Rheological and tribological properties of high internal phase emulsions stabilized by pH-induced soy protein isolate-carrageenan complex coacervates

Coacervates of protein-polysaccharide complexes that self-assemble through electrostatic interactions exhibit varying morphologies and functional properties. This study investigated the pH range of soy protein isolate (SPI) and x-carrageenan (xCG) to form complex coacervates in different states and their ability to stabilize high internal phase emulsions (HIPEs). With the increase of pH (from 4.0 to 5.5), electrostatic interaction between SPI and xCG weakened, the yield of SPI/xCG complex coacervates in the system as well as the degree of agglomeration of microstructure gradually decreased. However, in terms of HIPEs, pH5.0 and pH5.5 (especially pH5.5) complex coacervates exhibited better HIPEs formation ability. Excessively complex coacervates could seriously reduce the adsorption rearrangement rate and intermolecular crosslinking behavior of protein molecules at the interface, so the pH5.5 sample with the lowest coacervates yield showed smaller droplet size and higher elastic modulus. The pH5.0 sample exhibited higher initial viscosity in rheological tests, better deformation resistance in large amplitude oscillatory shear (LAOS) tests and better oral friction properties, due to higher complexation degree of coacervates. These findings give improved understandings of structure of pH-induced SPI-xCG complex coacervates in relation to their ability to stabilize HIPEs, which can guide for design of food emulsions.