M.A.A. El-Ghaffar, M.S. Hashem / Carbohydrate Polymers 81 (2010) 507–516
515
Fig. 12. Storage stability of the free and immobilized cellulase on chitosan–GDA
(
(
1%), chitosan–l-glutamic acid–GDA (1%) and chitosan–4-aminobutyric acid–GDA
1%) via cross-linking method.
Fig. 13. Influence of repeats on the activities of the immobilized cellulase
on chitosan–GDA (1%), chitosan–l-glutamic acid–GDA (1%) and chitosan–4-
aminobutyric acid–GDA (1%), via cross-linking method.
glutamic acid–GDA (1%). Also it was observed that the temperature
profile of the immobilized enzyme was slightly broader than that
of the free one. The increase in optimum temperature was caused
by changing the physical and chemical properties of the enzyme.
The covalent bond formation, via amino groups of the immobi-
lized cellulase, might also reduce the conformational flexibility and
may result in higher activation energy for the molecule to reorga-
nize the proper conformation for binding to the substrate (Arıca,
Sinan, Yasemin, & Adil, 2001; Peng, Zhi-Kang, Ai-Fu, Jian, & Patrick,
bilized cellulase using the previous mentioned polymers, in the
present study, is higher than the previous studies (Jain & Wilkins,
1
987; Yoshimoto, Li, Fakunaga, & Nakao, 2002). These results indi-
cate that the immobilized cellulase is relatively stable without sever
lose of its activity after several repeated uses.
4. Conclusions
2
005). These results demonstrate the effectiveness of the carriers
The present study demonstrates that chitosan and its amino
in protecting the enzyme activity under high temperature condi-
tions. It can be seen from Fig. 11 that, the free cellulase lost its
all activity at 80 C, while at 100 C, the retained activities of the
immobilized cellulase on chitosan–GDA (1%), chitosan–l-glutamic
acid–GDA (1%) and chitosan–4-aminobutyric acid–GDA (1%) were:
acids condensation adducts are promising carriers for the cel-
lulase enzyme. The immobilization of cellulase on chitosan and
chitosan–amino acids adducts as a new matrix for cellulase immo-
bilization, using covalent and cross-linking methods, promoted
cellulase stability to pH, temperature, storage and reuse compared
with the free one.
◦
◦
0%, 31.47%, 76.49% and 50.64% from their original activity respec-
tively.
◦
.3.4.3. Storage stability. The storage stabilities at 4 C in the dry
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