Insights into the pH-driven emulsifying properties and self-assembly behaviour of pea peptides

Peptide self-assembly is a special strategy for forming stable emulsion systems. In this study, the emulsifying properties and self-assembly behaviour of pea peptides and their controlled interfacial adsorption properties at different pH were investigated. Pea peptide-based emulsions exhibited a higher emulsifying activity index and emulsifying stability index at pH ≥ 7.0. Transmission electron microscope revealed that spherical assemblies of pea peptides formed large aggregates at pH 4.0, and that micellar structures of these pea peptides were formed at pH 7.0 and pH 9.0. These aggregates accelerated the adsorption of pea peptides at the oil-water interface but were not favourable for achieving emulsion stability. Compared to pH 7.0, the higher diffusion rate constant (K_diff) and lower rearrangement rate (K_R) of pea peptides at pH 9.0 corresponded to their increased surface hydrophobicity and surface charge. The interfacial adsorption properties of pea peptides at pH 7.0 may be attributed to the high relative contents of α-helix and random coil structures, which endowed these peptides with great structural flexibility. The interfacial adsorption properties were strongly dependent on the structure and morphology of pea peptide self-assemblies. These findings provide insights into the development of a pH-sensitive emulsifier for specialized delivery systems.