Water-in-water Pickering emulsion stabilized by cellulose nanocrystals as space-confined encapsulating systems: From establishment to stability

The development of new water-in-water (W/W) emulsion systems and the improvement of the long-term stability of emulsions could create opportunities for studying interfacial bionic systems and microencapsulation applications. In this study, the new W/W emulsion systems were constructed from hydroxypropyl methylcellulose (HPMC) and maltodextrin (MD). The effects of cellulose nanocrystals (CNC) and environmental factors (ionic strength and pH) on the stability of W/W Pickering emulsions were investigated. The stabilizing effect was observed at contents of CNC as low as 0.025 wt%. The W/W Pickering emulsion showed no phase separation within 30 days when the CNC concentration was above 0.025 wt%, indicating that the emulsions were stable during the observation period. The stability of W/W Pickering emulsions was driven by the electrostatic repulsion provided by the CNC adsorbed at the droplet interface, which decreased with increasing NaCl concentration. This was attributed to the charge-shielding effect of NaCl weakening the electrostatic repulsion of the CNCs at the emulsion droplet interface. Lactobacillus helveticus cells were encapsulated in the W/W Pickering emulsion. These results revealed that the developed W/W Pickering emulsions have potential applications in protecting the activity of probiotic bacteria and investigating the behavior of cells in restricted spaces.