Viscosity Testing
The shear properties of the wheat doughs were studied using
shear viscometry. The mixed dough was mounted on a controlled
stress rheometer (Stresstech, Reologica Instruments AB, Lund,
Sweden) in the parallel plate configuration (25 mm diameter). The
edge of the sample was coated with food-grade petroleum jelly.
Before starting the measurement, the dough was allowed to rest
for 45 min. A constant shear rate of 0.9644/sec was applied to the
sample and the viscosity was plotted against time. This moderate
shear rate was selected for the viscometry to allow comparison
with the shear rates experienced during mixing (»10/sec) (Bloksma
1990a) while still yielding a sufficient number of data points
before edge fracture of the sample occurs. Higher shear rates result
in rapid fracture of sample. Dough exhibits a shear thinning response
under viscometry; lower viscosities are measured when higher
shear rates are used (Phan-Thien et al 1997). Slippage was prevented
by using sandpaper glued to the parallel plates before testing (Safari-