Effect of CaCl2 on 2 heat-induced whey protein concentrate fibrillation pathways: Spontaneous and nuclear induction.

Amyloid fibrils have many excellent functional properties that facilitate their applications in the food industry. There are 2 pathways for whey protein concentrate (WPC) to form amyloid fibril aggregates: spontaneous pathway and nuclear induction pathway. Low ionic strength is a necessary condition for the spontaneous pathway to proceed successfully. In this paper, the effect of salt ions on 2 WPC fibrillation pathways was investigated by adding CaCl2. The results demonstrated WPC fibrils were unable to form normally through spontaneous pathway as adding CaCl2; but still could form through nuclear induction pathway with 20 to 30 mM CaCl2, the nuclei accelerated the fibrillation process led to the resistance to the disordered aggregation brought by CaCl2. Moreover, divalent cations (Ca2+, Mg2+) had much stronger effects than monovalent cations (Na+) on fibril formation, and the results of X-ray photoelectron spectrum together with Fourier-transform infrared spectroscopy suggested that Ca2+ had a greater effect on the fibril formation than Cl-.

Homogeneous nuclei-induced, secondary nuclei-induced, and spontaneous whey protein concentrate nanofibril formation through different pathways.

The addition of homogeneous nuclei (HN) or secondary nuclei (SN) could lead to different kinetics and thermodynamics as the nucleation energy barrier decreases and the lag time is shortened to different degrees compared with spontaneous fibrillation. To explain these differences, we monitored the formation and depletion of HN during fibril formation and found that both SN-induced fibrils and HN-induced fibrils follow the same nucleated growth pathway as spontaneously formed WPC fibrils. Moreover, there were also other paths, which were confirmed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. The surfaces of the SN could recruit monomers and resulted in stronger intersheet stacking and a larger fibril height and periodicity. The HN incorporation led to a propensity for hydrogen-bonding interactions and a longer fibril. Fibrillation by the addition HN and SN followed both common and distinct pathways, as spontaneous fibrillation and led to different capacities to induce fibrillation.