Characterisation of pullulan polysaccharide membranes cross-linked with epigallocatechin gallate and Fe3+ for passion fruit preservation.

Traditional packaging materials can cause serious environmental pollution, prompting increased interest in the development of green bioplastic packaging alternatives. Herein, epigallocatechin gallate (EGCG) and Fe3+ cross-linked pullulan polysaccharide (PUL) composite films were prepared using the solution casting method. Their structures and properties were measured. The application of PUL composite coatings in passion fruit preservation was also investigated. Fourier-transform infrared spectroscopy and X-ray diffraction analyses confirmed strong biocompatibility and interaction among PUL, EGCG and Fe3+. Scanning electron microscopy results further demonstrated good compatibility between the polymer and both EGCG and Fe3+. The metal-phenol-aldehyde network structure formed by EGCG and Fe3+ crosslinks with the PUL film, enhancing its structural density and significantly reducing water vapor permeability by 15.24 %. Additionally, the mechanical properties of the composite film were enhanced, with tensile strength increasing from 14.36 MPa to 27.68 MPa, 92.76 % improvement over pure PUL film. Concurrently, the incorporation of EGCG and Fe3+ substantially boosted the PUL film's UV barrier properties and antioxidant capacity. In passion fruit preservation experiments, PUL/EGCG/Fe3+-coated passion fruit exhibited the lowest weight loss rate (19.60 %) and shrinking index (3.3) after 10 days of storage compared to other treatment groups. This effectively delayed fruit quality deterioration and maintained appearance.