Lactic acid bacteria high-density culture method based on pH control system

Abstract

The invention discloses a lactic acid bacteria high-density culture method based on a pH control system, and relates to the technical field of lactic acid bacteria culture.The lactic acid bacteria culture stage is monitored in real time, a pH sensor and a PID control algorithm are adopted, the pH value in the fermentation process is maintained within the range of 6.7 + / -0.1, excessive accumulation of lactic acid is avoided, and large fluctuation of the pH value is avoided; the lactic acid bacteria efficiently grow in a stable acid-base environment, the fermentation efficiency and the thallus yield are greatly improved, more effective pH control is provided, the growth speed of the lactic acid bacteria is increased, high-density thallus culture is maintained, automatic adjustment is carried out in the fermentation process, continuity and stability are provided for the fermentation environment, the fermentation time is shortened, and the production cost is reduced. In the same fermentation period, the biomass of lactic acid bacteria is remarkably increased, the yield is improved, the overall production efficiency and economic benefits are improved, an automatic pH control system can continuously monitor the environment in the fermentation tank, automatic adjustment is conducted when the pH value changes, and the risk of personal errors is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of lactic acid bacteria cultivation, in particular to a high-density lactic acid bacteria cultivation method based on a pH control system. Background Art

[0002] The current high-density culture method of lactic acid bacteria faces multiple technical challenges, especially in the control of pH during the fermentation process, which has a crucial impact on the growth, metabolism and final yield of lactic acid bacteria.

[0003] In the traditional fermentation process, lactic acid bacteria will produce a large amount of lactic acid, causing the pH value of the fermentation liquid to drop rapidly. If the pH value drops too much, it will inhibit the growth and metabolism of lactic acid bacteria, ultimately affecting the yield and quality. In the traditional fermentation process, the pH value is usually monitored manually and adjusted by adding alkaline solutions (such as NaOH). Although manual adjustment can partially alleviate pH fluctuations, frequent human intervention not only increases the complexity of the operation, but also easily leads to untimely response or inaccurate adjustment. During the manual adjustment process, the pH value will fluctuate greatly, and it cannot be guaranteed to be always within the optimal growth range of lactic acid bacteria, resulting in a decrease in fermentation efficiency, which ultimately affects production stability and yield consistency.

[0004] The production efficiency of lactic acid bacteria fermentation is affected by many factors. In particular, when the pH value, temperature and other parameters in the fermentation process are not stably controlled, the growth rate of lactic acid bacteria will be significantly reduced, resulting in a prolonged fermentation cycle and low production efficiency. Therefore, a high-density culture method of lactic acid bacteria based on a pH control system is urgently needed to solve such problems. Summary of the invention

[0005] In view of the above existing problems, the present invention is proposed.

[0006] The present invention provides a high-density culture method for lactic acid bacteria based on a pH control system to solve the problem that the traditional method mainly relies on regular monitoring of fermentation parameters and manually adjusting the temperature and pH value to maintain the fermentation conditions, but cannot achieve real-time and precise adjustment. The metabolic state of the bacteria during the fermentation process is often affected by fluctuations, resulting in a long fermentation time.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] The present invention provides a method for high-density cultivation of lactic acid bacteria based on a pH control system, which comprises:

[0009] Step S1, prepare materials.

[0010] Including 3% soybean peptone, 2% yeast extract powder, 0.5% sodium acetate, 0.1% complex trace element solution, 0.05% complex vitamin solution, 0.2% trypsin, 0.5% acid-soluble protein (short peptide), 0.2% to 0.4% sodium citrate, 0.02% to 0.04% Mg2+ water-soluble compound, 0.01% to 0.02% Fe2+ water-soluble compound, 93.64% to 94.62% pure water,

[0011] Prepare MRS medium and adjust the pH to an initial value of 7.0. Sterilize the medium in an autoclave at 121°C for 15 minutes.

[0012] Step S2, fermentation tank setting,

[0013] Transfer the sterilized culture medium to a fermentation tank with a temperature and pH control system under sterile conditions;

[0014] Step S3, starting the pH control system and calibrating the pH sensor;

[0015] Step S4, real-time monitoring and adjustment,

[0016] When fermentation begins, the pH sensor monitors the pH value of the culture solution in the fermentation tank in real time.

