Drying Temperature and Relative Humidity Effects on Wheat Gluten Film Properties

Abstract

The mechanical and physical properties of glycerol-plasticized wheat gluten films dried at different temperatures (20, 50, and 80 °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 °C. Films produced at 80 °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 °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. Keywords: Wheat gluten film; drying conditions; water vapor transmission rate; solubility; mechanical properties