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Wheat Gluten Swelling and Partial Solubility with Potential Impact on Starch-from-Gluten Separation by Ethanol Washing

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

Swelling of wheat gluten may be a contributing factor in washing or displacement separation of gluten and starch using cold ethanol. To test this hypothesis, dissolution and swelling (settled volume or mass absorption) of a commercial gluten are reported here for the first time as a function of both temperature and ethanol solution concentration. In this test system, instant and substantial volumetric swelling was observed over most of the range of ethanol concentrations but not at 100%, v/v, ethanol. Settled volume reached a maximum of 50–70%, v/v, ethanol, and this was up to 3.5× the volume in absolute ethanol at 22°C and 2× the volume at −15°C. This maximum closely corresponds to the maximum dissolution of whole gluten and prior literature reports of full dissolution of gliadin. The reduction of settled volume at low temperature reflects the possible role of undissolved, gliadin-class proteins in reinforcing the gluten structure and limiting the ultimate swelling. The data suggest gluten-swelling properties as a contributing factor to the success of the cold ethanol, glutenfrom-starch separation process.