Built-in electrodialysis batch culture, a new approach to release of end product inhibition

Abstract

Electrodialysis fermentation (ED-F) was carried out to study the kinetic analysis of the release of end product inhibition in l-lactate fermentation. The l-lactate was continuously extracted by a dialyzer as it was being produced, and removed from the culture system so that the l-lactate concentration in the broth was maintained at a level as low as about 10 g/ l. In spite of such a low concentration, however, the release of end product inhibition was not as great as the release level expected from the lactate concentration in the broth. In a culture with a low initial sugar concentration of 50 g/ l, the fermentation rate was not stimulated by electrodialysis, while the fermentation rate for ED-F at a high initial sugar concentration of 85 g/ l was stimulated, resulting in a reduction of the fermentation time. The reason for this contradiction was explained by computer simulation. It was assumed that the fermentation rate was regulated by the lactate concentration in the culture system, which has a concentration gradient across the cell membrane. The lactate gradient is greater in the early and the middle stages of batch culture, so the effect of dialysis did not develop at low initial sugar concentrations. The lactate gradient gradually became smaller as the fermentation proceeded, thus permitting the effect of dialysis to develop at high initial sugar concentrations. The kinetic analysis using computer simulation, and the fact that the lactate concentration calculated with kinetic data from ED-F agreed well with the lactate concentration observed, supported this assumption.