Application of metal phenol-functionalized alginate packaging film in passion fruit preservation

Sodium alginate (SA) films/coatings possess weak barrier and antimicrobial properties, limiting their effectiveness in food preservation. To address this issue, this study developed tannic acid–iron (TA–Fe³⁺) cross-linked SA films with enhanced overall performance and systematically characterized their structure and properties. The results demonstrated that tannic acid, acting as a cross-linking agent, significantly improved the barrier and mechanical properties of SA films. Compared to SA–TA films, the TA–Fe³⁺ cross-linked films exhibited a 5.26 % increase in tensile strength (TS) and a 16.83 % reduction in water vapor permeability. These enhancements were supported by observations of a denser microstructure and improved thermal stability, indicating that the TA–Fe³⁺ complex reinforced the SA film network. Additionally, the incorporation of TA markedly enhanced the antioxidant and antibacterial properties of the SA film, while TA–Fe³⁺ cross-linking further increased the inhibition zones against Escherichia coli and Staphylococcus aureus by 8.07 mm and 10.63 mm, respectively. This improvement was mainly attributed to the TA–Fe³⁺ network's ability to modulate TA release, particularly under acidic pH conditions. Notably, the highly biocompatible TA–Fe³⁺ cross-linked SA coating showed superior performance in passion fruit preservation compared to SA and SA–TA coatings, more effectively reducing passion fruit weight loss and shrinkage.