Abstract:Response surface methodology （RSM）was used to optimize ultrasonic extraction process of polysaccharides from Tamarindus indica L.Pulp fruit （PFTP）.In single factor experiments，extraction time，ultrasonic power，extraction temperature and material solution ratio were used as independent variables and tested at three levels，while the polysaccharide yield was the response variable.The obtained optimumconditions were listed as follows：extraction time（40 min），ultrasonic power（200 W），extraction temperature（50 ℃），and the material solution ratio（1∶30 g/mL）.Under the optimized conditions，the yield was 31.94%，higher than the reported value （23.44%）which was obtained by thermal water extraction.Primary structure of the polysaccharide was determined by ultraviolet（UV）absorption spectrum，infrared（IR）absorption spectrum and high-performance anion-exchange chromatography （HPAEC），suggested that polysaccharides from PFTP contained protein but without nucleic acid.IR showed PFTP had characteristic absorption peaks of polysaccharide and β-glycosidic bond.PFTP were mainly composed of seven monosaccharide units，including arabinose，galactose，rhamnose，fucose，xylose，glucose and galacturonic acid with a molar ratio of 45.56∶15.67∶6.41∶1∶5.14∶14.27∶1.95.The relative molecular weight of the PFTP was 8.262×105 g/mol and the distribution was uniform by high performance size-exclusion chromatography （HPSEC）.The polysaccharide showed 30.02 % of uronic acid.