Effects of globular and flexible structures on the emulsifying and interfacial properties of mixed soy proteins

Abstract

In mixed protein system, the emulsifying and interfacial properties are affected by the composition and conformation of different proteins. To clarify the underlying mechanism, β-conglycinin and hydrolysates of glycinin (GH) were used as globular and flexible proteins, and the structural and functional properties of mixed proteins with different ratios were investigated. As GH content increased, the amount of β-sheet decreased significantly, whereas α-helix, β-turn, and random coil contents increased, which indicated the intramolecular structural flexibility of mixed soy protein was slightly reduced, whereas the intermolecular structural flexibility improved substantially. Interfacial shear rheology was used to assess the linear and nonlinear behavior of mixed soy proteins at the interface. As GH content increased, the elastic modulus was decreased while the width of the linear viscoelastic region (LVR) was slightly increased. For all samples, when small strain amplitudes were at 1–10% (within the LVR), the shape of the elastic Lissajous plots was perfectly elliptical. The elliptical shape changed to circular as strain increased. Compared with single 7S, the mixed soy proteins showed reduced levels of deformation in the elliptical shape, which were likely due to the greater resistance of the gelatinous network and its ability to resist permanent deformation. The particle size, zeta-potential, interfacial protein adsorption fraction, microstructure, and stability of emulsions formed of mixed soy proteins were also studied. Results showed that emulsion formed of mixed soy proteins with a ratio of 1:1 (GH-50%) was optimal. This study could potentially aid in the application of proteins with different structures and interfacial properties in emulsion.