Effect of surface charge density of bacterial cellulose nanofibrils on the properties of O/W Pickering emulsions co-stabilized with gelatin

In this study, the effect of bacterial cellulose nanofibrils (BCNF) surface charge density on the emulsification capacity of gelatin (GLT)/BCNF mixtures was investigated. Emulsions with 50 v% oil phase were co-stabilized by GLT and BCNFs (surface charge densities varied from 0.34 to 1.16 mmol/g) at pH 7.0 (GLT and BCNFs were negatively charged) and pH 4.7 (electrostatic equilibrium point for all GLT/BCNF mixtures). At pH 7.0, as BCNF surface charge density increased, the oil-water interfacial tension was decreased. Thus, the emulsion droplet size was reduced from 14.24 to 13.51 μm when the BCNF surface charge density was improved from 0.34 to 1.16 mmol/g. Additionally, the emulsion stability was significantly improved by the addition of highly-charged BCNF due to the increased electrostatic repulsion between dispersed droplets. At pH 4.7, the highest level of attractive electrostatic interaction was observed for GLT and BCNF with a surface charge density of 1.16 mmol/g (BCNF 1.16). Thus, the GLT/BCNF 1.16 suspension exhibited the highest viscoelastic modulus. At pH 4.7, the stability of GLT/BCNFs co-stabilized emulsions was improved by increasing BCNF surface charge density due to the enhanced viscosity. The emulsions prepared with GLT and BCNFs with surface charge density higher than 0.66 mmol/g at pH 4.7 could keep stable without creaming for 30 d. Furthermore, the GLT/BCNF 1.16, with the most remarkable emulsion stabilizing capacity, was successfully applied to prepare high internal phase emulsions with a more stable and higher viscoelastic behavior. This study was meaningful for the regulation of emulsion stability and rheological property.