Plant-Based Foam Stabilizers Based on Rice Protein Isolate-Sodium Alginate Composite Particles: Structure, Interfacial Properties, and Foam Performance

To address the low solubility and inferior interfacial activity of rice protein isolate (RPI), RPI/sodium alginate (SA) composite colloidal particles were fabricated via a facile heat-induced co-assembly. Incorporating SA stabilized the flexible, unfolded conformation of RPI while forming an outer hydrophilic shell, as evidenced by a reduction in surface hydrophobicity and an increased negative zeta potential. Consequently, both foamability and foam stability followed a bell-shaped trend with increasing SA proportion, peaking at RPI/SA mass ratios of 1:0.3 and 1:0.4. At these optimal ratios, the composites exhibited a minimum polydispersity index (0.20), a highly negative zeta potential (−43 mV), moderate apparent particle size (~1500 nm), and the highest interfacial dilatational modulus (~18–24 mN/m). Mechanistically, this balanced architecture facilitated rapid interfacial adsorption and subsequent molecular rearrangement at the air-water interface. Once adsorbed, the particles synergistically enhanced foam stability through robust electrostatic repulsion and steric hindrance—imparted by their surface charges and the hydrophilic SA shell—effectively suppressing bubble coalescence. Conversely, an excess of SA rendered the particles overly hydrophilic, hindering interfacial adsorption and impairing foaming performance. This work clarifies the composition–structure–foaming property relationships of RPI/SA composites and offers fundamental support for utilizing rice protein as a plant-derived foaming agent.