Production of low molecular weight chitosan by acid and oxidative pathways: Effect on physicochemical properties.

Abstract

Chitosan-based biomaterials with a low molecular weight (LMW) have been drawn attention due to the promising applications in the pharmaceutical and food fields. For this reason, the aim of this work was to study the effect of two distinct depolymerization pathways on the chitosan physicochemical properties. Chitosan was submitted to depolymerization reaction to obtain chitosan with low molecular weight (LMW), using the oxidative pathway (H2O2) and the acid pathway (HCl). The molecular weight reduction was investigated by kinetic study and chain scission mechanism. Chitosan characterization was performed according to its viscosimetric average molecular weight and deacetylation degree, respectively, through the viscosimetric method and proton nuclear magnetic resonance spectroscopy (1H NMR). The structural integrity was evaluated by Fourier transform infrared (FTIR) and energy dispersive spectroscopy (EDS). The crystalline and thermal properties were investigated, respectively, by X-ray diffraction (XRD) spectroscopy and thermogravimetric (TGA)/ differential thermal (DTA)/ differential scanning calorimetry (DSC) analysis. The water-chitosan interaction study was used to estimate the chitosan solubility. The results pointed out that both pathways resulted in chitosan with low molecular weight (<50 kDa). Moreover, the structural integrity of chitosan polymeric chains was preserved after depolymerization by oxidative pathway, while the acid pathway modified the polymer chain arrangement. Therefore, the chemical pathways resulted in two distinct low molecular weight chitosans, which allows different applications in food science.