Abstract: Using Syzygium jambos fruit as the raw material, the solid-liquid ratio, ultrasonic time, and ultrasonic temperature were selected as experimental factors. On the basis of single factor experiments, the response surface methodology was used to optimize the ultrasonic-assisted extraction process of crude polysaccharides from Syzygium jambos. The crude polysaccharide was purified by using the activated carbon method, Sevage method and the DEAE-52 column chromatography. ABTS free radical scavenging ability, DPPH free radical scavenging ability and iron reducing ability were used to determine the antioxidant activity. The results showed that the optimal extraction condition of the polysaccharide from Syzygium jambos fruit was ultrasonic time 58 min, ultrasonic temperature 77 ℃, and solid-liquid ratio 1∶50. Under this condition, the crude polysaccharide yield was （5.46±0.02）%. The pure polysaccharide SJP-Ⅰ and SJP-Ⅱ were purified from the crude polysaccharide, and both SJP-Ⅰ and SJP-Ⅱ had antioxidant capacity. SJP-Ⅱ had better antioxidant activity than SJP-Ⅰ, and its ABTS free radical scavenging rate was （0.30±0.01） mg/mL, DPPH free radical scavenging rate was （0.68±0.03） mg/mL, iron reducing ability was （166.41±0.15） μmol VitC/g. The extraction and purification technology was simple and stable, and the pure polysaccharide from Syzygium jambos fruit had certain antioxidant capacity, which provided a theoretical basis for the rational development and comprehensive utilization of Syzygium jambos fruit.

Key words: Syzygium jambos fruit, polysaccharides, antioxidant, extraction process