Effects of spelt and wheat bran on the performances of wheat gluten films

The individual and interactive effects of the spelt and wheat bran as well as glycerol, on the properties of wheat gluten based edible films were investigated in this work using response surface methodology. Tests were run to determine water vapour permeability (WVP), mechanical and dynamical properties and colour of the films as well as the rheological properties of the film forming solutions. Results highlight that the glycerol presence had a negative effect on water vapor permeability values of the films (increase of WVP), whereas the bran presence had a positive influence (decrease of WVP). The Elastic modulus (Ec) of the composite films increased with the increase of bran concentration and with the decrease of glycerol. The tenacity increased with the increase of glycerol and spelt bran up to a threshold value after which a decrease was observed. The complex modulus (E*) of the composite films increased with the decrease of the glycerol concentration and with the increase of the wheat bran. All film forming solutions presented pseudoplastic behaviour; moreover, the apparent viscosity increased with the increase of bran concentration due to the fact that a greater number of water molecules are immobilized. The complex viscosity (·*) was affected by a positive interaction between spelt bran and wheat bran. Results also showed that Yellow Index (YI) and b parameter of Hunter scale increased with the bran concentration, whereas the L values decreased. The glycerol increase determined a decrease in the YI and b value and an increase in L value.