Publication no. C-2004-0816-03R |  VIEW ARTICLE

Proteins Extracted by Water or Aqueous Ethanol During Refining of Developed Wheat Dough to Vital Wheat Gluten and Crude Starch as Determined by Capillary-Zone Electrophoresis (CZE).

G. H. Robertson (1,2) and T. K. Cao (1). (1) Bioproduct Chemistry and Engineering Research Unit, Western Regional Research Center, Pacific West Area, Agricultural Research Service, United States Department of Agriculture, 800 Buchanan Street, Albany, CA 94710. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. (2) Corresponding author. Phone: 510-559-5866. Fax: 510-559-5818. E-mail: <grobertson@pw.usda.gov> Cereal Chem. 81(5):673-680. Accepted May 17, 2004. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. American Association of Cereal Chemists, Inc., 2004.

Fluids applied to large-sale, technical separation of wheat starch and protein also extract soluble proteins. The degree and rate of extraction and the specific components extracted depend on the flour, the flour hydration and development, the starch-displacing fluid composition, the temperature, and the mechanical processing method. This study sought to identify major extracted protein groups using high-performance capillary zone electrophoresis (CZE) applied directly to fluids obtained during laboratory-scale technical separations. A dough-ball or compression separation method was applied using a Glutomatic system and a batter or dispersion method was applied using a a McDuffie mixer and Pharmasep vibratory separator. Process fluids were water at 22°C to model commercial practice and 70 vol% ethanol in water at –13°C to model the cold ethanol process being developed here. Data were referenced to use of 70 vol% ethanol in water at 22°C in the Glutomatic compression method. The dough processed by each method was developed by mixing to a separable state. When flooded with excess water, this dough immediately released starch and water-soluble or albumin proteins. When flooded with excess cold aqueous ethanol, neither the albumin nor gliadin proteins appeared in significant amounts until the bulk of the starch had been displaced, regardless of the mechanical method. Even with extraction and manipulation well beyond that necessary for starch displacement, the net amount of gliadin proteins dissolved was only approximately 10% of that available from wet developed dough using 70 vol% ethanol at 22°C. There was more gliadin protein in the fluids at earlier stages of processing when the batter dispersion method was applied using cold ethanol. The most common soluble proteins revealed in the electrophoresis patterns for the batter compression method using cold aqueous ethanol were initially albumins and later gamma-gliadins. Albumins not appearing as soluble in cold 70 vol% ethanol were found in the insoluble crude starch, suggesting their precipitation in the dough fluids during the change from free water to cold aqueous ethanol. These results establish that some protein is dissolved during starch displacement by cold aqueous ethanol, but that the amounts may be limited by control of the mechanical working of the dough in the presence of the displacing fluids.