Abstract: In the present study,we found the optimal conditions for the microwave-assisted extraction and deproteinization of Bletilla formosana polysaccharides and assessed the antioxidant activity of it.Herein,percentage of microwave rated power and pretreatment time and extraction temperature and time are employed to assess the effect of extraction technique on the yield of polysaccharide based on single factor experiments and orthogonal test.The optimum extraction parameters are as follow:40% rated power,60 s microwave pretreatment time,70 ℃ extraction temperature,and 2.5 h extraction time.Under these optimized conditions,the yield of polysaccharide was 38.33% (n=3).Subsequently,three deproteinization methods were evaluated for the effect of protein removal and polysaccharide loss rates,such as Sevag method,enzymatic hydrolysis and their combination.The results obtained showed that the Enzymatic-Sevag method was the optimal method,which provided the deproteinization rate was 80.01%,and the polysaccharide loss rate was 24.58%.In addition,the in vitro antioxidant activities of B.formosana polysaccharides were investigated by measuring clearance abilities of O^-·₂,1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) and ferric reducing antioxidant power (FRAP).The polysaccharide which was extracted from Enzyme method and the original polysaccharide showed good antioxidant activity.The half inhibitory concentration (IC₅₀) for scavenging of DPPH were 24.855 and 28.948 μg/mL,and superoxide anion radicals were 0.212 and 0.223 mg/mL,respectively.With this kind of investigation it would be easier to extract polysaccharide from B.formosana and other medicinal plants.Therefore,further research of precise chemical structures and biological functions of these medicinal plants polysaccharide would be currently in progress.

Key words: Bletilla formosana polysaccharide, extraction process, orthogonal design, deproteinization, antioxidant activity