Abstract: Taking the yield rate of polysaccharides as evaluation indicator, Box-Behnken response surface methodology was employed to optimize extraction technology of polysaccharides from Broussonetia papyrifera leaves by heating reflux extraction method based on single factor tests. And the antioxidant activity of polysaccharide from Broussonetia papyrifera leaves was evaluated through the scavenging capabilities of DPPH·, ABTS⁺·, ·OH and O2-· free radicals and reducing power. The results showed that the best extraction conditions were as follows： liquid ratio for 1∶40 g/mL, and extraction time for 2.5 h, extraction times 3 times. Under this condition, the yield rate of polysaccharides was （8.37±1.03）%. The crude polysaccharide and pure polysaccharide from Broussonetia papyrifera leaves had obvious effect on scavenging ability of DPPH·, ABTS⁺·, ·OH and O2-· free radicals, with IC₅₀ values of 2.62、0.067、0.94、2.07 mg/mL. And reducing power increased with the increase of polysaccharide concentration. The extraction technology of polysaccharide from Broussonetia papyrifera leaves is stable and feasible. And has good antioxidant activity in vitro, which can be used as a new antioxidants and free radical scavengers.

Key words: aerospace hybrid Broussonetia papyrifera leaves, polysaccharide, response surface method, in vitro antioxidant activity