Catalytic nucleation effect of the insoluble fraction of Persian gum on amyloid fibrillation of whey protein isolate

Abstract

Protein nanofibrils are supramolecular structures with unique physicochemical and functional properties that are greatly influenced by their microenvironment during the course of fibrillation. In this study, the formation of amyloid fibrils from whey protein isolate (WPI) was investigated in the presence of the insoluble fraction of Persian gum (IFPG). Whey protein isolate amyloid fibrils, either alone (WPF) or combined with IFPG (WPF + IFPG), were generated by heating the protein solution at 85 °C and pH 2, and their morphological, structural, and functional properties were evaluated. Thioflavin T and Congo Red spectroscopic assays showed that IFPG significantly increased the nucleation rate of the process, resulting in a shortened lag phase. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) also revealed that IFPG led to the formation of more mature and thinner nanofibrils. The results of circular dichroism (CD) spectroscopy confirmed that the secondary structure of the nanofibrils was primarily composed of β-sheet elements, with their composition being significantly influenced by the presence of IFPG and the change in pH. Additionally, SDS-PAGE profiles clearly indicated that the hydrolysates of β-lactoglobulin fraction were the main constituents of WPFs, with non-participating peptides accumulating in the solution. The apparent viscosity and surface activity of the WPF + IFPG sample were significantly higher than those of the WPF solution, which can be attributed to their morphological and structural differences. Furthermore, the presence of IFPG increased the surface hydrophobicity of the fibrils, while decreasing charge density, solubility, and turbidity. The nanofibrils underwent cleavage and aggregation as the pH increased from 2 to 7, resulting in shorter, thicker, and curved morphology. The increase in pH also caused a decrease in surface hydrophobicity and an increase in solution turbidity. These findings demonstrate the catalytic nucleation effect of IFPG particles, which accelerates fibrillation and has the potential to enhance the properties and functionalities of nanofibrils for various applications in the food and pharmaceutical industries.