Relationship between Secondary Structure and Surface Hydrophobicity of Soybean Protein Isolate Subjected to Heat Treatment

This study investigated relationship between secondary structure and surface hydrophobicity of soy protein isolate (SPI) subjected to a thermal treatment at 70 similar to 90 degrees C. Heat denaturation increased the surface hydrophobicity and surface hydrophobicity decreased as aggregate formed. Heat caused an increase in the relative amount of alpha-helix structures and an overall decrease in the amount of beta-sheet structures when compared with nontreated SPI. The relative amounts of secondary structures varied with time, temperature, and intensity of heat treatment applied. The beta-sheet structure was most important for its significant role in denaturation of 7S globulin and following formed aggregates and even in denaturation of 11S globulin. The amount of beta-sheet structure in SPI had an inverse correlation with the surface hydrophobicity when the temperature was kept below 90 degrees C. Besides, beta-turn structure increased as beta-7S/B-11S aggregate formated.