Abstract: N-phthaloyl chitosan oligosaccharides (NPCOSA, NPCOSB and NPCOSC), having various degrees of substitution (DS were 0.33, 0.55 and 0.65, respectively), were prepared by chemical modification of chitosan oligosaccharide. The chemical structures of the chitosan oligosaccharides derivatives were characterized by FTIR. Their antioxidant activities were evaluated by the scavenging of superoxide anion radicals(O2.–), hydroxyl radical (.OH), DPPH radical and for reducing power. The results indicated that all the N-phthaloyl chitosan oligosaccharides showed lower antioxidant activity than chitosan oligosaccharides, the scavenging effect on O2.– increased with the increasing of DS, and their scavenging effect on DPPH and reducing power both were decreased with the increasing of DS; the order of their scavenging effect on .OH was NPCOSB>NPCOSA>NPCOSC, and the NPCOSB showed the strongest scavenging effect on .OH.

Key words: chitosan oligosaccharide, N-phthaloyl chitosan oligosaccharide, antioxidant