Low molecular weight chitosans -: preparation by depolymerization with Aspergillus niger pectinase, and characterization

The viscosity of a chitosan solution was rapidly lowered in the presence of pectinase from Aspergillus niger at pH 3.0 and 37 degreesC. The low molecular weight chitosans (LMWC) had a molecular weight in the range 20,000-5000 Da. Circular dichroism spectra showed a decrease in the segment of acetylated glucosamine units, whereas X-ray diffraction and CP-MAS C-13 NMR indicated higher crystallinity and polymorphism in LMWC. The latter on thermal drying resulted in structural alterations, and yielded an insoluble product. FT-IR and X-ray diffraction showed no evidence of either Schiff's base linkage or any annealed polymorph. CP-MAS C-13 NMR showed marked changes in the chain conformations of LMWC, which are believed to be responsible for its loss of solubility and functionality. (C) 2003 Elsevier Science Ltd. All rights reserved.