Solvent Effects on the Molecular Structures of Crude Gliadins as Revealed by Density and Ultrasound Velocity Measurements

Gliadin is associated with some of the functional properties of dough and the breadmaking suitability of flours. This study was undertaken to characterize the effects of solvents on the molecular structure of crude gliadins in terms of the physical properties of these proteins as assessed by ultrasound velocity and density measurements.;For the solvent analyses, crude gliadins were extracted from Canada Western Red Spring (CWRS) wheat flour with 70% (v/v) aqueous ethanol solutions and then lyophilized. Lyophilized crude gliadins were dissolved in 70% (v/v) aqueous ethanol (EtOH) or 4 mM acetic acid (HAc) and the density and ultrasound properties were measured at 20°C. Good linear relationships of density, ultrasound velocity and ultrasound attenuation with solution concentrations were found. Solvent and sonication effects on the crude gliadins were discussed in terms of the values of the partial specific volume, nu o, and the partial specific adiabatic compressibility coefficient, boS&d1; , for crude gliadins. The ethanol soluble crude gliadins had a larger partial specific volume, nuo (0.747 mL·g-1), and larger partial specific adiabatic compressibility coefficient, boS&d1; (10.27 x 10-6 bar-1) than those for acidic soluble crude gliadins (nu o = 0.736 mL·g-1; boS&d1; 3.72 x 10-6 bar-1). These large values for the physical properties of ethanol soluble crude gliadins were thought to be evidence for the existence of complexes formed by some proteins (ethanol soluble LMW-glutenins and gliadins) and lipids in ethanol solutions and it was also found that the protein-lipid complexes were not destroyed by sonication treatment.;In the flour analyses, crude gliadins were extracted from wheat flours of different classes (Canada Western Red Spring, Canada Western Extra Strong and Soft White Spring) with 70% (v/v) aqueous ethanol solutions and freezed dried material was subsequently dissolved in 4 mM HAc. The density and ultrasound velocity and ultrasound attenuation were measured at 20°C. Good linearity of density and ultrasound properties with solution concentration was found for the crude gliadins from the three different flours. There was no evidence showing that gliadins change with different wheat flours and cause different volume and compressibility properties of crude gliadins. However, the volume and compressibility properties were found to be related to the protein contents of the crude gliadin solutions, as well as the protein contents of the flours, and proteins had positive contributions to the volume and compressibility properties of acidic soluble crude gliadins and non-protein components had negative contributions.;In the preliminary experiments, crude gliadins were extracted using modified Osborne fractionation from flours from four wheat cultivars (Glenlea, Katepwa, AC Reed and Genesis) and the ultrasound velocities of the crude gliadin serial dilutions were measured at 20°C. The ultrasound velocity values of the crude gliadins in alcoholic solutions exhibited non-linearity with solution concentrations. Thus, fresh 70% (v/v) aqueous ethanol solutions made of 95% (v/v) ethanol and water were selected for further experiments to extract the crude gliadins from wheat flours.