Extraction of pectic polysaccharides from sugar-beet cell walls

Abstract

Previous methods of extracting pectin from sugar-beet have used pulp as the starting material. As the temperature and pressure of the pulping process may modify the architecture of the cell wall, we have adapted a relatively non-disruptive method to characterise cell wall material (CWM) isolated directly from the sugar-beet. Cell walls from mature sugar-beets (Beta vulgaris L Aztec) were sequentially extracted four times with imidazole and twice with sodium carbonate to produce six heterogeneous pectic polysaccharide extracts, and with KOH to produce a hemicellulosic extract which was predominantly xylans. Heterogeneity of the extracted pectins was indicated by differences in FTIR spectra, uronic acid content, % methyl esterification, % feruloylation, % acetylation, molecular weight distribution and neutral sugar composition. The highest proportion of feruloyl esters was found in polysaccharides solubilised by the second sodium carbonate extraction. Anion exchange chromatography of these polysaccharides gave three fractions, one of which contained most of the feruloyl ester. These results indicate that feruloyl esters are not randomly distributed among the different pectic polysaccharides in the sugar-beet cell wall, and that esterification is likely to be dependent on the local sugar sequence or conformation. © 2000 Society of Chemical Industry