Valence-dependent evolution of hierarchical structure and functional properties in soy protein isolate-potato protein composite hydrogels.

Understanding how ionic valence regulates the hierarchical structure evolution of composite plant protein gels is essential for the rational design of functional food hydrogels. In this study, soy protein isolate (SPI)-potato protein (PP) hydrogels were employed as a model system to investigate the effects of ionic valence on multiscale structural characteristics and functional properties. Na+ at 100 mM formed a homogeneous dense network via electrostatic shielding, achieving peak water-holding capacity (WHC, 99.41%) and hardness among the Na+ series, accompanied by increased β-sheet content and hydrogen bonding. Ca2+ induced strong aggregation via ionic bridging, constructing a reinforced and elastic network at 20 mM, with the highest proportion of strongly bound water (9.20%). Fe3+ induced charge reversal at high concentrations through excessive charge neutralization, triggering rapid heterogeneous aggregation and increasing α-helix content, which ultimately caused deterioration in water retention and mechanical stability. Intermolecular force analysis revealed that ion treatment further strengthened the already dominant hydrophobic interactions while weakening electrostatic interactions.