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

Hydrolates are aqueous co-products of aromatic-plant distillation whose composition and functionality differ from those of the corresponding essential oils. This critical review links botanical source, distillation conditions, chemical composition, quantitative biological performance, food or agricultural application, and readiness for nano-enabled formulation. Direct hydrolate studies show marked heterogeneity: reported antimicrobial performance ranges from minimum inhibitory concentrations of 5.69–500 μL mL−1 to approximately 1–3.5 log reductions in food models, while antioxidant results depend strongly on the assay and reporting unit. Evidence in foods is most developed for fresh produce, seafood, dairy, meat, and beverages, but direct bakery validation remains a gap. Hydrolates offer aqueous compatibility and generally lower sensory intensity than essential oils, yet low active-compound concentrations, batch variability, microbiological susceptibility, and limited shelf stability restrict reproducible use. Among nano-enabled solutions, one direct lavender-hydrolate nanoemulsion study reported a diameter of 225.4 ± 3.2 nm and a polydispersity index of 0.098 ± 0.011, together with improved antibacterial activity; however, hydrolate-specific encapsulation efficiencies, release kinetics, long-term stability, food validation, and field trials are largely unreported. Liposomes, polymeric nanoparticles, nanogels, and active films therefore remain mostly transferable concepts supported by essential-oil, extract, or isolated-compound studies rather than established hydrolate technologies. Future work should use standardized production and quality markers, free-hydrolate and unloaded-carrier controls, realistic matrices, safety and non-target testing, scale-up analysis, and quantitative sustainability assessment. Hydrolates are promising sustainable phytochemical resources, but claims of nano-enabled advantage require direct comparative evidence.