The effect of ionic strength on structure and surface hydrophobicity of soy protein isolate

Surface hydrophobicity of proteins depends not only on source of protein,conditions and method of processing,but aslo on physicochemical properties and structure characteristics. In the viewpoint of protein molecular conformation and solution properties,this study focused on ionic strength on structure and surface hydrophobicity of soy protein isolate with biochemical,spectroscopic methods,to definite the relationship between the spatial conformation and surface hydrophobicity of soybean protein isolate. The main results were as follows:surface hydrophobicity of soy protein isolate significantly decreases at both sides of isoelectric point. Soy protein isolate showed “ salting- out ” phenomenon, surface hydrophobicity increased with the increasing ionic strength. The increasing λ_max of soybean protein isolate with ionic strength suggested that tryptophan residues tend to hydrophilic microenvironment. As ionic strength from 0.1 mol/L to 0.9 mol/L,the content of α-helix structure increased while the percentage of β-sheet structure decreased to 35.19%,the content of β-turn structure showed a slight reduction. Random coil structure showed a significant positive correlation with surface hydrophobicity value(r=0.81,p<0.05) from correlation analysis. The average particle size of protein molecular generally increased with ionic strength,the absolute value of zeta potential declined in general,and also showed a significant negative correlation with surface hydrophobicity(r=-0.86,p<0.05). This study provided theoretical basis for the deeper processing of soybean and application for high value.