Influence of high Mr glutenin subunits on glutenin polymers and rheological properties of glutens and gluten subfractions of near-isogenic lines of wheat Sicco

The gluten proteins of three near-isogenic lines of the wheat Sicco, which differed only in high Mr glutenin subunit composition, were studied. Gluten was extracted and fractionated by a sequential extraction procedure with dilute HC1. The deletion of Glu-A1 and -D1 encoded subunits decreased the total content of high Mr glutenin subunits by about one-half as determined by RP-HPLC and SDS-PAGE, and considerably increased glutenin extractability in sequential extraction procedures. At the same time, dynamic measurements in shear showed that viscoelasticity was diminished markedly, which SE-HPLC analysis indicated was due to a lower content of large glutenin polymers and a higher content of gliadin. The substitution of subunits 5 + 10 normally present in Sicco by subunits 2 + 12 changed neither the total amount of high Mr glutenin subunits nor the relative amounts of individual components. Glutens differed, however, in that their viscoelasticities were lower when subunits 2 and 12 were present, lower levels of unextractable large glutenin polymers were also present. On the other hand, gluten subfractions with the same distribution of polymer size showed the same viscoelastic behaviour independent of high Mr subunit composition. A very strong correlation was found between the proportion of large glutenin polymers and the viscoelasticity of gluten subfractions. It was concluded that both the quantity of high Mr glutenin subunits and subunit composition influence gluten viscoelasticity by modifying the polymer size distribution and aggregative properties of gluten proteins.