Submitted to: Cereal Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/5/2007
Publication Date: 9/5/2007
Citation: Robertson, G.H., Cao, T., Orts, W.J. 2007. Wheat proteins extracted from flour and butter with aqueous ethanol at subambient temperatures. Cereal Chemistry. 84(5): 497-501. Interpretive Summary: The purification and use of wheat gluten protein is important to the stability of the domestic wheat gluten/starch industry and to the expansion and creation of new biofuel industries producing ethanol. New methods such as the USDA/WRRC cold-ethanol method apply cold ethanol to the purification process and produce protein that is functionally different than that produced by the usual aqueous methods. One likely reason for this is alteration of the protein composition by partial extraction. This report applies capillary electrophoresis to describe proteins that are extracted from flour by ethanol solutions matching processing conditions. We found that the concentration of some of the subclasses of protein that are extracted will change as the temperature is lowered to process conditions. Further, proteins extracted from dry flour are not identical to those extracted from flour that has been wetted and developed mechanically. This data is useful to the interpretation of cold-ethanol process data and for explanation of functional properties of the resulting wheat protein or gluten.
Technical Abstract: Contact of wheat flour proteins with aqueous ethanol may enrich protein by starch displacement and/or deplete protein by extraction depending (1) on the concentration and temperature of the applied solvent and (2) the form of the contacted substrate. Generally, extraction at sub-ambient temperatures has not been described for specific wheat gliadin types for either dry flour with the protein in native configurations or for wet, developed batter or dough. The lack of this information limits the ability to interpret results of proposed technology for separations such as the cold-ethanol method developed by us. Here, we describe the composition of flour extracts by CZE in the 0% to 100% concentration range and for -12 to 22 degree C to determine specific albumin and gliadin-type extraction properties. We also compared these results to those for extracts from batter prepared by a previously-described sequential-batch or dispersion method and a continuous method with repeated compression and decompression of the batter. We found reduction of protein extraction for both albumin and gliadin protein as the temperature was reduced as well as narrowing of the concentration range for which extraction occurred. Extraction dropped precipitously between 0 and -7 degree C for both albumins and gliadins. Electrophoretically defined gliadin types extracted in constant proportion at 22 degree C and 30 to 80% ethanol, but as the temperature was lowered, there was relative enrichment of the alpha-gliadins and depletion of the beta-gliadins in the 30 to 55% range. Different proportions of sub-classes were determined for the contact of solution with wheat flour batter. We noted depletion of alpha and beta and enrichment of gamma relative to the dry flour contact suggesting that the electrophoretically slow eluting gamma-proteins are less well incorporated to the dough matrix than electrophoretically fast eluting alpha and beta-types.