Low-molecular-weight chitosans: Preparation and characterization

The chitosan depolymerization products prepared by enzymatic hydrolysis, oxidative reaction or microwave irradiation were characterized by FT-IR, MALDI TOF MS, solid state 13C CP/MAS NMR and GPC. Enzymatic hydrolysis resulted in two fractions of low-molecular-weight (LMW) chitosans with Mw 34 kDa (3.9 wt%) and 14.6 kDa (8.5 wt%). In the oxidative reaction at the hydrogen peroxide and acetic acid molar ratio equal to 1.7, two LMW chitosans with Mw 9 and 10 kDa (the deacetylation degree 69% and 94%, respectively) were isolated with the total yield 86 wt%. In microwave irradiation, the Mw of chitosan (175.5 kDa) decreased at most in two times. Two chitosan fractions with Mw 80 and 120 kDa (total yield 70 wt%) were obtained. In all cases, LMW chitosans served as fortifiers for chitosan oligomers, which were retained with the former through multiple hydrogen bonds. Their content in LMW chitosans was roughly 20–30 wt%.