Experimental simulation of oxygen profiles and their influence on baker's yeast production: II. Two-fermentor system.

A reactor configuration consisting of two reactors with an exchange flow was used for the experimental simulation of large-scale conditions. The influence of fluctuations in oxygen concentration on the growth and metabolite production of baker's yeast was investigated by sparging one fermentor with air and one with nitrogen gas. It was found that the biomass yield decreased and the metabolite formation increased with rising circulation time (longer oxygen-unlimited and oxygen-limited periods). Not only was the performance of the oxygen-limited fermentor characterised by (partly) reductive metabolism, but that of the oxygen-unlimited fermentor as well. The results of the experiments in this reactor system were compared with those from the experiments carried out in a one-fermentor system with periodically changing oxygen concentrations. The formation of acetic acid, which is characteristic for transient states, showed a distinct difference between the two reactor systems.