Extensional flow studies of wheat flour dough. I. Experimental method for measurements in contraction flow geometry and application to flours varyingin breadmaking performance

An experimental method is reported for extensional measurements on wheat fl our doughs in contraction flow geometry. In this method the transient stres s under constant extension rate was measured, followed by stress relaxation measurement after cessation of Bow. Four different wheat cultivars (with l arge differences in bread volume) were used to evaluate the usefulness of t he method and to find how different parameters relevant to baking quality c ould be extracted from the data. The plot of transient viscosity against ti me showed the effect known as strain hardening, appearing at a Hencky strai n roughly independent of the strain rate but differing between the wheat va rieties. The relaxation rate curves for the four wheat varieties were simil ar except at the highest strain rate, 7.40 s(-1). It was decided in the fol lowing case study to use the highest strain rate, 7.40 s(-1) and to extract three parameters from the stress growth plot and three parameters from the stress relaxation rate plot. In the case study, hours of 17 wheat varietie s were mixed in the Mixograph to maximum resistance before being subjected to the contraction flow measurement. The six parameters extracted from each wheat flour dough measurement, together with the corresponding protein con tent, Zeleny value, and bread volume, were evaluated by multivariate analys is. A model for predicting the bread volume from the contraction flow param eters explained 94.6% of the variation in bread volume, while a model with Zeleny Values and protein contents included explained 97.2%. (C) 1999 Acade mic Press.