Biomedical Engineering Reference
In-Depth Information
3.4.1.4
Effect of Inhibitors and Activators on Enzymatic Hydrolysis
Cellulase can be competitively inhibited by enzymatic reaction products and certain
substances similar to substrates, such as cellobiose, glucose, and methyl cellulose,
which are usually competitive inhibitors of cellulase. Some phenol, tannin, and
anthocyanidin in plants are natural inhibitors of cellulase. Halides, heavy metals,
detergents, dyes, and so on can also inactivate cellulase. Especially in the enzymatic
process, the cellobiose and glucose produced can cause obvious feedback inhibition
on the entire reaction and reduce the efficiency of enzymatic hydrolysis.
Based on the results of years' research, it was also found that many substances
could activate cellulase, such as Mg
2C
CoCl
2
,Ca
2C
,Ca
3
(PO
4
)
2
, and neutral salts.
When the conditions for enzymatic hydrolysis were changed, some substances could
be converted between the inhibitor and activator. For example, cellobiose is the
inhibitor in most cases, but seven types of cellulase can be activated by cellobiose
when cellulase acts on CMC.
3.4.2
Cellulase Enzymolysis
There are many ways of cellulase enzymolysis, such as batch enzymolysis, consec-
utive enzymolysis, and simultaneous saccharification and fermentation. Cellulase
enzymolysis is seriously inhibited by the product. So, according to the removal of
product inhibition under various processes, cellulase enzymolysis can be divided
into two categories: The product inhibition is not completely removed but just allevi-
ated; the product inhibition is removed completely. The former mainly includes the
direct enzymatic saccharification process and a synchronous process of enzyme pro-
duction and enzymatic hydrolysis. The latter mainly includes simultaneous sacchar-
ification and a coupling process of enzymatic hydrolysis and membrane separation.
3.4.2.1
Direct Enzymatic Hydrolysis and Saccharification Technology
In an earlier period, enzymatic hydrolysis of lignocellulose used the method of
single feeding [
79
]. But, the products of reaction exhibited significant inhibition of
the entire reaction and resulted in low efficiency of enzymatic hydrolysis. Later, this
was improved using batch enzymatic hydrolysis technology, by which the substrates
were fed to the reactor in a batch. It was reported that the enzymatic hydrolysis yield
when substrates were fed in a batch was higher than that when fed once when the
concentrations of substrate and enzyme dosage were the same. When the substrate
concentration was 15 % (w/v), the hydrolysis yield of batch-fed substrates increased
by 10 %. Because of the low concentration of CB in cellulase produced by
T. reesei
,
in cellulase enzymolysis CB cannot act synergistically with C
1
and C
x
, which results
in the accumulation of cellobiose. It has a strong inhibitory effect on the cellulase
and causes the inactivation of parts of the enzyme and the decline of the hydrolysis
yield.
