Wheat gluten: Composition and health effects

Abstract

Grains of cereals of the Gramineae family have been a required source of food for millennia. Wheat, rye, barley are unique among the edible grains because their flours have the protein complex called ,,gluten" that can be formed into a dough with the rheological properties required for the production of leavened bread. The gluten proteins consist of monomeric gliadins and polymeric glutenins. Glutenins and gliadins are recognised as the major wheat storage proteins, constituting about 60-85% of the total grain proteins and they tend to be rich in asparagine, glutamine, arginine or proline but very low in nutritionally important amino acids lysine, tryptophan and methionine. The gliadins are a polymorphic mixture of proteins soluble in 70% alcohol, and can be separated into α-, β-, γ-, and ω-gliadins with a molecular weight range of 30 to 80 kDa. Glutenins can be broadly classified into two groups, the high molecular weight (HMW) and the low molecular weight (LMW) subunits, with the molecular weight range of 75 to 120 kDa and 30 to 74 kDa, respectively, according to mobility on SDS-PAGE. They link together and form heterogeneous mixtures of polymers by disulfide bonded linkages of polypeptides. Generally, it is believed that gliadin controls the viscosity of dough and glutenin controls the elastic or strength properties. The precise balance between viscosity (extensibility) and elasticity (dough strength), or the glutenin to gliadin ratio, is important for bread making.In addition to their role in dough quality, gluten proteins can affect health in genetically susceptible individuals. Among the different gluten subunits, the a-gliadins are considered the most immunogenic, while γ-gliadins and glutenins are much less responsible for gluten intolerance. About 1% of the general population suffers from CD and numbers are increasing not only because of better diagnosis but also because of increased intake and usage of wheat constituents as food additives.