Preparation, structural characterization, and functional properties of a tilapia-soybean dual proteins: Effects of different complexation modes

The limited functional properties of tilapia protein isolate (TPI), such as low solubility, emulsification, and foaming, restrict its use in the food industry. However, combining it with hydrophilic proteins can improve these properties. Different assembly methods may affect the structure and functionality of the resulting dual proteins. To study this, tilapia-soybean protein mixtures (T-SPM), complexes (T-SPC), and co-precipitates (T-SPCP) were prepared using physical mixing, pH-regulated complexation, and pH-regulated co-precipitation. The effects of these methods on the structure and functional properties of the tilapia-soybean dual proteins were then analyzed. Structural analysis revealed that TPI combined with SPI through non-covalent forces and disulfide bonds under pH-regulation, leading to structural changes. Compared to T-SPCP, T-SPC showed more hydrophilic groups, with increased free sulfhydryl groups, disulfide bonds, α-helices, and zeta potential, alongside reduced surface hydrophobicity and smaller flake structures. Functional analysis indicated that pH-regulated assembly methods significantly improved the properties of the dual proteins compared to T-SPM. T-SPC exhibited higher solubility, emulsification, and foaming capacity than T-SPCP, which had a more aggregated structure due to pH adjustment to 4.5 during co-precipitation, contributing to its better thermal stability. Thus, T-SPC, assembled by pH-regulation from 12.0 to 7.0, demonstrated superior characteristics. This study offers a theoretical foundation for developing functional dual proteins and their food industry applications.