Low molecular weight chitosans—preparation by depolymerization with Aspergillus niger pectinase, and characterization Original Research Article

The viscosity of a chitosan solution was rapidly lowered in the presence of pectinase from Aspergillus niger at pH 3.0 and 37 °C. 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 13C 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 Schiffʹs base linkage or any annealed polymorph. CP-MAS 13C NMR showed marked changes in the chain conformations of LMWC, which are believed to be responsible for its loss of solubility and functionality.