Biomedical Engineering Reference
In-Depth Information
inoculation is not necessary because seed culture is time consuming, and too much
metabolic waste affects normal fermentation.
Inoculum age is the physiological age when culture in seed pots can begin to
be planted to the next tank or fermentor. Generally, it is better to plant at a late
logarithmic growth phase. Too young an inoculum age will make offspring culture
growth slow, extending the fermentation period, but too old an inoculum age will
cause the strain to decline prematurely, leading to a decline in production capacity.
Inoculation manner has a certain influence on the formation of fermentation
products. Generally, inoculation manner includes seed liquid direct inoculation,
spore inoculation, dug lump inoculation, mycelial inoculation, or cultured cell
inoculation after centrifugal separation and washing. For aerobic bacteria, seed is
apt to be cultured by baffled reactor for inoculation. Different inoculation methods
lead to differences in nutrient consumption rate, the pH value change, the mycelium
morphology characteristic as well as product formation way [
91
]. Some studies have
shown [
92
] that, under the same fermentation conditions, the final cellulase activity
is similar regardless of the spore inoculum or mycelial inoculation. Because the
germination and growth stages are necessary for spore inoculum, the fermentation
period is long. To improve the production efficiency of enzyme, mycelia should be
inoculated appropriately.
③
Medium
The composition of the medium has a great impact on cellulase formation, which
mainly includes the following aspects:
(a)
Carbon source.
Generally, cellulose-containing material is used as a carbon
source for the fermentation of cellulase. In China, crude fiber raw materials
are usually rice straw, stover, corncob, pulp, wheat bran, furfural residue,
and so on. In the fermentation process for cellulase, a mixture of bran and
other coarse fiber is usually used as a carbon source. The effect of bran on
cellulase production includes two aspects. On the one hand, it provides the
necessary nutrient factors for enzyme production. On the other hand, the degree
of fluffiness will increase if the amount of bran is increased, reducing ventilation
in the medium, which affects cellulase production. The amount of bran added
is different for different strains.
(b)
Nitrogen source
. Nitrogen sources include inorganic nitrogen or organic nitro-
gen. There are few differences between them, and ammonium nitrate is usually
used. During the fermentation process, it is necessary to pay attention to a
reasonable ratio of carbon and nitrogen. A low carbon and nitrogen ratio in
culture will lead to excessive bacterial growth at an early stage and excessive
consumption of carbon sources. A high carbon-to-nitrogen ratio (C/N) causes
slow growth and reproduction of the strain because the nitrogen source is less
than needed for the emergence of strain.
Mao et al. investigated the effect of different carbon and nitrogen ratios on
the synthesis of xylanase enzyme with
Trichoderma reesei
Rut C-30. The results
showed that a low C/N is helpful for promoting the synthesis of endo-beta-
xylanase and inhibiting the synthesis of exo-
“
-xylosidase, selectively producing
