Storage-Induced Changes in Plasticizer Emigration and Structural Properties of Soybean Isolate Protein-Based Composite Films

Previous study found soybean isolate protein (SPI)-corn starch (CS) composite films (SPI:CS (4:1) composite film, SPI:CS (1:1) composite film) exhibited good mechanical property and better stability during the short-term storage pre-experiment. In order to accordingly understanding the causes, plasticizer emigration and structural properties of SPI-based composite films stored at different temperatures (5 ℃, 20 ℃, 35 ℃) were systematically investigated over a period of time. High storage temperature (> 20 ℃) accelerated plasticizer emigration, which reflected in increased emigration rate of glycerol molecules and decreased moisture content. Furthermore, the decreased free SH partly formed new disulfide bonds and non-covalent inter-molecular interactions (hydrogen bonds) significantly weakened the protein structure, which influenced mechanical properties changes of SPI-based composite films during storage. The polymerization and aggregation appeared in network structure of the films was bond with disulfide bonds, and plasticizer emigration promoted the reorganization into others, with prevalence of extended β -sheet conformation.