Fuels and Chemicals from Hemicellulose Sugars - Biotechnology in China: Biofuels and Bioenergy - page 216

neutralization combined with activated carbon adsorption after dilute acid
hydrolysis. The final succinic acid yield was greater than 72% with the detoxified
hydrolyzate as the carbon source in anaerobic culture. Yu et al. [ 139 ] developed a
process for succinic acid production from corncob hydrolyzate by A. succinogenes
without detoxification, involving medium optimization, selecting yeast extract as
the nitrogen source, and MgCO 3 as the neutralization agent. A total of 23.64 g/L
succinic acid with a yield of 0.58 g/g could be obtained.
In summary, apart from the above three organic acids, other organic acids such
as itaconic acid, xylonic acid, etc. can also be obtained from hemicellulose sugars
[ 140 , 141 ]. However, to improve the utilization efficiency of hemicellulose sugars,
apart from the measures traditionally used such as process development of raw
material pretreatment, strain improvement, and fermentation optimization, future
research focus should be placed on elucidating the mechanism of metabolism of
different sugars which exist in the hemicellulose hydrolyzates. In addition, the
strain tolerance of inhibitors should be enhanced based on the analysis of the strain
response mechanisms.
3.5 Others
Besides the fuels and chemicals mentioned above, hemicellulose sugars can be
converted to other industrially significant products such as single cell protein
(SCP), furfural, methane gas, etc.
Qu et al. [ 142 ] extracted steam-exploded cellulosic biomass with hot water and
obtained a liquor containing 16.0-47.7 g/L of total sugar. This is known as steam-
exploded hemicellulose autohydrolyzate liquor (SEHAL). A mutant yeast
Trichosporon cutaneum capable of direct utilization of oligomers of xylose was
then used to produce SCP from SEHAL. This mutant can grow quickly in the
medium with an increased protein content of 47.0%. By continuous fermentation
with a dilution rate of 0.33 h -1 , a cell concentration of 10.5 g/L, a cell mass yield
of 0.72 g/g total sugar, and a cell productivity of 3.0 g/(L h) were obtained. Chen
et al. [ 143 ] obtained a total hemicellulose sugar concentration of 87.6 g/L through
optimizing the sugar leaching process for steam-exploded straw. By using a
repeated fed-batch fermentation strategy, a biomass concentration of 45.0 g/L and
a productivity of 4.4 g/(L h) were obtained. Finally, SCP was separated from the
broth by spray drying. In a more recent study, high enzyme activity of cellulase
and SCP were co-produced from steam-exploded cornstalk using a mixed fer-
mentation by Trichoderma reesei and C. tropicalis. In this strategy, the hemicel-
lulose and cellulose fractions were both used sufficiently [ 144 ]. Similarly, corn
stalk pretreated with diluted sulfuric acid was degraded with Trichoderma sp., and
then converted successfully to SCP using the same yeast [ 145 ]. The co-fermen-
tation by Trichoderma sp. and yeast degraded 70% of the total cornstalks and 60%
of the cellulose content. This is an efficient and low-cost method for converting