Tannic Acid-Grafted Chitosan/Fe3+ Composite Coatings: Enhanced Multifunctional Properties and Fruit Preservation Efficacy

A chitosan (CS)-tannic acid (TA) composite film incorporating Fe 3+ was fabricated, with a controlled grafting ratio of 20% between CS and TA. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis confirmed the uniform distribution and favorable compatibility of TA/Fe 3+ within the CS matrix. The composite film demonstrated a 16.95% lower water vapor transmission rate than CS and exhibited inhibition zones of 41.67 ± 2.08 mm and 47.33 ± 4.16 mm against Escherichia coli and Staphylococcus aureus , respectively. Moreover, strawberries packaged with the CS/TA/Fe composite film exhibited an 89.52% reduction in decay index after 7 days of storage compared to the control. After 7 days of storage, the CS/TA/Fe film significantly reduced the total viable count (TVC) in strawberries by 32.9% compared to the control. Applied as a coating on mangoes inoculated with Colletotrichum gloeosporioides , the CS/TA/Fe film suppressed lesion diameter expansion by 72.58% relative to uncoated fruit. The corresponding TVC for mangoes coated with CS/TA/Fe was 6.58 ± 0.51 log CFU/g on day 7, also demonstrating the lowest microbial load among all treatment groups. These results indicate the promising potential of this composite as an active packaging or coating material for food preservation applications.