Composition and structural features of cell wall polysaccharides from tomato fruits

Abstract

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.