Abstract:To optimize the extraction process of summer and autumn tea polysaccharides，analyze their structural characteristics，and evaluate their antioxidant activity，Xinyang summer-autumn tea was used as the raw material，polysaccharides were extracted by compound enzyme-assisted ultrasonic extraction. The extraction process was optimized based on single-factor experiments and Box-Behnken response surface methodology.The structure was characterized by high-performance gel permeation chromatography，infrared spectroscopy，thermogravimetric analysis，and X-ray diffraction. The in vitro antioxidant activity was evaluated by DPPH radical and ABTS+ radical scavenging assays. The results showed that the optimal process conditions were as follows：compound enzyme （cellulase∶pectinase∶neutral protease=1∶1∶1，mass ratio） dosage of 12%，enzymatic hydrolysis temperature of 45 ℃，enzymatic hydrolysis time of 60 min，ultrasonic temperature of 60 ℃，ultrasonic time of 30 min，and ultrasonic power of 280 W. Under these conditions，the extraction yield of polysaccharides from summer and autumn tea reached 12.3%. The polysaccharides from summer and autumn tea were acidic heteropolysaccharides with a loose and porous structure，which were formed by the aggregation of irregular flake structures with smooth surfaces. Both crystalline and amorphous structures existed inside，and the polysaccharides possessed good thermal stability below 163.9 ℃. The antioxidant activity tests showed that the half maximal inhibitory concentrations （IC50）value of polysaccharides against DPPH· and ABTS+· were 0.39 mg/mL and 0.57 mg/mL，respectively，indicating that the polysaccharides had favorable antioxidant activity.