Abstract: Objective: To optimize the extraction and purification process for polysaccharides from green asparagus (Asparagus officinalis) and to explore their in vitro antioxidant effects. Methods: Ethanol reflux extraction followed by enzymatic deproteinization was used to extract and purify polysaccharides from freshly picked green asparagus. A 9-run, 3-factor, 4-level orthogonal array design was applied to optimize temperature as well as extraction duration and number that influence extraction efficiency. The effects of temperature, hydrolysis duration and enzyme dose for polysaccharide deproteinization using papain, neutral protease or alkaline protease were explored based on a 9-run, 3-factor, 3-level orthogonal array design. Total sugar and reducing sugar were determined by phenol-sulphate and salicylic acid methods. Finally, the free radical scavenging effect of green asparagus polysaccharides and their inhibitory effect on erythrocyte hemolysis and swelling of liver mitochondria. Results: The once extraction at 100 ℃ for 3 h with a solid/liquid ratio of 1:20 (g/mL) provided the highest extraction efficiency, (8.50± 1.07)%, and the purity of the resulting product was increased to (52.40 ± 0.47)% after optimized alkaline protease hydrolysis. Green asparagus polysaccharides could dramatically scavenge DPPH, hydroxyl and superoxide anion free radicals, and inhibit erythrocyte hemolysis and liver mitochondrial swelling. Conclusion: Green asparagus polysaccharides have good antioxidant effects in vitro.

Key words: green asparagus polysaccharides, extraction, purification, antioxidant activity