Preparation of mechanically strong and active composite films based on fish myofibrillar proteins: The dual effects of oxidized polyphenol crosslinking and layered double hydroxide reinforcement

To improve the properties of films prepared from silver carp muscle, a cross-linked nanocomposite antioxidant film based on myofibrillar protein (MP) was prepared using oxidized caffeic acid (OC), p-coumaric acid (OP), eriodictyol (OE) and naringenin (ON) as crosslinking agents in combination with layered double hydroxide (LDH). The structural, physical properties and antioxidant activity of the film were investigated. The examination of the changes in the side-chain groups of MP revealed that the addition of oxidized polyphenols decreased total sulfhydryl and free amino acid levels, showing a greater decrease in OC and OE with o-phenolic hydroxyl groups, whereas LDH showed no significant effect. Additionally, FTIR (Fourier transform infrared) and XRD (X-ray diffraction) confirmed the covalent or non-covalent interactions between oxidized polyphenols, LDH and MP, in which resulted in increased surface hydrophobicity of MP and a shift of the α-helical structure to random coils. This suggests that the protein underwent unfolding, which tends to induce intermolecular aggregation. Additionally, the microregional structure in the film became more compact. Moreover, the mechanical properties of MP-based films were significantly enhanced by the combination of oxidized polyphenols and LDH, especially the incorporation of OE and LDH resulted in a tensile strength reaching 17.4 MPa. Furthermore, the water vapor and oxygen permeability, surface hydrophobicity, UV barrier and thermal stability of MP-based films were also improved. Therefore, the dual effect of oxidized polyphenol cross-linking and LDH complex confers excellent free radical scavenging abilities and iron-reducing antioxidant functions to MP films.