Effect of d-galactose on physicochemical and functional properties of soy protein isolate during Maillard reaction

Maillard reaction (MR) of soy protein isolate (SPI) and d-galactose with the mass ratio (4:1, 2:1, and 1:1) was conducted. The conformation of SPI was changed from ordered to disordered and the SPI molecule was unfolded and stretched after MR. The amino acids covalently bonded to the carbonyl group of d-galactose are mainly lysine and arginine of SPI. In addition, sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated the formation of constituents with high-molecular-weight during MR. The more the d-galactose content in MR, the higher the degree of glycation and surface hydrophobicity of SPI-d-galactose conjugates. The solubility at different pH, emulsifying and foaming properties of SPI were enhanced after MR, and these properties increased with the increasing of d-galactose content in MR. d-galactose enhanced the viscosity of SPI, and changed its viscoelasticity. Meanwhile, the hydrophilic d-galactose group improved the physiological and biological properties of amphiphilic SPI, the more d-galactose content in MR, the more significant the enhancement of the properties including the fat binding capacity, bile acid binding capacity, hypoglycemic effect, antioxidant and antibacterial activity. Our work showed that d-galactose had a great influence on the structure of SPI, and further affected its functionalities.