[0017] Step S5, process maintenance,

[0018] The temperature in the fermenter is maintained at a constant 37°C, and the pH control system keeps the pH value within the set range.

[0019] After continuing the fermentation for 30 hours, the fermentation was terminated and the culture solution was collected;

[0020] The pH control system is used to realize fully automated monitoring and regulation of the fermentation environment. During the fermentation process, the pH value is one of the key factors for the growth of lactic acid bacteria. In traditional fermentation methods, the pH value fluctuates greatly, often leading to unstable growth of bacteria and fluctuations in yield and quality. In the present invention, the pH sensor can collect the pH value of the fermentation liquid in real time and continuously, avoiding the inhibition of bacterial growth caused by pH fluctuations.

[0021] Furthermore, in step S2, the temperature of the fermentation tank is adjusted to 37°C.

[0022] Further, in step S3, the pH controller is set to 6.7±0.1.

[0023] Furthermore, in step S4, when the pH value is lower than the preset lower limit of 6.6, the pH controller sends a signal to start the pump connected to the control system.

[0024] Furthermore, in step S4, 20% NaOH solution is automatically added from the liquid storage barrel, and the pump adds alkaline solution based on flow control to restore the pH value to the set range of 6.7±0.1.

[0025] Further, the pH control system components include:

[0026] pH sensor is used to detect the pH value of fermentation liquid in real time and transmit the data to pH controller.

[0027] The pH controller is used to determine whether the pH value is within the set range based on the input data of the pH sensor, and decide whether to start the pump to add acid or alkali. The PID control algorithm is used in pH control to further improve the flexibility and accuracy of control. The PID control can dynamically adjust the operation of the pump. By calculating the pH error value and adding NaOH solution, the pH value is kept within the preset range, so that the pH value in the fermentation tank is always within the suitable range for lactic acid bacteria, reducing human errors, and being able to respond quickly when the pH value changes slightly, effectively improving the growth rate and fermentation efficiency of lactic acid bacteria.

[0028] Furthermore, the pH control system component also includes:

[0029] The pump and storage tank are connected to the pH controller to add acid or alkaline solution as needed to keep the pH stable.

[0030] Furthermore, during the high-density culture of lactic acid bacteria in the pH control system, the pH monitoring and adjustment methods include:

[0031] During the fermentation process, the pH sensor continuously collects the pH value of the fermentation liquid, uses Kalman filtering to eliminate noise, and transmits the processed data to the controller in real time.

[0032] The controller uses the PID control algorithm to make adjustment decisions based on the pH value information transmitted by the sensor.

[0033] Furthermore, during the high-density culture of lactic acid bacteria in the pH control system, the pH monitoring and adjustment method also includes:

[0034] The PID control algorithm calculates the difference between the current pH value and the target pH value, and adjusts the controller output through proportional, integral and differential terms to control the start or stop of the pump. The combination of the pH control system and the fermentation tank improves the automation and controllability of the entire fermentation process. Based on the joint regulation of temperature and pH, it provides the best conditions for the efficient growth of lactic acid bacteria, continuously and automatically adjusts, reduces dependence on manual operation, improves production efficiency, and reduces the risk of contamination during operation.

[0035] Furthermore, during the high-density culture of lactic acid bacteria in the pH control system, the pH monitoring and adjustment method also includes:

[0036] Based on the instructions of the controller, the pump uses a flow control algorithm to calculate the amount of NaOH solution delivered by the pump and adjusts the pump flow in real time according to the deviation of the pH value.

[0037] The beneficial effects of the present invention are:

[0038] The present invention performs real-time monitoring of the lactic acid bacteria cultivation stage, adopts a pH sensor and a PID control algorithm, maintains the pH value in the range of 6.7±0.1 during the fermentation process, reduces excessive accumulation of lactic acid, avoids large fluctuations in the pH value, enables lactic acid bacteria to grow efficiently in a stable acid-base environment, and greatly improves the fermentation efficiency and bacterial yield.

