Properties of soy protein isolate/nano‐silica bilayer films during storage

The development of bionanocomposite materials for packages has received increasing attention due to environmental pollution issues. However, storage results in many undesirable properties in films. This study evaluated the effects of storage on simple layer and bilayer soy protein isolate/nano‐silica (SPI/nano‐SiO₂) films, which may reduce the migration of nanoparticles, and on the properties (mechanical, barrier, and optical) and parameters (moisture content, sulfhydryl content, and glycerol migration rate) of the films. Compared to SPI films, SPI/nano‐SiO₂ films had a higher moisture content, higher sulfhydryl content, lower glycerol migration rate and better properties after storage. Fourier transform infrared spectroscopy showed that hydrogen bonding existed between SPI and nano‐SiO₂ and that α‐helix, β‐sheet, β‐turn, and random coil structures transformed due to bond breaking and formation during storage. Scanning electron microscopy indicated that SS‐3‐2 film had better morphologies after storage. In conclusion, bilayer films are safer and may replace simple layer films in food packaging. PRACTICAL APPLICATIONS: Based on an EFSA (European Food Safety Authority) scientific opinion, SiO₂ is approved in the European Union. However, nanoparticles have been reported to process certain characteristics that pose a health hazard. To reduce the migration of nano‐SiO₂, the contact area between the food and films with nano‐SiO₂ must be reduced. SPI film is a biodegradable packaging material and has been widely studied due to its biodegradable properties, which are attributed to the lack of repeating units in peptides compared to petroleum synthetic polymers. However, the properties of SPI film change during storage, which limits its application. Therefore, the present study aimed to evaluate the effects of storage on the properties of simple layer and bilayer SPI/nano‐SiO₂ films.