1. Impact of bacterial contamination on different fermentation processes
(1) Penicillin fermentation process:
Bacterial contamination will seriously affect the yield and quality of penicillin, because many bacteria can produce penicillinase, which will decompose and destroy penicillin. Therefore, bacterial contamination must be strictly controlled in the early, middle and late stages of fermentation.
(2) Nucleoside or nucleotide fermentation process:
Since the production strains used are a variety of nutritionally deficient microorganisms, their growth ability is poor and the required culture medium is rich in nutrients, they are easily contaminated by bacteria. After bacterial contamination in the early and middle stages of fermentation, the nutrients in the culture medium are rapidly consumed, which seriously inhibits the growth of production bacteria and the production of metabolites.
(3) Fermentation process of organic acids such as citric acid:
Generally, the pH value of the fermentation liquid is relatively low after acid production, and it is very difficult for bacteria to grow. Bacterial contamination is unlikely to occur in the middle and late stages of fermentation. The main thing is to prevent bacterial contamination in the early stage of fermentation.
(4) Glutamic acid fermentation:
Glutamic acid fermentation cycle is short, production bacteria reproduce quickly, and the culture medium is not too rich, so there is generally less contamination by bacteria. If the seed tank is contaminated with bacteria, it will cause great harm, so the occurrence of seed contamination should be strictly controlled. Once the seeds are found to be contaminated by bacteria, they should be discarded after sterilization, and the seed tanks, pipes, etc. should be carefully inspected and thoroughly sterilized.
2. The impact of different times of infection on fermentation
2.1. Infection during seed culture
Seed culture is mainly about growing and reproducing bacteria. The bacterial concentration is low and the culture medium is rich in nutrients, which makes it easy to be infected. Seed contamination should be strictly controlled. When seeds are found to be contaminated, they should be sterilized and discarded, and the seed tanks and pipelines should be inspected and thoroughly sterilized. The impact of infection during seed culture on fermentation is mainly reflected in the following aspects:
(1) Metabolic obstruction: If the seed culture is infected, the growth and reproduction of the production bacteria and the production of metabolites will be seriously disturbed. Miscellaneous bacteria will compete with the production bacteria for nutrients and oxygen, resulting in the obstruction of the growth of the production bacteria.
(2) Decreased seed quality: Infection will lead to a decline in seed quality, because the growth of miscellaneous bacteria will consume the nutrients in the culture medium, making it impossible for the production bacteria to obtain sufficient nutrients, thereby affecting their performance in the fermentation process.
(3) Instability of the fermentation process:
Bacterial contamination during the seed culture period will cause the fermentation process to become unstable, because the growth and reproduction of foreign bacteria will change the physical and chemical properties of the fermentation liquid, such as a decrease in pH value, rapid consumption of sugar and nitrogen, etc., which will in turn affect the metabolism of the production bacteria and the production of products.
(4) Degradation of product quality:
If bacterial contamination occurs during the seed culture period, it will have a negative impact on the quality of the product. For example, after the fermentation of filamentous fungi is contaminated, a large amount of mycelium will be autolyzed, the fermentation liquid will become sticky, and some will even smell bad. It is difficult to filter the fermentation liquid, and it is even more difficult to filter the contaminated bacteria in the early stage of fermentation, which seriously affects the extraction rate and product quality of the product.
2.2. Bacterial contamination in the early stage of fermentation
The early stage of fermentation is mainly the growth and reproduction of the bacteria, and very few metabolites are produced. At this time, it is easy to be contaminated. After contamination, foreign bacteria will multiply rapidly, competing with the production bacteria for nutrients and oxygen, seriously interfering with the growth and reproduction of the production bacteria and the production of products. It is particularly important to prevent bacterial contamination in the early stage of fermentation. When bacterial contamination occurs in the early stage of fermentation, if the consumption of nutrients is not large, it should be quickly re-sterilized, the necessary nutrients should be supplemented, and the fermentation should be re-inoculated. The impact of bacterial contamination in the early stage of fermentation on fermentation is mainly reflected in the following aspects:
(1) Enzyme activity:
Bacterial contamination in the early stage of fermentation will affect the amount of enzymes. Miscellaneous bacteria reproduce rapidly, consume nutrients in the culture medium, affect the reproduction of production bacteria, and thus reduce the amount of enzymes.
