Effects of ascorbate and hydroxyl radical degradations on the structural, physicochemical, antioxidant and film forming properties of chitosan

In this study, chitosan (CS) was degraded by ascorbate radical (Asc^•-) and hydroxyl radical (^•OH), respectively. The structural, physicochemical, antioxidant and film forming properties of Asc^•- and ^•OH degraded CS were compared for the first time. Results showed the structure and physicochemical property of Asc^•- degraded CS were significantly different from those of CS. Asc^•- had a deamination effect on CS with the formation of several unsaturated bonds. Accordingly, Asc^•- degraded CS showed decreased crystallinity and thermal stability as well as a planar morphology. By contrast, OH degraded CS showed similar structure, crystallinity and thermal stability to CS. However, OH had an erosion effect on CS with the formation of many cavities inside. Antioxidant assay further demonstrated that the in vitro antioxidant activity of CS was improved by Asc^•- and OH degradations. Moreover, film forming property of CS was also altered by Asc^•- and OH degradations. Asc^•- and OH degraded CS films showed higher thicknesses, UV-vis light barrier property and water vapor permeability than CS film. Besides, Asc^•- degraded CS film had better mechanical properties than CS and OH degraded CS films. Therefore, Asc^•- degradation could be a useful approach to improve the antioxidant and film forming properties of CS.