Protein fibrillation complex mechanisms led to an emerging trend in research for years. The mechanisms behind whey protein isolate (WPI) fibrillation driven by divalent cations remained still a matter of speculation. All cations (Ca2+, Fe2+, Mg2+, and Zn2+) enhanced the microenvironment polarity through π-π stacking, and the amide I and II shifts confirmed the fibrillation. The Fe2+ followed the nucleation-growth mechanism attested by spider-like microstructure, maximum fibril length (654.96 nm) and β-sheets. The hydrophobic forces were mainly involved while disulfide bonds had no key role. The Ca2+ and Mg2+ followed the nucleated conformational conversion and electrostatic shielding which induced mature multilayer fibrils. The Zn2+ induced wormlike fibrils probably showing the low conversion rate regarding the high binding affinity toward WPI which stabilized the structure, so simple nucleated polymerization conducted the fibrillation. More ionic strength improved the exposure of hydrophobic amino acids in the surface, accelerating the growth phase by increased number of nuclei.

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