Biomedical Engineering Reference
In-Depth Information
Then, the second system separation is carried out. Such cellulase can be adsorbed
by fresh substrate by repeating the steps. High enzymatic hydrolysis efficiency of
cellulose is obtained this way. The minimum average amount of cellulase reaches
6 IU/g substrate, which is lower than the minimum amount of industrial standard of
cellulase used for ethanol production, 10 IU
g
1
substrate [
59
].
(5) Recovery method for the enzyme component [
55
]
①
Residues and free cellulase are used together. Residue obtained from saccharifi-
cation is separated from the liquid by centrifugation and then is used together with
free cellulose recycled from the supernatant.
②
Residue immersion liquid and free cellulose are used together. Acetic acid buffer
solution with ten times the amount of residues leaches down cellulase adsorbed on
the residue. Then, the leaching cellulase solution is used together with free cellulose
recycled from supernatant.
③
Saccharification-terminated liquid is directly recycled. Tannins are added directly
into the saccharification-terminated liquid. Supernatant (sugar) and precipitant
(containing substrate residue and a compound formed by tannins and free enzyme
or adsorption enzyme) are obtained by centrifugation. Then, PEG is added to
the precipitant. After sufficient stirring and centrifuging, the supernatant is the
recovered cellulose liquid.
11.2.6.2
Cellulase Immobilization Methods
The immobilization of cellulase enzyme includes physical and chemical methods.
The physical methods include the physical adsorption method, ionic bonding
method, and entrapment method. The advantage of immobilizing enzyme with a
physical method is that the enzyme does not participate in the chemical reaction.
So, the overall structure of the enzyme is maintained, and the catalytic activity of
the enzyme is well retained. However, because the embedding or a semipermeable
membrane have a certain spatial or steric hindrance effect, the physical method is
not suitable for some reactions. The chemical methods include the cross-linking
method and the covalent bonding method. Enzyme is chemically bonded to a natural
or synthetic polymer carrier using a coupling agent to cross-link the group on the
surface of the enzyme. Then, insoluble immobilized enzyme is formed that has a
relatively greater molecular mass. Different enzymes have different fixed strategies.
For certain enzymes, orientation may be important. For others, the environment
caused by the carrier may be important. Therefore, the optimum conditions of
immobilization for each enzyme are still specific. There is no uniform theory; the
reasons may be that there are too many mutual effect factors, and the enzyme is
composed of a protein with complex composition and spatial structure, but there is
no obvious causal link [
60
].
