Nanoencapsulation of Cinnamon Essential Oil in Zein: Physicochemical Properties, In Vitro Release, and Antifungal Activity

Prolonged use and improper application of conventional fungicides can lead to pathogen resistance, pose risks to nontarget organisms, and increase environmental contamination. For instance, bean anthracnose, caused by Colletotrichum lindemuthianum, is a highly aggressive foliar disease affecting common bean crops. To address this, a zein-based nanocarrier loaded with cinnamon essential oil (Z-CEO) was developed as a promising and eco-friendly solution for controlling bean anthracnose without inducing toxic effects in zebrafish (Danio rerio), a model nontarget organism. The nanoparticles were prepared via ultrasound-assisted nanoprecipitation and characterized using UV–vis spectroscopy, FT-IR, TGA, DLS, SEM, and TEM. Z-CEO nanoparticles exhibited a spherical morphology with an average particle size of 208 nm and a zeta potential of +9.70 mV. FT-IR spectra revealed hydrophobic interactions and hydrogen bonding between zein and CEO, while thermal analysis confirmed enhanced thermal stability of encapsulated CEO compared to its free form. Over 1 year of storage, the nanoparticles increased in size by approximately 30 nm, indicating that their submicron size was largely maintained. High encapsulation efficiency was also retained, with CEO loss below 10%. In vitro release studies showed similar CEO release rates at pH 4.0 and 8.0, with slower release at pH 6.0. Z-CEO completely inhibited mycelial growth at 0.5 mg/mL and significantly reduced disease severity in in vivo trials, particularly at 1.5 mg/mL. The reduction in disease severity may be related to the decreased contact angle of Z-CEO on the leaf surface, which likely promoted the formation of a protective film. Biosafety assessments confirmed that treatment with Z-CEO did not affect photosynthetic pigment levels in bean plants compared to water-treated controls. Furthermore, at environmentally relevant concentrations (0.001–1 mg/L), the formulation was nontoxic to adult zebrafish, with survival rates remaining unchanged, indicating its safety. Overall, this study successfully developed a sustainable nanobiofungicide with strong potential for the safe and effective management bean anthracnose.