Effect of microwave modification on mechanical properties and structural characteristics of soy protein isolate and zein blended film

Soy protein isolate (SPI) and zein were blended at different ratios, and native and microwave-modified films were prepared at pH 12 in an ethanol/water (20 : 80) mixture. The effect of the microwave modification on the mechanical properties and structural characteristics of the SPI and zein blended films was investigated. The results show that the microwave-modified blended film of 3 : 1 SPI-zein demonstrated the best mechanical properties: the highest breaking strength (2900 g) and the highest fracturing distance (16.08 mm). The morphology of the microwave-modified film was more homogeneous and had fewer pinholes than the zein-only film. In addition, the glass transition temperature of the microwave-modified film rose by nearly half compared to the zein-only film, while the melting temperature increased by almost 2.5%. The secondary structure analysis indicates that a moderate amount of microwave treatment will promote a decrease in α-helix, β-turn, and random coil content and an increase in β-sheet content. This study provides an edible material with better flexibility for food packaging.