Fuels and Chemicals from Hemicellulose Sugars - Biotechnology in China: Biofuels and Bioenergy - page 206

Table 4 Characteristics of the most relevant microorganisms considered for ethanol production
from hemicelluloses (adapted from [ 14 ])
Characteristics Microorganism

E. coli Z. mobilis S. cerevisiae P. stipitis

D-Glucose fermentation + + + +

Other hexose utilization
(D-galactose andD-mannose)

+ - + +

Pentose utilization
(D-xylose andL-arabinose)

+ - - +

Direct hemicellulose utilization - - - w

Anaerobic fermentation + + + -

Mixed-product formation + w w w

High ethanol productivity
(from glucose)

- + + w

Ethanol tolerance w w + w

Tolerance to lignocellulose-derived inhibitors w w + w

Osmotolerance - - + w

Acidic pH range - - + w

GRAS microorganism - + + +

+ Positive, - negative, w weak, GRAS generally recognized as safe

then using the pentose-rich hydrolyzate as substrate for ethanol production by cells
of recombinant S. cerevisiae immobilized by Ca-alginate. An ethanol concentra-
tion of 31.1 g/L and a corresponding ethanol yield on fermentable sugars of 0.406
g/g were obtained within 72 h in batch fermentation of the detoxified hydrolyzate
with immobilized cells. Sugarcane bagasse, the most abundant agricultural
material in southern China, was recently used as a substrate for production of
ethanol using P. tannophilus [ 34 ]. The detoxification of the sugarcane bagasse
hemicellulose hydrolyzate used electrodialysis, which decreased the loss of sugar
and increased acetic acid removal, leading to better fermentability. A batch culture
with electrodialytically pretreated hydrolyzate as substrate was developed, giving
21 g/L ethanol with a yield of 0.35 g/g sugar and productivity of 0.59 g/(L h). Chen
et al. [ 37 ] performed a laboratory xylose/cellulose fractionation and separate
fermentation (XCFSF) process for ethanol production. Three xylose/cellulose
fractionation strategies, dilute sulfuric acid hydrolysis and detoxification, lime
pretreatment and xylanase hydrolysis, bio-treatment with Phanerochaete
chrysosporium and xylanase hydrolysis, were applied to corn cobs. The xylose was
dissolved in acid and the enzymatic hydrolyzates was fermented to ethanol by
C. shahatae, while the cellulose remaining in solid residues was converted
to ethanol by simultaneous saccharification and fermentation with S. cerevisiae.
Finally, using the three fractionation methods, 70.40, 52.87, and 39.22% of
hemicellulose and 89.77, 84.30, and 71.90% of cellulose in corn cobs were
converted to ethanol, respectively.