L, MnSO4·H2O 5 mg / L, FeSO4·7H2O 5 mg / L, V H 10 mg / L.

[0029] The Brevibacterium flavum GDK-9 seed liquid was inoculated into a 10-L small fermenter containing 6 L of fermentation medium at an inoculation amount of 10% for fermentation culture for 36 h; then 0.25 g / L of sucrose laurate was added to the fermenter, and direct current was passed with a current intensity of 5 mA, and fermentation was continued for 12 h, and the fermentation broth was collected; During the whole fermentation process, the fermentation temperature was controlled at 36 °C, the ventilation ratio was 1:0.7, the stirring speed was 200 r / min, and the dissolved oxygen was maintained at 25%; during the whole fermentation process, glucose with a mass percentage of 50% was fed to maintain the residual sugar not lower than 1.0%, antifoaming agent was added to defoam, and at the same time ammonia water was added to control the pH value of the fermentation broth to 7.0; The preparation method of the fermentation medium is as follows: take the raw materials of the fermentation medium and prepare them according to the following concentrations: glucose 80 g / L, corn steep liquor powder 20 g / L, ammonium chloride 5 g / L, K2HPO4 2 g / L, MgSO4·7H2O 50 mg / L, MnSO4·H2O 10 mg / L, FeSO4·7H2O 10 mg / L, VB1 5 mg / L, biotin 10 μg / L; after stirring the raw materials evenly, sterilize at 121 °C for 15 min and cool naturally to obtain the fermentation medium.

[0030] Comparative Example 1 A method for improving the fermentation efficiency of glutamic acid, which comprises the following steps: Seed culture: The activated Brevibacterium flavum GDK-9 was inoculated into the seed medium for seed culture until the OD600 was 12; the culture conditions were: the temperature was maintained at 33 °C, the dissolved oxygen was controlled at 20%, and the pH was controlled at about 7.0 by ammonia water. The seed medium was: glucose 30 g / L, corn steep liquor powder 6 g / L, yeast extract 4 g / L, KH2PO4 1 g / L, K2HPO4 1 g / L, MgSO4·7H2O 0.6 g / L, MnSO4·H2O 5 mg / L, FeSO4·7H2O 5 mg / L, V H 10 mg / L.

[0031] The Brevibacterium flavum GDK-9 seed liquid was inoculated into a 10-L small fermenter containing 6 L of fermentation medium at an inoculation amount of 8% for fermentation culture for 48 h, and the fermentation broth was collected; During the whole fermentation process, the fermentation temperature was controlled at 36 °C, the ventilation ratio was 1:0.7, the stirring speed was 200 r / min, and the dissolved oxygen was maintained at 25%; during the whole fermentation process, glucose with a mass percentage of 50% was added continuously to maintain the residual sugar not less than 1.0%, antifoaming agent was added for defoaming, and ammonia water was added simultaneously to control the pH value of the fermentation broth to 7.0; the preparation method of the fermentation medium was as follows: take the raw materials of the fermentation medium and prepare them according to the following concentrations, glucose 80 g / L, corn steep liquor powder 20 g / L, ammonium chloride 5 g / L, K2HPO4 2 g / L, MgSO4·7H2O 50 mg / L, MnSO4·H2O 10 mg / L, FeSO4·7H2O 10 mg / L, VB1 5 mg / L, biotin 10 μg / L; after stirring the raw materials evenly, sterilize them at 121 °C for 15 min and cool them naturally to obtain the fermentation medium.

[0032] Comparative Example 2 A method for improving the glutamic acid fermentation efficiency, which comprises the following steps: Seed culture: Inoculate the activated Brevibacterium flavum GDK-9 into the seed medium for seed culture until the OD600 is 12; the culture conditions are: the temperature is maintained at 33 °C, the dissolved oxygen is controlled at 20%, and the pH is controlled at about 7.0 by ammonia water. The seed medium is: glucose 30 g / L, corn steep liquor powder 6 g / L, yeast extract 4 g / L, KH2PO4 1 g / L, K2HPO4 1 g / L, MgSO4·7H2O 0.6 g / L, MnSO4·H2O 5 mg / L, FeSO4·7H2O 5 mg / L, V H 10 mg / L.

