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

Area of Science:

• Materials Science
• Food Science
• Polymer Chemistry

Background:

• Chitosan (CS) is a biopolymer with potential for food packaging.
• Developing active and intelligent food packaging is crucial for reducing food waste and plastic pollution.
• Functionalizing chitosan films with antimicrobial agents and stimuli-responsive elements enhances their performance.

Purpose of the Study:

• To develop pH-responsive antimicrobial food packaging films using chitosan functionalized with cinnamaldehyde (CIN)-derived Schiff base and Fe³⁺ coordination.
• To investigate the structural, mechanical, and antimicrobial properties of the developed films.
• To evaluate the efficacy of the films in preserving fresh produce and assess their safety.

Main Methods:

• Fabrication of chitosan films incorporating Schiff base derived from cinnamaldehyde and Fe³⁺.
• Characterization using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA).
• Assessment of mechanical properties (tensile strength), water vapor permeability, pH-triggered release, antimicrobial activity against foodborne pathogens, antioxidant activity (ABTS assay), and cytotoxicity (hemolysis assay).
• Application trials on strawberries and passion fruit to evaluate shelf-life extension.

Main Results:

• The Schiff base-Fe³⁺ crosslinking significantly enhanced tensile strength (+39.59%) and reduced water vapor permeability (-11.25%).
• The films exhibited pH-triggered release of cinnamaldehyde via acid-hydrolyzable imine bonds.
• Effective bactericidal activity against Escherichia coli (89.52%) and Staphylococcus aureus (82.98%) was observed.
• Moderate antioxidant activity (37.41% ABTS scavenging at 30 min) and significant weight loss reduction in coated fruits (strawberries: 33.17%, passion fruit: 29.36%) were achieved.
• The films demonstrated excellent safety with low cytotoxicity (<0.21% hemolysis) and high biocompatibility (>80% cell viability).

Conclusions:

• The developed chitosan/cinnamaldehyde/Fe³⁺ films represent a sustainable strategy for intelligent food packaging.
• The dynamic Schiff base-metal coordination provides pH-responsive antimicrobial properties and enhanced mechanical performance.
• These films effectively extend the shelf life of fruits by inhibiting spoilage mechanisms.
• The study addresses critical issues of food waste and plastic pollution through innovative biomaterial development.