Studies of Molecular Association of Glutenins and Maltodextrin in Solution by Capillary Electrophoresis

Abstract

Molecular associations of wheat glutenins and carbohydrates are important in bread systems and believed to contribute to differences of a number of dough and baking quality characteristics. In this investigation, the study of molecular association of glutenins with carbohydrates in solution was performed by capillary zone electrophoresis (CZE). The carbohydrate used was a maltodextrin of average molecular weight 2000. To follow the molecular association of major glutenin subunits with the maltodextrin of interest, the extracted proteins from hard red winter wheat (cv. Scout 66) were fractionated first by reversed‐phase chromatography (RPC). Four major RPC fractions were collected, each of which still exhibited more than one glutenin component when reanalyzed by CZE. These RPC fractions were then incubated with the maltodextrin of interest, and the pre‐equilibrated glutenin‐maltodextrin complexes thus obtained were analyzed by CZE. Since maltodextrin is a neutral polymer, its binding to the glutenins results in decreasing the charge‐to‐mass ratio of the glutenins, and consequently, the effective electrophoretic mobility of protein–maltodextrin complex decreases with increasing maltodextrin concentration in the incubation solution. The evaluation of glutenin–maltodextrin interactions was only qualitative and the calculation of binding constants was hampered by various factors including the heterogeneity of the glutenin RPC fractions. The components of each RPC fraction yielded mobility lines (i.e., plots of electrophoretic mobility vs. percentage of maltodextrin in the glutenin sample) that paralleled each other indicating that these components have the same binding energetics magnitude with maltodextrin. This observation was substantiated by the sodium dodecyl sulfate capillary gel electrophoresis (SDS‐CGE) analysis, which showed that the various components of each RPC fraction are probably formed from one kind or one group of glutenin subunit with very similar properties. In addition, the mobility curves did not exhibit the usual rectangular hyperbolic forms of 1:1 binding isotherms.

Keywords:

• Wheat glutenin
• Capillary electrophoresis
• High performance liquid chromatography
• Glutenin–maltodextrin associations

Acknowledgments

P. R.‐D. acknowledges the financial support by a grant from the Food Research Initiative Program, Oklahoma Agricultural Experiment Station, Oklahoma State University. Z.E.R. acknowledges the financial support, in part by the Environmental Institute's Centers for Water and Energy Research Programs at Oklahoma State University.