Biodegradable bilayer active packaging with unidirectional release: PLA/ZnO/MgO outer layer and gelatin electrospun mat incorporating eugenol-thymol for cucumber preservation.

Fresh cucumbers are highly perishable due to moisture loss, microbial infection, and oxidative deterioration. In this study, a biodegradable bilayer active packaging film with unidirectional release was developed for cucumber preservation. The outer PLA layer was reinforced with 2 wt% of a 1:1 ZnO/MgO nanoparticle mixture, exhibiting enhanced hydrophobicity, mechanical strength (tensile strength 62.75 MPa), reduced water vapor permeability (88.7 g/m2·24 h), and excellent UV-blocking. The inner layer was prepared by electrospinning gelatin loaded with 0.2-0.4 wt% eugenol (EUG) and thymol (THY). Unidirectional release evaluation showed that >92% of EUG and THY were released toward the food simulant via a non-Fickian diffusion mechanism (n = 0.54-0.57). The films exhibited concentration-dependent antimicrobial and antioxidant activities. During 21 days of storage at 4 °C, cucumbers packaged with the EUG/THY-loaded bilayer films showed significantly lower weight loss, reduced color deterioration, and enhanced antioxidant enzyme activities. The 0.4% EUG/THY formulation extended cucumber shelf life to 18-20 days. This bilayer design offers a promising strategy for eco-friendly active packaging with unidirectional release for fresh produce preservation.