RELAXATION BEHAVIOR AND THE APPLICATION OF INTEGRAL CONSTITUTIVE-EQUATIONS TO WHEAT DOUGH

The small amplitude rheological properties of doughs of different comp ositions were measured using a dynamic rheometer. In the first study, the effect of water, flour, and added gluten on the dynamic properties was investigated. Frequency sweep was carried out in the range of 0.1 to 100 s(-1) at an applied strain of 0.1%. Storage (G') and loss (G ' ') moduli for each composition were recorded. The storage modulus vers us frequency plots were a series of parallel curves indicating that th e moisture-to-flour ratio was the most important parameter. The loss m odulus versus frequency plot showed a falling-off after a frequency of 40 s(-1). A plot of tan delta versus frequency indicated a more elast ic dough at shorter time scales (or higher frequencies). Data from the dynamic shear experiment were used to determine the parameters of the generalized Maxwell model. Depending on composition, the doughs exhib ited unimodal or bimodal distributions. Stresses relaxed faster when t he flour-to-water ratio was high. In the second study, the dynamic and transient properties of three commercial doughs were investigated. St ress-strain behavior of a short cookie dough showed strain softening a t higher stains. Dough samples did not exhibit initial stress overshoo t at the shear rates investigated. A time-strain separability, valid f or many polymer melts, was observed for cracker doughs, which encourag ed the use of the factorable KBKZ model. The integral constitutive Wag ner equation was applied to the transient data and was found to give a reasonably good fit except at short times where stress maximum occurr ed. The Yamamoto model, on the other hand, gave a poor fit to the shea r viscosity data.