Biomedical Engineering Reference
In-Depth Information
45-50
ı
C and about pH 4.8. Cellulase is not a single substance; it consists of three
main components: endoglucanase, exoglucanase, and
“
-glucanase. Endoglucanase
cuts the
-1,4-glycosidic bonds randomly, making cellulose have long strand
breaks. Broken molecular chains still have a reducing end and a nonreducing end.
Exoglucanase has two components: hydrolyze and cellobiose from the reducing end
of the cellulose long chain.
“
-Glucanase decomposes cellobiose and short-chain
oligosaccharides into glucose. The enzymatic hydrolysis can be carried out at room
temperature and under atmospheric pressure. The culture and maintenance of the
microorganisms and maintenance only require fewer raw materials, reducing the
energy consumption of process. Cellulase has a high selectivity and generates a
single product, so a high sugar yield can be obtained (
“
95 %).
Cellulase requires arriving at a molecule to degrade cellulose; therefore, ligno-
celluloses should be pretreated to remove hemicelluloses or lignin and to destroy
the crystalline structure of cellulose. Acid hydrolysis and enzymatic hydrolysis
are usually combined. Acid hydrolysis is used to pretreat cellulose to facilitate
enzymatic hydrolysis.
>
11.3.4.2
Sugar Platform Components and Content
When solid residue insufficiently reacted was removed, liquid product rich in
monosaccharides and soluble oligosaccharides could be obtained. It is necessary
to qualitatively and quantitatively analyze the liquid products and solid residues
and to investigate the application of product and the process and mechanism of
reaction. Sugar products could be analyzed by determining the reducing sugar or
hydrolyzing subsequent residues with acid quantitatively into monosaccharides.
The monosaccharides include glucose, xylose, arabinose, mannose, galactose,
rhamnose, and other soluble sugars. In the liquid product of hydrolysis, soluble
sugar is only part of the whole. Xylooligosaccharides from hemicellulose hydrolysis
and oligomeric gluconate from cellulose hydrolysis are also main components of
the liquid product. The health protective effects of these two types of sugar have
gradually attracted attention.
(1) Determination of reducing sugar content
The DNS standard method is used for determination of the reducing sugar content;
the method was introduced in Sect.
11.1
.
(2) Qualitative and quantitative analysis of monosaccharides
Generally, chromatographic methods for qualitative and quantitative measurement
of monosaccharides include paper chromatography, thin-layer chromatography
(TLC), GC, and HPLC.
Chang et al. [
133
] proposed determination of the content of monosaccharides
(glucose, fructose, and xylose) in the liquid mixed sugar obtained by hydrolyzing
cellulosic material with a TLC determination method. Silica gel G was taken as the
solid adsorbent, and glass was used as supports to make TLC plates. For eluent, the
ratio of
n
-butanol, 37 % acetic acid, and water (volume ratio) was 3:2:2. The pH of
