Microwave-Assisted Rapid Extraction of Oleuropein from Olive Leaf By-Product and Processing into Oleuropein@Zeolite Nanohybrids for Antioxidant Food Applications (Fortified Salt and Active Gelatin Films)

Olive leaves are an abundant agro-industrial by-product rich in oleuropein, yet they remain largely underutilized. The objective of this study is to a) develop a green microwave-assisted extraction (MAE) method for an oleuropein-rich extract, b) encapsulate it into edible natural zeolite to form OLE@NZ nanohybrids, and, c) evaluate their application in fortified salt and active gelatin films. MAE using only water at 96 °C for 5 min yielded a dry extract with 25.4% (w/w) oleuropein and a total phenolic content of 781 mg GAE/100 mL. The extract was successfully adsorbed onto clinoptilolite-type zeolite and the resulting nanohybrids showed strong antioxidant activity (EC50,DPPH = 2.74 mg, TPC = 426 mg GAE/g). A fortified salt containing 5% w/w OLE@NZ fully preserved the nanohybrid’s antioxidant activity. Extruded gelatin films incorporating 5–15% OLE@NZ exhibited a concentration-dependent increase in antioxidant activity (up to 14-fold higher than the blank film), together with a 5- to 7-fold enhancement, while maintaining good mechanical properties. The total phenolic content of the films correlated linearly with nanohybrid loading, with phenolic recovery of 68% both at 5 and 10% loading and 58% at 15%). Overall, these findings demonstrate that MAE is a rapid, and environ-mentally friendly approach for obtaining oleuropein-rich olive leaf extract (OLE), while OLE@NZ nanohybrids provide effective antioxidant additives for functional salt formulations and active gelatin films, supporting a circular bioeconomy strategy.