Biomedical Engineering Reference
In-Depth Information
of a large number of by-products, such as formic acid, acetic acid, furfural, 5-
hydroxymethyl furfural, and benzene compounds. Therefore, acid hydrolysis is
gradually being replaced by biotechnology.
1.4.1.2
Enzymatic Hydrolysis Process
Enzymatic hydrolysis has many advantages, such as mild conditions, high speci-
ficity, fewer by-products, high sugar yield, simple equipment, and no need for
corrosion-resistant materials and an acid recovery device; it is without pollution and
is suitable for miniature local production where raw material is produced. Therefore,
the study of the enzymatic hydrolysis process has aroused extensive attention and
in-depth research recently.
As early as 1850, the phenomenon of microbial decomposition of cellulose has
been observed. However, the study of cellulase gradually attracted the attention
of the world after 1906, when it was found that cellulase in the snail's digestive
juice could break down cellulose. Cellulase is a highly specific biocatalyst for the
hydrolysis of lignocellulose and a general term for a group of enzymes that degrade
lignocellulose to generate glucose. It is not a single enzyme but a multicomponent
enzyme system with synergistic effects on each other. Cellulase can be produced
by fungi, bacteria, actinomycetes, and so on. Generally, fungi are still the major
producer of cellulase, especially
Trichoderma
spp. and
Aspergillus
spp., obtained
through deep and thorough research.
Trichoderma viride
and
Aspergillus
spp.
are recognized as the most stable and nontoxic strains for cellulase production.
Cellulase can also be produced by bacteria, such as
Cytophaga
and
Cellulomonas
spp., and actinomycetes, such as
A. roseus
and
A. cellulosae
.
Bioconversion of renewable natural lignocellulose is one of the most advanced
technologies with the ability to solve such current world problems as food shortages,
energy crises, and environmental pollution because coal, oil, and other mineral raw
materials will be exhausted in a few hundred years and environmental pollution is
increasingly serious. But, the key factors to restrict the enzymatic hydrolysis of
lignocellulose include an inefficient enzymatic hydrolysis rate and higher prices
for the enzyme, resulting in higher production costs. Therefore, the focus of
saccharification conducted by the enzymatic hydrolysis method is to improve the
utilization efficiency of cellulase and reduce production costs. In searching for how
to improve the efficiency of the enzymatic hydrolysis of lignocellulose significantly,
scholars have carried out much research, mainly in the following areas:
1. Pretreatment technology before enzymatic hydrolysis: The compact structure
of lignocellulose, constructed of cellulose, hemicellulose, and lignin, hinders
the entry of the cellulase. Appropriate pretreatment technology is necessary to
enhance the accessibility of cellulase.
2. Compounds of multiple enzymes: Multiple cellulases act synergistically on the
cellulosic substrate to enhance the enzymatic hydrolysis rate by providing each
other with new accessible sites, removing obstacles to eliminate product inhibi-