[0033] Inoculate the Brevibacterium flavum GDK-9 seed liquid into a 10 L small fermenter containing 6 L of fermentation medium at an inoculation amount of 8% for fermentation culture for 36 h; then add 0.5 g / L of sucrose laurate to the fermenter and continue fermentation for 12 h, and collect the fermentation broth; During the whole fermentation process, the fermentation temperature was controlled at 36 °C, the ventilation ratio was 1:0.7, the stirring speed was 200 r / min, and the dissolved oxygen was maintained at 25%; during the whole fermentation process, glucose with a mass percentage of 50% was fed to maintain the residual sugar not less than 1.0%, antifoaming agent was added to defoam, and at the same time ammonia water was added to control the pH value of the fermentation broth to 7.0; the preparation method of the fermentation medium was as follows: take the raw materials of the fermentation medium and prepare them according to the following concentrations, glucose 80 g / L, corn steep liquor dry powder 20 g / L, ammonium chloride 5 g / L, K2HPO4 2 g / L, MgSO4·7H2O 50 mg / L, MnSO4·H2O 10 mg / L, FeSO4·7H2O 10 mg / L, VB1 5 mg / L, biotin 10 μg / L; after stirring the raw materials evenly, sterilize at 121 °C for 15 min and cool naturally to obtain the fermentation medium.

[0034] Comparative Example 3 A method for improving the fermentation efficiency of glutamic acid, which comprises the following steps: Seed culture: The activated Brevibacterium flavum GDK-9 was inoculated into the seed medium for seed culture until the OD600 reached 12; the culture conditions were: the temperature was maintained at 33 °C, the dissolved oxygen was controlled at 20%, and the pH was controlled at about 7.0 by ammonia water. The seed medium was: glucose 30 g / L, corn steep liquor dry powder 6 g / L, yeast extract 4 g / L, KH2PO4 1 g / L, K2HPO4 1 g / L, MgSO4·7H2O 0.6 g / L, MnSO4·H2O 5 mg / L, FeSO4·7H2O 5 mg / L, V H 10 mg / L.

[0035] The Brevibacterium flavum GDK-9 seed liquid was inoculated into a 10 L small fermenter containing 6 L of fermentation medium at an inoculation amount of 8% for fermentation culture for 36 h; then direct current was passed, the current intensity was 10 mA, and fermentation continued for 12 h, and the fermentation broth was collected; during the whole fermentation process, the fermentation temperature was controlled at 36 °C, the ventilation ratio was 1:0.7, the stirring speed was 200 r / min, and the dissolved oxygen was maintained at 25%; during the whole fermentation process, glucose with a mass percentage of 50% was fed to maintain the residual sugar not less than 1.0%, antifoaming agent was added to defoam, and at the same time ammonia water was added to control the pH value of the fermentation broth to 7.0; the preparation method of the fermentation medium was as follows: take the raw materials of the fermentation medium and prepare them according to the following concentrations, glucose 80 g / L, corn steep liquor dry powder 20 g / L, ammonium chloride 5 g / L, K2HPO4 2 g / L, MgSO4·7H2O 50 mg / L, MnSO4·H2O 10 mg / L, FeSO4·7H2O 10 mg / L, VB1 5 mg / L, biotin 10 μg / L; after stirring the raw materials evenly, sterilize at 121 °C for 15 min and cool naturally to obtain the fermentation medium.

[0036] Example 3 1. Research shows that surfactants can affect the cell surface structure. We studied the effects of three environmentally friendly surfactants, namely sucrose laurate, glyceryl triacetate, and calcium stearoyl lactate, on glutamic acid fermentation. Based on Comparative Example 1, surfactants were added at 36 hours of fermentation. Three parallel experimental groups of sucrose laurate, glyceryl triacetate, and calcium stearoyl lactate were set up. In each experimental group, the added concentration of the surfactant was set at 0, 0.25, 0.5, 1, 2, a total of five concentration gradients, with the unit of g / L. As Figure 1 shown, there is a positive correlation between sucrose laurate and glutamic acid fermentation. As the concentration of sucrose laurate increases, the content of glutamic acid increases. When the addition amount is 0.5 g / L, the content of glutamic acid increases by about 5.6%. Continuing to increase the sucrose laurate, there is no significant change in the glutamic acid content; glyceryl triacetate and calcium stearoyl lactate have no obvious effect on the yield of glutamic acid.

[0037] The treatment with sucrose laurate may affect the cell surface membrane structure of the strain and promote the secretion and efflux of glutamic acid. However, the secretion and efflux of glutamic acid are affected by multiple factors, and the effect of a single factor may be limited.

