Preparation of water-soluble chitosan oligosaccharides by oxidative hydrolysis of chitosan powder with hydrogen peroxide.

Chitosan (CS) is only soluble in weak acid medium, thereby limiting its wide utilisation in the field of biomedicine, food, and agriculture. In this report, we present a method for preparing water-soluble CS oligosaccharides (COSs) at high concentration (∼10%, w/v) via the oxidative hydrolysis of CS powder with molecular weight (Mw) ∼90,000 g/mol) in 2% HO solution at ambient temperature by a two-step process, namely, the heterogeneous hydrolysis step and homogeneous hydrolysis step. The resultant COSs were characterised by gel permeation chromatography (GPC), fourier transforms infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-Vis), proton nuclear magnetic resonance spectroscopy (H NMR) and X-ray diffraction (XRD) spectroscopy. The resulting products were composed of COSs (Mw of 2000-6600 g/mol) that were completely soluble in water. The results also indicated that the structure of COSs was almost unchanged compared with the original CS unless Mw was low. Accordingly, COSs with low Mw (∼2000 g/mol) and high concentration (10%, w/v) could be effectively prepared by the oxidative hydrolysis of CS powder using hydrogen peroxide under ambient conditions.