Biomedical Engineering Reference
In-Depth Information
In batch enzymatic process, enzymatic speed increases logarithmically at first,
followed by the rapid increase of soluble sugar yield; then, the degradation of
cellulose decreases stably. The data reflecting that initial enzymatic reaction kinetics
trend coincide with the classic Michaelis-Menten equation model. Study showed
that, in the early stage of a fast reaction, enzyme adsorption and mass transfer
rates do not influence the reaction rate. The active binding sites of enzyme on
the substrate almost remain constant, ensuring a high substrate-to-enzyme-ratio.
However, this model is not suitable for the later stage of enzymatic hydrolysis
because it ignores the inhibition of enzyme, the change of cellulosic structure, and
the dynamic changes of interaction between enzyme and substrate interface.
Many enzymatic kinetics models have been proposed, but most are for a specific
enzymatic system or a certain enzymatic system and will not be suitable if the
substrate or enzymes change. This is because the reaction kinetics of enzymatic
hydrolysis are influenced by many interrelated factors, making it difficult to quantify
each individual factor.
3.4
Cellulose Enzymatic Hydrolysis and Saccharification
Along with economy development, population growth, and increasing energy
consumption, lignocellulose as the most abundant and cheapest renewable resource
on Earth has received considerable attention. However, because of the complex
structure of the cellulosic biomass, its chemical properties and mechanical prop-
erties are relatively stable. Generally, it is extremely difficult to dissolve in solvent,
and can be utilized further only when it is hydrolyzed into monosaccharides.
The enzymatic saccharification of cellulose has many advantages, such as
mild conditions, simple equipment, low energy consumption, and less pollution.
However, the industrial applications of enzymatic hydrolysis and saccharification
of cellulose are limited because of the expense of enzyme preparation, the slower
rate of hydrolysis, lack of an effective response system to meet the complex
heterogeneous interface catalytic reaction, and so on.
3.4.1
Factors Affecting Cellulose Enzymatic Hydrolysis
The main factors affecting cellulase include substrates, enzyme activity, and
reaction conditions (temperature, pH, and other operating conditions). To improve
enzymolysis efficiency and yield, much research has been performed to optimize
the hydrolysis conditions and improve enzymatic activity.
