Wheat gluten (WG) is a protein composite found in foods processed from wheat and related grain species, including barley and rye. WG husk is the composite of a gliadin and a glutenin (Fig. 15.4), which is conjoined with starch in the endosperm of various grass-related grains.

The prolamin and glutelin from wheat (gliadin, which is alcohol-soluble, and glutenin, which is only soluble in dilute acids or alkalis) constitute about 80% of the protein contained in wheat fruit.

The gliadin and glutenin components contribute to dough quality either in an independent manner (additive genetic effects) or in interactive manner (epistatic effects). Commercial WG has a mean composition of 72.5% protein (77.5% on dry basis), 5.7% total fat, 6.4% moisture and 0.7% ash; carbohydrates, mainly starches, are the other major

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 disulfide 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 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.

The film forming property of hydrated wheat gluten is a direct outcome of its viscoelasticity. Whenever carbon dioxide or water vapor forms internally in a gluten mass with sufficient pressure to partially overcome the elasticity, the gluten expands to a spongy cellular structure. In such structures, pockets or voids are created which
are surrounded by a continuous protein phase to entrap and contain the gas or vapor. This new shape and structure can then be rendered dimensionally stable by applying sufficient heat to cause the protein to denature or devitalize and set up irreversibly into a fixed moist gel structure or to a crisp fragile state, depending on final moisture content.