E.L. Sliwinski

Large-deformation Properties of Wheat Flour and Gluten Dough in Uni- and Biaxial Deformation

Keywords: Wheat, gluten protein, bread, puff pastry, flour dough, gluten dough, rheology , uniaxial extension, biaxial extension, fracture. Rheological and fracture properties of flour and gluten doughs from eight wheat cultivars were studied and related to gluten protein composition and baking performance in bread and puff pastry. For both uniaxial and biaxial extension flour dough showed a more than proportional increase of stress with increasing strain, a phenomenon called strain hardening. In uniaxial extension ( i ) stresses at a certain strain were higher and (ii) stress was less dependent on strain rate than in biaxial extension. Stress at a certain strain and strain hardening depended much stronger on the type of deformation for gluten than for flour dough. These findings are consistent with published data on birefringence of gluten and show that orientation of structure elements in elongational flow plays an important role in flour and gluten dough. For flour dough fracture stress and strain increased with increasing strain rate. At higher strain rates and lower temperatures fracture strains hardly differed between different flour doughs no matter the protein content or composition. At lower strain rates and higher temperatures the smallest fracture strains were found for flour doughs with the lowest glutenin contents and/or the lowest protein contents. We concluded that the strain rate and temperature-dependency of the fracture strain is a very important factor to relate to protein composition. Fracture stresses were much higher for gluten than for flour dough, while fracture strains were in the same range or higher. Contrary to flour dough, the smallest fracture strains were found for glutens with the largest glutenin contents. Puff pastry volume was positively correlated with strain hardening and negatively with the strain rate-dependency of the stress and the strain rate and temperature-dependency of the fracture stress and strain. For bread it were the doughs with intermediate dough strength that gave the highest loaf volume, while loaf volumes of flours with high dough strength (i.e. high stress-level and high strain hardening coefficient) gave intermediate loaf volumes. We concluded that a high internal stress limits the deformability of dough films between gas cells and with that of the loaf volume that can be obtained.