Abstract: The health protection function of polysaccharides has been payed attention and affirmed by the sphere of leaning. Polysaccharides is rich in Nostoc sphaeroids kutz. Nostoc sphaeroids kutz was pretretmented with alkali and papain, and the best pretreatment method was defined with the orthogonal test. The condition of the extracting polysacchariedes are that the material hydraulic proportion 1: 300, extracted 2 times at 90℃ water baths for 2 h. The results showed: the optimal enzyme pretreatment conditions are 10 mg papain added to the 100 mg Nostoc sphaeroids kutz material, pretreatmented for 10 h at 50 ℃. The polysaccharides is 29.53%; The optimal alkali treatment conditions are the NaOH content 0.4 mol/L, pretreatmented for 2 h at 40 ℃. The polysaccharides yield is 35.15%. Pretreatmenting Nostoc sphaeroids kutz with alkali and papain, the highest polysaccharides yield is 47.56%, higher 25.12% than the contrast.

Key words: Nostoc sphaeroids kutz papain, alkali, polysaccharides, extraction