Further evaluation on structural and antioxidant capacities of soy protein isolate under multiple freeze–thaw cycles

Multiple freeze–thaw (F–T) treatments could change a protein structure and affect its physicochemical activities. In this work, soy protein isolate (SPI) was subjected to multiple F–T treatments, and the changes in its physicochemical and functional properties were investigated. The three-dimensional fluorescence spectroscopy indicated that F–T treatments changed the structure of SPI, including an increase in surface hydrophobicity. Fourier transform infrared spectroscopy showed that SPI underwent denaturation, unfolding and aggregation due to the interchange of sulfhydryl-disulfide bonds and the exposure of hydrophobic groups. Correspondingly, the particle size of SPI increased significantly and the protein precipitation rate also increased from 16.69%/25.33% to 52.52%/55.79% after nine F–T treatments. The F–T treated SPI had a higher antioxidant capacity. Results indicate that F–T treatments may be used as a strategy to ameliorate preparation methods and improve functional characteristics of SPI, and suggest that multiple F–T treatment is an alternative way to recover soy proteins.