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FAQ
The formation of fermentation foam and the selection of defoamers?
Causes of foam generation during fermentation:
1. High aeration and strong stirring power during fermentation increase the amount of foam;
2. The microorganisms in fermentation are too active, the culture medium is rich in nutrients and has high viscosity, resulting in a lot of foam;
3. Poor sterilization quality of the culture medium destroys sugar and nitrogen, inhibiting microbial growth, causing the seed mycelium to autolyze, and producing a large amount of foam.
4. High-quality strains grow quickly, and soluble nitrogen sources are utilized rapidly, leading to an increase in the protein concentration of the fermentation broth, which enhances foam production;
5. The rupture of microbial cells in the fermentation tank leads to the release of a large amount of protein, causing continuous expansion in the liquid and the formation of numerous bubbles upon contact with air.
6. Influenced by the environment, the temperature rises rapidly during fermentation, and continuous stirring during the process leads to an increase in bubbles.
The selection of defoamers should meet the following characteristics:
1. Insoluble or poorly soluble in the foaming liquid.
To break the foam, the defoamer should concentrate and accumulate on the foam film. For breaking foam agents, they should concentrate and accumulate instantly, while for anti-foaming situations, they should maintain this state frequently. Therefore, the defoamer is in a supersaturated state in the foaming liquid, and only being insoluble or poorly soluble makes it easier to achieve a supersaturated state. Insoluble or poorly soluble substances are more likely to gather at the gas-liquid interface and concentrate on the foam film, allowing them to function effectively at lower concentrations. For defoamers used in aqueous systems, the active ingredient molecules must be strongly hydrophobic and weakly hydrophilic, with an HLB value in the range of 1.5-3 for optimal performance.
2. Surface tension lower than that of the foaming liquid.
Only when the intermolecular forces of the defoamer are small and the surface tension is lower than that of the foaming liquid can the defoamer particles penetrate and spread on the foam film. It is worth noting that the surface tension of the foaming liquid is not the same as that of the solution, but rather the surface tension of the foaming solution.
3. Certain degree of affinity with the foaming liquid.
Since the defoaming process is essentially a competition between the rate of foam collapse and the rate of foam generation, the defoamer must be able to disperse quickly in the foaming liquid to act broadly within the foaming liquid. To ensure rapid diffusion of the defoamer, the active components of the defoamer must have a certain degree of affinity with the foaming liquid. If the active components of the defoamer are too compatible with the foaming liquid, they will dissolve; if they are too incompatible, they will be difficult to disperse. Only with appropriate compatibility can the effectiveness be good.
4. No chemical reaction with the foaming liquid.
If the defoamer reacts with the foaming liquid, on one hand, the defoamer will lose its effectiveness, and on the other hand, harmful substances may be produced, affecting microbial growth.
5. Low volatility and long-lasting effect.
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