Properties of gluten-based sheet produced by twin-screw extruder

Wheat gluten sheet plasticized with glycerol was successfully produced using a twin-screw extruder and the formation of the translucent sheet was found to occur when temperature of the melt was around 137 °C. Water sorption, thermal, mechanical and gas permeability properties of the extruded gluten sheet were studied at various relative humidities. The water sorption isotherms obtained were typical for a plasticized high protein content material and could be described by the Guggenheim-Anderson-de Boer (GAB) and Brunauer-Emmett-Teller (BET) equations. The glass transition temperatures (T_g) of extruded gluten sheet at various water contents were measured by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and dielectric analysis (DEA). T_g of anhydrous sheet was markedly below room temperature and was found to decrease with increasing water content. A decrease in Young's modulus, tensile strength at break and elongation at break was observed with increasing relative humidity. Water vapor permeability of the sheet increased with increasing relative humidity. The water vapor permeabilities obtained were high as compared to the permeabilities of synthetic polymers but comparable to those reported for cast wheat gluten films. Oxygen permeability of the extruded gluten sheet was low and comparable to those reported for cast wheat gluten films.