Nanoparticles assembled from mixtures of whey protein isolate and soluble soybean polysaccharides. Structure, interfacial behavior and application on emulsions subjected to freeze-thawing

In this article, the freeze-thaw stability of emulsions prepared with nanoparticles assembled from mixtures of whey protein isolate (WPI, 2.0% w/w) and soluble soybean polysaccharides (SSPS, 0.5% w/w) was assessed. The assembly was performed by pH adjustment to 3.0 without and with heating (90 degrees C, 15 min). Moreover, the order of addition of SSPS to proteins, before or after heating, was also studied. The complexes were characterized by dynamic light scattering, turbidity, non-sedimentable protein content, aromatic surface hydrophobicity (H0), interfacial tension and interfacial rheology measurements at the oil/water interface. In all cases, the dispersions evidenced slightly-positive zeta-potential values due to electrostatic associative interactions between proteins and SSPS. Moreover, the complexation increased the particle size, the interfacial activity and the non-sedimentable protein content. Oil-in-water emulsions (30% w/w sunflower oil) prepared with unheated WPI/SSPS mixtures were more stable to freeze-thawing (-18 degrees C, 72 h; 20 degrees C, 2 h) respect to those prepared with WPI alone. When SSPS was added to previously heated proteins, the resultant emulsions also evidenced a high freeze-thaw stability. The large sedimentable species, which contributed to form a film of high viscoelasticity, could stabilize the emulsions by a Pickering mechanism. However, when SSPS and WPI were heated together, the resultant emulsions exhibited a low freeze-thaw stability due to a combination of poor emulsification ability and limited interfacial adsorption of large particles. The results of this article might have important implications in the preparation of highly acidic emulsion-based products resistant to freeze-thaw treatments.