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.

DPPH radical scavenging capacity and the reducing power of free and bound phenolics from wheat and porcino (Boletus edulis) flours

“…In the porcino flour the situation is opposite and free phenolics were 28.3 times higher than bound phenolics. This indicates that the phenolics in the investigated wheat flour sample are mainly present in a bound form, as earlier investigation by Paker, et al [7] also showed, while in the porcino flour phenolics are mainly present in a free form. Comparing the contents of phenolics in wheat and porcino flours, the content of free phenolics and the content of total phenolics (obtained by content summation of free and bound phenolics), was higher in the porcino flour than in the wheat flour.…”

“…free [6]. Phenolic acids represent the most common compounds of phenolics in wheat and are present mainly in bound forms, linked through the ester bond to the cell wall structural components such as cellulose, lignin and proteins [7]. The bound phenolics are considered to have a greater antioxidant capacity because they escape from gastrointestinal digestion along with the cell wall materials and are absorbed into the blood plasma during digestion by intestinal micro flora [1].…”

Strategic Distribution of Protective Proteins within Bran Layers of Wheat Protects the Nutrient-Rich Endosperm

“…The carbohydrate composition of wheat bran (Fig. 6) clearly indicates that the nucellar layer has a higher ratio of Xyl to Ara than all the other bran tissues (Parker et al, 2005), which means that this tissue is highly susceptible to xylanase degradation. Thus, the location of XIPs in these high-Xyl tissues highlights their importance in protecting the inner layer and endosperm from biotic attack.…”

Microwave-Assisted Extraction of Bound Phenolic Acids in Bran and Flour Fractions from Sorghum and Maize Cultivars Varying in Hardness

“…There were large differences between the sorghum and maize phenolic acid contents despite the two cereal grains being similar in structure, chemical composition and basis for grain hardness 17 . The differences in the diferulic acids content and composition of sorghum and maize cultivars could be due to variations in their biosynthesis and cross-linking hence affecting the degree of alkaline hydrolysis and breakage of ether bonds 18 . The time for extraction could have been insufficient to break all the sorghum ether bonds and release the diferulic acids despite the likelihood that the temperature generated would enhance mass transfer by increasing solid solubility and diffusion of solubilised phenolic acids into the alkali and reduce extraction time 19 .…”