Fabrication of anti-UV absorbing and antibacterial soybean protein isolate composite film modified with thyme and mangosteen peel extracts

In order to reduce the threat of 'plastic pollution' and reduce or eliminate some traditional polymer packaging materials, in this study, soybean protein isolate (SPI) composite film, a biodegradable natural polymer film, was prepared by tape casting method with Thyme (Thy) and mangosteen peel extracts (MPE) as antibacterial agents. The antibacterial rates of the composite films against E. coli and S. aureus were 95.79% and 92.63%, respectively, and the DPPH free radical scavenging rate was 70.28%. The composite film had good UV-visible barrier properties. Compared with the pure SPI film, the tensile strength of the composite film was improved, the water absorption, water solubility, and water vapor permeability were reduced, and the contact angle was improved. The maximum thermal decomposition temperature of the composite film increased and the thermal stability increased. Fourier Transform Infrared Spectroscopy (FTIR) studies showed the polyphenol-protein of the composite film was bound by hydrophobic interaction. X-ray Photoelectron Spectroscopy (XPS) showed good interaction with the protein structure by adding antibacterial substances and their aromatic quinone structures. X-ray Diffraction (XRD) studies showed that the crystallinity of the composite films increased. Therefore, the composite membrane in this study can be used to prepare high-strength packaging materials with antibacterial functions.