Development of food-grade Pickering emulsions stabilized by a biological macromolecule (xanthan gum) and zein

In this work, food-grade sunflower oil/W Pickering emulsions stabilized by xanthan gum-zein complex were developed. For this purpose, laser diffraction, rheological, multiple light scattering, confocal laser scanning microscopy (CLSM) and field emission scanning electron microscopy (FESEM) measurements were carried out. A response surface methodology was used to determine the optimized zein and oil concentration of the emulsion by using D_4,3 and Turbiscan Stability Index (TSI) as objective functions to minimize. Subsequently, the optimized formulation with minimum D_4,3 was selected and the biological macromolecule, advanced performance xanthan gum (APXG), was added. CLSM results of emulsions without gum showed the location of zein in the oil-water interface protecting droplets against coalescence as Pickering stabilizer. They also demonstrated that zein did not present important aggregation at the working pH. The addition of APXG changed the flow behaviour from Newtonian to shear thinning which fitted to the Cross model. This fact provoked the occurrence of viscoelastic properties and an increase in stability. FESEM results suggested the formation of a zein-gum complex, which forms a layer covering the droplets, protecting them against oxidation and physical destabilization. Therefore, this research supports the role of zein-APXG complex as a stabilizer of future emulsions.