Impact of Mg2+, K+, and Na+ on rheological properties and chain conformation of soy hull soluble polysaccharide

This study aims to evaluate soy hull soluble polysaccharide fractions (SHSPs) obtained by gradient alcohol precipitation induced by Mg2+, K+, and Na+ via rheological and chain conformation analysis. The temperature sweep amplitude oscillatory-shear tests show that Mg2+, K+, and Na+ can promote gelation for SHSP20 and SHSP40, and the gel strength of SHSP20 is higher than SHSP40 at various temperatures. SHSP60 does not form gel induced by these metal ions, even at a concentration of 0.40 mol/L. In addition, atomic force microscopy further confirmed the various morphologies of these SHSP fractions induced by metal ions. SHSP20 can form a denser network structure, induced by Mg2+, K+, and Na+, than SHSP40. What's more, with the increase in metal ion concentrations, the molecular chain of SHSP60 formed aggregation, and did not form a network structure. This may be the reason why SHSP60 do not undergo a gel reaction. Furthermore, combined with rheological and atomic force microscopy results, it can be concluded that Mg2+ form a more stable and uniform network structure than K+ and Na+, which may be the reason why the gel thus formed is more resistant to temperature increase. For K+ and Na+ at the same concentration, the gel strength of SHSP20 and SHSP40 induced by Na+ is inferior to K+, because K+ induces SHSP formation as a uniform network structure, and Na+ results in an uneven form. These results suggest that SHSP fractions provided different rheological and gel properties, and can be used as ingredients in different foodstuffs.