Abstract:In order to explore the effect of freezing on soybean protein isolate（SPI），this research chose 0.04 g/mL soy protein isolate solution for research，used-5℃ and-20℃ as freezing temperature for 3 days，and used Fourier infrared spectroscopy，endogenous fluorescence spectroscopy，sodium dodecyl sulfate polyacrylamide gel electrophoresis（SDS-PAGE），inverted fluorescence microscope and other methods to investigate the changes in microstructure and emulsifying properties of SPI.The electrophoresis results showed that the composition of the frozen SPI subunits was basically the same as that of the non-freezing SPI，indicated that freezing made the protein reversible；through endogenous fluorescence spectroscopy，it was found that the maximum absorption peak of the frozen samples were at 340 nm，tertiary conformation of the frozen SPI changed；application Fourier infrared spectroscopy and Gaussian smoothing and deconvolution analysis of the spectrum showed that the that the β-type structure of the protein after freezing was less than 80%，β-sheet and random coil structure of the protein increased after freezing，and the β -turn decreased，indicated that the freezing made the structure of the SPI tended to be ordering.Through studied the particle size distribution，stability and microstructure of the 0.002 g/mL SPI emulsion，it was found that the particle size of the SPI emulsion without freezing treatment was mostly below 20 μm.After freezing，the particle size peak shape of the emulsion had widened，and most of the particle size distribution were between 10 μm-50 μm，indicating that aggregates were produced；Through the observation of the microstructure of the emulsion and the determination of the stability，it was found that there were protein aggregates in the frozen SPI emulsion and the stability was significantly worse than that of the protein emulsion without freezing，it showed that freezing treatment had an adverse effect on the structure and emulsifying properties of SPI.