Hydrolates as Sustainable Phytochemical Platforms for Nano-Enabled Strategies in Food Preservation, Active Packaging, and Sustainable Agriculture

Hydrolates are aqueous distillation byproducts generated during the production of essential oils from aromatic and medicinal plants. Although historically considered low-value residual streams, they contain water-compatible volatile and semi-volatile compounds, including oxygenated terpenes, phenolic derivatives, alcohols, aldehydes, and ketones, which may support antimicrobial, antioxidant, and complementary biological activities. This review critically examines hydrolates as sustainable phytochemical platforms for nano-enabled applications in food preservation, active packaging, and agriculture. Particular attention is given to the relationship between hydrolate composition, biological activity, technological limitations, and formulation strategies. The current evidence indicates that hydrolates should not be interpreted as diluted essential oils, but rather as chemically distinct aqueous systems with specific advantages, including compatibility with hydrophilic matrices, lower sensory intensity, and potential contribution to circular economy models. However, their practical application remains limited by compositional variability, low concentration of bioactive compounds, physicochemical and microbiological instability, lack of standardized production and characterization protocols, and limited validation under real application conditions. Nano-enabled systems, including nanoemulsions, liposomes, polymeric nanoparticles, nanogels, thermoresponsive matrices, and active films or coatings, may improve hydrolate stability, retention, controlled release, and functional performance. Nevertheless, hydrolate-specific evidence remains scarce, and many current perspectives are still extrapolated from studies on essential oils, plant extracts, or isolated natural compounds. Future research should prioritize quantitative bioactivity assessment, stability studies, realistic food and agricultural models, safety evaluation, scalability, regulatory planning, and sustainability analysis. Overall, hydrolate valorization through nano-enabled strategies represents a promising but still emerging pathway for transforming aqueous distillation byproducts into functional systems for sustainable applications.