The uniqueness of wheat among cereal grains depends mostly upon the characteristics of its protein content.
In wheat, as in other plants, protein is developed from simpler substances extracted from environment.
As a plant develops from seed, two metabolic processes take place in the cells – photosynthesis and nitrogen fixation.
Photosynthesis involves formation of carbohydrates from carbon dioxide, water and energy while nitrogen fixation is the conversion of nitrogen gas into chemically combined nitrogen that can readily assimilated by the plant.
Nitrogen fixation can be carried out by legumes which bear root nodules containing certain kinds of bacteria by same algae, by chemical synthesis by electrical discharges in the atmosphere (lightning).The protein of wheat are complex and there is no simple explanation of their constitution or biological function.
Neither differences in the amounts of the various classes of proteins nor differences in the amount or kind of amino acids account for the wide variations in rheological and baking proteins of flours.
From a practical viewpoint, the great weakness in the multitude of ingenious approaches to the characterization of wheat proteins has been lack of proof of their direct association with quality.
The storage proteins in wheat kernels are the sources of gluten, which is the complex of nitrogenous compounds that give wheat flour dough their cohesive and elastic properties.
Gluten can be separated from wheat flour by making a stiff dough from a mixture of flour and water, then washing (manually or mechanically) this dough in an excess of water (as in a stream water) until the starch granules and all soluble materials have been removed.
Gluten appears to be a mixture of two major components called glutenin and gliadin.
The gliadin fraction is soluble in neutral 70% aqueous ethanol. It consists mainly of monomeric proteins that associate by non-covalent hydrogen bonding and by hypothesis interactions, but also contains polymeric proteins that are related structurally to some glutenin subunits.
The glutenins are essentially insoluble in 70% ethanol and appear to consist of proteins or subunits that are aggregated into high molecular weight polymers by covalent disulfide bonds.
Proteins with enzyme activity are the albumins and globulins located in the embryo, aleurone and endosperm.
The protein content of wheat kernels is affected both by the genetic constitution of the plant and by environmental conditions during growth of the plant and development of the seed.
Typically, hard red spring wheat and durum will analyze about 13 to 17% protein.
Hard red winter wheat will test at 11 to 15% protein, in most cases. Soft winter and club wheat would ordinarily fall in the range of 7 to 11% protein.
Of course in the normal course of events many samples will be found that fall outside this range because of unusual weather events, heavy fertilizer applications, disease or characteristics of a particular variety.
Proteins in Wheat
