pH-responsive chitosan films based on Schiff base-Fe³⁺ complexes for fruit preservation

Chitosan (CS) films functionalized with cinnamaldehyde (CIN)-derived Schiff base and Fe³⁺ coordination were developed for pH-responsive antimicrobial food packaging. The Schiff base-Fe³⁺ crosslinking system enhanced tensile strength by 39.59% and reduced water vapor permeability by 11.25%, while imparting pH-triggered CIN release via acid-hydrolyzable imine bonds. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis confirmed uniform dispersion of CIN/Fe and improved crystallinity. The films demonstrated bactericidal activity against foodborne pathogens (89.52% for Escherichia coli ATCC 25922, 82.98% for Staphylococcus aureus ATCC 25923) combined with moderate 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) scavenging (37.41% at 30 min), suggesting primary application in antimicrobial packaging. In fruit preservation trials, strawberries and passion fruit coated with CS/CIN/Fe films showed 33.17% and 29.36% lower weight loss, respectively, extending shelf life by suppressing respiration-driven spoilage. Cytotoxicity (<0.21% hemolysis) and biocompatibility (>80% cell viability) validated safety. This work presents a sustainable strategy for intelligent packaging by integrating dynamic Schiff base-metal coordination, addressing both food waste and plastic pollution.