The difference in yield between fermentation in tanks and fermentation in shaker flasks is affected by a number of factors and the size of the difference varies from case to case.
Fermentation scale and spatial environment differences
Fermenters are large in size, ranging from a few cubic metres to hundreds of cubic metres. This large-scale fermentation is able to process large quantities of fermentation broth at one time, achieving a high total yield.
For example, in the industrial production of antibiotics, large fermentation tanks can hold several tonnes of fermentation medium, and by controlling the fermentation conditions in a reasonable manner, large quantities of antibiotic products can be harvested.
The environment inside the fermenter is relatively stable and can provide uniform conditions of temperature, pH, dissolved oxygen and so on. These parameters can be precisely adjusted through the stirring device, ventilation system, etc., so that the microorganisms are in a more suitable environment throughout the fermentation process, which is conducive to the growth of microorganisms and product synthesis.
For example, by adjusting the stirring speed and the amount of aeration, it is possible to ensure that the microorganisms in all parts of the fermenter have access to sufficient oxygen, thus improving the fermentation efficiency.
Shake flasks are small in size, typically ranging from tens of millilitres to several litres. This limits the size of their fermentation and the amount of product that can be obtained from each fermentation is relatively small.
For example, 250 ml or 500 ml shake flasks are commonly used in the laboratory for the initial screening of microbial metabolites, and the fermentation products obtained may be sufficient only for preliminary compositional analyses and activity assays.
The uniformity of the environment inside the shaker is relatively poor. During the shaking process of the shaker, although it can make the culture medium and microorganisms mix uniformly to a certain extent, its control precision of temperature, dissolved oxygen and other conditions is lower compared with that of the fermenter.
For example, microorganisms near the wall and in the centre of a shaker bottle may grow differently due to differences in temperature and dissolved oxygen.
Differences in oxygen supply capacity
Fermenters are usually equipped with efficient aeration systems, such as air filters and distributors. Air can enter the fermentation broth evenly through the distributor, and under the action of the stirrer, the air bubbles can be fully dispersed in the fermentation broth, so that the microorganisms can be fully exposed to oxygen.
For example, during aerobic microbial fermentation for the production of amino acids, the fermenter can be used to increase the yield of amino acids by accurately controlling the amount of aeration and the rate of agitation to maintain the level of dissolved oxygen in the optimal range required for microbial growth and product synthesis.
Some advanced fermenters also use special oxygen supply techniques, such as pure oxygen aeration and oxygen-enriched aeration, to further increase the concentration of dissolved oxygen in the fermentation broth, thereby promoting microbial growth and product synthesis.
This efficient oxygen supply can meet the oxygen demand of microorganisms in high concentration and high activity state, which helps to increase the fermentation yield.
Shaker flasks rely primarily on the shaking of the shaker to allow air to enter the fermentation liquid. When the shaker oscillates on the shaker, the liquid forms a wave-like motion inside the bottle, bringing air into contact with the surface of the liquid, thus achieving a certain degree of oxygen transfer.
However, this type of oxygen supply is relatively limited. On the one hand, the small opening of the shaker flask restricts the amount and speed of air entry; on the other hand, as the concentration of microorganisms in the fermentation broth increases and the metabolic activity is enhanced, the demand for oxygen increases rapidly, and the oxygen supply method of the shaker flask may not be able to meet the demand of the microorganisms, thus limiting the fermentation yield.
In practice, the yield of fermentation in fermenters is usually much higher than that of shaker fermentation, which may be several times, tens of times or even higher. However, the specific yield difference also needs to take into account a variety of factors such as microbial species, type of fermentation product, fermentation conditions, and so on.
In laboratory research, shake flask fermentation is commonly used for strain screening and preliminary optimisation of fermentation conditions due to its simplicity and low cost, while in industrial production, fermentation in fermenters is the main way to achieve large-scale and efficient production.
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