| Summary: | The objective of this study was to prepare a functional biodegradable soy protein isolate (SPI) food packaging film by introducing a natural antimicrobial agent, mangosteen peel extract (MPE, 10 wt% based on SPI), and different concentrations of functional modifiers, ZnO NPs, into the natural polymer SPI by solution casting method. The physical, antioxidant, antibacterial properties and chemical structures were also investigated. The composite film with 5% ZnO NPs had the maximum tensile strength of 8.84 MPa and the lowest water vapor transmission rate of 9.23 g mm/m<sup>2</sup> h Pa. The composite film also exhibited excellent UV-blocking, antioxidant, and antibacterial properties against <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>. The TGA results showed that the introduction of MPE and ZnO NPs improved the thermal stability of SPI films. The microstructure of the films was analyzed by SEM to determine the smooth surface of the composite films. ATR-FTIR and XPS analyses demonstrated the strong hydrogen bonding of SPI, MPE, and ZnO NPs in the films. The presence of ZnO NPs in the composite films was also proved by EDX and XRD. These results suggest that SPI/MPE/ZnO composite film is promising for food-active packaging to extend the shelf life of food products.
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