Purification and identification of interacting components in a wheat starch–soy protein system

The objective of this research was to quantify the solubility, hydrophobicity and interaction characteristics of wheat–starch proteins (puroindoline, gliadin and glutenin) and protein-containing soy fractions (soy flour isolate [SFI], SFI 7S and 11S fractions, hexane-extracted textured soy flour [TVP] isolate, TVP 7S and 11S fractions, expelled, extruded soy flour [TSP] isolate, TSP 7S and11S fractions). Functional characteristics were assessed in aqueous sucrose solutions at pH 5.5 and 7.5 after heating to 25, 50, and 100 °C. Textured soy protein fractions were more soluble and had higher surface hydrophobicity profiles than their untextured counterparts. Sucrose addition decreased hydrophobicity in the textured proteins but increased it in untextured proteins. Characteristics of the isolate, as a whole, appear to be dictated by those of its 11S moiety. Dissociation constants (Kd values) for soy protein and starch-derived puroindoline were determined and indicated an extremely short association in all cases. The 11S fractions formed a complex with puroindoline in solution; however 7S fractions did not.