Solvent effects on the molecular structures of crude gliadins as revealed by density and ultrasound velocity measurements

Gliadins were extracted from hard red spring wheat flour with 70% (v/v) aqueous ethanol and lyophilized. These crude gliadins were dissolved in 70% (v/v) aqueous ethanol or 4 mM acetic acid with or without ultrasonication. Precise measurements of the density and ultrasound velocity of the solutions were made at 20 °C. For non-sonicated solutions, crude gliadins solubilized in ethanol had a slightly larger partial specific volume (0.76 cm3 g−1), and a larger partial specific adiabatic compressibility coefficient (15 × 10−11 Pa−1) compared to those solubilized in acid (0.739 cm3 g−1, 3.1 × 10−11 Pa−1, respectively). Larger values are consistent with the existence of complexes formed by gliadins and lipids in aqueous ethanol solutions. Utrasonication had no effect on these protein–lipid complexes based on measurements of density, but it did alter the compressibility of gliadins in dilute acid (making them almost twice as compressible). Novel insights into gluten protein properties can be gained from compressibility measurements of solutions using ultrasonic resonators when coupled with measurements of protein specific volume.

► We use resonating technologies to measure specific volume and compressibility of gliadins to accuracies of ppm.
► Gliadins solubilized in acetic acid were more compact and less compressible than those solubilized in ethanol.
► Sonication during gliadin solubilization causes significant changes in gliadin compressibility.