Liquid Submerged fermentation

Liquid deep fermentation
1、 The operating method of liquid deep fermentation. According to different operating methods, liquid deep fermentation mainly includes three types: batch fermentation, continuous fermentation, and fed batch fermentation.
1. Batch fermentation. Nutrients and bacterial strains are added for cultivation at once until they are released, and there is no material exchange with the outside except for air entering and exhaust gas being discharged. Features: disposable; During the fermentation process, nutrients continuously decrease, microorganisms continue to proliferate, and the environment is unstable; The four stages of microbial growth are evident. Application: Widely used.
2. Continuous fermentation. Continuous fermentation refers to adding fresh culture medium to a fermentation tank at a certain speed, while flowing out the culture solution at the same speed, so as to maintain a constant amount of liquid in the fermentation tank and allow microorganisms to grow in a stable state. Stable state can effectively prolong the logarithmic phase in batch culture. Characteristics: equal inflow and outflow of culture medium; Various changes=0; The four stages of microbial community growth do not exist. Application: Commonly used in industries such as wastewater treatment, gluconic acid, alcohol, amino acid fermentation, etc. Advantages: Stable operation; Beneficial for machinery and automation; Improve the utilization rate of equipment; Reduce sterilization frequency; Easy to optimize the process. Disadvantages: susceptible to bacterial infection; Microorganisms are prone to mutation; Not widely adaptable to product types; High requirements for equipment and accessories.
3. Batch fermentation with supplementary materials. Batch fermentation with supplementary materials, also known as semi continuous fermentation, is a fermentation technology that falls between batch fermentation and continuous fermentation. It refers to the cultivation technique of adding certain materials to the cultivation system in a certain way during microbial batch fermentation. By supplementing the culture system with materials, the concentration of nutrients in the culture medium can be maintained within a certain range for a long time, ensuring the growth needs of microorganisms without causing adverse effects, thereby achieving the goal of improving yield. Characteristics: It can relieve substrate inhibition, product inhibition, decomposition inhibition, or overcome microbial overgrowth; Improve the conversion rate of useful products; Application: Widely used in industries such as bread yeast, amino acids, antibiotics, etc;
2、 Fermentation process control. During the fermentation process, in order to achieve necessary control over the production process, it is necessary to regularly sample and measure relevant process parameters or conduct continuous measurements. The parameters that reflect changes in the fermentation process can be divided into two categories:
(1) Direct parameters: Specific sensor detected parameters can be directly used. They include parameters reflecting changes in physical and chemical environment, such as temperature, pressure, mixing power, rotational speed, foam, fermentation broth viscosity, turbidity pH、 Ionic concentration, dissolved oxygen, matrix concentration, etc.
(2) Indirect parameters: parameters that are still difficult to detect with sensors, including cell growth rate, product synthesis rate, and respiration rate. These parameters need to be obtained through computer calculations and specific mathematical models based on some direct parameters. Among the above parameters, temperature has a significant impact on the fermentation process pH、 Dissolved oxygen concentration, etc.
1. Temperature: Temperature can affect enzyme activity and also impact biosynthetic pathways. Temperature can also affect the physical properties of fermentation broth, as well as the decomposition and absorption of nutrients by bacterial strains. Fermentation tanks equipped with heat exchange devices should be used.
2. PH: pH can affect enzyme activity and the charged state of the cell membrane. It will also affect the decomposition of nutrients in the culture medium. Common control methods include: ① adjusting the ratio of physiological alkalinity and acidic salts; ② Choose different types and ratios of C and N; ③ Add buffering agent.
3. Dissolved oxygen: During the fermentation process, bacterial strains can only utilize dissolved oxygen. Therefore, it is necessary to continuously supplement a large amount of oxygen into the fermentation broth and constantly stir it to improve the solubility of oxygen in the fermentation broth.
4. Foam: During fermentation, foam may be produced by aeration, agitation, microbial metabolism and decomposition of some ingredients in the culture medium. Too much persistent foam is bad for fermentation. Mechanical defoaming and defoaming agents are commonly used for foam reduction.
5. The concentration of nutrients: The concentration of various nutrients in the fermentation broth, especially the carbon nitrogen ratio, inorganic salts, and vitamins, directly affects the growth of bacterial cells and the accumulation of metabolic products.
3、 Fermentation equipment. The equipment used for deep cultivation of microorganisms is collectively referred to as fermentation tanks. Due to the distinction between aerobic and anaerobic microorganisms, their cultivation equipment is correspondingly divided into aerobic fermentation equipment and anaerobic fermentation equipment.
(1) Liquid aerobic fermentation tank. Features: There is a cooling device. There is a ventilation device. Representative: Mechanical stirring fermentation tank, ventilated stirring fermentation tank.
(2) Liquid anaerobic fermentation tank. Features: There is a cooling device. There is no ventilation device. Representative: Alcohol fermentation tank, beer fermentation tank. 1. Mechanical stirring fermentation tank. It utilizes the function of a mechanical stirrer to thoroughly mix air and fermentation broth, promote oxygen dissolution, and ensure the supply of dissolved oxygen required for microbial growth, reproduction, and metabolism. Type: Universal fermentation tank, self-priming fermentation tank. 2. Ventilated stirred fermentation tank. In a ventilated stirred fermentation tank, the purpose of ventilation is not only to supply the oxygen needed by microorganisms, but also to use the air introduced into the fermentation tank instead of the agitator to evenly mix the fermentation broth. Type: Circulating ventilated fermentation tank (air lift fermentation tank or lift fermentation tank), high-level tower fermentation tank. 3. Anaerobic fermentation equipment. Characteristic: The main feature of strict anaerobic liquid deep fermentation is the elimination of oxygen from the fermentation tank. Type: Alcohol fermentation tank and cone bottom vertical fermentation tank used for beer production.