Glutenin (a type of glutelin) is the major protein within wheat flour, making up 47% of the total protein content. The glutenins are protein aggregates of high molecular weight (HMW) and low molecular weight (LMW) subunits with molar masses from c. 200,000 to a few million, which are stabilized by intermolecular disulfide bonds, hydrophobic interactions and other forces. Glutelin is responsible for the strength and elasticity of dough.
Wheat gluten proteins consist of two major fractions: the gliadins and the glutenins. Gliadins are monomeric proteins that can be separated into four groups, alpha-, beta-, gamma- and omega-gliadins. Glutenins occur as multimeric aggregates of high molecular weight (HMW) and low-molecular-weight (LMW) subunits held together by disulphide bonds. In wheat, omega- and gamma-gliadins are encoded by genes at the Gli-1 loci located on the short arms of group 1 chromosomes, while alpha and beta-gliadin-encoding genes are located on the short arms of group 6 chromosomes. LMW glutenins are encoded by genes at the Glu-3 loci that are closely linked to the Gli-1 loci. HMW glutenins are encoded by genes at the Glu-1 loci found on the long arms of group 1 chromosomes. Each Glu-1 locus consists of two tightly linked genes encoding one ‘x’-type and one ‘y’-type HMW glutenin, with polymorphism giving rise to a number of different alleles at each locus . The y-type genes at the Glu-A1 locus are not expressed in hexaploid wheat. Due to the very close linkage between the x and y type genes, HMW glutenins are classified into alleles according to the x and y type subunits expressed.
Considerable efforts have been made to understand the relationship between gliadin and glutenin composition and rheological properties of wheat dough. It is now well understood that the properties of various wheat storage proteins have a major effect on dough rheological properties. The gliadin and glutenin components contribute to dough quality either in an independent manner (additive genetic effects) or in interactive manner (epistatic effects). It was suggested that the apparent effects of gliadins on dough quality should be attributed to the LMW glutenins due to the close linkage of the Gli-1 and Glu-3 loci. Generally, HMW glutenins have been found to be more important than gliadins and LMW glutenins for dough rheological properties.
Breadmaking qualities are largely dependent on the number and composition of HMW glutenin subunits. It has been demonstrated that alleles Glu-A1b (Ax2∗) and Glu-D1d (Dx5 + Dy10) are normally associated with superior end-use quality, especially dough strength.
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