Biotechnological Applications of Hemicellulosic Derived Sugars: State-of-the-Art - Sustainable Biotechnology: Sources of Renewable Energy - page 81

production, and they present the most challenges to maintaining a constant rate of
2, 3-BD formation during the entire course of the fermentation reaction.
3.4 Other Products
Besides ethanol, xylitol, and 2, 3-BD, other industrially significant products such
as lactic acid, itaconic acid, and single cell protein (SCP) can be manufactured
using hemicellulose sugars. These products have wide applications in the food,
feed, pharmaceutical, and cosmetics industries. Garde et al. [59]. reported lac-
tic acid production from wet-oxidized wheat straw by Lactobacillus brevis and
L. pentosus. Sugar cane bagasse hemicellulosic hydrolysate was converted into lac-
tic acid by thermotolerant acidophilic Bacillus sp. in a simultaneous saccharification
and fermentation approach [60].
SCP production from hemicellulose is another cutting-edge area in hemicellu-
lose biotechnology. Microorganism Candida blankii UOVS-64.2 was employed for
SCP production from hemicellulose hydrolysates, and was increased by intraspe-
cific protoplast fusion of auxotrophic mutants produced by UV irradiation followed
by nystatin enrichment [61]. Pessoa et al. [62] showed microbial protein produc-
tion from sugar cane bagasse hemicellulosic hydrolysate using Candida tropicalis
IZ 1824 with a net cell mass of 11.8 g L -1 and a yield coefficient (Y x/s )of0.50gg -1 .
4 Expert Commentary and Five-Year View
The current shortages and high prices of gasoline products are making it clear
that a sustainable, economical, and environmentally benign process for producing
fuel is needed. In the future, lignocellulosic-derived products are poised for sharp
growth. According to a recent McKinsey report, the bio-based products market is
expected to exceed $182.91 billion by 2015 [34]. Lignocellulosic-derived products
may play a pivotal role to match this expectation and future markets seem very
promising for ethanol, xylitol, organic acids, and 2, 3-BD. Mechanisms for higher
yield and productivity of these value-added products can be developed by exploring
the hemicellulose fraction of the cell wall in depth.
The fermentation of pentose sugars is not as easy as that of cellulosic-derived
hexose sugars due to the unavailability of appropriate microorganisms and the
lack of an established bioconversion process. In-depth studies of methods for
hemicellulosic degradation are required. This will assist in limiting the role of fer-
mentation inhibitors during hemicellulosic degradation. In the past five years, there
has been substantial development in the area of hemicellulose hydrolysis using rou-
tine methodologies with known microorganisms. A newer approach to hydrolyzing
technologies using a battery of hemicellulase titers needs to be developed to pro-
duce high yields of sugar monomers and eventually convert them into value-added
products. Isolation and screening of potent hemicellulase-producing microorgan-
isms and further development of mutants/cloned microorganisms may improve the