PROCEDURE FOR ISOLATING MONOMERIC PROTEINS AND POLYMERIC GLUTENIN OF WHEAT-FLOUR

A new method for fractionation of monomeric (albumins, globulins, and gliadins) and polymeric (native unreduced) glutenin proteins of wheat flour has been developed. Proteins were first separated into 50% (v/v) 1-propanol soluble (50PS) and insoluble (50PI) fractions. The 50PI pr otein was essentially free of monomeric proteins and comprised mainly glutenin; 50PS protein was a mixture of monomeric proteins and polymer ic glutenin. Polymeric glutenin in 50PS protein was isolated under non reducing conditions by precipitation with 1-propanol to a concentratio n of 70%. Polyacrylamide gel electrophoresis at pH 3.1 showed that the precipitated glutenin fraction (70PI) contained some monomeric protei ns, mainly omega-gliadins. Sodium dodecyl sulfate polyacrylamide gel e lectrophoresis showed that no polymeric glutenin remained soluble in a queous 70% 1-propanol. The fractionation procedure was therefore highl y selective. This fractionation procedure, in conjunction with reverse d-phase high-performance liquid chromatography was then used to examin e the flour proteins of two Canadian wheat cultivars (Glenlea and Kate pwa) of diverse dough strength. While the amounts of total polymeric g lutenin (approximate to 50% of flour protein) and the proportions of o mega-gliadins in 70PI glutenin (approximate to 30%) were comparable fo r both cultivars, flour of the very strong mixing Glenlea contained 21 % more insoluble (50PI) glutenin and 30% less soluble (70PI) glutenin as determined by Kjeldahl analysis. The ratios of 50PI to 70PI gluteni n (4.5 and 2.8 for Glenlea and Katepwa, respectively) were directly pr oportional to the mixograph dough development times. Results showed th at 50PI and 70PI glutenins had the same subunit composition and simila r high molecular weight to low molecular weight subunit ratios. The di fference in solubility of the polymeric glutenin in l-propanol is prob ably due to a difference in molecular size. The results obtained in th is study confirmed the importance of both the soluble and insoluble po lymeric glutenin in determining flour strength. The protein isolation procedure should be useful for physicochemical characterization of sol uble and insoluble glutenin fractions, and for isolating pure glutenin from gliadin-glutenin mixtures.