On the relationship between gluten protein composition of wheat flours and large-deformation properties of their doughs

Abstract

Six European and two Canadian wheat cultivars selected according to their different performance in baked cereal products. The gluten protein composition of the respective flours was studied and related to the rheological and fracture properties of optimally mixed flour doughs tested in uniaxial extension. Water addition required for optimum dough development was positively correlated with gluten protein content, indicating that all glutens required similar amounts of water for proper hydration. Both water addition and gluten protein content were positively correlated with the fracture strain. Mixing time required for optimum dough development was correlated with several stress-related dough properties: positively with the stress at a large strain and strain hardening and negatively with the strain rate-dependency of the stress. These stress-related dough properties were correlated with differences in the amount and the size-distribution of the gluten proteins. A positive correlation was found the stress at large strain and the percentage of polymeric protein of large size (UEP+P1) and a negative correlation between the strain rate-dependency of the stress and the percentage of high molecular weight glutenin subunits on total protein. These findings are consistent with the known strong dependence of rheological properties on molecular weight and molecular weight distribution for polymers in general. The effect of temperature on the large-deformation properties of flour and gluten dough was studied for three cultivars that were considered representative for the whole set. The fracture properties of flour dough strongly depended on strain rate and temperature. At higher strain rates and lower temperatures, fracture strains scarcely differed between the flour doughs no matter the protein content or composition. On the other hand at lower strain rates and higher temperatures the smallest fracture strain was found for dough of flour with the lowest glutenin content and/or the lowest protein content. In contrast to the flour doughs, for gluten–water mixtures (gluten doughs) the fracture strain was largely independent of strain rate and temperature. The smallest fracture strain was found for the gluten dough with the highest glutenin content. Thus, the behaviours of flour and gluten doughs with respect to protein composition, strain rate and temperature effect on fracture strain clearly are different. The differences observed in large deformation and fracture properties are most likely due to the large differences in starch and gluten protein content between flour and gluten doughs.