Abstract: In this paper,ginger polysaccharides (GPs) were extracted by hot water method (HWGPs) and ultrasonic method (UEGPs).A comparative analysis of physicochemical properties and antioxidant activities were researched.The physicochemical properties of GPs were researched by FTIR,SEM and TG.The scavenging effects of GPs on DPPH free radical (DPPH·),hydroxyl free radical (OH·) and superoxide free radical (O^-·₂) were used to evaluate the antioxidant activities of GPs.The results showed that the ultrasonic treatment did not change the characteristic group of GPs,but the conformation property and the thermodynamic properties were changed,the particle structures become smaller and easily degradable.The half-inhibitory concentration (IC₅₀) of UEGPs based on scavenging activities against DPPH· and OH· were 2.72 and 1.94 mg/mL respectively.The IC₅₀ of HWGPs against DPPH· and OH· was higher than that of UEGPs,but the scavenging effect on O^-·₂ was stronger than that of UEGPs.The difference of antioxidant activities of GPs are relevant to change of conformation property thermodynamic properties caused by ultrasonic treatment.We provided a reference for the study on the structure-activity relationship of plant polysaccharides.

Key words: ginger polysaccharides, ultrasonic treatment, physicochemical properties, antioxidant activities