Fuels and Chemicals from Hemicellulose Sugars - Biotechnology in China: Biofuels and Bioenergy - page 207

Table 5 Microbial production of xylitol using different hemicellulosic substrates
Raw material Strain Xylitol

yield
(g/g) a

Xylitol
productivity (g/
(L h))

Reference

Brewer's spent grain
hemicellulose hydrolyzate

Candida guilliermondii 0.73 0.52 [ 47 ]

Eucalyptus globulus wood
hemicellulose hydrolyzate

Debaryomyces hansenii 0.84 0.53 [ 50 ]

Hardwood hemicellulose
hydrolyzate

Pachysolen tannophilus 0.63 0.41 [ 51 ]

Glucose-xylose mixtures Escherichia coli

(recombinant)

0.63 - [ 53 ]

Glucose-xylose mixtures Saccharomyces

cerevisiae
(recombinant)

0.95 0.40 [ 54 ]

Glucose-xylose mixtures Corynebacterium

glutamicum
(recombinant)

- 7.90 [ 55 ]

Corncob hemicellulose
hydrolyzate

Candida tropicalis 0.70 0.95 [ 58 ]

a

Means g xylitol per g xylose

3.2 Xylitol

Xylitol, a naturally occurring five-carbon sugar alcohol, has attracted worldwide
interest because of its unique properties and huge potential. Xylitol has important
applications in pharmaceuticals and food industries due to its high sweetening
properties, lower energy value, non- and anti-carcinogenicity property, and
microbial growth inhibition capacity [ 41 ]. Xylitol has been used as a sugar sub-
stitute in dietary foods, especially those for insulin-deficiency diabetics. Due to its
anti-carcinogenicity, pleasant taste, and no unpleasant aftertaste, xylitol has been
widely applied in the dental industry.
Xylitol can be produced by either chemical synthesis or fermentation. Indus-
trially, it is produced by catalytic hydrogenation of xylose under high temperature
and high pressure conditions. Compared with traditional chemical synthesis, the
microbial fermentation process is easier to control, and also the in-vitro enzyme-
based conversion has higher selectivity [ 42 ]. With the increase of interest in
exploring more environment-friendly and economic xylitol production methods,
the biosynthesis of xylitol by microorganisms is becoming increasingly popular.
Many studies have investigated the use of the hemicellulose portion of agri-
cultural residues like corn stover [ 43 ], rice straw [ 44 ], sugarcane bagasse [ 45 ],
eucalyptus [ 46 ], spent grain [ 47 ], and corncob [ 48 ] for xylitol production. Among
the various agricultural crop residues, corncob is one of the most abundant feed-
stocks for xylitol production in China. Xylose can be converted to xylitol by
several microorganisms including Candida guilliermondii [ 47 , 49 ], Debaryomyces