Asymmetric Janus composite films with superior humidity regulation capabilities for the efficient preservation of strawberry fruit

This study aims to report the limitations of single-layer film packaging to control relative humidity and preventing water vapor condensation within packaging systems. It introduces the development of an asymmetrically structured Janus humidity-regulated composite film. The composite film consists of an inner active layer made of polyvinyl alcohol/chitosan (PVA/CS) with a fibrous structure, and an outer barrier layer composed of PVA_{x% humic acid (HA)} with a dense configuration. The PVA/CS inner active layer exhibits excellent water uptake properties (0.36 g/g) and rapid adsorption-desorption kinetics, reaching equilibrium in 17 min. The PVA_x%HA outer barrier exhibits favorable water vapor barrier characteristics, with a water vapor permeability of (0.64 ± 0.01) × 10⁻¹¹ g·m/(m²·s·Pa). In strawberry preservation, the PVA/CS-PVA_1.5%HA composite film boosted storage relative humidity by 135.24 % and kept strawberries fresh for 7 days. This humidity-regulating film packaging offers a promising approach to extending the shelf life of fruits with high moisture content.