Biomedical Engineering Reference
In-Depth Information
Table 11.3
Comparison of constant-temperature fermentation and
segmental heating fermentation
Constant-temperature
fermentation
Segmental heating
fermentation
Fermentation method
Glucose (%)
4:0
10.56
Crude protein (%)
19:13
19.86
Cellulose (%)
20:07
18.65
7
6
5
4
3
2
0
24
48
72
96
120
144
168
Time (h)
Fig. 11.2
pH changes in the liquid fermentation process
enzyme production. Generally, the optimum temperatures of microorganism growth
and enzyme production are inconsistent, so segmented warming can be used to
improve the yield of cellulase. Zhang et al. used segmented warming to improve
the conversion ratio of cellulose [
97
]. Table
11.3
is a comparison of constant-
temperature fermentation and segmental heating fermentation.
⑦
pH value
Any microorganism has a suitable pH range for its growth. Thus, in the early stage
and the process of culture, pH directly affects the growth of microorganisms and the
synthesis of enzyme. Further, with lignocellulosic feedstock, microorganisms can
often simultaneously generate several enzymes. Each enzyme has its own optimum
growth pH and enzyme production pH. Therefore, by regulating the culture pH at
the early stage and process of culturing, a certain kind of enzyme can be selectively
obtained. Zhang et al. investigated pH changes (Fig.
11.2
) in the process of cellulase
production with submerged fermentation. It was found that the general trend of pH
value in the fermentation process was declining. Some people think that this decline
is the result of strain self-regulation because the optimum pH of growth and enzyme
production for general microorganisms is inconsistent. For example, the optimum
growth pH value of
Trichoderma viride
is about 5.5, and the optimum pH value
of enzyme production is about 3.5. So, it is not necessary to interfere with the pH
changes. Acidic pH has two sides. On one hand, it is suitable for enzyme production.
