Ultrasound-assited extraction and structural identification of polysaccharides from Isodon lophanthoides var. gerardianus (Bentham) H. Hara

Ultrasound-assisted extraction was employed to prepare polysaccharides from Isodon lophanthoides var. gerardianus (Bentham) H. Hara (Xihuangcao). Response surface methodology was used to optimize the ultrasound-assisted extraction parameters. Central-composite design was applied to estimate the effects of ultrasonic time, liquid/solid ratio and pH on the yield of the polysaccharides from I. lophanthoides var. gerardianus (Bentham) H. Hara (ILHP). A mathematical model with high fitness was obtained. Ultrasonic time, liquid/solid ratio and pH exhibited independent and interactive effects on ILHP yield. Gas chromatography analysis suggested that ILHP-3 comprised Rha, Man, Glc with relative molar percentages of 3.9%, 8.0% and 88.1%, respectively. The assay of glycosidic linkage showed that ILHP-3 was consisted of →2)-Man-(1→, →6)-Glc-(1→, →3)-Rha-(1→ with a molar proportion of 1.9:26.5:1. The average molecular weight of ILHP-3 was measured to be 247 kDa by high-performance gel permeation chromatography. Furthermore, a good antioxidant activity was observed for ILHP-3.