Designing Gel-Inspired Food-Grade O/W Pickering Emulsions with Bacterial Nanocellulose–Chitosan Complexes

This study explored the potential of chitosan (CH)/bacterial cellulose (BC) complexes (0.5% <i>w</i>/<i>v</i>) as novel emulsifiers to stabilize oil-in-water (o/w) Pickering emulsions (20% <i>v</i>/<i>v</i> sunflower oil), with a focus on their gel-like behavior. Emulsions were prepared using CH combined with BNC derived via H₂SO₄ (BNC1) or H₂SO₄-HCl (BNC2) hydrolysis. Increasing BNC content improved stability by reducing phase separation and enhancing viscosity, while CH contributed interfacial activity and electrostatic stabilization. CH/BNC1_25:75 emulsions showed the highest stability, maintaining an emulsion stability index (ESI) of up to 100% after 3 days, with minimal change in droplet size (R_h ~8.5-8.8 μm) and a positive ζ-potential (15.1-29.8 mV), as confirmed by dynamic/electrophoretic light scattering. pH adjustment to 4 and 10 had little effect on their ESI, while ionic strength studies showed that 0.1 M NaCl caused only a slight increase in droplet size combined with the highest ζ-potential (-35.2 mV). Higher salt concentrations led to coalescence and disruption of their gel-like structure. Rheological analysis of CH/BNC1_25:75 emulsions revealed shear-thinning behavior and dominant elastic properties (G' > G″), indicating a soft gel network. Incorporating sunflower-seed protein isolates into CH/BNC1 (25:75) emulsions led to coacervate formation (three-layer system), characterized by a decrease in droplet size and an increase in ζ-potential (up to 32.8 mV) over 7 days. These findings highlight CH/BNC complexes as sustainable stabilizers for food-grade Pickering emulsions, supporting the development of biopolymer-based emulsifiers aligned with bioeconomy principles.