Impact of pH shifting on structural and emulsifying characteristics of whey protein isolate amyloid fibrils

Whey protein isolate amyloid fibrils (WPIFs) were prepared via acidic thermal treatment at pH 2.0, 85 °C for10 h. The aim was to investigate the influence of different pH values (2.0–8.0) on the structural features of WPIFs and emulsifying properties of WPIFs-stabilized Pickering emulsions. Thioflavin T (ThT) fluorescence confirmed WPIFs formation at pH 2.0. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) revealed that WPIFs maintained long fibrils at pH 2.0–3.0, whereas short fibrils were observed at pH 7.0–8.0. At pH 4.0–6.0, WPIFs underwent aggregation which resulted in increased particle size and decreased zeta potential, with the most distinct aggregates forming at pH 5.0. The structure of WPIFs affected by pH changes determined the emulsification of WPIFs Pickering emulsions. Specifically, WPIFs at pH 5.0 exhibited relatively low emulsifying activity index (EAI) of 14.84 ± 0.37 m 2 /g and high emulsifying stability index (ESI) of 93.25 ± 1.54%. WPIFs Pickering emulsion at pH 5.0 showed increased droplet sizes and enhanced viscoelasticity. The results indicated that the emulsifying properties of WPIFs Pickering emulsions were dependent on the structural features of WPIFs. These findings provide valuable insights into the pH-dependent structural regulation of WPIFs and highlight the application prospects of amyloid fibril-stabilized Pickering emulsions.