Biomedical Engineering Reference
In-Depth Information
In 1945, Leonard and Hajny adjusted the pH from 9 to 10 with Ca(OH)
2
and then
adjusted it back to 5.5 with H
2
SO
4
. The hydrolysate with pH adjusted with Ca(OH)
2
had a better fermentation performance than that of NaOH. The reason may be that
the former has a precipitation effect [
84
] for inhibiting substances.
②
Associated method with sulfite and excess alkali
Larsson et al. [
85
] used sodium sulfite to treat the dilute acid hydrolysis product of
handle fir. The concentrations of furfural and HMF were effectively reduced. It was
confirmed by experiment that an associated method with sulfite and excess alkali
was effective for treating hemicellulose hydrolysate of willow for fermentation with
E. coli
[
86
]. After 40 h fermentation, only 24 % of the xylose was consumed.
However, if the hydrolysate was treated only with excess alkali, xylose would be
completely consumed. Compared to treating only with excessive alkali, if 0.1 %
sulfite was added to the hydrolysate and heated at 90
ı
C for 30 min, the fermentation
time would shorten by 30 %.
As weak acids, furan derivatives and benzene-based compounds inhibit the
fermentation of cellulose hydrolysis products; the interactive negative effect would
enhance the inhibition effect [
87
]. If benzene compounds are removed by laccase,
inhibition could reduced significantly [
75
], suggesting that benzene compounds are
major inhibitory substances in the process of cellulose hydrolysate fermentation.
The inhibitor removal methods mentioned are detoxing methods before fermen-
tation. Another favorable method is to breed highly resistant strains and improve
internal tolerance. The inhibitory influence is reduced or eliminated by controlling
external factors through the fermentation process. High-resistance strains mainly are
bred by evolutionary engineering and genetic engineering [
88
].
11.3.3
Cellulase Production with Fermentation
and Its Isolation Methods
Since Seillieve discovered cellulase that hydrolyzes cellulose in the digestive juices
of the snail in 1906, cellulase has received much research and discussion. In the
1970s, the United States, Japan, West Germany, and other developed countries
produced cellulase industrially. In the 1970s, China began to research cellulase and
to apply it in alcohol, white wine, soy sauce, and other industries. However, the
expensive price of cellulase limits its application in industrial production. Therefore,
breeding of strains with high cellulase activity has become a critical factor.
Cellulase is a collective name for a class of enzymes that degrade the
-1,4-
glucoside bond. According to the different functions, cellulase can be divided into
three categories: endoglucanase, exoglucanase, and
“
-glucosidase. Many microor-
ganisms produce cellulase, and the enzyme that is most suitable for cellulose
hydrolysis is from wood-rot fungus,
Trichoderma
. The cellulase production methods
mainly include solid-state fermentation and deep liquid fermentation, and the
isolation methods mainly include salting-out method, organic solvent method, and
tannin extraction method.
“