[0039] The present invention provides more effective pH control, accelerates the growth rate of lactic acid bacteria, maintains high-density bacterial culture, performs automatic adjustment during the fermentation process, provides continuity and stability for the fermentation environment, shortens the fermentation time, and significantly increases the biomass of lactic acid bacteria and improves the yield within the same fermentation cycle, thereby improving the overall production efficiency and economic benefits.

[0040] The present invention provides an automated pH control system capable of continuously monitoring the environment in the fermentation tank, automatically adjusting when the pH value changes, and injecting NaOH solution through a pump to maintain a stable pH value, thereby reducing the necessity of manual operation and the risk of human error.

[0041] The present invention integrates pH control and temperature control systems, which significantly improves the controllability of the fermentation process. The combined regulation of temperature and pH enables lactic acid bacteria to grow in a more suitable environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0043] Figure 1 The figure is a schematic diagram of the process of the high-density culture method of lactic acid bacteria of the present invention. DETAILED DESCRIPTION

[0044] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0045] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0046] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0047] Example 1: High-density culture of lactic acid bacteria

[0048] Preparation steps:

[0049] According to the capacity of the fermentation tank, weigh each component in proportion, dissolve each component in distilled water, use a pH meter to adjust the pH value of the medium to 6.7, sterilize in an autoclave at 121°C for 15 minutes, and inoculate the lactic acid bacteria into the sterilized medium under sterile conditions.

[0050] The culture medium was transferred to the fermentation tank, the temperature of the fermentation tank was set to 37°C, the pH monitoring system was started, and the pH value of the culture solution was monitored in real time. When the pH value was lower than 6.6, 20% NaOH solution was added automatically or manually to adjust and maintain the pH value at 6.7±0.1.

[0051] The above conditions were maintained for fermentation for 30 hours. After 30 hours, the fermentation was stopped and the culture solution was collected;

[0052] Example 2: High-density culture of lactic acid bacteria

[0053] Prepare the culture medium: 3% soybean peptone, 2% yeast extract powder, 0.5% sodium acetate, 0.1% complex trace element solution, 0.05% complex vitamin solution, 0.2% trypsin, 0.5% acid-soluble protein (short peptide), 0.2% sodium citrate, 0.02% Mg2+ water-soluble compound, 0.02% Fe2+ water-soluble compound, and the rest is pure water;

[0054] Preparation steps:

[0055] According to the capacity of the fermentation tank, weigh each component in proportion, dissolve each component in distilled water, use a pH meter to adjust the pH value of the medium to 7.0, sterilize in an autoclave at 121°C for 15 minutes, and inoculate the lactic acid bacteria into the sterilized medium under sterile conditions.

[0056] The culture medium was transferred to the fermentation tank, the temperature of the fermentation tank was set to 37°C, the pH monitoring system was started, and the pH value of the culture solution was monitored in real time. When the pH value was lower than 6.6, 20% NaOH solution was added automatically or manually to adjust and maintain the pH value at 7.0±0.1.

[0057] The above conditions were maintained for fermentation for 30 hours. After 30 hours, the fermentation was stopped and the culture solution was collected;

[0058] Example 3: High-density culture of lactic acid bacteria

[0059] Prepare the culture medium: 3% soybean peptone, 2% yeast extract powder, 0.5% sodium acetate, 0.1% complex trace element solution, 0.05% complex vitamin solution, 0.2% trypsin, 0.5% acid-soluble protein (short peptide), 0.2% sodium citrate, 0.02% Mg2+ water-soluble compound, 0.02% Fe2+ water-soluble compound, and the rest is pure water;

[0060] Preparation steps:

[0061] According to the capacity of the fermentation tank, weigh each component in proportion, dissolve each component in distilled water, use a pH meter to adjust the pH value of the medium to 7.5, sterilize in an autoclave at 121°C for 15 minutes, and inoculate the lactic acid bacteria into the sterilized medium under sterile conditions.

