Chemical composition and sugar spectroscopy of soy hull polysaccharides obtained by microwave‐assisted salt extraction

Soy hull polysaccharides (SHP) have superior physicochemical properties, such as emulsification, stability, dispersibility, and high solubility, and also have high nutritional value. This study aimed to investigate the effects of different salt extractants and microwave-assisted extraction on the structural properties of SHP. It found that the extraction rate was significantly higher (P < .05) when ammonium oxalate was used as the extractant than sodium citrate. Microwave-assisted extraction increased the extraction rate of polysaccharides and uronic acid content, reduced the protein content, and facilitated the extraction of macromolecules. The SHP extracted by microwave-assisted salt extraction were all dominated by galacturonic acid, arabinose, mannose, and galactose, with the relative molecular weights in the range of 104–106 Da. The infrared spectra showed that all these polysaccharides contained hydroxyl, amide, ester, carboxyl, and ether bonds. The ammonium oxalate polysaccharide showed a helical conformation in an aqueous solution, and the sodium citrate polysaccharide showed a circular conformation. Sugar spectroscopy analysis showed that the main chain composition and molecular weight of SHP obtained by different extraction methods were similar. The characteristic fingerprints of SHP from different extraction processes could be distinguished by high-performance size exclusion chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry after enzymatic digestion. In this study, we systematically investigated the effect of microwave-assisted salt extraction on the structure and conformation of SHP, investigated the spectral differences after polysaccharide hydrolysis using glycomics, and provided new insights into the differentiation of polysaccharides. Novelty impact statement Microwave-assisted salt extraction of SHP was built. The main constituent unit of SHP was α-1,4-D-GalpA. Sugar spectroscopy is used in polysaccharide structural analysis.