Functionality-Composition relationships of wheat flour as a result of variation in sulfur availability

Abstract

Some recently developed methods for analysing wheat protein composition have been applied to studying the composition/functionality relationships for flours from grain samples of the wheat variety Olympic, grown under differing nitrogen/sulfur fertilizer treatments. In this way, the effects of changing protein composition on functional properties could be followed without the complication of allelic variation. Previous work had established that sulfur deficiency caused an imbalance in dough properties characterized by an increase in dough strength (extensograph maximum resistance, Rmax) and a decrease in extensibility (Ext). In the present study, decreasing flour sulfur content was accompanied by an increase in the ratio of high (HMW) to low (LMW) molecular weight glutenin subunits. As a result, the portion of polymeric proteins (those proteins such as glutenins whose molecules contain multiple polypeptide chains) that is unextractable in SDS-buffer solution (%UPP, a measure of molecular size distribution) also increased with a decrease in sulfur content. A highly significant correlation was found between Rmax and %UPP. In contrast, Rmax showed a high negative correlation with the percentage of polymeric protein in the total protein. Results are generally in agreement with previous studies of wheat samples which varied considerably in genotype but not in environment, thus establishing fundamental relationships between protein composition and dough properties. Extensibility related positively to the percentage of polymeric protein in the flour, but evidence suggested that Ext can be limited by a shift in the molecular weight distribution to too high molecular weight. Reduction in the percentage of polymeric protein in flour (and Ext) as a result of sulfur deficiency was due to a decrease in LMW glutenin subunits which are normally present in greater amounts than the HMW subunits. Dependence of dough mixing and baking performance parameters on protein composition is also reported.