3.4. Batch and fed-batch fermentations from lignocellulosic
hydrolyzates
Batch and fed-batch fermentations were performed in a 7-l bioreactor
and the pH was controlled at 6.3 with 10 M NaOH. For fedbatch
fermentation, the initial substrate was the lignocellulosic
hydrolyzates supernatant obtained in enzymatic saccharification.
But for batch fermentation, enzymatic saccharification was completed
in the 7-l bioreactor, and after that, the seed culture was
inoculated. Therefore, the solid residues after enzymatic saccharification
were retained in batch fermentation.
Results of fed-batch fermentation were shown in Fig. 5A. The
initial concentration of sugars in lignocellulosic hydrolyzates,
including glucose, cellobiose, and xylose, was about 88 g l1. After
42 h, the total sugars were less than 5 and 61.28 g l1
L-lactic acid
was produced. Then, glucose powder was fed and the resultant
concentration of glucose was 25.34 g l1. The fermentation ended
at 72 h and a total of 450 g sugars were added. The final concentration
of L-lactic acid was 75.03 g l1, the yield was 74.5%, and the
average productivity was 1.04 g l1 h1 (Fig. 5A).
The profile of batch fermentation could be divided into two distinct
phases. During the first 48 h, enzymatic saccharification was