The linear/nonlinear rheological behaviors of Pickering emulsion stabilized by Zein and Xanthan gum: Effect of interfacial assembly strategies

Abstract

Protein/polysaccharide complexes have been widely used to fabricate Pickering emulsions, yet their linear and nonlinear rheological behaviors have received little attention. In this work, two interfacial assembly strategies of layer-by-layer (LBL) and directly mixed (DM) were employed to create zein (2%, 1%, w/v)/xanthan gum (XG) (0.8%, 0.4%, 0.2%, w/v) complex Pickering emulsions (oil phase: aqueous phase = 1:2). Both small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS) behaviors were investigated. Results showed that regardless of interfacial assembly strategies, emulsions exhibited relatively smaller droplet size, but had higher viscosity and storage modulus (SAOS test) with XG concentrations at 0.8% (w/v). The steady shear test showed LBL emulsions had superior viscosity, with a minor difference between DM and LBL emulsions in the linear SAOS test. Both interfacial assembly strategies resulted in emulsions exhibiting a hysteresis loop and a thixotropic recovery rate above 85%. The Elastic/Viscous Lissajous plots revealed that the elasticity and stiffness were affected by interfacial assembly strategies. LBL emulsions showed a more pronounced secondary loop, accompanied by a greater thixotropic restructuring time scale. The micromorphology contributed to the diverse linear and nonlinear behaviors, with the zein-XG complex mixed layer coating the oil droplets in DM emulsions and XG being added to a previously zein-emulsified emulsion to form a multilayer in LBL emulsions. In addition, emulsions showed a well-distributed nature, with no oil-off phenomena observed during centrifugal, salt, and thermal treatments. Results illustrated the effect of interfacial assembly strategies on the linear/nonlinear rheological behavior of Pickering emulsion. Our study might be helpful in preparing Pickering emulsion as edible ink for 3D printing and as a fat replacer.