Fibrillation of soy protein isolate in the presence of metal ions: Structure and gelation behavior.

The structure and functional properties of protein fibrils are closely related to environmental factors in fibrillation. Herein, soy protein isolate fibrils (SPIFs, 22 mg/mL) were prepared under acid-heating conditions in the presence of 100 mM metal ions (K, Na, Ca, Mg, and Fe). Except for Fe, fibrillation and subsequent larger fibril aggregates were promoted, ultimately leading to gel formation. Compared with K or Na, the addition of Ca or Mg resulted in more organized SPIF structures with increased β-sheet contents and higher ThT fluorescence intensities. Furthermore, both of them resulted in longer fibrils with an average contour length of 700-800 nm, which significantly enhanced the storage modulus. However, the presence of Fe accelerated protein hydrolysis and inhibited SPIF formation, resulting in samples consistently exhibited liquid behavior. These findings provide a foundation for understanding the influence of metal ions on regulating the fibrillation and gelling properties of SPIFs.