depicts the ethanol formation profile with different
initial cell concentrations. The maximum ethanol yield was
6.81 g ethanol/100 g sweet sorghum with initial cell concentration of 4.0× 106 cells/g raw sorghum stalks. Flask with initial
cell concentration of 2.0 × 106 cells/g raw sorghum stalks could
reach almost the same value. Lower ethanol yield was
obtained with higher initial cell concentration. This may
result from overuse of sugars for growth and maintenance at
high cell concentrations. However, it's obvious that higher
initial cell concentrations resulted in shorter fermentation
period and reduced the chance of contamination. Therefore,
cell concentration of 4.0 × 106 cells/g raw sorghum stalks was
used in the following experiments.