Wheat-flour dough extensibility as a discriminator for wheat varieties

The extension testing of wheat-flour dough has become one of the key cereal chemistry links to end product quality assessment, because of its perceived relevance to baking performance, and because of the various correlations that have been inferred and assumed since the extensibility of a dough was first investigated in the late 19th century. As a consequence, from a plant breeding perspective, there is a need to understand and interpret the extensibility of a dough in terms of the molecular dynamics occurring during its extension, not only as it relates to its baking, but also to the HMW/LMW glutenin and gliadin composition of the wheat. The focus of this paper is the direct measurement of extensibility on a micro-extension tester. The theoretical justification is that the resulting extensogram represents an encapsulation of the extensional rheology of the dough. The paper reports on a graphical and statistical analysis of extension tests performed on eight representative flours. They yield validation for the conclusion that the historic assessment of extensibility as Ext_Rupture should be replaced by Ext_Rmax and the difference Ext_Rupture - Ext_Rmax. It is relatively easy to obtain accurate estimates of R _max, Ext_Rmax and Ext_Rupture from electronically recorded extensograms. Among other things, it is established that, in terms of the glutenin classification of flours based on electrophoresis, HPLC or DNA markers, R_max yields a far better differentiation than is achieved with either Ext_Rupture or Ext _Rmax. It follows, as a corollary to such results, that the extensions to the earlier rheological phases in an extensogram are just as, if not more, important in identifying connections between the gluten composition of wheat varieties and the traditional Ext_Rupture and R _max. In particular, it is shown that, like R_max, the scaled difference R_max/(Ext_Rupture - Ext_Rmax) represents an alternative strategy to relate quality to the glutenin composition of wheat varieties, determined by electrophoresis, HPLC and DNA markers.