RELATIONSHIP BETWEEN THE METHOD OF OBTENTION AND THE STRUCTURAL AND FUNCTIONAL-PROPERTIES OF SOY PROTEIN ISOLATES .1. STRUCTURAL AND HYDRATION PROPERTIES

Soy protein isolates exhibit heterogeneous protein subunit compositions; their structural and functional properties are determined by the processing conditions. Drastic thermal conditions at pH 7 and 9 result in protein denaturation and polymerization, as evidenced by increased water retention capacity and lower solubility, surface hydrophobicity, and a higher level of AB-11S aggregates. Treatments of glycinin with urea and Na2SO3 at pH 7 incorporated 20% of sulfonate groups, resulted in no solubility losses of 11S protein A and B polypeptides, but increased their surface hydrophobicity. The increase of 7S fraction leads to an increase of aliphatic hydrophobicity. Thermal treatments at pH 7 and lower protein content lead to high solubility and high surface hydrophobicity isolates. 7S globulin was completely denatured, while 11S denaturation depended on the treatment conditions; different proportions of AB-11S, beta-7S, and B-11S aggregates were formed. Thermal treatments at pH 9 favored dissociation and denaturation of AB-11S protein.