Features Of Cell-wall Polysaccharides Research Articles

Isolation and characterisation of cell wall polysaccharides from cocoa (Theobroma cacao L.) beans.

Cell wall material (CWM) was prepared from sun-dried cocoa (Theobroma cacao L.) bean cotyledons before and after fermentation. The monosaccharide composition of the CWM was identical for unfermented and fermented beans. Polysaccharides of the CWM were solubilised by sequential extraction with 0.05 M trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA), 0.05 M Na2CO3, and 1 M, 4 M and 8 M KOH. The non-cellulosic sugar composition for each fraction was similar for unfermented and fermented samples, indicating that fermentation caused no significant modification of the structural features of individual cell wall polysaccharides. Pectic polysaccharides accounted for 60% of the cell wall polysaccharides but only small amounts could be solubilised in solutions of CDTA, Na2CO3, and 1 M and 4 M KOH. The bulk of the pectic polysaccharides were solubilised in 8 M KOH and were characterised by a rhamnogalacturonan backbone heavily substituted with side-chains of 5-linked arabinose and 4-linked galactose. Linkage analysis indicated the presence of additional acidic polysaccharides, including a xylogalacturonan and a glucuronoxylan. Cellulose, xyloglucan and a galactoglucomannan accounted for 28%, 8% and 3% of the cell wall polysaccharides, respectively. It is concluded that the types and structural features of cell wall polysaccharides in cocoa beans resemble those found in the parenchymatous tissue of many fruits and vegetables rather than those reported for many seed storage polysaccharides.

Structural features of cell wall polysaccharides from the cotyledons of mung bean Vigna radiata

The first analysis is reported of the cell wall of a food legume by methods that minimise the degradation of pectic polysaccharides. The cell walls of mung bean cotyledons ( Vigna radiata, var. T77) were extracted in sequence with 0.05 M trans-1,2-cyclohexanediamine- N, N, N′, N′-tetraacetate, sodium salt (CDTA) at 20°C, 0.05 M Na 2CO 3 at 1 and 20°C, 0.5 M KOH at 1°C, 1 M KOH at 1 and 20°C, 4 M KOH at 20°C, and 4 M KOH containing 4% of boric acid at 20°C. The isolated polymers were fractionated by anion-exchange chromatography. The CDTA-solubilised pectic polysaccharides were less branched than those solubilised by Na 2CO 3; less than 10% of the cell wall was solubilised by these reagents. 0.5 and 1 M KOH released only 3.2% by weight of the cell wall; the extracts consisted of mixtures of xyloglucans and pectic polysaccharides. The bulk of the extractable pectic polysaccharides were only released by 4 M KOH. They were highly branched arabinorhamnogalacturonans and contained significant amounts of terminal xylopyranosyl residues. Preliminary evidence is given to show that at least some of the xylopyranosyl residues are attached to the 3-position of 1,4-linked galactopyranuronosyl residues of the backbone. Some of the pectic polysaccharides were associated with small amounts of xyloglucan even after refractionation by anion-exchange chromatography, suggesting that they may be covalently attached in a complex. Little neutral arabinan was detected. High levels of arabinans, released from the walls of other legume-cotyledons by earlier workers, were probably artefacts caused by β-elimination under their extraction conditions. In this

Composition and structural features of cell wall polysaccharides from tomato fruits

Cell wall material was isolated from the pericarp of unripe and ripe tomatoes, free from intracellular compounds and active wall degrading enzymes. The wall preparations were sequentially extracted with cyclohexane-trans-1,2-diaminetetra-acetate (CDTA) at 20°, 0.05 M Na 2CO 3 at 1°, 0.05 M Na 2CO 3 at 20°, and 0.5, 1 and 4 M KOH at 20° to leave the α-cellulose residue, which contained a significant amount of pectic material. The polysaccharides isolated from the extracts were fractionated by anion-exchange chromatography and selected fractions were subjected to methylation analysis. The CDTA-soluble pectic polysaccharides had slightly-branched rhamnogalacturonan back-bones compared with the sodium carbonate-soluble pectic polysaccharides. The side chains of the pectic polysaccharides were mainly composed of β-(1→4)-Iinked galactopyranosyl and α-(1→5)-Iinked arabinofuranosyl residues, and the evidence for this was obtained by both methylation analysis and 13C NMR spectroscopy. The major hemicellulosic polysaccharide was a xyloglucomannan and there was evidence for the occurrence of a small amount of a xylan-pectic complex. The ripe fruit contained much less pectic galactans compared with the unripe fruit, and there was a significant decrease in the content of galactan side-chains of the ripe fruit. The hemicelluloses of the unripe and ripe fruit, however, showed negligible difference in composition.