pH-dependent emulsifying properties of pea protein isolate: Investigation of the structure - Function relationship

This study investigated the relationship between pea protein isolates (PPI) emulsifying properties and their structural, interfacial, and physicochemical characteristics at various pH values (native pH, 7, 5, and 3). Emulsion characteristics including emulsifying activity and stability, droplet size, flocculation index (FI) and coalescence index (CI) were examined. Additionally, physicochemical properties such as solubility, zeta potential, surface hydrophobicity, interfacial protein adsorption and protein conformation were analyzed. Results revealed significant pH-dependent variations in emulsifying performance. The poorest emulsifying performance was observed at pH 5, with the largest droplet size (28.84 μm) and highest CI (38.94 %). Optimal emulsifying properties were noticed at native pH, with the smallest droplet size (7.73 μm) and lowest CI (4.69). At pH 3, good emulsifying ability with the highest physical stability (5.43) were observed, associated with increased surface hydrophobicity and the presence of some aggregates contributing to the formation of cohesive interfacial film. Structural elements, particularly β-sheets and random coils, were positively correlated with emulsifying activity and stability, while β-turns had a negative impact. These findings provide insights into the pH-dependent emulsifying behavior of PPI, highlighting the complex relationship between protein structure and functionality, enabling the optimization of the use of PPI as an emulsifier in food applications.