[0062] The culture medium was transferred to the fermentation tank, the temperature of the fermentation tank was set to 37°C, the pH monitoring system was started, and the pH value of the culture solution was monitored in real time. When the pH value was lower than 6.6, 20% NaOH solution was added automatically or manually to adjust and maintain the pH value at 7.5±0.1.

[0063] The above conditions were maintained for fermentation for 30 hours. After 30 hours, the fermentation was stopped and the culture solution was collected;

[0064] Example 4: High-density culture of lactic acid bacteria

[0065] Prepare the culture medium: 3% soybean peptone, 2% yeast extract powder, 0.5% sodium acetate, 0.1% complex trace element solution, 0.05% complex vitamin solution, 0.2% trypsin, 0.5% acid-soluble protein (short peptide), 0.2% sodium citrate, 0.02% Mg2+ water-soluble compound, 0.02% Fe2+ water-soluble compound, and the rest is pure water;

[0066] Preparation steps:

[0067] According to the capacity of the fermentation tank, weigh each component in proportion, dissolve each component in distilled water, use a pH meter to adjust the pH value of the medium to 8.0, sterilize in an autoclave at 121°C for 15 minutes, and inoculate the lactic acid bacteria into the sterilized medium under sterile conditions.

[0068] The culture medium was transferred to the fermentation tank, the temperature of the fermentation tank was set to 37°C, the pH monitoring system was started, and the pH value of the culture solution was monitored in real time. When the pH value was lower than 6.6, 20% NaOH solution was added automatically or manually to adjust and maintain the pH value at 8.0±0.1.

[0069] The above conditions were maintained for fermentation for 30 hours. After 30 hours, the fermentation was stopped and the culture solution was collected;

[0070] Example 5: High-density culture of lactic acid bacteria

[0071] Prepare the culture medium: 3% soybean peptone, 2% yeast extract powder, 0.5% sodium acetate, 0.1% complex trace element solution, 0.05% complex vitamin solution, 0.2% trypsin, 0.5% acid-soluble protein (short peptide), 0.2% sodium citrate, 0.02% Mg2+ water-soluble compound, 0.02% Fe2+ water-soluble compound, and the rest is pure water;

[0072] Preparation steps:

[0073] According to the capacity of the fermentation tank, weigh each component in proportion, dissolve each component in distilled water, use a pH meter to adjust the pH value of the medium to 8.5, sterilize in an autoclave at 121°C for 15 minutes, and inoculate the lactic acid bacteria into the sterilized medium under sterile conditions.

[0074] The culture medium was transferred to the fermentation tank, the temperature of the fermentation tank was set to 37°C, the pH monitoring system was started, and the pH value of the culture solution was monitored in real time. When the pH value was lower than 6.6, 20% NaOH solution was added automatically or manually to adjust and maintain the pH value at 8.5±0.1.

[0075] The above conditions were maintained for fermentation for 30 hours. After 30 hours, the fermentation was stopped and the culture solution was collected;

[0076] Experimental Example 1: Effect of pH conditions on the growth of lactic acid bacteria

[0077] 1 Materials and methods

[0078] 1.1 Culture medium

[0079] Prepare the culture medium: 3% soybean peptone, 2% yeast extract powder, 0.5% sodium acetate, 0.1% complex trace element solution, 0.05% complex vitamin solution, 0.2% trypsin, 0.5% acid-soluble protein (short peptide), 0.2% sodium citrate, 0.02% Mg2+ water-soluble compound, 0.02% Fe2+ water-soluble compound, and the rest is pure water;

[0080] 1.2 Reagents and instruments

[0081] 1.2.1 Reagents

[0082] Gram staining solution; bromocresol purple indicator; Griess reagent (nitrite reagent); diphenylamine-sulfuric acid reagent (nitrate reagent);

[0083] 1.2.2 Instruments

[0084] LDZX-50KB vertical electric heating pressure steam sterilizer (Shanghai Shen'an Medical Equipment Factory); FA1004 electronic balance (Shanghai Tianping Instrument Factory); 0.5-10μL and 20-200μL micropipette (Thermo); ZHJH-2109C clean bench (Shanghai Zhicheng Analytical Instrument Manufacturing Co., Ltd.); SPX-250B intelligent biochemical incubator (Jiangsu Jintan Zhengji Instrument Co., Ltd.); E-201-C PHS-BE (pH meter) (Shanghai Precision Scientific Instrument Co., Ltd.); 722 spectrophotometer (Shanghai Third Analytical Instrument Factory); DMBA300LED electron microscope (McOdy Industrial Group Co., Ltd.); E221LED optical microscope (McOdy Industrial Group Co., Ltd.)

