RÉSUMÉ
OBJECTIVE：To isolate and purify the polysaccharides from Cucumis satiuus ，and to investigate its in vitro antioxidant activity. METHODS ：The crude polysaccharides （CCL）were extracted from C. satiuus by water extraction and alcohol precipitation. CCL was separated and purified on Amberlite FPA 90Cl anion and Amberlite FPC 3500H cation exchange resin column and DEAE cellulose 52 column，so as to obtain 3 kinds of polysaccharides as CCL-M 2，CCL-M3，CCL-M6. The purity ， molecular weight ，structure and monosaccharide composition of 3 kinds of polysaccharides were analyzed by HPLC-ELSD ， UPLC-QTOF/MS，UV and IR. Using vitamin C （VC）as positive control ，the scavenging activity of CCL-M 2，CCL-M3 and CCL-M6（0.4，0.8，1.2，1.6，2.0 mg/mL）to 1，1-dibenzene-2-trinitrobenzene free radicals （DPPH·），hydroxyl free radicals （·OH） and superoxycyclic anion free radicals （O2－·）were investigated ，and IC50 was calculated. RESULTS ：CCL-M2，CCL-M3 and CCL-M6 were homogeneous polysaccharides in the form of pyranose ，with molecular weights of 9.614×106，2.024×107 and 3.343× 107 Da，respectively. CCL-M 2 monosaccharides were composed of rhamnose ，semi-lactose aldehyde acid ，glucose， semi-lactose and arabic sugar ，with a molar ratio of 5.1∶2.6∶1.7∶1.4∶31.6. CCL-M 3 and CCL-M 6 monosaccharides were composed of mannose， rhamnose，glucose，semi-lactose，arabic sugar ，with a molar ratio of 1.7 ∶ 3.8 ∶ 6.4 ∶ 3.3 ∶ 1.3 and 1.3 ∶ 3.0 ∶ 3.2 ∶ 4.4 ∶ 8.9. The results of antioxidant activity in vitro showed that 3 kinds of homogeneous polysaccharides had certain scavenging activity on DPPH ·，·OH and O 2－·；the order of scavenging activity to DPPH ·was VC ＞CCL-M2＞CCL-M3＞CCL-M6（IC50 was 0.309， 1.240， 1.489 and 1.713 mg/mL）； the order of scavenging activity to ·OH was VC ＞CCL-M2＞CCL-M6＞CCL-M3（IC50 was 0.968，1.032，1.233，1.356 mg/mL）；the order of scavenging activity to O 2 －· was VC ＞CCL-M2＞CCL-M3＞CCL-M6 （IC50 was 0.335， 0.379， 0.812， 1.662 mg/mL）. CONCLUSIONS：3 kinds of monosaccharides in the form of pyranose are isolated from C. satiuus ，and all of them have antioxidant activity in vitro ，and CCL-M 2 is the best.