SIZE CHARACTERIZATION OF WHEAT PROTEINS, PARTICULARLY GLUTENIN, BY ASYMMETRICAL FLOW-FIELD FLOW FRACTIONATION

Asymmetrical flow held-how fractionation was demonstrated to fractiona te the most high molecular weight proteins of glutenin found in flour from wheat cultivars with excellent bread-making performances. The fra ctionation occurs in a flow of liquid on the basis of differences in d iffusion coefficients, and therefore hydrodynamic diameters, and appli es to large molecules and colloidal particles. Microgram quantities of glutenin were analysed and shown to have hydrodynamic diameters of 5 to 45 nm. Much larger sizes can be analysed because the method does no t have an upper size limit as do gel electrophoresis and gel filtratio n. Fractionations can often be done in less than 5 minutes. Sonication in combination with a surfactant, SDS, dissolved proteins from freeze -dried extracts of flour obtained by sequential extraction using progr essively increasing concentrations of dilute HCl. An early fraction sh owed a response around 8 nm hydrodynamic diameter, which corresponds t o a molecular weight range of 23 000-128 000. This indicated the prese nce of gliadins. Later fractions gave responses up to 35 nm, which tra nslated to the molecular weight range 440 000-11 million, which is con sistent with the fact that these fractions contain glutenin. Reduction of a late-fraction sample shifted the band to 8 nm, which corresponds to glutenin subunits. The method appears to be a viable procedure to obtain rapid size fractionations of unreduced glutenin. (C) 1996 Acade mic Press Limited