Gellan gum and pullulan-based films with triple functionalities of antioxidant, antibacterial and freshness indication properties for food packaging

The objective of this research was to fabricate pH-responsive and active films based on gellan gum (GG) and pullulan (PL) with extracts of Broussonetia papyrifera fruits (BPFE) and leaves (BPLE) by a casting method. Results indicated that the extracts had good compatibility with GG and PL, which were uniformly distributed throughout the matrix. The incorporation of BPFE and BPLE increased the thickness, UV–vis barrier property, mechanical strength, thermal stability and moisture content of the films, while decreasing the water contact angle. Notably, the films exhibited enhanced antioxidant properties, with maximum radical scavenging rates of 77.45 % using 2,2 Diphenyl-1-picrylhydrazyl and 66.21 % using 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid). The antibacterial capability of the films also increased significantly after adding BPLE and BPFE. The results of XRD and FTIR showed that BPFE was bound to GG and PL by hydrogen bond. The release behavior of BPFE from the films agreed best with the first-level kinetic model. Furthermore, the films displayed obvious color responses to ammonia gas and different pH environments. Simultaneously, the films were applied to monitor the freshness of Pelteobagrus fulvidraco fish. The color parameters of the films demonstrated high correlations with the freshness indexes measured through standard laboratory procedures.