Protease-induced soy protein isolate (SPI) characteristics and structure evolution on the oil–water interface of emulsion

The evolution of the microstructures and properties of soy protein isolate (SPI) at the oil–water interface under the induction of protease within 0.5 h and 2.0 h were analyzed by macroscopic characterization and structural analysis. There were significant differences in average particle size, zeta potential, microstructure, FT-IR, Raman and endogenous fluorescence of emulsion samples produced by different treatment times. Visual comparison showed the relatively uniform aggregation and distribution of SPI on the interface when induced for 1.0 h and characterized by zeta potential and rheology. Moreover, in FT-IR, Raman and intrinsic fluorescence spectra, it was found that with the induction of 0.5–2.0 h, the content of the β-turn structure was highest at 1.0 h, and strong fluorescence quenching occurred, which indicated that SPI at the interface was hydrolyzed into small peptides, and aggregated at 1.0 h and then hydrolyzed. What is more, no significant change in rheological properties was observed after induction for 1.5 h and 2.0 h. The results indicated that there existed –CO– and –NH binding due to electrostatic interaction and hydrogen bonding at 1.0 h, which caused the recombination of SPI molecules at the interface.