H. Zhang et Sh. Neau, In vitro degradation of chitosan by a commercial enzyme preparation: effect of molecular weight and degree of deacetylation, BIOMATERIAL, 22(12), 2001, pp. 1653-1658
A commercially available almond emulsin beta -glucosidase preparation has b
een reported to have chitobiose activity, and can hydrolyze chitin substrat
es due to a chitinase present in the enzyme preparation. This beta -glucosi
dase preparation was used to investigate hydrolytic activity on five chitos
an samples with different molecular weight and degree of deacetylation. The
degree of deacetylation and molecular weight of the chitosan samples were
determined using a circular dichroism and a viscometric method. respectivel
y. The hydrolytic activity of this beta -glucosidase preparation on chitosa
n was monitored viscometrically as the most convenient means of screening.
Solutions of chitosan in pH 5.0 acetate buffer were prepared using the diff
erent viscosity grades of chitosan. The specific viscosity, measured after
addition of beta -glucosidase to the above solutions, decreased dramaticall
y over time in comparison to that of the respective control mixture without
enzyme. Eadie-Hofstee plots established that hydrolysis of chitosan by thi
s enzyme preparation obeyed Michaelis-Menten kinetics. Apparent Michaelis-M
enten parameters and initial degradation rates were calculated and compared
to determine the influences of the degree of deacetylation and molecular w
eight on the hydrolysis. The results show that higher molecular weight and
higher degree of deacetylation chitosans possessed a lower affinity for the
enzyme and a slower degradation rate. Faster degradation rates, then, are
expected with lower molecular weight and low degree of deacetylation chitos
ans. Hydrolysis of these chitosan samples confirms the existence of a chiti
nase in the almond emulsin beta -glucosidase preparation, and further studi
es are warranted. (C) 2001 Elsevier Science Ltd. All rights reserved.