What are the abnormal phenomena in fermentation production? (Poor cell growth, abnormal pH value, abnormal dissolved oxygen level, abnormal foam, etc.)
Poor bacterial growth
Poor seed quality: Seeds may lack vitality, such as prolonged storage time or improper storage conditions, leading to a decrease in seed cell activity and affecting their germination and growth rate in fermentation media;
Or the seed purity may be insufficient, containing miscellaneous bacteria or other impurities, which compete with the target strain for nutrients and growth space during the early stages of fermentation, inhibiting the normal growth of the target strain.
Poor fermentation performance of bacterial strains:
The strain itself may have genetic defects or variations that prevent it from efficiently utilizing nutrients for growth and metabolism during the fermentation process;
Or the strain may have poor adaptability to the fermentation environment, such as a narrow tolerance range to environmental conditions such as temperature, pH, and dissolved oxygen, and may not grow normally when there are slight fluctuations in fermentation conditions.
Poor environmental conditions:
Improper temperature control during fermentation can affect the activity of microbial enzymes, thereby affecting the metabolic rate and growth rate of bacterial cells;
Inappropriate pH value may lead to an imbalance of acid-base balance within microbial cells, affecting the normal progress of various biochemical reactions within the cells; Insufficient dissolved oxygen can limit the respiration of aerobic microorganisms, thereby inhibiting bacterial growth.
Insufficient inoculation amount: Insufficient inoculation amount can slow down the growth of bacterial cells in the early stages of fermentation, as the number of available bacterial cells is limited in the initial stage, requiring a long time to adapt to the new environment and reproduce to a sufficient quantity to achieve normal growth rate.
During this period, it is susceptible to contamination from other microorganisms or interference from environmental factors.
PH value too high or too low
Imbalance in nutrient metabolism: During the fermentation process, microorganisms can produce acidic or alkaline substances by metabolizing nutrients such as carbon and nitrogen sources.
For example, when microorganisms extensively utilize nitrogen-containing compounds, they may produce alkaline substances such as ammonia, leading to an increase in pH value;
When organic acids (such as lactic acid, acetic acid, etc.) accumulate from carbon source metabolism, the pH value will decrease. If this metabolic imbalance persists, it will cause abnormal pH values.
Effect of ventilation volume:
Excessive or insufficient ventilation may affect the pH value. When the ventilation rate is too high, carbon dioxide in the fermentation broth is excessively discharged, resulting in a decrease in the carbonate content and an increase in the pH value of the fermentation broth;
When the ventilation rate is too low, microorganisms may engage in anaerobic respiration, producing more acidic metabolites and lowering the pH value.
Abnormal dissolved oxygen levels (taking glutamic acid fermentation as an example)
In the early stage of fermentation, the dissolved oxygen remains basically unchanged: In the early stage of fermentation, the bacterial cells have just been introduced into the fermentation tank and are in the stage of adapting to the new environment.
At this time, the metabolic activity of the bacterial cells is relatively weak, and the demand for oxygen is relatively low, so the dissolved oxygen concentration remains basically stable.
During the logarithmic growth phase, dissolved oxygen decreases and maintains a certain level:
As the bacterial cells gradually adapt to the environment and enter the logarithmic growth phase, they grow rapidly, the number of cells increases significantly, metabolic activity is vigorous, and the consumption of oxygen increases sharply, leading to a rapid decrease in dissolved oxygen concentration.
When the oxygen supply rate of the fermentation system reaches equilibrium with the oxygen consumption rate of the bacterial cells, the dissolved oxygen concentration will be maintained at a relatively stable level.
In the later stage of fermentation, dissolved oxygen rises again:
In the late stage of fermentation, the growth of bacterial cells gradually enters the aging stage, with decreased cell vitality, slowed metabolic rate, and reduced demand for oxygen.
At this time, the oxygen supply rate of the fermentation system remains relatively unchanged, so the dissolved oxygen concentration will rise again.
Too much foam, poor growth and slow metabolism:
When the growth of bacteria is poor and the metabolism is slow, it may lead to the accumulation or imbalance of some substances in the fermentation liquid, thus changing the physical and chemical properties of the fermentation liquid, making it easier to produce foam.
For example, the poor growth of bacteria may change the concentration and properties of colloidal substances such as proteins in the fermentation broth, and increase the stability of foam.
There are many protein colloidal substances:
The fermentation broth contains more protein, polypeptide and other colloidal substances, which have surface activity, can reduce the surface tension of the liquid, and is easy to form foam in the fermentation process.
Moreover, these colloidal substances may be adsorbed on the surface of bubbles to form a stable foam layer, making foam not easy to break.
Improper sterilization of culture medium:
When sterilizing the culture medium, if the temperature is too high or the time is too long, it will cause chemical reactions of glucose and other components, producing substances such as amino sugars.
Amino sugar has certain surface activity, which can increase the foam property of fermentation liquid, and may also inhibit the growth of bacteria, further affecting the normal process of fermentation.
