The interfacial behavior and structure of pea proteins from a colloidal perspective

Understanding how plant proteins stabilize emulsions is crucial for optimizing product quality. Despite many studies highlighting the complexities of plant proteins, there is little understanding of their structures at the interface, arising from the diverse colloidal states. Our research addresses this gap by comparing the interfacial properties of three pea protein isolates with varying colloidal states: an industrially processed isolate, the same isolate post-homogenization, and a mildly extracted isolate obtained via isoelectric precipitation. This comparison allowed for a holistic overview of the critical intrinsic and extrinsic factors which affect pea protein interfacial structures.

The industrially processed pea protein contained a mixture of small oligomers and few large, aggregated proteins, which, after homogenization, were transformed into a homogeneous dispersion of aggregated proteins. Conversely, the mildly extracted pea protein was primarily composed of small oligomeric proteins.

Drop tensiometry measurements showed that while all dispersions readily adsorbed at the oil/water interface, the dispersions had distinct adsorption dynamics and interfacial dilatational and shear viscoelasticities. Interfaces formed by the homogenized commercial pea protein reached the lowest interfacial tension, and were characterized by a low viscoelasticity. Alternatively, the commercial and mildly extracted pea protein formed the most elastic interfaces and showed large changes in the network formation at more polar interfaces. Thus, it was concluded that interfaces stabilized by homogenized pea protein were predominantly composed of aggregated proteins, resulting in weaker interfaces due to the lack of interfacial rearrangements and network formation. In contrast, both the industrially processed and mildly extracted pea protein formed polydisperse interfaces stabilized by small, oligomeric proteins, yielding more viscoelastic interfaces. In conclusion, our findings highlight the role of the various colloidal states in influencing interfacial behavior and, consequently, the functionality of plant protein ingredients, which has implications for optimizing the design and application of pea protein ingredients in emulsions.