Author: Ferenc Békés
Principally the physical and chemical properties of wheat proteins determine the baking quality of wheat flour and the strength of gluten. Wheat gluten, a unique complex compound is formed during dough mixing from interacting hydrated glutenin and gliadin proteins of the flour. Glutenins are the macropolymers, built up by polypeptide subunits, gliadins are monomer type single polypeptides. The glutenins are responsible for the elasticity of the
dough, while the gliadins are responsible for the plasticity.
Wheat proteins can be distinguished as soluble and insoluble proteins. The soluble proteins belong to the groups of the albumins and globulins. Numerous polypeptides form the group of the insoluble proteins group, the above mentioned gluten proteins: α–, β-, γ– and ω-gliadins, low and high molecular weight glutenin subunits (LMW GS and HMW GS, respectively). Based on the genetic background of these polypeptides they also can be grouped as sulphur poor, sulphur rich and high molecular weight (HMW) prolamins.
Research activity on wheat proteins has shifted in the direction of molecular biology during the last 25 years, supported by polymer- and colloid chemistry. Nowadays, with the applications of available methods and new analytical equipment allow the determination of the dough properties using just a few grams of wheat sample. As the state of the art of these methods, it is possible to make a baking trial from 2 grams of flour in a thimble sized special oven. The chemical composition and functional properties of flour can be examined directly or indirectly in in vivo and in vitro conditions. The gene of an ω-gliadin analogue of barley, called C hordein, has been systematically modified to produce analogue glutenin proteins (ANG) by varying the size of the gene as well as the number and location of cysteine groups in the polypeptide. The effects of supplementing the bacterially expressed ANG proteins into the flour on the mixing properties have been tested by in vitro incorporation experiments and the optimal gene variant has been selected for wheat transformation. The successfully produced transgenic wheat showed an 11% improvement in baking quality, while the mixing energy consumption decreased by 20%.
In the light of wheat breeding, the most important outcome of these model based investigations is that, instead of targeting the introduction of a certain individual allele of HMW GS, it is more desirable to construct different allele combinations, because the high impact of the allele-allele interactions.
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