High-strength and antioxidant gelatin/(oxidized) olive polyphenol films by melt extrusion method

Polyphenols are organic molecules containing phenolic hydroxyl groups. Due to their excellent antioxidant properties and biocompatibility, they have attracted extensive attention in the field of food packaging. However, the phenolic hydroxyl groups are prone to be oxidized into conjugated di-ketone structures, thereby altering their antioxidant and biocompatibility. In this study, the olive polyphenols (OP) were oxidized and then melt-extruded with fish gelatin (FG) to prepare edible films. The cross-linking patterns of different functional groups of polyphenols with proteins were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Both OP and Oxidized olive polyphenols (OOP) formed hydrogen bonds with the chains of gelatin. On this basis, the oxidative olive polyphenol/gelatin (FG-OOP) films also underwent Schiff base reactions and Michael addition reactions, resulting in the formation of covalent cross-links. Compared with FG, the Tensile strength (TS) of FG-2 %OP and FG-2 %OOP increased by 61.08 % and 102.25 %, respectively. Besides, the gelatin-polyphenol/oxidized polyphenol films obtained after hot extrusion have better thermal stability and water resistance, which provides a new strategy for the efficient utilization of polyphenols and oxidized polyphenols and the preparation of high-performance edible films.