NADH fluorscence in a carbon‐limited fermentation

The continuous flow acetone-butanol fermentation conducted at lowered inlet feed sugar concentrations and at a constant dilution rate D =0.075 h(-1) demonstrated a significant decreases in the availability of the cell population "reduction energy" (F/X), resulting in an exclusive accumulation of intermediate acids under those conditions. The cultures resumed its solvent production activity when the inlet sugar concentration in the feed stream was increased from 20 to 40 g/L at the same low growth/dilution rates. A linear correlation between the culture reduction content (F/X) and the specific butanol rate (q(B)) was observed under the present conditions, indicating the necessity of the NADH availability for the increased solvent production.