Interfacial and (emulsion) gel rheology of hydrophobised whey proteins

Hydrophobisation of whey proteins, followed by erythritol addition into the hydrophobised protein dispersion, enables formation of water-in-water (W/W) emulsions of the proteins and alginate. In this study, we investigated the interfacial and gel rheology of whey proteins as affected by hydrophobisation, heat denaturation and erythritol addition. Additionally, the gel rheology of the resultant W/W emulsion was assessed. Hydrophobisation shortened the linear viscoelastic region and decreased the surface storage modulus (G_s ^'), the flow stress and the flow strain of protein layer at the air-liquid interface. Erythritol addition into the hydrophobised protein caused a further reduction of G_s ^'. In accordance with interfacial rheology, protein hydrophobisation and erythritol addition decreased the dynamic moduli of acid-induced protein gels. Frequency sweep tests indicated that the gelled emulsion had higher dynamic moduli than all WPI gels. The higher firmness of the emulsion gel was ascribed, based on microstructural images, to micro-phase separation of alginate droplets.