Biomedical Engineering Reference
In-Depth Information
Cellulase with high activity is usually obtained by batch and fed-batch fermen-
tation. Cellulase with the highest activity is obtained by fed-batch fermentation.
Fed-batch fermentation has been increasingly widely used in industrial production
and scientific research. Fed-batch fermentation can avoid the inhibition of high
substrate concentration or catabolic repression. The highest strain concentration
and maximum yield per unit volume could be achieved, leading to low cost of the
downstream extraction [
89
].
Yong et al. [
90
] prepared cellulase with
Trichoderma reesei
by fed-batch
fermentation using pulp as a carbon source. In a 10-L fermentor, cellulase was
produced by batch fermentation. The concentration of the carbon source in the
medium was 15 g
L
1
. Filter paper activity, cellobiose enzyme activity, enzyme
production rate, and enzyme yield were 2.15 FPIU
mL
1
,0.20IU
mL
1
, 16.3
h)
1
, and 143.3 FPIU
g
1
, respectively. If carbon source concentration
FPIU
(L
L
1
by adding the carbon source with a batch method,
filter paper enzyme activity, cellobiose enzyme activity, enzyme production rate, and
enzyme yield were 3.90 FPIU
was increased to 27.5 g
mL
1
,0.35IU
mL
1
, 23.2 FPIU
h)
1
, and 141.8
(L
g
1
, respectively. Studies revealed that by fed-batch fermentation technology,
enzyme activity and enzyme production rate were enhanced with the increase of
carbon source in the culture medium. Enzyme yield remained the same. So, the cost
of cellulase production was reduced.
FPIU
(2) Research on liquid fermentation process factors
In the process of liquid fermentation for cellulase, the main factors affecting
fermentation yield and efficiency include medium ratio, fermentation temperature,
fermentation pH, stirring speed and foam, and other factors in addition to the
bacteria. Different strains have different fermentation requirements. Several major
factors affecting the production of cellulase are discussed next.
①
Strains
During fermentation, the speed of strain growth and the amount of product synthesis
depend largely on the quality of the strain. Generally, an enzyme-producing strain
must comply with the following conditions: First, it is not a pathogen. Second, it is
able to use cheap raw materials with a short fermentation period and high enzyme
yield. Third, it hardly mutates and degrades and is not easily infected with phage.
Fourth, it is better to produce extracellular enzymes, which are helpful for separating
enzymes with a high recovery rate. In addition, if enzyme is used for medicine and
food, safety issues should be considered.
②
Inoculum size, inoculum age, and inoculation manner
An appropriate inoculum size has a great impact on the production of enzymes.
Usually, the fermentation inoculation amounts are as follows: 1-5 % for bacteria, 5-
10 % for yeast, and 7-15 % and sometimes 20-25 % for mold. When the inoculation
amount is too low, the activity of the enzyme is not high, and the production
cycle is extended. When the inoculum amount is high, microorganisms immediately
enter the logarithmic growth phase, so the cellulase synthesis is advanced, and the
opportunities for the growth of various bacteria can be reduced. However, excessive
