Preparation and antioxidant activity of xanthan oligosaccharides derivatives with similar substituting degrees

Maleoyl xanthan oligosaccharides (XGOSMAs) and phthaloyl xanthan oligosaccharides (XGOSPAs) were prepared by reacting xanthan oligosaccharides with maleic anhydride and phthalic anhydride, respectively. The substituting degrees (DSs) of XGOSMAs and XGOSPAs were determined by a neutralization reaction. XGOAMA-1 (DS=0.30), XGOSPA (DS=0.31), XGOSMA-2 (DS=0.62) and XGOSPA-2 (DS=0.60) were selected for structural characterization and antioxidant activity evaluation. Their structural changes were confirmed by Fourier transform infrared spectra (FT-IR), and their molecular weights were determined with a gel permeation chromatography method (GPC). The pyruvate acid and reducing sugar contents were determined by ultraviolet spectrophotometry and the dinitrosalicylic acid method. The antioxidant activity was evaluated by the scavenging of the superoxide anion radical (O2(-)), hydroxyl radical (OH), 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and determination of reducing power. The results indicated that XGOSPA exhibited higher antioxidant activity than XGOSMA with similar substituting degrees in all the above mentioned antioxidant evaluation systems, which may be related to the fact that phthaloyl group has a stronger electron-withdrawing effect than the maleoyl group.