The radiation assisted-Maillard reaction comprehensively improves the freeze-thaw stability of soy protein-stabilized oil-in-water emulsions

For the first time, the irradiation technology combined with Maillard reaction were used to improve the freeze - thaw stability of soybean protein emulsion. The freeze-thaw stability of emulsions prepared with soy protein isolate (SPI), soy protein isolate and maltose mixture (SPI + M) or glycosylated soy protein isolate with maltose formed by irradiation of 7.5 kGy and 12.5 kGy (named SPI-M7.5 and SPI-M12.5, respectively) was compared. Fourier transform infrared spectroscopy, fluorescence spectroscopy and ultraviolet spectroscopy confirmed the change of the structure of soy protein isolate, indicating that maltose was covalently linked to soybean protein isolate. Scanning electron microscopy showed that the modified protein particles were more loose, uniform in size, and significantly reduced in molecular aggregation than untreated protein. The freeze-thaw stability of SPI, SPI + M, and SPI-M7.5 and SPI-M12.5 emulsions was evaluated. It was found that after three freeze-thaw cycles, the creaming index, oiling off, particle size, coalescence degree and flocculation degree of emulsions prepared with irradiated SPI samples were all lower than those prepared with SPI and SPI + M. Zeta potential, laser confocal and optical microscopy showed that the emulsion was still in a relatively stable state, and the SPI-M7.5 emulsion after freeze-thaw treatment was more stable than the SPI-M12.5 emulsion.