In vitro degradation of chitosan by a commercial enzyme preparation: effect of molecular weight and degree of deacetylation

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.