UV-C induced modification of heat-cured soy protein films: Mechanical, optical, barrier, and morphological properties

• The effect of UV-C radiation on properties of heat-cured soy protein film-forming solution and heat-cured preformed soy protein film was investigated. • UV-C treatment was found to induce an increase in the film tensile strength. • The greatest tensile strength was demonstrated by heat-cured preformed film exposed to UV-C at 12 J/cm 2 , which was 337% of that of the control. • Covalent dityrosine cross-linking, as induced by UV-C irradiation, was confirmed in the UV-C-irradiated films by fluorescence spectroscopy. • Apart from mechanical properties, higher UV-C doses resulted in an increase in yellowness and water vapor permeability, with a decrease in water solubility of the films. This study aimed to explore the effect of UV-C irradiation on the properties of soy protein isolate film. UV-C treatments at different doses (4, 8, 12, and 16 J/cm 2 ) were administered to either heat-cured film-forming solution or to heat-cured preformed films. The films were assessed in terms of their mechanical, barrier, optical, and morphological properties. UV-C treatment on preformed films at higher doses posed a significant impact on tensile strength, water solubility, color, and transparency of the films, while elongation at break was minimally affected. The UV-C-treated films generally exhibited increasing tensile strength, transparency, and yellowness while demonstrating decreasing water solubility as compared to the control. The heat-cured pre-formed film exposed to UV-C at 12 J/cm 2 possessed the greatest tensile strength (6.37 MPa), which was 3.4-fold higher than the control. UV-C treatment on heat-cured preformed film or film-forming solution significantly increased water vapor permeability (WVP). UV-C exposure at higher doses also tended to increase surface hydrophobicity. The SEM micrographs revealed cracks and pinholes in the UV-C-treated film matrices. In conclusion, UV-C irradiation was proven to be an effective technique for enhancing the mechanical strength of soy protein film by promoting the formation of dityrosine covalent cross-links among protein chains.