Studies On Extraction, Fractionation And Structural Characterization Of Polysaccharides From Sophora Alopecuroides L. Seeds

Sophora Alopecuroides L. is distributed widely in China, mainly in the northwestern rigion. Sophora Alopecuroides L. is rich in nutrients and bioactive components such as alkaloids, polysaccharides, flavonoids, and proteins. Currently, there are few studies on the polysaccharides of Sophora Alopecuroides L. when compared to the abundant researches of its alkaloids wordwide. In this paper, the crude polysaccharide was extracted optimally from seeds of Sophora Alopecuroides L. and its fractionation, purification, physico-chemical properties and primary structure were also investigated. The main results were given as follows:I. The single-factor test combined with response surface methodology was used to optimize ultrasonic extraction of crude polysaccharide from seeds of Sophora Alopecuroides L., and the optimal conditions were: an ultrasonic time of 30 min, an ultrasonic power of 280 W, an extraction temperature of 50 ℃ and water to seed ratio of 50:1. At this optimum point, the yield of crude polysaccharide was 8.51%, which was in close agreement with the predicted value without significant difference.II. According to the results of HPSEC and HPAEC-PAD, the crude polysaccharide was in a wide range of molecular weight and mainly composed of rhamnose(Rha), arabinose(Ara), galactose(Gal), glucose(Glc), xylose(Xyl) and mannose(Man), which were in an approximate molar ratio of 1.00 : 8.57 : 36.43 : 1.94 : 4.02 : 36.00. UV spectrum indicated that the crude polysaccharide possessed trace proteins while no nucleic acids. The information from FT-IR spectrum manifested that there were α-glycosidic linkages in the primary structure of the crude polysaccharide in addition to other characteristic peaks of polysaccharide. Furthermore, the crude polysaccharide was fractionated into F15, F25, F35 and F60 by cetyltrimethylammonium bromide(CTAB) and ethanol.III. The spectra of HPSEC and HPAEC-PAD indicated that F25 had a weight-average molecular weight of 288.81 kDa, of which the polydispersity index(PDI) was 2.43 and monosaccharide components were Ara, Gal, Glc and Man in the molar ratio of 1.17 : 31.19 : 1.00 : 46.22. In FT-IR spectra, characteristic absorptions of polysaccharide were observed for F15, F25, F35 and F60. Upon methylation analysis with gas chromatography-mass spectrography(GC-MS), it was possibly proposed that F25 was essentially a galactomannan(M/G=1.48) consisting of a linear main chain of(1â†'4)-β-D-mannopyranosyl units attached by(1â†'6) linkages with α-D-galactopyranosyl, α-D-glucopyranosyl and α-L-arabinofuranosyl residues, of which the repeating unit might be exhibited as below:...