Biomedical Engineering Reference
In-Depth Information
and seriously pollutes the environment. For this reason, Chen et al. from the Institute
of Process Engineering (IPE), Chinese Academy of Sciences (CAS), studied high-
density fermentation using hemicellulose hydrolysate from steam explosion for
SCP production to achieve the lowest energy consumption and wastewater emitted
in the cell separation process and finally achieve cleaner production [
1
]. In the
experiments,
Trichosporon cutaneum
851 strains were used as the fermentation
strain; the aqueous extract from the steam explosion of wheat straw (1.5 MPa and
10 min) was used for the medium with the addition of an appropriate amount
of N sources, S source, and other trace elements to produce SCP. The repeated
fed-batch fermentation experiment was carried out in a 2-L automatic fermentor
with mechanical mixing and a cell dry weight of 45 g
L
1
; a production rate of
h)
1
4.4 g
(L
was obtained in the experiments.
5.1.1.5
Production Instance of SCP Fermentation
(1) Yeast production using hydrolyzate of plant fiber
This technique is an indirect conversion process. The cellulose and hemicellulose
are first hydrolyzed into sugars by acid or enzyme; after that, the hydrolyzate is
used to produce SCP by yeast fermentation. Zhou et al. used sorghum straw as raw
materials that have been hydrolyzed by cellulase to produce SCP by
Saccharomyces
cerevisiae
fermentation. The fermentation process includes raw material smashing,
burdening, sterilization, enzymatic hydrolysis, and fermentation [
20
]. Although
SCP produced by fermentation of straw hydrolyzate has a higher nutritional value,
its production is difficult to industrialize because of the high cost of the process.
(2) Feed protein production from liquid fermentation using straw as the substrate
Cellulose-degrading microorganisms not only produce cellulase and hemicellulase
to degrade cellulose and hemicellulose in the growth process but also utilize
inorganic nitrogen to synthesize bacterial proteins. Therefore, the fermentation pro-
cesses of cellulose-degrading microorganisms can transform the straw into protein
feed. Wu et al. studied the production of SCP by mixed liquid culture technology
using bagasse as the only carbon resource. The results showed that hybrid strains
of
Rhizopus nigricans
and
Trichoderma
sp. showed better decomposing activities in
the mixed fermentation of
Cellulomonas
sp.,
Trichoderma
sp.,
Rhizopus nigricans,
and
Saccharomyces
sp. The crude protein content of the dry fermentation product
was 260 g
kg
1
under cultivation at 32
ı
C for 108 h using bagasse without any
treatment [
11
,
21
].
It can be found from the fermentation process discussed that when adopting
liquid fermentation, by directly using the straw as substrate and inoculating
cellulose-degrading bacteria to produce protein feed, the fermentation conditions
are easier to control and are suitable for microbial growth, and the product has a
higher nutritional value. However, liquid fermentation produces large amounts of
wastewater after harvest of the fermentation product, and the specific fermentation
