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

An experimental method is reported for extensional measurements on wheat flour doughs in contraction flow geometry. In this method the transient stress under constant extension rate was measured, followed by stress relaxation measurement after cessation of Bow. Four different wheat cultivars (with large differences in bread volume) were used to evaluate the usefulness of the method and to find how different parameters relevant to baking quality could be extracted from the data. The plot of transient viscosity against time showed the effect known as strain hardening, appearing at a Hencky strain roughly independent of the strain rate but differing between the wheat varieties. The relaxation rate curves for the four wheat varieties were similar except at the highest strain rate, 7.40 s(-1). It was decided in the following 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 varieties 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 content, Zeleny value, and bread volume, were evaluated by multivariate analysis. A model for predicting the bread volume from the contraction flow parameters explained 94.6% of the variation in bread volume, while a model with Zeleny Values and protein contents included explained 97.2%. (C) 1999 Academic Press.