Process improvement for fermentation coupling with foam separation: a convenient strategy for cell recycle

Abstract

Applications of fermentation coupling with foam separation technology show great advantages in many natural biosurfactants fermentation such as nisin, surfactin, and polymyxin E. However, only a few reports focus on process improvement, i.e. cells overflowing with foam. Because the cells also have hydrophobicity, it will overflow during foam separation, which decrease the productivity and contaminate the environment. Therefore, it is important to prevent cell from overflowing. In this study, a new approach was proposed to increase yield, using fermentation coupling with foam separation technology. Meanwhile, we tried to prevent cell from overflowing. This strategy was characterized by enrichment, recovery percentage, and inactivity percentage for product and cells. The results indicated pH was the most important factor in foam separation of polymyxin E. The optimal condition for fermentation coupling with foam separation was determined. The maximum total titer of polymyxin E reached 917 932.31 U (1147.4 U/mL) using coupling strategy that was 1.36 times more than total titer in shaken-flask culture. Additionally, the adsorption mechanism for polymyxin E and cells was studied. The results indicated polymyxin E were mainly adsorbed on bubble, while the cells were partly in liquid form and partly adsorbed on undesired protein. Undesired protein can be considered as a stabilizer in foam separation of polymyxin E.

Foam fractionation methods in aerobic fermentation processes

“… drainage effects are increased and the foam becomes dryer combined with high H / D ratios, the wall effect results in more dryer foam (D. Zhang et al, 2015)…”

“…A higher column height further results in a larger wall contact area between the rising foam and the column wall. Here, the drainage velocity of the entrapped liquid is higher between gas bubbles and the column's wall compared to the foam bulk, leading to an even dryer foam due to the wall effect (Lu et al, 2013; D. Zhang et al, 2015). However, increasing the column diameter D while maintaining the same column height would cause a decrease in the foam rising velocity, thus resulting in a higher residence time.…”

“…Additionally, the media composition has a direct effect on foaming behavior as well (Stiefelmaier et al, 2018). The applied pH value may affect both growth and metabolite synthesis, as well as the solubility and stability of the synthesized target metabolite (Liu et al, 2010; D. Zhang et al, 2015). Both are crucial parameters that highly affect foaming.…”

“…Besides the target molecule, other media components can also accumulate in the foam, entrapped in the liquid layers between gas bubbles. The most often encountered problem when integrating foam fractionation in a fermentation process is the loss of biomass due to foaming, leading to reduced specific productivity and complicated downstream processing (Alonso & Martin, 2016; D. Zhang et al, 2015). The extent of this issue depends on cell surface hydrophobicity, morphology, and size and is influenced by the media composition.…”

New Continuous Process for the Production of Lipopeptide Biosurfactants in Foam Overflowing Bioreactor

“…The addition of antifoam can also be detrimental for the analysis of the compounds of the culture medium using very sensitive analytical techniques such as NMR. Foaming culture processes coupled with foam separation were investigated for surfactant (Winterburn et al, 2011;Zhang et al, 2015) and lipopeptide production. The authors first optimized the foam overflowing rate by defining appropriate mixing and air supply conditions (Davis et al, 2001).…”