[0085] 1.3 Sample collection, strain isolation and preservation

[0086] 1.3.1 Sample collection

[0087] 1.3.2 Isolation and purification of lactic acid bacteria

[0088] After measuring the temperature and pH value of the sample, the lactic acid bacteria were separated and purified: the sample was diluted in a gradient manner and inoculated on MRS agar medium and BCP medium by streak method and coating method respectively, and cultured at 37°C for 24-48 hours. The rod-shaped, spherical or streptococcal Gram-positive bacteria that produced acid but not gas in catalase (negative test), did not reduce nitrate, did not liquefy gelatin, and sugar fermentation experiments were preliminarily identified as lactic acid bacteria, and further purified, cultured and preserved.

[0089] 1.4 Experiments and observations at different pH values

[0090] The pH value of the solution is monitored in real time using a pH sensor.

[0091] The controller receives the sensor data and responds to it, and the target pH range can be set.

[0092] A pump was used to automatically add acid or base to adjust the pH, which was set to: pH 3.5, 4.3, 4.5, 5.7, 6.5, 8.5, 9.6;

[0093] 2 Results and analysis

[0094] 2.1 Isolation and preliminary identification of lactic acid bacteria in dairy products

[0095] The four dairy products collected in this experiment were separated and purified, and the pH value was automatically adjusted;

[0096] 2.2 Pretreatment and result observation of pH change experiment

[0097] The experimental results show that the pH value of the culture medium before and after sterilization has no obvious difference under acidic conditions, and is slightly reduced. The difference is more obvious under alkaline conditions, mainly manifested as a decrease. According to the pretreatment results, the experiment appropriately adjusted the pH value before sterilization (as shown in Table 2) and took corresponding sterilization measures.

[0098] Table 2: pH requirements of culture medium and correction values ​​before sterilization

[0099]

[0100] 2.3 Effect of pH on the growth of lactic acid bacteria

[0101] Combining the optical density value and the visual test results of the medium turbidity, it can be seen from Tables 3 and 4 that more lactic acid bacteria strains grow when the pH value is 4.3-8.5, and the optimal pH value is 6.5. As the culture time increases, the pH value continues to increase, and the number of lactic acid bacteria continues to increase, reaching a maximum value and then decreasing. The lowest pH value after the decrease is 3.4. When the pH value is 8.5, cocci SN2 can reduce the pH value to 4.5. At the same time, it can be concluded from Tables 3 and 4 that these 10 strains have different tolerance to acid and alkali and have different pH ranges;

[0102] Table 3: pH values ​​before and after lactic acid bacteria growth

[0103]

[0104]

[0105] Note: The incubation temperature for pH determination is 20°C

[0106] Table 4: pH range for growth of various strains

[0107]

[0108] It can be seen that long metabolism is carried out in an acidic environment with low pH. When the environmental pH drops to a certain level, lactic acid bacteria will stop growing in the low pH environment. At the same time, pH also affects the production of metabolites.

[0109] 3.1.2 Effect of pH on the growth of lactic acid bacteria

[0110] The pH of the culture medium directly affects the growth of lactic acid bacteria. This is because the H+ concentration is directly related to the entry of nutrients into the cell body. The pH affects the absorption of nutrients by bacteria. The increase in pH causes the chemical balance between ions in the original culture medium to shift, generating precipitation and reducing the effective ingredients in the culture medium. The experimental results show that the optimal pH for the growth of lactic acid bacteria is 6.5. As the pH decreases or increases, the growth of the bacteria is inhibited to a certain extent.

