Importance of amounts and proportions of high molecular weight subunits of glutenin for wheat quality

High molecular weight (HMW) subunits of wheat glutenin are generally considered to play a key role in gluten formation and structure, and to be closely related to wheat quality. Though quantities of HMW subunits in flour have been proposed to be as important for wheat quality as their structures, only few quantitative data are available in the literature. Therefore, two assortments of wheat consisting of 13 international and 16 German cultivars were analyzed for their contents and proportions of single HMW subunits using an extraction and HPLC procedure on a micro-scale. The results were compared with quantitative data from the literature that were obtained by sodium dodecylsulfate polyacrylamide gel electrophoresis combined with densitometry or by reversed-phase HPLC combined with UV detection. The quantitative analyses demonstrated that the contents of HMW subunits varied within a broad range dependent on genotype and growing conditions. The proportions of subunits within a given subunit combination, however, varied only within a small range. Generally, subunits 2, 5, 7, 10 and 12 were major components and subunits 1, 2*, 6, 8 and 9 were minor components. The levels of HMW subunits were highly correlated to dough development time, maximum resistance of dough and gluten, and bread volume. Among HMW subunits the x-type components (subunits 1-7) were much more important than the y-type components (subunits 8-12). In particular, the presence of subunit 5 (which has an additional cysteine residue) and of subunit 7 (which occurs in the greatest amounts) contributed to high wheat quality.