The influence of cyclic glucose feeding on a continuous bakers' yeast culture

Conclusions

Except for the pronounced adaptation-hysteresis effect, the pulse experiments exhibited the expected trend: deviation from the steady feed reference curve was greatest at lowest dilution rates. Under conditions of lowest glucose level the effect of pulsing would be expected to cause the largest fluctuations in glucose, causing a certain fraction of the cells to ferment. Generally over the entire dilution rate range the biomass production was decreased and the ethanol was increased by pulsing the feed stream. There is, however, some evidence that pulse feeding can trigger quite unexpected results. Point (6) at D=0.3 h⁻¹ in Fig. 1 exhibit a biomass productivity which was about 20% greater than the continuous feeding reference value (DX=3.6 kg m⁻³ h⁻¹ as compared with 3.0 kg m⁻³ h⁻¹). Such performance would be of significant commercial value, but the poor reproducibility due to adaptation, as seen here, certainly would preclude its application.

The results obtained should also be applicable to fed batch operation at the corresponding glucose level. Further experiments including the variation of the glucose feeding period would be necessary to obtain a conclusive picture. The observed phenomena are likely to occur in other fermentations and could eventually explain some of the problems existing with scale up of fermentation processes.