•Maleoyl xanthan and phthaloyl xanthan oligosaccharides were prepared.•Maleoyl xanthan oligosaccharides exhibited higher antioxidant activity.•It may be related to phthaloyl has stronger electron-withdrawing effect than maleoyl.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.

Two kinds of water soluble xanthan oligosaccharides (XGOS-A and XGOS-B) with similar molecular weights were prepared by oxidative degradation of xanthan gum (XG) under acidic and alkaline condition, respectively. Antioxidant activity of XGOS-A and XGOS-B was evaluated by the scavenging of superoxide anion radical (O2−), hydroxyl radical (OH), 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, hydrogen peroxide (H2O2), determination of ferrous ion chelating activity and reducing power. All the above antioxidant evaluation indicated that XGOS-A and XGOS-B exhibited good antioxidant activity in a concentration-dependent manner. The XGOS-B exhibited better antioxidant activity than XGOS-A. These results may be related to the different structure properties of XGOS-A and XGOS-B especially the different contents of pyruvate acid and reducing sugar.Highlights► Two kinds of xanthan oligosaccharides with similar molecular weights were prepared by different degradation methods. ► XGOS-B (prepared under alkaline condition) showed better antioxidant activity than XGOS-A (prepared under acidic condition). ► The antioxidant activity of xanthan oligosaccharides was influenced by the pyruvate acid content and reducing sugar content. ► The relationship of antioxidant activity and degradation method was revealed.

N-Maleoyl chitosan oligosaccharide (NMCOS) and N  -succinyl chitosan oligosaccharide (NSCOS) were prepared by acylation with maleic anhydride and succinic anhydride, respectively. Their structural changes were confirmed by Fourier-transform infrared (FT-IR) spectroscopy and their substituting degrees were determined both as 0.49 by conductometric titration. Their antioxidant activities were evaluated by scavenging superoxide anion O2·-, hydroxyl radical OH and determination of reducing power. The 50% inhibition concentrations (IC50) of NMCOS and NSCOS scavenging effect on O2·- were 2.25 and 3.27 mg/mL, respectively. The IC50 of NMCOS scavenging effect on OH was 0.24 mg/mL, however, at the same concentration determined, the value of NSCOS on OH was 30.5%. The reducing powers of NMCOS and NSCOS at the concentration of 2.40 mg/mL were determined as 0.46 and 0.41, respectively. The above results showed that NMCOS has better antioxidant activities, which may be related to the fact that maleoyl has stronger electron-withdrawing effect than succinyl.N-Maleoyl chitosan oligosaccharide (NMCOS) and N-succinyl chitosan oligosaccharide (NSCOS) with the same substituting degree of 0.49 showed different superoxide anion, hydroxyl radical scavenging activity and reducing power. The difference may be related to the fact that maleoyl has stronger electron-withdrawing effect than succinyl.