The phenolic acid and polysaccharide composition of cell walls of bran layers of mature wheat (Triticum aestivum L. cv. Avalon) grains

Abstract

The purpose of this study was to examine the carbohydrate and phenolic-ester composition of cell walls in wheat bran layers. Four defined layers of wheat bran were separated manually from mature grains of wheat (Triticum aestivum L. cv. Avalon) to give samples of beeswing bran (outer pericarp), cross cells, testa + nucellar epidermis and aleurone cells. The cell-wall material from each layer, and from a sample of intact bran, was analysed for carbohydrates and wall-bound esterified phenolic acids. The cell-wall material of intact bran was rich in arabinose and xylose with significant quantities of glucose and uronic acid and a relatively small amount of galactose and mannose. The varying ratios of arabinose:xylose in cell walls of isolated bran layers indicated that the heteroxylans had tissue-specific substitution patterns. HPLC analysis of phenolic acids identified significant amounts of esterified ferulic acid and 8-8′- (aryltetralin form), 5-8′-, 5-5′-, 8-0-4′- and 5-8′-(benzofuran form)-dehydrodiferulic acids in the isolated cell walls. Ferulic acid was highly concentrated in the aleurone layer, whereas dehydrodiferulates were concentrated in the beeswing bran and cross cells. The role of phenolic cross-linking is discussed in relation to the architecture of the cell walls of wheat bran and to processing implications. © 2005 Society of Chemical Industry.