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.

No 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.

No abstract

The aim of this work was to investigate heat‐induced changes in cell wall polysaccharides of carrot in relation to texture. Discs of fresh carrot (Daucus carota cv Amstrong) tissue were subjected to cooking (100°C, 20 min), with or without a pre‐cooking treatment (50°C, 30 min). Alcohol‐insoluble residues were prepared from the tissues and were extracted sequentially with water, NaCl, CDTA, Na2CO3 and 0·5 M KOH to leave a residue. These were analysed for their carbohydrate compositions, their degree of methyl esterification and the molecular size of selected soluble polysaccharides. Cooking caused tissues to soften. This involved cell separation, an increase in water‐ and salt‐soluble, high‐molecular‐weight pectic polysaccharides and a concomitant decrease in the pectic polymers in all wall extracts and the residue. Pre‐cooking prior to cooking enhanced cell–cell adhesion and reduced the extent of softening. This was accompanied by a general reduction in the degree of methylesterification of cell‐wall pectic polymers, and a decrease in the cooking‐induced modification to all pectic fractions. The firming effect of pre‐cooking could be reversed by extracting the precooked+cooked tissue with CDTA, a chelating agent. The role of Ca2+ cross‐linked polymers and pre‐cooking in the enhancement of firmness are discussed. © 1997 SCI.

Atomic force microscopy has been used to visualize the ultrastructure of hydrated plant cell wall material from prepared apple (Malus pumila MILL; Cox orange pippin), water chestnut (Eleocharis dulcis L.), potato (Solanum tuberosum L.; Bintje), and carrot (Daucus carota L.; Amsterdamse bak) parenchyma. Samples of cell wall material in aqueous suspension were deposited onto freshly cleaved mica. Excess water was blotted away and the moist samples were imaged in air at ambient temperature and humidity. The three-dimensional images obtained highlighted the layered structure of the plant cell walls and revealed features interpreted as individual cellulose microfibrils and plasmodesmata.

No abstract

13C NMR with magic angle spinning (MAS) has been employed to investigate the cell walls of potatoes and Chinese water chestnuts over a range of hydration levels. Both single-pulse excitation (SPEMAS) and cross-polarization (CPMAS) experiments were carried out. Hydration led to a substantial increase in signal intensities of galactan and galacturonan in the SPEMAS spectra and a decrease in line width, implying mobilization in the backbone and side chains of pectin. In CPMAS spectra of both samples, noncellulose components showed signal loss as hydration increased. However, the signals of some galacturonan in the 3(1) helix configuration remained in the spectra even when the water content was as high as 110%. Cellulose was unaffected. It is concluded that the pectic polysaccharides experience a distribution of molecular conformations and mobility, whereas cellulose remained as typical rigid solid.