Abstract: Ledum palustre L.,is a kind of source plant widely distributed in the northeast of China.In this study,water-soluble polysaccharide extracted from L.palustre with high extraction yield was successfully studied by the method of water extraction and ethanol deposition.To improve the extraction yield of the Ledum polysaccharides,a Box-Behnken design was employed based on four factor experiments.The four independent variables,namely extraction temperature,particle size,solid-liquid ratio and extraction time on extraction yield of polysaccharides were evaluated by response surface methodology (RSM).The results showed that the optimum conditions for extracting Ledum polysaccharide were as follows:extraction temperature 80 ℃,particle size of Ledum 0.178 mm,solid-liquid ratio 1:35,and extraction time 6h.Under the optimal conditions,the extraction yield achieved 4.19%.Furthermore,FT-IR and UV analyses showed that L.palustre extract contained typical group of polysaccharide,the content of polysaccharide in the crude extract of L.palustre was determined to be 92.6%.

Key words: Ledum, response surface methodology, polysaccharide, extraction