Relationship Between Surface Hydrophobicity and Structure of Soy Protein Isolate Subjected to Different Ionic Strength

The impact of ionic strength on surface hydrophobicity, solubility, and spatial structure of soy protein isolate were investigated in this article. Surface hydrophobicity was found to be negatively correlated with its solubility as ionic strength increased. The changes in spatial structure of soy protein isolate accounted for the increased surface hydrophobicity caused by ionic strength. Specifically, changes in secondary structures by increased ionic strength were mainly reflected in the increased random coil and decreased alpha-helices content, which suggested that ionic effects may loosen the protein structures and result in the modification of surface amino acid distribution. This is further verified by the shifted lambda(max) in fluorescence spectra of tryptophan and relative high I-850/I-830 value in Raman spectra, which was an indicator of the exposure degree of tyrosine residues on the surface of the protein. In addition, the changes in vibration modes of disulfide bonds reflected by Raman spectra also support the impact of saline on the surface hydrophobicity and structure of soy protein isolate. It is believed that these findings could be helpful to understand the impact of salinity on the surface hydrophobicity of soy protein isolate as well as to predict the other functional characteristics of soy protein isolate in system.