Effects of Hofmeister cations (K+, Na+, Mg2+, Ca2+) on the structure, texture, and digestion of high-moisture extruded pea protein meat analogs

ABSTRACT: This study systematically investigated the influence and underlying mechanism of Hofmeister cationic salts (KCl, NaCl, MgCl 2 , and CaCl 2 at 1% w/w) on the physicochemical, structural, and digestive properties of pea protein isolate (PPI)-based meat analogs produced by high-moisture extrusion. Results demonstrated that all salts significantly enhanced the viscoelasticity of the protein melt, hardness, chewiness, and density of the extrudates, but decreased the in vitro protein digestibility (IVPD), following the specific order of the Hofmeister cation series: K + < Na + < Mg 2+ < Ca 2+ . Conversely, the improvements in tensile resistance force, fibrous degree and moisture content followed the order of K + > Na + > Mg 2+ > Ca 2+ . Mechanistic insights revealed that chaotropic ions (Mg 2+ /Ca 2+ ) promoted protein aggregation primarily through enhanced hydrophobic interactions, and increased β-turn structures by 5.33%-6.55%, leading to the formation of packed domains and rigid structures in extrudates with higher hardness (39.06-43.29 kg) but lower IVPD (60.51-65.00%). In contrast, kosmotropic ions (K + /Na + ) more effectively facilitated hydrogen bonding and the conversion of α-helices to β-sheets, resulting in the generation of more obvious anisotropic fibrous structures. These findings provided a theoretical basis for the precise texture design in plant-based meat analogs through rational cation selection.