Molecular weight distribution of wheat proteins

The molecular weight distribution (MWD) of wheat proteins is becoming recog nized as the main determinant of physical dough properties. Studies of high polymers have shown that properties such as tensile strength are related t o a fraction of polymer with molecular weight above a critical value and th e MWD of this fraction. Elongation to break is treated as a kinetic process with energies of activation for breaking noncovalent bonds and for chain s lippage through entanglements. These considerations are related to tensile properties of wheat flour doughs such as those measured by the extensigraph . The MWD of wheat proteins is determined by the relative amounts of monome ric and polymeric proteins and the MWD of the polymeric proteins. The latte r, in turn, depends on the ratio of high molecular weight glutenin subunits (HMW-GS) to low molecular weight glutenin subunits (LMW-GS), the specific HMW-GS that result from allelic variation, and the presence of modified gli adins that act as chain terminators. The role of these compositional variab les in determining dough extensional properties is discussed in terms of pr esent knowledge. Determination of MWD of wheat proteins is hindered by the difficulty of their solubilization and the lack of methods for reliably mea suring very high molecular weights. Among the promising techniques for achi eving these measurements are multiangle laser light scattering (MALLS) and field flow fractionation (FFF).