Comparative evaluation of stability and interfacial characteristics of Pickering emulsions co-stabilized by zein and hydrocolloids: Role of charge profile, emulsifying ability, and rheological properties

This study provides the first systematic investigation of guar gum (GG) alongside xanthan gum (XG) and gum arabic (GA) in zein nanoparticle (ZNP)-stabilized Pickering emulsions, highlighting the critical role of each hydrocolloid's charge profile. While previous research has largely addressed single polysaccharide-protein systems, the interfacial behavior and functional implications of combining ZNPs with hydrocolloids of different ionic character remain underexplored. Specifically, XG imparted strong negative charges (-65.5 mV) due to its high anionic density, GA moderately shifted the charge (approximately -28 mV), and GG, being largely non-ionic, remained near neutral. Fourier-transform infrared spectroscopy and ζ-potential measurements suggest that XG stabilizes emulsions primarily through electrostatic interactions and hydrogen bonding, GA provides moderate interfacial activity via amphiphilic adsorption and weak electrostatic interactions, while GG, being non-ionic, enhances emulsion stability through steric exclusion and bulk-phase viscosity enhancement. However, given the indirect nature of these findings, the potential role of bulk-phase stabilization was not excluded. Confocal laser scanning microscopy and scanning electron microscopy confirmed the formation of dense interfacial layers in all emulsions. Among the samples, XG-based emulsions exhibited smaller droplets (15.5-17 μm) and higher storage moduli, resulting in robust gel-like networks. Under varying environmental stresses (pH 2-11, ionic strength 0-500 mM, and temperatures up to 80 °C), XG-emulsions displayed minimal droplet growth, demonstrating exceptional resilience. GA-stabilized emulsions exhibited intermediate droplet sizes (∼22 ± 2 μm) and FTIR shifts indicative of partial interaction with zein suggesting a moderately stabilizing interfacial contribution, while GG-based emulsions showed droplet sizes within 12.8-29 μm, reflecting the dominant steric stabilization. Overall, this work highlights the importance of the selection of hydrocolloids to tailor emulsion functionality. These findings offer insights for designing stable, high-performance Pickering emulsions for food and pharmaceutical applications.