Effect of thermal treatments on functional properties of edible films made from wheat gluten fractions

The effect of thermal treatments on selected properties of films based on gliadins and glutenins prepared from commercial wheat gluten was studied. Gliadin- and glutenin-rich films were heat cured at 40, 55, 70, 85, 95 and 115 °C for 24 h. The effect of heat curing on moisture content, colour, total soluble matter in water, water vapour permeability, tensile strength and elongation at breakpoint of the films was evaluated. Mechanical and water barrier properties of films changed sharply in the range of 55–75 °C. Films became stronger and less extensible with lower water vapour permeability. No changes in the equilibrium moisture content at 50% relative humidity of films associated with thermal treatments were observed. From 70 °C, gliadin films kept their integrity in water whereas film disintegration was observed in other cases. Films became darker with a yellow-brown coloration with the increase of temperature treatment; so in order to preserve the film appearance temperature no higher than 70–75 °C for gliadin and glutenin, respectively, will be recommendable. Thermal treatment can effectively be applied to optimize the use and application of gliadin- and glutenin-rich films.