Cinnamaldehyde-loaded chitosan-Dunaliella salina protein composite coating films with humidity/pH dual-responsive release for strawberry preservation.

Abstract

This study developed a composite film based on sustainable Dunaliella salina protein (DSP) and chitosan (CS), incorporating cinnamaldehyde (CA) to establish a controlled release system responsive to humidity and pH. At an optimized CA concentration of 0.2% (w/v), the composite film exhibited pronounced broad-spectrum antimicrobial activity, achieving inhibition rates of 98.21%, 98.71%, and 96.54% against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Botrytis cinerea (B. cinerea), respectively. Furthermore, it demonstrated notable antioxidant capacity, with DPPH and ABTS radical scavenging efficiencies reaching 85.80% and 77.52%, respectively. The system displayed distinct stimulus-responsive release behavior under high humidity and mildly acidic conditions, suggesting its potential to regulate CA availability in response to environmental changes. FTIR and XPS results suggested the presence of pronounced intermolecular interactions among the components and indicated that CA was likely successfully incorporated into the composite matrix, thereby providing structural support for its functional performance. Furthermore, the composite film showed enhanced mechanical properties, reduced water vapor permeability, and a compact and homogeneous microstructure. Application tests on strawberries demonstrated that the coating effectively delayed quality deterioration, with the humidity- and pH-responsive characteristics contributing to the maintenance of CA availability and fruit quality during storage for at least 8 days. Overall, this work demonstrates the potential of the developed composite film as a sustainable and stimuli-responsive active material for fruit preservation applications.