Design of starch/fatty acid-quaternized chitosan/ellagic acid bilayer films with integrated water-barrier and active preservation functions for strawberry packaging.

In this study, multifunctional bilayer packaging films were successfully constructed by integrating a starch/fatty acid (S/FA) layer with a quaternized chitosan/ellagic acid (QCS/EA) layer. The bilayer design enabled the implementation of both water-barrier protection and active preservation functions. The fatty acid particles embedded in the S/FA layer retarded moisture permeation, while the EA reduced the accessibility of the hydrophilic domains within the QCS layer. Together, these effects suppressed water adsorption, diffusion, and surface wetting in the films. Moreover, the presence of EA endowed the bilayer films with almost complete UV-blocking properties in the wavelength range from 200 to 400 nm. Among all the films evaluated, QCS/EA-20-D exhibited the best active performance, demonstrating superior antioxidant activity with a FRAP value of 109.9 μmol Fe2+/g and an inhibition rate of 96.70% against S. aureus. The bilayer films were shown to be highly effective in delaying spoilage, reducing moisture loss, and maintaining the quality of packaged strawberries, highlighting their great potential for sustainable food packaging applications.