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Molecular Weight Distribution of Wheat Proteins

¹BRI Australia Ltd, P.O. Box 7, North Ryde, 2113 Australia. ²Department of Grain Science and Industry, Kansas State University, Manhattan KS 66506-2201. ³Corresponding author. Phone: 785/532-6199. Fax: 785/532-7010. E-mail: fim@wheat.ksu.edu

The molecular weight distribution (MWD) of wheat proteins is becoming recognized as the main determinant of physical dough properties. Studies of high polymers have shown that properties such as tensile strength are related to a fraction of polymer with molecular weight above a critical value and the MWD of this fraction. Elongation to break is treated as a kinetic process with energies of activation for breaking noncovalent bonds and for chain slippage 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 monomeric and polymeric proteins and the MWD of the polymeric proteins. The latter, 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 gliadins that act as chain terminators. The role of these compositional variables in determining dough extensional properties is discussed in terms of present knowledge. Determination of MWD of wheat proteins is hindered by the difficulty of their solubilization and the lack of methods for reliably measuring very high molecular weights. Among the promising techniques for achieving these measurements are multiangle laser light scattering (MALLS) and field flow fractionation (FFF).