Effect of Acid Modification of Soy Glycinin on Its Interfacial and Emulsifying Properties

Abstract Soybean glycinin [11S] was modified by an acidic pH treatment to improve its emulsifying properties. Glycinin was obtained by isoelectric precipitation (11Sn) and then treated with acid (11St). The oil–water interfacial tension and rheology were measured. The rate constants of adsorption ( k a ) and rearrangement ( k r ) of proteins at the interface and the dilational ( E ), elastic ( E d ), and viscous modulus ( E v ) of the protein interfacial film were determined. Particle size distribution (PSD), interfacial protein concentration (Γ), and the creaming destabilization rate constants k s (for the smaller droplets) and k l (for the larger droplets) were analyzed in oil‐in‐water emulsions (25% v/v of oil and 75% v/v of 1 mg/mL protein solution in 10 mM sodium phosphate buffers, pH 7.0 and 2.5, respectively). Compared to the native protein, the acid treatment caused irreversible denaturation of 11S and significantly increased Г, k a , E , E d , and E v ( P ≤ 0.05), resulting in a greater rate of protein adsorption to the interface and a stronger interfacial film. PSD showed a bimodal distribution with peaks above and below 4 μm. Smaller droplets moved toward smaller diameters for 11St. It also showed lower values of creaming destabilization constants k s ( d ≤ 4 μm) and k l ( d ≥ 4 μm) than 11Sn. In conclusion, acid treatment of 11S enhances the creaming stability of its emulsions by improving the interfacial properties and reducing the droplet size.