Abstract: The objective of this research was to extract polysaccharides from Isatis indigotica Fortune (INF) roots and determine their molar mass distribution. INF root powder was sequentially refluxed with petroleum ether and 95% ethanol to remove ether-soluble and ethanol-soluble components before polysaccharide extraction by hot water reflux. Polysaccharide content was quantified by phenol-sulfuric acid method and polysaccharide molar mass distribution was determined after hollow fiber membrane filtration for the removal of impurities. The content of ether-soluble and ethanol-soluble components in INF roots was 4.89%. Three repeated hot water reflux extraction for 1.5 h each time at a material-to-liquid ratio of 1:9 (g/mL) for the first extraction and of 1:7 for the second and third extractions was found optimal for INF roots with and without the above pretreatments. The polysaccharide yields after the first, second and third extractions and total polysaccharide yield from pretreated INF roots were 7.34%, 4.65%, 3.12% and 15.11%, respectively and those from non-pretreated INF roots 6.51%, 6.04%, 5.69% and 18.24%. The molar mass distribution of polysaccharides from INF was mainly from 2×104 to 5×104 g/mol and polysaccharides with a molar mass from 1×104 to 1×105 g/mol accounted for 90.8%. The results indicate that INF roots planted in Daqing are rich in polysaccharides. The method developed in this study to determine the molar mass distribution of polysaccharides from INF roots is simple and reliable with the avoidance of tedious operations and experimental errors resulting from repeated separation and purification.

Key words: Isatis indigotica Fortune, polysaccharide content, molar mass distribution