Composition, morphology, interfacial rheology and emulsifying ability of soy hull polysaccharides extracted with ammonium oxalate and sodium citrate as extractants

Soy hull, a by-product of crop processing, is rich in pectin-like polysaccharides that have potential for thickening, gelling and emulsifying applications. The effect of ammonium oxalate (SHPA) and sodium citrate (SHPS) on the conformation, physicochemical properties and emulsifying ability of soy hull polysaccharide (SHP) were investigated.The composition analysis showed that SHPS had more polysaccharide, protein, and higher molecular weight than SHPA. Images of atomic force microscopy (AFM) and scanning electron microscopy (SEM) showed that SHPS molecules appeared spherical bodies with smooth and firm surfaces, while SHPA molecules appeared chain-like bodies with rough and wrinkled surface. At the oil-water interface, SHPS adsorbed faster and formed a more elastic interfacial layer than SHPA. The characterization of the prepared emulsions showed that the SHPS emulsion was a smaller particle size and more stable system within 30 days than SHPA emulsion, especially at the SHPS concentration of 9 mg mL-1 . Images of cryo-scanning electron microscopy (cryo-SEM) also demonstrated SHPS formed clearer network structure on the surface of the oil droplets, compared to SHPA.Overall, ammonium oxalate and sodium citrate significantly influenced the composition and properties of the SHP. SHPS exhibited a better emulsifying ability than SHPA, which was mainly due to the higher protein content of SHPS and the sodium ion (Na+ ) residue of sodium citrate. This study is useful for the extraction and application of SHP and other plant-based polysaccharides. © 2023 Society of Chemical Industry.