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

Abstract

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. The preparation process of SPI emulsion samples and the structural changes of SPI molecules in the oil-water interface under different protease induction times were investigated. • Evolution of structure and properties of SPI at oil–water interface protease treated. • SPI at the oil–water interface undergo aggregation and recombination after 1.0 h. • Longer treatment time reduces the viscosity and viscoelasticity of SPI emulsion. • Electrostatic interaction and hydrogen cause the aggregation and recombination of SPI.