[0038] In the early and middle stages of fermentation, mainly the strain is producing, and the yield of glutamic acid is relatively low. The feedback and inhibition mechanisms of glutamic acid have not been fully activated. At this time, the effect of adding surfactants is not obvious, and it is most appropriate to add them in the middle and later stages.

[0039] 2. Living cells must constantly exchange substances with the surrounding environment to carry out metabolic activities continuously, and ion channels are the windows for substance exchange. Research shows that the secretion and transport of L-glutamic acid are different from those of other amino acids, and its transport is completed through sensitive channel proteins. We continued to study the effect of current on the secretion and efflux of glutamic acid. Based on Comparative Example 1, direct current stimulation of different intensities was added at 12, 24, and 36 hours of fermentation. The direct current intensity was set at: 0, 5, 10, 20, 40, with the unit of mA (milliamperes), and the current input time was controlled at 12 h. As Figure 2As shown in the figure, direct current can promote the secretion of glutamate, but the effect of current on cells shows different characteristics with the difference of current intensity. At the current intensity of 40mA, the production of glutamate decreases significantly, which may be because under the action of strong current, the cell wall suffers a certain degree of electrical damage, causing cell membrane electroporation and even cell death. The appropriate direct current (36h, 10mA) may promote the transport of glutamate by promoting the expression of sensitive channel proteins or changing protein conformation, which is 4.8% higher than that of comparative example 1. In the early and middle stages of fermentation, the production and proliferation of strains are the main focus, the production of glutamate is relatively low, and the feedback and inhibition mechanism of glutamate has not yet been fully activated. Therefore, the current is applied in the middle and late stages of fermentation (36h).

[0040] 3. Based on the above research, the concentration of sucrose laurate was 0.5g / L and the current intensity was 10mA (12h) for the test. Figure 3 As shown, compared with comparative example 1, the glutamate production in Example 1 increased by 14.0%, in comparative example 2 (sucrose laurate group) increased by 5.6%, and in comparative example 3 (current stimulation group) increased by 4.8%. It can be seen that the excretion of glutamate is a complex multi-factor overlapping process, and the effect of a single factor on the production of glutamate is relatively limited. The present invention adopts a dual-factor regulation method of sucrose laurate and direct current, which greatly increases the production of glutamate, is environmentally friendly, and has low cost.

[0041] The above examples are only the best specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples, and many variations are possible. All variations that can be directly derived or associated with the contents disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for improving the efficiency of glutamic acid fermentation, characterized in that The method comprises the following steps: Using a glutamic acid-producing strain to ferment and produce glutamic acid. During the fermentation process, 0.25 - 1 g / L of a surfactant is added, and direct current is passed through.

2. The method according to claim 1, wherein The surfactant is sucrose laurate.

3. The method according to claim 1, wherein The current intensity of the direct current is 5 - 10 mA.

4. The method according to claim 2, wherein The addition amount of the sucrose laurate is 0.5 g / L.

5. The method according to any one of claims 1-4, characterized in that, The addition timing of the surfactant is in the middle and late stages of fermentation.

6. The method according to claim 1 or 3, characterized in that The time for passing the direct current is in the middle and late stages of fermentation.

7. The method according to any one of claims 1-4, characterized in that, The method includes: Inoculating a Brevibacterium flavum seed solution capable of producing glutamic acid into a fermenter filled with a fermentation medium at an inoculation amount of 5 - 15%, and performing fermentation for 36 h; then adding 0.5 g / L of sucrose laurate to the fermenter, and passing direct current with a current intensity of 10 mA, and continuing fermentation for 12 h, and collecting the fermentation broth.

8. The method according to claim 7, wherein The preparation method of the fermentation medium is as follows: taking the raw materials of the fermentation medium and preparing them according to the following concentrations: glucose 80 g / L, corn steep liquor dry powder 20 g / L, ammonium chloride 5 g / L, K2HPO4 2 g / L, MgSO4·7H2O 50 mg / L, MnSO4·H2O 10 mg / L, FeSO4·7H2O 10 mg / L, VB1 5 mg / L, biotin 10 μg / L; after stirring the raw materials evenly, sterilizing at 121 °C for 15 min, and naturally cooling to obtain the fermentation medium.

9. The method according to claim 7, wherein During the fermentation process, the fermentation temperature is controlled at 36 °C, the stirring speed is 200 r / min, and the dissolved oxygen is maintained at 25%; a glucose solution is fed to maintain the residual sugar not lower than 1.0%, an antifoaming agent is fed to defoam, and at the same time ammonia water is fed to control the pH value of the fermentation broth to 7.0.

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