The critical DO level was also examined for a six-blade turbine
impeller, where a medium concentration of 0.5-fold and an
agitator speed of 600 rpm were used. For DO levels of 2.5%, 5%
and 10% air saturation, all cell concentrations achieved 1.7 g/L;
on the other hand, the HA yields were 1.1, 1.3 and 1.3 g/L,
respectively. The corresponding Y
’s obtained were 0.65 and
0.76 g HA/g cell for 2.5% and 5% air saturation, respectively.
Obviously, these results are also in good agreement with those
obtained above. Fermentations with 0.5-fold medium concentration
were also performed using the gate impeller, and essentially
the same results were obtained.