Tensile Properties of Soy Protein Isolate Films Produced by a Thermal Compaction Technique

Soy protein isolate (SPI) was utilized as a biopolymer and glycerol was used as a plasticizer to successfully produce light‐yellow, transparent protein films by a thermal compaction technique. Flexible films, approximately 180 micrometers, could be produced at a processing temperature of 150 °C and compaction pressure and time of 10 MPa and 2 min, respectively. The dispersion of glycerol among SPI macromolecules was found to be a diffusion‐limited process that could be accelerated by intensive mixing. Films containing 30 wt% glycerol made from intensively mixed material had average tensile strength and elongation values that were, respectively, 6% and 300% higher than those of films made from unaged, manually mixed material.