Biomedical Engineering Reference
In-Depth Information
PEG can resolve cellulase from a cellulase-tannin complex. The amount of tannins
and PEG used is related to the protein content in the enzyme solution. Excessive
PEG to some extent would activate enzyme, which makes cellulase activity recovery
more than 100 %. Too much PEG causes phase change, thereby inactivating the
enzyme and drastically reducing the cellulase activity [
124
].
(4) Other extraction methods
①
Spray drying method
. Fermentation liquid is filtered to remove solids (mainly
bacterial cells and impurities). The obtained supernatant is spray dried at 50
ı
C.
Then, it will be milled and sieved. With spray-dried extraction, the cellulase yield
(ratio of enzyme dry powder weight to volume of enzyme solution) reaches 5.6 %,
which is higher than that obtained by the salting-out method. But, the enzyme
activity is low because the CMCase activity is 3,909 U, and the FPA activity is
306.67 U. The reason for low enzyme activity may be low purity and more slag.
The advantage of extracting the cellulase with a spray-drying method is that the
process is simple, and there is less salt [
125
].
②
Expanded bed adsorption method
. Cellulase is directly extracted from the
fermented liquid with expanded bed adsorption. The principle is that cellulase is
absorbed by an affinity effect of a porous structural analog of cellulase on cellulase.
For absorption with an expanded bed, the effect of microcrystalline cellulose is best.
Cellulase produced by
Bacillus
sp. B21 is purified by the expanded bed; as a result,
cellulase is purified 18-fold with a recovery rate of 97 %. If the expanded bed is
eluted by 1 M NaOH, it could be used more than ten times. The adsorption capacity
and recovery rate are essentially the same [
126
].
③
Aqueous two-phase extraction
. An aqueous two-phase system of PEG/(NH
4
)
2
SO
4
is used. Cellulase allocation in the PEG ammonium sulfate aqueous two-phase
system is mainly because of electrostatic interactions, hydrophobic interactions,
and a biological affinity effect. In an aqueous two-phase system, cellulase is an
amphoteric compound. There are many acid and basic groups on the surface of
cellulase, such as carboxyl acid. The concentrations of cellulase in the upper and
lower phase are different because of charge action and the various forces (e.g.,
hydrophobic bond, hydrogen bond, ionic bond, etc.) and the presence and influence
of environmental factors. When aqueous two-phase extraction system is used to
extract cellulase with PEG mass fraction 18 %, molecular weight 2000, (NH
4
)
2
SO
4
16 %, 25
ı
C, and pH 5.5, the distribution coefficient K and the extraction rate y are
8.23 and 0.947, respectively [
127
].
11.3.4
Cellulose Sugar Platform
11.3.4.1
Methods to Construct a Cellulose Sugar Platform
The sugar platform refers to the use of biomass containing an average of more
than 75 % carbohydrates. These carbohydrates are the intermediates of the sugar