(2) Enzyme application effect:
Bacterial contamination in the early stage of fermentation will affect the application effect of enzymes. Miscellaneous bacteria will produce some metabolites, which may competitively inhibit the enzymes of production bacteria, thereby affecting the application effect of enzymes.
(3) Production sequence:
Bacterial contamination in the early stage of fermentation will affect the production sequence. After contamination, the equipment needs to be disinfected, which will affect the production progress and tank discharge plan. In addition, if miscellaneous bacteria reproduce too much, it may have a negative impact on the quality of the fermentation liquid.
2.3. Bacterial contamination in the middle stage of fermentation
Bacterial contamination in the middle stage of fermentation will seriously interfere with the metabolism of production bacteria and affect the production of products. Some bacteria produce acidic substances after reproduction, which lowers the pH value, consumes sugar and nitrogen rapidly, causes mycelium (hyphae) to autolyze, makes the fermentation liquid sticky, produces a lot of foam, and rapidly reduces or stops the accumulation of metabolic products. Some of the products that have been produced will also be utilized or destroyed, and some fermentation liquids will smell bad. The impact of bacterial contamination in the middle of fermentation on fermentation is mainly reflected in the following aspects:
(1) Interference with metabolism:
Bacterial contamination in the middle of fermentation will seriously interfere with the metabolism of production bacteria. The large amount of acid produced by bacteria causes the pH of the culture liquid to drop, which may damage the cell membrane and cell wall of the production bacteria and affect its growth and reproduction. At the same time, the consumption rate of sugar and nitrogen is accelerated, causing the fermentation liquid to become sticky, mycelium to autolyze, and product secretion to decrease or stop.
(2) Produce toxins:
Some bacteria produce toxins, which may be toxic to production bacteria and even cause fermentation failure. For example, Escherichia coli contamination may cause the culture liquid to turn black, smelly, and produce a lot of foam.
(3) Destroy products:
Sometimes bacteria use the products that have been produced to reproduce, which will destroy the structure and function of the products and cause a decrease in the quality and quantity of the products. (4) Impact on later processing: If the fermentation broth is seriously contaminated by foreign bacteria, it may have a negative impact on the later processing process. For example, excessive growth of foreign bacteria will make filtration difficult and affect the extraction and refining of the product.
2.4. Contamination in the late fermentation stage
In the late fermentation stage, the product accumulates more and nutrients such as sugar are about to be exhausted. If the amount of contamination is not too much, the fermentation can continue; if the contamination is serious and the damage is large, measures can be taken to release the tank in advance. The impact of contamination in the late fermentation stage on fermentation is mainly reflected in the following aspects:
(1) Destruction of products: In the late fermentation stage, a large amount of products, especially antibiotics, have accumulated in the fermentation broth. These antibiotics have a certain inhibitory or killing effect on foreign bacteria. If contamination occurs at this stage, it may cause the already generated products to decompose, resulting in product loss and quality degradation.
(2) Deterioration of fermentation broth quality: In the late fermentation stage, contamination will lead to a decline in the quality of the fermentation broth. The growth of foreign bacteria will consume the nutrients in the culture medium, change the pH value, and produce some metabolites. These products may have a destructive effect on the cell membrane and cell wall of the production bacteria, affecting the quality and yield of the product.
(3) Increased risk of bacterial contamination: In the later stages of fermentation, bacterial contamination may cause the fermentation liquid to stink, turn black, and produce a large amount of foam. These phenomena may increase the risk of bacterial contamination and make the fermentation process more unstable and uncontrollable.
3. Prevention and control of bacterial contamination
During the fermentation process, bacterial contamination is an issue that requires close attention. Bacterial contamination may lead to a decline in the quality of fermented products, a decrease in yield, and even the failure of the fermentation process. Therefore, prevention and control of bacterial contamination is of great significance to the fermentation industry. The following will discuss the prevention and control measures for fermentation bacterial contamination from the aspects of raw material control, sterilization, inoculation purification, equipment cleaning, process monitoring, prevention of air pollution, strain preservation and wastewater treatment.
(1) Raw material control
Raw material control is the first line of defense to prevent fermentation bacterial contamination. Qualified raw materials are the prerequisite for the smooth progress of the fermentation process. Therefore, the raw materials must be strictly screened to ensure that they do not contain foreign bacteria. At the same time, the storage and management of raw materials are also crucial. The raw material warehouse must be kept clean and dry to prevent the raw materials from being damp, moldy and contaminated. Unqualified raw materials should be handled and replaced in a timely manner. In addition, the management of raw material suppliers should be strengthened to ensure the reliability of the raw material supply chain.
