PUL/HPMC water-in-water Pickering emulsions stabilized by cellulose nanocrystals and cellulose nanofibers: construction, stabilization mechanism, and stability

Water-in-water (W/W) Pickering emulsions have aligned with the increasing consumer demands for health foods due to their entirely aqueous formulation with oil-free. In this work, Pullulan (PUL) and Hydroxypropyl methylcellulose (HPMC) were used to construct polysaccharide-based W/W Pickering emulsion system. PUL and HPMC concentrations played crucial roles in droplet sizes and phase behavior of PUL/HPMC Pickering emulsions. Cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) were used as stabilizers to prepare PUL/HPMC Pickering emulsions and the stabilization mechanisms were investigated. PUL/HPMC Pickering emulsions stabilized by CNCs with a rigid rod-like structure and strong interfacial adsorption capacity exhibited smaller and more uniform droplet morphology and higher storage stability, whereas the flexible fibrillar CNFs tended to form entangled networks in the continuous phase and bridge droplets, resulting in droplet deformation and coalescence. Furthermore, environmental stability of PUL/HPMC Pickering emulsions revealed that increasing CNCs concentration could significantly enhance their centrifugal and thermal stability. This work would provide a novel insight into the stabilization behavior of nanocellulose with different morphologies in W/W Pickering emulsions and broaden potential applications of W/W Pickering emulsions in functional food fields.