Chitosan-based nanoemulsions as eugenol/hexyl gallate delivery systems against Xanthomonas citri

Two systems of nanoemulsions encapsulating hexyl gallate-eugenol (GaOi) were developed for sustainable plant protection. A water-based system (GaOi-Water, F24) and a 1 % (w/v) chitosan-stabilized system (GaOi-Qs, F64) were prepared using high-energy emulsification and analyzed using DLS, AFM, and TEM. F24 displayed narrowly distributed spherical droplets (AFM: 40-150 nm; DLS mean similar to 140 nm; PDI <0.3), whereas F64 formed a chitosan-encapsulated core-shell network with larger aggregates (>400 nm) embedding smaller nanodomains (20-50 nm), consistent with a polymeric shell that may confer sustained-release kinetics. Transmission electron microscopy corroborated these architectures, showing well-defined core-shell morphologies that correlated with the sustained release behavior of F64. In addition, F64 exhibited high encapsulation efficiency and pronounced colloidal stability (vertical bar zeta vertical bar > 50 mV). Functionally, microbroth (REMA) assays showed that F64 was an order of magnitude more potent than F24 (IC90/MBC: 0.03125 %, 0.125 % v/v), an effect attributed to the potential disruption of the membrane by possible synergistic interaction and the prolonged availability of the antifungal on the surface. Crucially, acute ecotoxicity tests on two stingless bee species (Melipona scutellaris and Scaptotrigona postica) revealed no mortality or feeding impairment at active doses. Greenhouse trials on sweet orange demonstrated lesion reductions comparable to commercial copper sprays, using markedly lower active loads. Thus, the results link nano-architecture to release behavior and biological outcomes, illustrating a materials-driven pathway for high-efficacy, pollinator-safe crop protection. The GaOi-chitosan system represents a scalable and environmentally sound alternative to metal-based bactericides with strong potential for field translation.