Sprayable ultra-stable chitosan-based water-in-water emulsion gels for enhanced fruit preservation

Aqueous two-phase system (ATPS) is widely used in biotechnology owing to their excellent permeability, affinity partitioning, biocompatibility, and mild all-aqueous conditions. However, their extremely low interfacial tension renders them vulnerable to droplet collisions and prone to stratification, resulting in poor stability and low utilization efficiency. Herein, we report an ultra-stable water-in-water (W/W) emulsion gels derived from an ATPS, using dextran/poly(ethylene glycol) as the template and chitosan (CS) as the emulsifier. The CS molecules were conjugated with 2-furaldehyde (FAL) via imine bonds, enabling the formation of emulsion gels within 2 min. The W/W emulsion gels exhibited no macroscopic phase separation for up to 6 months, and withstood low/high temperatures (-18 °C/70 °C) as well as centrifugation (6000 rpm, for 40 min). They also showed sprayability and excellent physicochemical properties, which effectively alleviated retention and coverage issues by reducing fragmentation and enhancing local pinning and wetting processes. With mangoes used as a model system, microbial proliferation on mango surfaces was significantly inhibited after spraying with the W/W emulsion gels, achieving a 99.8 % antibacterial inhibition rate and reducing mango decay by 46.0 %. This work presents a promising strategy for developing scalable, low-cost, biodegradable, and eco-friendly antibacterial preservation systems.