[0111] Conclusion: The growth of microorganisms is affected by the environmental pH. The degree of influence varies greatly at different pH values ​​and temperatures. The optimum pH value for the growth of lactic acid bacteria isolated in the experiment is around 6.7, and the pH value set by the present invention is the optimum pH value.

[0112] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for high-density cultivation of lactic acid bacteria based on a pH control system, characterized in that: include, Step S1, preparing materials, including 3% soy peptone, 2% yeast extract powder, 0.5% sodium acetate, 0.1% complex trace element solution, 0.05% complex vitamin solution, 0.2% trypsin, 0.5% acid-soluble protein, 0.2% to 0.4% sodium citrate, 0.02% to 0.04% Mg2+ water-soluble compound, 0.01% to 0.02% Fe2+ water-soluble compound, and 93.64% to 94.62% pure water, Prepare MRS medium and adjust the pH to an initial value of 7.0, and sterilize the medium in an autoclave at 121°C for 15 minutes; Step S2, setting up a fermentation tank, and transferring the sterilized culture medium to a fermentation tank with a temperature control and pH control system under sterile conditions; Step S3, starting the pH control system and calibrating the pH sensor; Step S4, real-time monitoring and adjustment: when fermentation starts, the pH sensor monitors the pH value of the culture solution in the fermentation tank in real time. Step S5, the fermentation process is maintained, the temperature in the fermenter is maintained at a constant 37° C., and the pH control system maintains the pH value within a set range. After fermentation continues for 30 hours, the fermentation is terminated and the culture fluid is collected.

2. The method for high-density cultivation of lactic acid bacteria based on a pH control system according to claim 1, characterized in that: In step S2, the temperature of the fermentation tank is adjusted to 37°C.

3. The method for high-density cultivation of lactic acid bacteria based on a pH control system according to claim 2, characterized in that: In step S3, the pH controller is set to 6.7±0.

1.

4. The method for high-density cultivation of lactic acid bacteria based on a pH control system according to claim 3, characterized in that: In step S4, when the pH value is lower than the preset lower limit of 6.6, the pH controller sends a signal to start the pump connected to the control system.

5. The method for high-density cultivation of lactic acid bacteria based on a pH control system according to claim 4, characterized in that: In step S4, 20% NaOH solution is automatically added from the liquid storage barrel, and the pump adds alkaline solution based on flow control to restore the pH value to the set range of 6.7±0.

1.

6. The method for high-density cultivation of lactic acid bacteria based on a pH control system according to claim 5, characterized in that: pH control system components include: pH sensor is used to detect the pH value of fermentation liquid in real time and transmit the data to pH controller. The pH controller is used to determine whether the pH value is within the set range based on the input data of the pH sensor, and decide whether to start the pump to add acid or alkali.

7. The method for high-density cultivation of lactic acid bacteria based on a pH control system according to claim 6, characterized in that: pH control system components also include: The pump and storage tank are connected to the pH controller to add acid or alkaline solution as needed to keep the pH stable.

8. The method for high-density cultivation of lactic acid bacteria based on a pH control system according to claim 7, characterized in that: During the high-density culture of lactic acid bacteria in the pH control system, the pH monitoring and adjustment methods include: During the fermentation process, the pH sensor continuously collects the pH value of the fermentation liquid, uses Kalman filtering to eliminate noise, and transmits the processed data to the controller in real time. The controller uses the PID control algorithm to make adjustment decisions based on the pH value information transmitted by the sensor.

9. The method for high-density cultivation of lactic acid bacteria based on a pH control system according to claim 8, characterized in that: During the high-density culture of lactic acid bacteria in the pH control system, the pH monitoring and adjustment methods also include: The PID control algorithm calculates the difference between the current pH value and the target pH value and adjusts the controller output through proportional, integral and differential terms to control the start or stop of the pump.

10. The method for high-density cultivation of lactic acid bacteria based on a pH control system according to claim 9, characterized in that: During the high-density culture of lactic acid bacteria in the pH control system, the pH monitoring and adjustment methods also include: Based on the instructions of the controller, the pump uses a flow control algorithm to calculate the amount of NaOH solution delivered by the pump and adjusts the pump flow in real time according to the deviation of the pH value.

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