Dear Purnima,

The formation of foam during a submerged fermentation can be due to the presence in your culture media of some elements such as corn steep, yeast extract etc.; These elements can promote the formation of foaming agents during your culture.

To remedy this, different techniques can be used.

- "chemical" factor such as the use of anti-foaming agents or even vegetable oil.

Be careful that all products introduced into your culture medium must be eliminated during purification and oils such as certain anti-foaming agents are viscous

- physical factor such as a device "eliminating" the foam (from experience, this device is not always effective if you use a rich medium)

Another possibility is to create a counter pressure in order to limit the foam.

I remain at your disposal for further explanations.

Dear Paladugu Purnima, foam formation in bioreactors can have several causes:

1) Biochemical: As already mentioned by Benoît Moreau, the composition of the medium plays an important role. Substrates (peptides, proteins) can influence foam formation as well as (un-)wanted products like biosurfactants. The composition of the medium cannot usually be changed, or only to a limited extent, and is therefore often not the first choice.

2) Physical: In stirred tank bioreactors, for instance, increasing the stirring rate can lead to the formation of a vortex and thus to the intake of additional air, which favours the formation of foam. In submerged aerated bioreactors, aeration itself via gassing rings/lances also promotes foam formation, with higher aeration rates leading to stronger foam formation. Optimum conditions must be found. However, antifoam agents are often added, but these can cause problems in the downstream process.

3) Bioreactor design: There are various bioreactor designs on the market, with the classic stirred tank bioreactor usually being the first choice. However, the phenomena described above occur in this type of bioreactor. Therefore, for some applications, it makes sense to use alternative bioreactor designs, such as orbital shaken bioreactors. Put simply, these are large shaking flasks with a working volume of up to 2500 litres. As there are no mechanical internals (no stirrer) and aeration takes place via the headspace, foaming is significantly reduced.

I hope this helps you!

Causes:

Mitigation Strategies

Choosing the most effective mitigation strategy depends on the specific factors contributing to foam formation in your bioreactor. It's often a combination of these approaches that provides the best results.