Effect of xanthan gum on walnut protein/xanthan gum mixtures, interfacial adsorption, and emulsion properties

Effect of xanthan gum (XG) on the walnut protein/xanthan gum mixtures (WP/XG, 1.2 wt% WP and 0–0.30 wt% XG), interfacial adsorption and emulsions properties was studied. As XG concentrations increased, the aqueous solutions of WP/XG mixtures were clear at pH 7.0 as shown by phase diagram, however, bigger hydrodynamic diameter (DH) and lower negative ζ-potential were observed which might be resulted from the formation of the co-solubilized WP/XG mixtures induced by electrostatic and hydrophobic interactions. As adsorption time prolonged, interfacial pressure (π), dilatational modulus (E), and dilatational elasticity (Ed) continuously increased, diffusion rate (kdiff) firstly increased and then decreased, inversely, penetration rate (kP), rearrangement rate (kR), dilatational viscosity (Ev) and loss-angle tangent (tanθ) decreased. These results indicated that XG promoted WP molecules to be continuously adsorbed to oil-water interface and formed firmer elastic interfacial films, possibly due to lower thermodynamic compatibility or higher viscosity. The oil droplets in emulsions stabilized by WP/XG mixtures had larger d4,3 and lower negative ζ-potential, and flocs were observed by CLSM images, which might be related to the adsorption of WP. Emulsions exhibited pseudo-plastic and shear-thinning properties by flow behavior measurements, and emulsions stability presented by creaming index (CI) was firstly decreased caused by flocs and then increased due to higher viscosity.