Fuente: Molecules - Revista científica (MDPI) Molecules, Vol. 31, Pages 1833: 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)
Molecules doi: 10.3390/molecules31111833
Authors:
Achilleas Kechagias
Andreas Giannakas
Panagiotis Stathopoulos
Maria Xenaki
Areti A. Leontiou
Anna Kopsacheili
Nikolaos Chalmpes
Emmanuel P. Giannelis
Constantinos E. Salmas
Charalampos Proestos
Aris E. Giannakas

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.