Abstract: The crude polysaccharide extracted from soybean dregs was purified and fractionated into two soluble acid polysaccharide fractions with uniform charge, SSPS-A1 and SSPS-A2. SSPS-A1 was further subjected to gel filtration chromatography, yielding a homogenous polysaccharide with uniform charge, SSPS-A1-c. Its molecular mass and monosaccharide composition were measured, and its structure was analyzed by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy. The results showed that SSPS-A1-c had a molecular mass of 31.6 kDa, mainly composed of galacturonic acid (GalA), galactose (Gal) and arabinose (Ara) with a molar ratio of 17.3:44.9:19.1 together with lesser amounts of rhamnose (Rha), glucose (Glc) and xylose (Xyl). IR spectroscopy analysis showed that SSPS-A1-c had the characteristic absorption peaks of acidic polysaccharides such as O–H, C–H and C=O and it may be methylated or acetylated to a certain extent. NMR results showed that SSPS-A1-c had chemical shifts of α-1,5-Araf, α-t-Araf and β-t-Galp, which was speculated to contain arabinogalactan (AG)-type pectin domain. Besides, it also exhibited chemical shift of α-1,4-GalpA, which was inferred to contain the homogalacturonan (HG)-type pectin domain. The NMR results were consistent with the monosaccharide composition and infrared analysis results. The research results will provide a theoretical basis for the application of soluble acidic polysaccharides from soybean dregs, and will be of great significance to the comprehensive development and utilization of soybean dregs.

Key words: soybean okara; soluble acid sugar; separation and purification; structure analysis