Cell wall polysaccharides of Brassica campestris seed cake: isolation and structural features

Brassica campestris seed cake is an important source of water-soluble polysaccharides. The polysaccharides extracted with acid and dilute alkali represented 270 mg/g of defatted meal. These polymers, which have high amount of neutral sugars are arabinan, rhamnogalacturonan I and arabinogalactan proteins. These polymers have been analyzed by size exclusion chromatography. Two overlapping peaks have been found. Structural characterization of 4 M KOH-soluble hemicellulosic polysaccharides using specific enzyme hydrolysis, ion exchange chromatography (HPAEC) and matrix-assisted laser desorption ionization-time of flight mass spectroscopy showed that mustard meal xyloglucan is of XXXG type and contained XXXG, XXFG, XXLG and XLFG (named according to Fry et al. [Physiol. Plant. 89 (1993) 1]) as the major building sub-units. Hydrolysis with endo-β-(1→4)-d-xylanase and analysis of the xylan derived oligosaccharides showed the presence of xylose (27%), xylobiose (26%) and acidic xylan fragments containing 4-O-methyl-d-glucuronic acid residue (47%).