(2) Sterilization
Sterilization is a key step in preventing fermentation bacterial contamination. Before fermentation begins, the culture medium, fermentation equipment, pipelines, etc. need to be thoroughly sterilized. Common sterilization methods include dry heat sterilization, moist heat sterilization, and radiation sterilization. Choosing a suitable sterilization method requires considering factors such as the properties and heat resistance of the fermentation product. At the same time, choosing a suitable disinfectant is also an important part of sterilization. The disinfectant should have broad-spectrum antibacterial properties and be able to effectively kill various bacteria. At the same time, its residual effect should also be considered. When using disinfectants, it is necessary to follow the instructions for use to ensure the effectiveness and safety of the disinfectant.
(3) Inoculation and purification
Inoculation and purification is an important part of preventing fermentation bacteria from being contaminated. Before inoculation, the strains need to be purified and screened to ensure that they do not contain bacteria. At the same time, the fermentation equipment, pipelines, etc. need to be thoroughly cleaned and disinfected to avoid the residue of bacteria. During the inoculation process, the introduction of bacteria should be avoided, such as using sterile inoculation equipment and standardized operating procedures. After inoculation, the fermentation liquid needs to be quality tested. If bacteria contamination is found, timely measures should be taken to deal with it.
(4) Equipment cleaning
Equipment cleaning is one of the important measures to prevent fermentation bacteria from being contaminated. Equipment cleaning includes cleaning, disinfection, and dust removal of the equipment surface. Cleaning equipment can remove dirt, bacteria and other debris on the surface of the equipment to prevent it from becoming a breeding ground for bacteria. At the same time, choosing the right cleaning agent and disinfectant is also key. Cleaning agents and disinfectants should have broad-spectrum antibacterial properties and be able to effectively kill various bacteria. At the same time, their residual effects and safety of use should also be considered. During the cleaning and disinfection process, attention should be paid to easily overlooked places such as dead corners and gaps in the equipment to ensure the cleaning effect of the equipment.
(5) Process monitoring
Process monitoring is an important means to prevent fermentation bacteria contamination. Process monitoring includes real-time monitoring and recording of parameters such as temperature, humidity, pressure, gas composition, and material flow during the fermentation process to promptly detect problems such as bacteria contamination. At the same time, after the fermentation is completed, the fermentation liquid needs to be tested for quality. If problems such as bacteria contamination are found, the causes should be analyzed and summarized in a timely manner, and measures should be taken to improve them.
(6) Preventing air pollution
Air is one of the important ways for bacteria to spread. In order to prevent air pollution, a series of measures need to be taken. First, the source of pollution should be controlled to avoid the use of raw materials and equipment containing bacteria. Secondly, ventilation should be strengthened to keep the fermentation workshop clean and dry to prevent humidity and dust in the air from affecting the fermentation process. In addition, air filters and other methods can be used to remove bacteria and dust in the air, thereby reducing air pollution to the fermentation process.
(7) Strain preservation
Strain preservation is one of the important measures to prevent bacterial contamination. Selecting appropriate preservation conditions and methods can extend the shelf life of the strain and prevent bacterial contamination. Commonly used preservation methods include glycerol preservation, vacuum drying preservation, liquid nitrogen preservation, etc. During the preservation process, attention should be paid to the control of parameters such as temperature, humidity, and oxygen to ensure the safety and stability of the strain. At the same time, the strain should be regularly tested for quality. If problems such as bacterial contamination are found, timely measures should be taken to deal with them.
(8) Wastewater treatment
Wastewater treatment is one of the important links in preventing bacterial contamination in the fermentation industry. Wastewater treatment should follow strict wastewater treatment standards to ensure that the discharged wastewater meets environmental protection requirements. Commonly used wastewater treatment methods include physical methods, chemical methods, and biological methods. When choosing a wastewater treatment method, factors such as the nature and composition of the wastewater need to be considered. At the same time, the selection of wastewater treatment equipment is also crucial. The equipment should be efficient, stable, and durable, and be able to effectively remove bacteria and harmful substances in the wastewater to ensure the effectiveness and reliability of wastewater treatment.
