Michel Cornec

Biochemical basis of flour properties in bread wheats. II. Changes in polymeric protein formation and dough/gluten properties associated with the loss of low Mr or high Mr glutenin subunits

Abstract Polymeric protein plays a critical role in governing the functional properties of wheat flour. Wheat genetic lines lacking high M r and, similarly, low M r glutenin subunits from one, two or all three Glu-1 or Glu-3 loci, respectively, were thus used to investigate the effects of these polypeptides on glutenin polymer formation and dough/gluten properties. Polymer formation (quantity, size distribution) was studied by size-exclusion high-performance liquid chromatography (SE-HPLC) using extractable, unextractable and total protein from flour, as well as by diagonal electrophoresis using total protein extracts. The loss of Glu-1 or Glu-3 subunits had significant effects on the quantity of total, extractable and unextractable polymeric protein and on the dough and gluten properties of these lines. Dough and gluten properties were significantly correlated with the proportions of both total and unextractable polymers (a measure of the relative molecular size distribution of polymeric protein), although more strongly with the proportions of unextractable polymers in the case of Glu-1 null lines. The proportion of total polymeric protein decreased more markedly when all the Glu-3 subunits were deleted than when all the Glu-1 subunits were absent, which was in accordance with the relative quantities of these two types of the subunits in the grains. In contrast, loss of all the Glu-1 subunits, on an equal weight basis, reduced the amounts of the larger polymers to a much greater extent than the loss of all the Glu-3 subunits, reflecting more than the molecular size differences in these subunits. SE-HPLC and diagonal electrophoresis of total protein extracts from the triple Glu-1 and Glu-3 null lines also revealed that Glu-1 or Glu-3 subunits form large polymers on their own. When both high and low M r glutenin subunits were present together, however, the amount of large polymer was much greater than the sum of the amounts when only one group was present, suggesting a positive interaction between these two groups of subunits with respect to polymer formation.

Relations between aggregative, viscoelastic and molecular properties in gluten from genetic variants of bread wheat

Glutens differing in their low- and high-molecular-weight glutenin subunits (LMW-GS and HMW-GS) were extracted from genetic variants of bread wheat. Their composition was analysed by electrophoresis, the glutenin size distribution was determined by size-exclusion chromatography. Rheological measurements in the dynamic regime and electron spin resonance spin-labelling experiments gave data on the viscoelasticity and the protein flexibility of the glutens, respectively. In glutens differing in their HMW-GS, a relation is observed between the composition, aggregative properties, segmental flexibility and viscoelastic behaviour. This is not found in glutens with different LMW-GS. However, the proportion of rigid polypeptide segment is related to the height of the elastic plateau in all cases. The organisation of the protein network in gluten is discussed in reference to this data.