|Bietz, Jerold - USDA-ARS (RETIRED)|
|Wirtz, Denis - JOHNS HOPKINS UNIV|
Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 15, 2000
Publication Date: N/A
Interpretive Summary: The bread making quality of wheat flour depends on mechanical properties of its proteins, especially gluten. Gluten possesses many unique physical properties that make this material suitable for numerous food and non-food industrial uses, including films and biodegradable plastics. Gluten is viscoelastic material, that is, it has both solid and fluid properties. The study of mechanical properties of viscoelastic material is called rheology. The rheological properties of complex gluten doughs constitutes a rich field of study. Processing conditions, including mixing procedure, mixing time, and rest time, all are known to have a large effect on the measured rheological properties of gluten doughs. Variations in any of the processing parameters can result in gluten doughs with widely-varying rheological properties. Due to the complex native of gluten doughs, it has been difficult to establish a baseline of rheological parameters for dough. An aim of the present study was to eliminate these difficulties in dough rheology by examining the rheological properties of vital wheat gluten suspensions. The results of this study provide a clearer understanding of gluten rheology. We observed a dramatic change in viscoelastic properties within a very narrow concentration range. Our results indicate that gluten underwent a structure shift between a small concentration change. This study will be beneficial to scientists in this field to understand gluten more rigorously.
Technical Abstract: Flour and doughs represent rheologically complex materials whose properties are dependent on many factors including processing conditions. In order to avoid some of the problems associated with the rheological characterization of dough, we have initiated a study focused on the rheological properties of one of the major components of dough, namely, vital wheat gluten. Suspensions of vital wheat gluten were prepared with concentrations ranging from 225 to 325 mg/ml. The moduli of the gluten suspensions ranged from 0.2 Pa at 225 mg/ml to 37 Pa at 325 mg/ml. Below 250 mg/ml, the gluten suspensions exhibited fluid-like behavior. The crossover frequency, i.e., G'(w) = G"(w), shifted slightly from 0.5 rad/s at 225 mg/ml to 0.9 rad/s at 250 mg/ml. Above 300 mg/ml, the suspensions exhibited solid-like behavior. The crossover frequencies were independent of concentration and were equal to 100 rad/s. Below 250 mg/ml, the high-frequency behavior of moduli were proportional to w**3/4, as expected for a semi-flexible coil. Above 300 mg/ml, the high-frequency behavior of moduli were proportional to w**1/2, indicating a flexible coil. These results suggest vital wheat gluten suspensions undergo a structural change between 250 and 300 mg/ml.