Viscoelastic, thermal, and microstructural characterization of soy protein isolate films

Viscoelastic, thermal, and microstructural properties of plasticized soy protein isolate (SPI) films processed by thermal compaction are discussed. Thermogravimetric analysis indicates that protein films exhibit substantial thermal degradation at temperatures above 180 °C and that the processing temperature limit is about 150 °C. Dynamic mechanical analysis indicates the existence of multiple glass transition temperatures associated with glycerol- and protein-rich phases. Scanning electron micrographs of the cross-sections of films containing 30 and 40 wt% glycerol indicate the presence of ridges and valleys resulting from an extensive local deformation of the 'protein matrix,' which explains the large flexibility of these films as compared to those containing only 20 wt% plasticizer