Large-deformation properties of wheat dough in uni- and biaxial extension. Part II. Gluten dough
Sliwinski, E.L. ; Hoef, M. van der; Kolster, P. ; Vliet, T. van - \ 2004
Rheologica Acta 43 (2004)4. - ISSN 0035-4511 - p. 321 - 332.
rheological properties - flour doughs - rupture properties - subfractions - protein - breadmaking - elasticity - viscosity - behavior - quality
Glutens were isolated from flour of three European wheat cultivars which perform differently in cereal products. The rheological and fracture properties of gluten-water doughs were determined in uniaxial and biaxial extension at large deformations and small angle sinusoidal oscillation tests and compared with the mechanical properties of the parental flour doughs. At 25 °C the linear region was in the same range as that of flour dough, while at a higher temperature (45 °C) the linear region was more than an order of magnitude higher. At 45 °C the storage modulus and tan were lower than at 25 °C. Variation in moduli between cultivars was much more pronounced for gluten than for flour doughs. Similarly to flour dough in both uniaxial and biaxial extension the stress () increased more than proportionally with the strain, a phenomenon called strain hardening. The stress at a set strain and strain hardening depended much more strongly on the type of deformation for gluten than for flour dough: was higher in biaxial extension for gluten than for flour dough, but was much higher in uniaxial extension. This indicates that orientational effects in elongational flow are of even larger importance for the mechanical properties of gluten than of flour dough. It is likely that it is the glutenin fraction that, because of its large size, confers these direction dependent properties to gluten and flour doughs. Fracture stresses were much higher for gluten than for flour dough, while fracture strains were in the same range or higher. For gluten dough fracture strains increased less strongly with increasing strain rate than for flour dough. Glutens exhibiting a higher stress at a certain strain had a smaller fracture strain. Our findings confirm the conviction that the large deformation properties of flour dough are mainly governed by the gluten fraction. However, there are also differences. Compared to flour dough gluten dough exhibits (i) a stronger strain hardening, (ii) a larger difference in between uniaxial and biaxial extension and (iii) a smaller strain rate dependency of the fracture strain.
Large-deformation properties of wheat dough in uni- and biaxial extension. Part I. Flour dough
Sliwinski, E.L. ; Kolster, P. ; Vliet, T. van - \ 2004
Rheologica Acta 43 (2004)4. - ISSN 0035-4511 - p. 306 - 320.
rheological properties - rupture properties - bread dough - gluten - behavior - performance - tests
Rheological and fracture properties of optimally mixed flour doughs from three wheat cultivars which perform differently in cereal products were studied in uniaxial and biaxial extension. Doughs were also tested in small angle sinusoidal oscillation. In accordance with previously published results the linear region was found to be very small. The rheological properties at small deformations hardly depended on the cultivar. A higher water content of the dough resulted in a lower value for the storage modulus and a slightly higher value for tan ?. For both uniaxial and biaxial extension a more than proportional increase in stress was found with increasing strain, a phenomenon called strain hardening. In uniaxial extension (i) stresses at a certain strain were higher and (ii) the stress was less dependent on the strain rate than in biaxial extension. This indicates that in elongational flow orientational effects are of large importance for the mechanical properties of flour dough. This conclusion is consistent with published data on birefringence of stretched gluten. Fracture stress and strain increased with increasing deformation rate. The observed time-dependency of fracture properties can best be explained by inefficient transport of energy to the crack tip. Presumably, this is caused by energy dissipation due to inhomogeneous deformation because of friction between structural elements, e.g. between dispersed particles and the network. Differences in the rheological properties at large deformations between the cultivars were observed with respect to (i) stress, (ii) strain hardening, (iii) strain rate dependency of the stress, (iv) fracture properties and (v) the stress difference between uniaxial and biaxial extension. keyword(s) Dough rheology, Strain hardening, Uniaxial extension, Biaxial extension, Fracture properties,
The Kieffer dough and gluten extensibility rig - An experimental evaluation
Dunnewind, B. ; Sliwinski, E.L. ; Grolle, K.C.F. ; Vliet, T. van - \ 2003
Journal of Texture Studies 34 (2003)5-6. - ISSN 0022-4901 - p. 537 - 560.
wheat-flour doughs - rheological properties - extension tests - breadmaking performance - elongational rheometer - rupture properties - large-deformation - microscale
Load-extension tests on flour dough are widely used by plant breeders, millers and bakers. The 'Kieffer dough and gluten extensibility rig' is a small-scale version of the Brabender extensograph, in which test pieces of about 0.4 g are extended. With the Kieffer rig, lower strain rates can be applied than in the Brabender extensograph and the experimental data can be expressed in terms of stress and strain. In this paper the performance of the Kieffer rig is illustrated by measurements on a weak and a strong dough. Formulas are given for the calculation of fundamental rheological parameters from the results of measurements with the Kieffer rig. Sagging and bending of the test pieces before measurements could be started, caused difficulties in the determination of the exact starting point of extension. The deformation was not purely uniaxial extension, because a shear component was also observed. The amount of dough that is extended did not increase throughout the test. This is probably due to the occurrence of a shear component fracture which occurred mainly near the hook. A relatively large variation in stress and strain at fracture was observed. The maximum in stress represents the strain at which the sample fractures macroscopically better than the maximum in force. Variation in deformation history and volume of the test pieces have a negative effect on the reproducibility.