Rheology of Mixtures of Glutenin Subfractions

Abstract

The dynamic rheological behaviours of mixtures of glutenin fractions extracted from wheat cultivar Hereward were investigated as a function of the relative concentration of high to low molecular weight glutenin concatenations. Time-temperature superposition could be applied to both the mixtures and to the total gluten, as long as heat-treated samples were distinguished from unheated samples. The ratio of high to low molecular weight concatenations was found to be very important for the rheological behaviour of the network. High molecular weight fractions promoted the network properties of the mixture, as could be seen from the presence of a plateau in the rheological spectrum. Low molecular weight fractions gave rise to a plasticizing effect as indicated by their narrowing effect on the width of the plateau region in the rheological spectrum. Upon heating, the modulus increased over the full range of frequencies, as for single fractions. This increase indicated that a thermal association occurred in the concatenations at temperatures around 40 °C. As a result of heating, the transition zone became apparent in the spectrum at high frequencies. The slopes of the loss modulus G” in the transition zone were found to be higher for mixtures rich in low molecular weight concatenations. The effect of the relative abundance of each fraction on the rheological characteristics of the mixtures was summarized in a number of simple rheological blending rules for the small-deformation rheological properties of glutenin.