The effects of ultrasonic/microwave assisted treatment on the properties of soy protein isolate/titanium dioxide films

Soy protein isolate (SPI, 5.0 g/100 mL,) films embedded with nano-TiO₂ (0, 0.5, 1.0, 1.5 and 2.0 g/100 mL) were prepared by solution casting and modified by ultrasonic/microwave assisted treatment (UMAT). The effects of nano-TiO₂ content and UMAT time on the films' physical properties and structure were investigated. Incorporation of nano-TiO₂ significantly enhanced films' mechanical properties and barrier properties, because of the intermolecular force between nano-TiO₂ and SPI. UMAT time ≤20 min obviously improved films' tensile strength values (15.77 MPa, 245% higher than the control), and reduced water vapor permeability (1.8457 × 10⁻¹¹ g cm⁻¹ s⁻¹ Pa⁻¹, 72.11% lower than the control) and oxygen permeability values (0.8897 × 10⁻⁵ cm³ m⁻² d⁻¹ Pa⁻¹, 57.66% lower than the control). SEM images also revealed a more compact and dense structure of films when UMAT time ≤20 min. Films' water adsorption properties were evaluated. GAB and Henderson models exhibited the best to fit experimental data, thus it was predicted that films (1.5 g nano-TiO₂/100 ml) could be stable at low moisture content (0.27 kg of water/kg dry mass).