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Mechanical and Biochemical Characterisation of Wheat Gluten Films as a Function of pH and Co-solvent*Dispersions of wheat gluten were prepared at different pHs (4, 6 and 11) in the presence or absence of ethanol. Films were obtained after casting suspensions followed by evaporation of the solvent. Films prepared at pH 11 were significantly stronger than the films prepared at pH 4 and 6 with tensile strengths of approximately 7 vs. 2 MPa. With increasing strength, the elongation at break was moderately reduced from approximately 300% to 190%. No significant variations of water vapour transfer rate properties were observed among the films. The solubility of gluten films in aqueous and 1.5% sodium dodecyl sulfate (SDS) solution decreased with increasing pH of films. Tricine sodium dodecyl sulfate-polyacrylamide gel (SDS-PAGE) patterns of wheat gluten and film showed the formation of high molecular weight fractions. The amount of free amino groups in the wheat gluten decreased during film formation. Amino acid analysis showed the presence of lysinoalanine (LAL). All these results indicate the formation of irreversible intermolecular cross-linking upon film formation at pH 11.

The mechanical and physical properties of glycerol-plasticized wheat gluten films dried at different temperatures (20, 50, and 80 degrees C) and relative humidities (35 and 70% RH) were investigated. Dispersion of wheat gluten was prepared at pH 11 in aqueous solution. Films were obtained by casting the wheat gluten suspension, followed by solvent evaporation in a temperature and relative humidity controlled chamber. Decreasing relative humidity altered most of the mechanical properties. At 35% RH, tensile strength increased when drying temperature increased. However, at 70% RH, tensile strength decreased when temperature increased. Thickness of the films decreased by increasing temperature. Hypothetical coating strength increased with increasing drying temperature at 35% RH. However, at 70% RH, a maximum value was observed at 50 degrees C. Films produced at 80 degrees C exhibited low solubility in aqueous solution. Addition of 1.5% (w/v) sodium dodecyl sulfate increased solubility of all of the films except the film dried at 50 degrees C and 70% RH. Overall, drying temperature and relative humidity affected mechanical and physical properties of the wheat gluten films. However, the effect of drying temperature was more pronounced than the effect of relative humidity.