An optimized high performance liquid chromatography (HPLC) procedure has been developed for the analysis and quantification of all of the known ferulic acid dehydrodimers, and the principle phenolic aldehydes and acids, found in the cell walls of higher plants. The HPLC system uses an ODS2 reverse phase column (5 μm particle size) eluted with a methanol, acetonitrile and water gradient with detection at 280 nm. In addition to providing baseline resolution of most components, the method employs a spectrometric detector which enables the precise identification of eluted components through the analysis of their spectral properties. Analysis of the cell wall phenolics of wheat straw stem (Triticum vulgare) was carried out using this method which is highly versatile and, for certain components, more sensitive than the current gas chromatography–mass spectrometry methodology.

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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.