Antioxidant Nanohybrid Materials Derived via Olive Leaves Extract Incorporation in Layered Double Hydroxide: Preparation, Characterization, and Evaluation for Applications

In this study, an innovative approach for the valorization of olive leaves—an underutilized agro-industrial by-product—was employed through enzymatic-assisted aqueous extraction to obtain a polyphenol-rich olive leaf extract (OLE). The extract was found to contain significant levels of hydroxytyrosol (0.53 mg/L), luteolin-7-O-glucoside (0.70 mg/L), apigenin-4-O-glucoside (0.18 mg/L), and oleuropein (4.24 mg/L). For the first time, this OLE was successfully nanoencapsulated into layered double hydroxides (LDHs) synthesized at three Zn²⁺/Al³⁺ molar ratios (1:1, 2:1, and 3:1) to form OLE@LDH_Zn/Al_x/1 nanohybrids. The hybrids were thoroughly characterized by XRD, FTIR, and SEM, confirming the intercalation of OLE into the LDH interlayer structure. Antioxidant activity (via DPPH assay), total polyphenol content (TPC), and antibacterial tests (disk diffusion, MIC, and MBC) were conducted to evaluate functionality. Among the nanohybrids, OLE@LDH_Zn/Al_1/1 exhibited the highest TPC (606.6 ± 7.0 mg GAE/L), the lowest EC₅₀ (83.64 ± 5.45 μg/mL), and superior antibacterial performance against E. coli and S. aureus. Moreover, pH-dependent release profiles confirmed targeted release at acidic conditions (pH 1), simulating gastric environments. These findings suggest that LDHs, especially with a Zn/Al ratio of 1:1, are promising carriers for the stabilization and controlled release of bioactive polyphenols in nutritional and biomedical applications.