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M. R. KASAAI, Department of Food Science and Nutrition, Laval University, Faculty of Agriculture and Food Sciences, Pavillon Comtois, Sainte-Foy, Quebec, QC G1K 7P4, Canada and J. Arul.

Chitosan is a copolymer of glucosamine and N-acetylated glucosamine. Its polycationic nature is unique among polysaccharides, and it confers to it diverse biological properties such as antimicrobial activity, elicitation of plant defense reactions, wound-healing property, and cholesterol-lowering effect. The effectiveness of chitosan appears to be dependent on its molecular weight in various applications. Development of an efficient process for reduction in molecular size of chitosan without altering its chemical structure is desirable.

The objective was to investigate the possibility of fragmentation of chitosan in an aqueous solution by microfluidization and to evaluate molecular weight, molecular weight distribution, and the structure of the resultant fragments.

Microfluidization was performed under different conditions of interaction chamber pressure and number of passes. The effect of concentration and initial molecular weight of chitosan was also examined. Degree of fragmentation was followed by viscometry and size-exclusion chromatography. The chemical structure of chitosan and its fragments was examined by elemental analysis and 1H NMR spectroscopy.

The effect of interaction chamber pressure on chain scission was linear and appears to be the dominant factor, more than the number of passes in the fragmentation process. Chain scission increased with an increase in initial molecular weight of chitosan and a decrease in chitosan concentration. Molecular weight distribution of the fragments was narrower than that of the original polymer. The degree of acetylation of fragments increased in 0.1 M CH₃COOH as the aqueous solvent but not in 0.04 M HCl.

The results suggest that at any given pressure, the molecular weight of chitosan reaches a limiting value beyond which no degradation occurs, and that larger macromolecules were more susceptible to fragmentation. This method is useful for reduction of solution viscosity and partial degradation of high polymer.