Abstract: In this study, chemical modification was used to enhance the antioxidant properties of inulin and the relationship between the structure and antioxidant activity of the modified inulin was investigated. Phenolic-functionalized inulin derivatives were prepared by sequential bromination, nucleophilic substitution and condensation, improving the antioxidant activity of inulin by the introduction of active groups into the molecule. The antioxidant activity of the inulin derivatives in terms of reducing power, ferrous ion chelating ability, and scavenging activity toward 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl and superoxide anion radical was significantly stronger than that of inulin. The inulin derivatives with diphenol (component 3C, 3D) showed much stronger free radical scavenging capacity than those with monophenol, and had stronger DPPH radical scavenging activity than vitamin E with a half maximal inhibitory concentration (IC50) of 0.007?mg/mL. In addition, the IC50 for O2-· scavenging activity of component 3C and iron ion chelating capacity of component 3B were 0.042? and 0.006?mg/mL, respectively. Meanwhile, the possible radical scavenging mechanism was explored by studying electron or proton transfer and intermediates. The in vitro cytotoxicity test showed that the inulin derivatives had good biocompatibility. These observations will contribute to the development of inulin derivatives to be applied as antioxidants or free radical scavengers.

Key words: inulin; chemical modification; antioxidant; phenolic