Impact of whey protein complexation with phytic acid on its emulsification and stabilization properties

Abstract

The functional performance of food proteins can sometimes be enhanced by forming conjugates or complexes with other food-grade molecules. In this study, the impact of fabrication conditions (pH and mixing ratio) on the formation and properties of phytic acid (PA)-whey protein isolate (WPI) complexes was evaluated. In addition, the ability of the complexes to form and stabilize oil-in-water emulsions was characterized. Emulsions were formed using a high-shear mixer to simulate the production of commercial foods such as dressings and sauces. Most emulsions were highly unstable to creaming due to the relatively large size of the oil droplets they contained (d > 30 μm). Under acidic conditions, emulsions stabilized by PA-WPI complexes were more resistant to creaming and formed thicker cream layers than those stabilized by WPI alone, which was attributed to electrostatic bridging of the cationic protein-coated oil droplets by anionic phytic acid. Evidence for increased droplet-droplet attraction was confirmed by bulk rheology measurements: emulsions stabilized by PA-WPI complexes had a much higher viscosity than those stabilized by WPI. Interfacial tension measurements showed that the PA-WPI complexes adsorbed to an oil-water interface more rapidly than either PA or WPI molecules, as well as producing a greater reduction in interfacial tension. Surface rheology measurements indicated that the dilatational elastic modulus of the interfaces formed by the PA-WPI complexes was less than that formed by WPI alone, indicating that the PA inhibited interfacial protein cross-linking. Our results, indicate that even relatively low PA-to-WPI ratios (1:20) can be used to modulate the physicochemical properties and long-term stability of protein-coated oil droplets, thereby providing an effective strategy for designing food emulsions with improved functionality.