Inducing covalent cross-links in soy protein film through ferulic acid incorporation and UV irradiation and its effect on film properties

Abstract

This study aimed to investigate the impact of ferulic acid (FA) and UV-C curing on the properties of soy protein isolate (SPI) films. The films were fabricated from SPI with 1.5% FA and subjected to UV-C radiation at three doses (1.56, 4, and 12 J/cm²) applied either to pre-formed films or film-forming solutions. The SPI film without FA and UV-C treatments was considered as a control. The mechanical, physicochemical, and morphological properties of the films were investigated. Protein cross-linking via C-N and dityrosine bonds was confirmed using FTIR and fluorescence spectroscopic techniques, respectively. FA addition significantly influenced thickness and transparency, but had little effect on tensile strength, elongation at break, film solubility, color values, water vapor permeability (WVP), and film hydrophobicity. Furthermore, UV-C treatment of either the film-forming solution or preformed FA+SPI films significantly improved tensile strength, elongation at break, hydrophobicity, and yellowness, while decreasing transparency compared to the control film. Exposure to UV-C at 12 J/cm², whether pre-formed film or film-forming solution, increased tensile strength and elongation at break approximately 1.3 times and 1.7 times, respectively, compared to the control. UV-C exposure slightly increased WVP and had a minimal effect on film solubility compared to the control. The surface hydrophobicity of the films increased with higher doses, particularly in treatments applied to preformed films. The SEM micrographs revealed cracks and pinholes in the UV-treated film matrices. Our findings demonstrate that UV-C irradiation can effectively improve the tensile properties of SPI films containing ferulic acid.