Mechanism of structural interplay between rice proteins and soy protein isolates to design novel protein hydrocolloids

Water solubility of food proteins plays a significant role in their functionalities like foaming and emulsifying, especially for those with high surface hydrophobicity. In this paper, we report that by co-dissolving rice proteins (RPs) and soy protein isolates (SPIs) upon a mass ratio of 1:0.1 (R/S) at pH 12 for 1 h, followed by readjusting to pH 7 at ambient temperature, the water solubility of RPs was enhanced to be over 82% (from 1.84%). Fluorescence and near-UV CD spectra demonstrated that, under alkali denaturation, the unfolded backbones of RPs and SPIs interacted via hydrogen bonding, and folded together to bury apolar groups whereas expose polar moieties. The cross-linked structures lost the susceptibility to the subsequent acid renaturation due to significantly improved structural strength, and were packed into well-defined particles sized between 80 and 130 nm by hydrophobic and ionic interactions inside the protein bodies. The formation of helix segments with considerable surface charges around the spherical exteriors protected the architectures against merging and aggregation. The simplicity and effectiveness of this protocol suggest that it is an excellent strategy for the high-throughput modification of insoluble edible proteins toward hydrocolloids in food industry and other relevant areas.