Clove Oil–Loaded Zein Nanoparticles: Eugenol Release and Repellent Activity against <i>Sitophilus zeamais</i>

Pest and pathogen infestations represent major challenges in agriculture, compromising crop production and grain storage, with significant economic and social impacts on food security. Nanotechnology has emerged as a promising tool for pest management through the development of nanoparticles carrying bioactive compounds such as essential oils. Among these, clove essential oil extracted from <i>Syzygium aromaticum</i> stands out for its insecticidal and repellent activities, although its high volatility, susceptibility to photodegradation, and oxidation limit direct applications. Encapsulation in biodegradable polymeric matrices is an effective strategy to enhance stability and extend functionality. In this study, clove oil (CO) and its main component, eugenol (Eug), were incorporated into zein, a maize-derived protein, to investigate <i>in vitro</i> release kinetics and <i>in vivo</i> bioactivity against <i>Sitophilus zeamais</i>. CO was extracted from flower buds by hydrodistillation, yielding 10.3% (w/w) with 78.6% (v/v) Eug content. Zein nanoparticles (NPZ), along with CO- and Eug-loaded systems (NPZ-CO, NPZ-Eug), exhibited mean hydrodynamic diameters around 300 nm and spherical morphology. Storage assays indicated improved stability under refrigeration. <i>In vitro</i> release studies revealed gradual Eug release from NPZ-CO and NPZ-Eug over 200 min, best described by Korsmeyer-Peppas (R² > 0.93) and Weibull (R² > 0.94) models, indicating an initial burst followed by diffusion-controlled release. <i>In vivo</i> assays showed that, while the tested doses did not produce significant toxicity against <i>S. zeamais</i>, encapsulated formulations (NPZ-CO, NPZ-Eug) exhibited enhanced repellent activity compared to the free compounds after 24 h of exposure. Overall, these results indicate that zein-based nanocarriers can improve the stability of essential oils, leading to a more effective repellent response.