Influence of spelt bran on the physical properties of WPI composite films

In this study, the properties of whey protein isolate (WPI)-based films with different levels of glycerol and spelt bran were investigated using response surface methodology. Tests were carried out to determine to what extent the water vapor permeability (WVP) of the films can be improved by adding the bran. Moreover, the mechanical and dynamical properties, colour of the films and the rheological properties of the film-forming solutions were also investigated. Results highlighted that the WVP was significantly affected by the spelt bran concentration: increasing the spelt bran concentration led to decrease in water vapor permeability, whereas the glycerol concentration incremented the WVP values of the films. The elastic modulus (EC) and complex modulus (E*) of the composite films increased with the decrease of the glycerol content and the increase of the bran concentration. Glycerol addition, acting as a plasticizer, led to more flexible films. Regarding the rheological characteristics, the WPI solutions with the lower bran concentration behaved as Newtonian fluid. As the bran concentration increased the solutions demonstrated a non-Newtonian behaviour. Colour results highlighted that yellow index (YI), a and b parameter of Hunter scale increased with the bran concentration increase; on the contrary, L parameter decreased with the bran concentration increase.