Abstract: Objective: To determine total carbohydrate content in cucumber, isolate polysaccharides from it and analyze uronic acid content, monosaccharide composition and in vitro antioxidant activity of extracts obtained. Methods: Phenol-sulfuric acid and sulfuric acid-carbazole methods were employed to evaluate total carbohydrate content and uronic acid content, respectively. In addition, high performance liquid chromatography (HPLC) based on pre-column derivatization with 1-phenyl-3-methyl-5-pyrazolone (PMP) was employed to analyze the monosaccharide composition of cucumber polysaccharides. Moreover, the scavenging activity of cucumber polysaccharides against 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide anion (O2－ ·) and hydroxyl ( ·OH) free radicals and total reducing power (TRP) of cucumber polysaccharides were evaluated in vitro. Results: The total carbohydrate and uronic acid contents in cucumber polysaccharides were 63.5% and 10.6%, respectively. The monosaccharide composition of cucumber polysaccharides was made up of D-mannose (Man), L-rhamnose (Rha), D-glucuronic acid (GlcUA), D-galacturonic acid (GalUA), D-glucose (Glc), D-xylose (Xyl), D-galactose (Gal), L-arabinose (Ara) with a molar ratio of 4.08:2.78:1.00:5.82:6.07:2.78:8.48:6.58. Cucumber polysaccharides revealed high antioxidant activity, and the scavenging rates at the concentration of 20 mg/mL against DPPH, superoxide anion and hydroxyl free radicals were 92.31%, 83.57% and 77.59%, respectively. Moreover, cucumber polysaccharides also exhibited strong reducing power. Conclusion: Cucumber polysaccharides are typically heteropolysaccharides with stronger antioxidant activity.

Key words: cucumber, polysaccharide, monosaccharide composition, free radical, antioxidant activity in vitro