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Wheat Arabinoxylan Structure Provides Insight into Function

¹Department of Crop and Soil Sciences, Washington State University, Pullman, WA 99164-6376; affiliated with the USDA-ARS Western Wheat Quality Laboratory. 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. ²USDA-ARS Western Wheat Quality Laboratory, E-202 Food Quality Bldg., Washington State University, P.O. Box 646394, Pullman, WA 99164-6394. ³Corresponding author. Phone: (509) 335-4062. Fax: (509) 335-8573. E-mail: morrisc@wsu.edu

Recent attention to dietary fiber in wheat (Triticum aestivum L.) has invigorated research in the nonstarch carbohydrate arabinoxylan (AX). AX molecules are composed of a linear xylose backbone with arabinose substitutions along the backbone. These arabinose substituents can also carry a ferulic acid moiety. AX molecules can be fractionated into two categories based on extraction properties that have a structural and conformational basis: water-extractable (WEAX) and water-unextractable (WUAX) molecules. The ferulic acid moieties also allow for oxidative cross-linking between AX molecules or the tyrosine residues of proteins. The contents of total AX and WEAX molecules are primarily influenced by genetic differences; however, there is also evidence of environmental influence on content. There are several useful methods for quantifying AX molecules, providing varying levels of structural information as well as accuracy and precision. The high water-absorption capacity of AX molecules results in a strong influence of AX on end-use quality. Whereas WEAX molecules, in particular, tend to be detrimental for the quality of soft wheat products such as cookies, WEAX molecules are beneficial to the quality of hard wheat products such as bread. The role of WUAX molecules among the range of soft wheat products is as yet unclear; however, WUAX molecules tend to have a detrimental influence on bread. Because of the variable influence of AX structure on end-use product functionality, closer examination of structure–function relationships may provide key insights into how to direct breeding efforts to maximize these relationships between AX molecules and other ingredients. Further investigation is necessary to obtain a more complete understanding of how the arabinose substitution levels and patterns affect end-use quality and how the genetic basis of these traits can be resolved and manipulated for optimum end-use quality.