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Effect of Morphology of Mechanically Developed Wheat Flour and Water on Starch from Gluten Separation Using Cold Ethanol Displacement

¹Process 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. ²Corresponding author. Phone: 510-559-5866. Fax: 510-559-5818. E-mail: grobertson@pw.usda.gov ³Formerly published as Delilah W. Irving.

The mechanical development of wheat flour and water creates micro and macro structures in dough or batter that critically influence the ability to separate starch from protein by fluid displacement. This study sought to identify specific structural and rheological features and to relate these to separation as indexed by the separation factor. Structural features, especially protein and starch distributions, were examined using visible light microscopy applied to dough samples that had been exposed to a protein dye. Flour and water samples were developed in a Brabender microfarinograph at conditions (water content and time of development) generally suitable for use of the USDA Western Regional Research Center, cold-ethanol fluid-displacement method. No truly homogenous structures were observed. However, distinct segregation of protein and starch were apparent at all conditions. Structural features correlated qualitatively with the success of separation indexed by the overall separation factor (α_p/s) for the separation process. Highly segregated states characterized by large protein bands, clustered starch, and large open spaces were obtained with intermediate development (25 ± 5 min) and were most readily separated (α_p/s = 118 ± 7). Segregated states with relatively thin protein bands (≤10 μm dia) in complex networks entrapping starch were obtained after additional development (≥45 min) and were less completely separable (α_p/s = 32 ± 2). Segregated states with irregularly organized protein in the form of clumps and bands were obtained with minimal development and were partially separable (α_p/s = 65 ± 4). Consistency indicated on the microfarinograph increases monotonically throughout and beyond the period of maximum separability. However, elasticity changes and a high rate of increase in consistency evident in the microfarinogram may reflect changes in the structure that also reduce separability. The study demonstrated the use of the ethanol method to isolate development from displacement phenomena forindependent study.