Biomedical Engineering Reference
In-Depth Information
On the other hand, the conversion of glucose to gluconic acid and gluconic
ketoacid in the oxygen-rich environment by
Acetobacter
spp. would reduce the yield
of cellulose. Optimizing fermentation conditions, such as pH value, temperature,
and inoculum amount; choosing a suitable source of nitrogen; supplying sufficient
oxygen and increasing the enhancing intensity of oxygen in culturing; and adding
cellulase, ethanol, agar, and other substances to the culture medium will be
advantageous in producing bacterial cellulose and increasing its yield.
7.8.3.3
Solid-State Fermentation on Inert Adsorption Carrier to Produce
Bacterial Cellulose
Solid-state fermentation on an inert adsorption carrier is a new type of solid-state
fermentation that overcomes problems in conventional solid-state fermentation such
as formation of substrate caking, low efficiency of mass transfer and heat transfer,
and substrate unevenness. Meanwhile, the high porosity of the solid carrier provides
a great interface for microbial growth so that the microorganisms can obtain the
oxygen needed for growth from outside under the conditions that a small amount
of air or oxygen or none is passed. The solid carrier provides a more conducive
environment for microbial growth and metabolism and overcomes the problem of
high energy consumption in liquid agitation aerobic fermentation, as well as the
damage by shear stress [
142
,
143
].
Chen and Weng [
144
,
145
] studied the factors that affected cellulose production
in the carrier solid-state fermentation process with
Acetobacter xylinum
using
polyurethane plastic foam as an adsorption carrier. The results showed that bacterial
cellulose production reached 4.86 g
L
1
, and the productivity of the entire volume
d
1
after 72 h at the following conditions: solid-
liquid ratio of 1:16, carrier particle size less than 1.25 cm, bed depth of 3 cm,
and initial glucose concentration of 20 g
L
1
of fermentation reached 1.62 g
L
1
. Compared with conventional liquid
static fermentation, the yield and volumetric productivity increased 5.65 times and
3.16 times, respectively. By comparing liquid fermentation and flask fermentation,
the two liquid fermentation productions of bacterial cellulose were not improved
because of a DO limitation when the initial carbon source concentration increased.
The introduction of adsorption carrier solid-state fermentation solves the problem
of the low carbon utilization rate to a certain extent, and the product is of finer
microstructure and a low degree of polymerization. But, there is no change in the
composition and structure. In addition, a pressure pulsation solid-state fermentation
device was used to further promote mass transfer to increase the product yield 7.8 %.
As a kind of polysaccharide polymer of enormous commercial prospects in
industrial production, if bacterial cellulose can be produced with biomass resources
of low cost and wide range of sources to a large-scale production, it will be
applied to act as a high-value-added bio-based material. A preliminary investigation
was conducted by Weng and Chen that studied the fermentation performance of
the enzymatic hydrolysis of steam-exploded straw with
Acetobacter xylinum
to
produce bacterial cellulose. As the enzymatic hydrolyzate of steam-exploded straw
