Structural insights into acidic heating-induced amyloid fibrils derived from soy protein as a function of protein concentration

Amyloid fibrillation of food-derived dietary proteins has been increasingly accepted as an effective approach to enhance protein functionality. Soy protein, an abundant and environmentally sustainable protein, has been widely used in food applications. However, the mechanism for amyloid fibrillation at various protein concentrations during the acidic heating process is not fully understood, along with an incomplete understanding of the structural polymorphism. In this study, we systematically investigated the influence of protein concentration on amyloid fibrillation of soy protein by means of atomic force microscopy (AFM), 1-anililo-naphthalene-8-sulfonate (ANS) and thioflavin T (Th T) fluorescence, reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared spectrometer (FTIR). AFM analysis showed that soy protein-derived amyloid fibrils (SAFs) demonstrated very rich and diverse polymorphism and exhibited at least five kinds of long-rigid fibrils that had distinct periodicity, height, and handedness. The polypeptides hydrolysis behavior and the parallel to antiparallel β-sheet ratios were found to be protein concentration-dependent. Results obtained from this study will lead to a deeper understanding of formation mechanism of SAFs and lay the foundation for SAFs severing as functional ingredients in food field.