Interactions between whey protein isolate and soy protein fractions at oil-water interfaces: Effects of heat and concentration of protein in the aqueous phase

The 2 main storage proteins of soy-glycinin (11S) and beta-conglycinin (7S)-exhibit unique behaviors during processing, such as gelling, emulsifying, or foaming. The objective of this work was to observe the interactions between soy protein isolates enriched in 7S or 11S and whey protein isolate (WPI) in oil-water emulsion systems. Soy oil emulsion droplets were stabilized by either soy proteins (7S or 11S rich fractions) or whey proteins, and then whey proteins or soy proteins were added to the aqueous phase. Although the emulsifying behavior of these proteins has been studied separately, the effect of the presence of mixed protein systems at interfaces on the bulk properties of the emulsions has yet to be characterised. The particle size distribution and viscosity of the emulsions were measured before and after heating at 80 and 90 degrees C for 10 min. In addition, SDS-PAGE electrophoresis was carried out to determine of protein adsorption or exchanges at the interface occurred after heating. When WPI was added to soy protein emulsions, gelling occurred with heat treatment at WPI concentrations > 2.5%. In addition, whey proteins were found adsorbed at the oil-water interface together with 7SS or 11S proteins. When 7S or 11S fractions were added 11S formed complexes at the interface with whey proteins during heating.