Functional and Structural Properties of 2S Soy Protein in Relation to Other Molecular Protein Fractions

Abstract

The purpose of this investigation is to develop a better understanding of the structure-function relationship of the 2S fraction of soy protein that has not been considered in earnest by the research community. Defatted soy flour was used to extract the three major fractions of the protein (2S, 7S, and 11S). It was found that 2S exhibits better foaming and emulsification properties than the other two molecular fractions. Work was extended to structural properties, which were monitored using spectrophotometry, atomic force microscopy, scanning electron microscopy, small-deformation dynamic oscillation on shear, and large-deformation compression testing. An experimental protocol utilizing glucono-delta-lactone (GDL), GDL with N-ethylmaleimide, or GDL with urea was capable of identifying the nature of molecular interactions responsible for gelation. Surprisingly, it was found that in the initial stages of structure formation, 2S fared better than 7S, with 11S exhibiting the highest rates of aggregation. Given time, however, 7S produced a firmer network with a better water-holding capacity than that of 2S. Non-covalent interactions, as opposed to disulfide bridging, were found to be largely responsible for the changing functionality of the molecular fractions throughout the experimentation from the formation of a vestigial structure to that of a mature gel.