Cereal Chem. 73 (1):143-152 |
Procedure for Isolating Monomeric Proteins and Polymeric Glutenin of Wheat Flour (1).
B. X. Fu and H. D. Sapirstein. (1) Publication 257 of the Department of Food Science, University of Manitoba, Winnipeg, MB Canada R3T 2N2. Accepted October 23, 1995. Copyright 1996 by the American Association of Cereal Chemists, Inc.
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 protein was essentially free of monomeric proteins and comprised mainly glutenin; 50PS protein was a mixture of monomeric proteins and polymeric glutenin. Polymeric glutenin in 50PS protein was isolated under nonreducing conditions by precipitation with 1-propanol to a concentration of 70%. Polyacrylamide gel electrophoresis at pH 3.1 showed that the precipitated glutenin fraction (70PI) contained some monomeric proteins, mainly omega-gliadins. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that no polymeric glutenin remained soluble in aqueous 70% 1-propanol. The fractionation procedure was therefore highly selective. This fractionation procedure, in conjunction with reversed-phase high-performance liquid chromatography was then used to examine the flour proteins of two Canadian wheat cultivars (Glenlea and Katepwa) of diverse dough strength. While the amounts of total polymeric glutenin (approximately 50% of flour protein) and the proportions of omega-gliadins in 70PI glutenin (approximately 30%) were comparable for 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 glutenin (4.5 and 2.8 for Glenlea and Katepwa, respectively) were directly proportional to the mixograph dough development times. Results showed that 50PI and 70PI glutenins had the same subunit composition and similar high molecular weight to low molecular weight subunit ratios. The difference in solubility of the polymeric glutenin in 1-propanol is probably due to a difference in molecular size. The results obtained in this study confirmed the importance of both the soluble and insoluble polymeric glutenin in determining flour strength. The protein isolation procedure should be useful for physicochemical characterization of soluble and insoluble glutenin fractions, and for isolating pure glutenin from gliadin-glutenin mixtures.