The pH-responsive interfacial behaviour of rice bran nanocellulose and its impact on Pickering emulsion stability and...

Rice bran nanofibers (RBNFs) are promising sustainable, food-grade stabilizers for Pickering emulsions (PEs) due to their interfacial activity and network-forming ability. In this study, the pH-responsive interfacial behaviour of RBNFs and its effect on PEs stability and structural progression were investigated. Interfacial properties at air-water and water-oil interfaces demonstrated significantly improved rearrangement kinetics (-50.00 × 10^-4 s^-1 and - 57.67 × 10^-4 s^-1, respectively) at pH 10, indicating a higher affinity for interfacial rearrangement. Interfacial rheology and the Lissajous plots showed that RBNFs at higher pH exhibited enhanced interfacial elasticity and more resilient interfacial networks at both air-water and water -oil interfaces. At pH 10, positive S-factors of 0.8 and 5.12 at air-water and oil-water interface respectively indicate intra-cycle strain stiffening, confirming interfacial network resilience. Physicochemical characterisations, including particle size distribution, zeta potential, rheological properties, confocal laser scanning microscopy (CLSM) and creaming index measurements, demonstrated that emulsions prepared at pH 7 and pH 10 exhibited the highest colloidal stability. PEs at pH 7 and 10 displayed comparable droplet sizes (D [4,3] of approximately 3 μm after 35 days of storage), shear-thinning flow behaviour, and gel-like viscoelasticity (G' > G″). The emulsions at pH 7 were further used to develop "creams" which, exhibited spreadable rheological characteristics acted as the bulk structuring agents. Cryo-SEM imaging demonstrated the retention of entrapped oil droplets within a dense nanofiber network. Overall, this work demonstrates that pH-modulated interfacial behaviour of RBNFs can be used to design texture-driven Pickering systems, expanding their potential applications in clean-label food formulations.