Investigation of the occurrence of xylan-xyloglucan complexes in the cell walls of olive pulp (Olea europaea)

Previously we reported the possible occurrence of a complex containing glucuronoxylan and xyloglucan in the cell walls of olive pulp. In order to investigate the nature of this complex, the 1 M KOH (1 degrees C)-soluble polysaccharides in which it was prevalent, were separated by graded ethanol precipitation followed by anion-exchange chromatography. A slightly acidic fraction was obtained and, by methylation analysis, glycosidic linkages typical of both xylan and xyloglucan were detected. Two distinct populations of the xylan-xyloglucan complexes were resolved by gel-filtration chromatography (2000 and 100 kDa) and the structural features were determined by methylation analysis. Cross-linking of the xylan-xyloglucan moieties was investigated by digestion of the xylan component with a purified, specific, endoxylanase. Although only the xylan element was digested, as verified by methylation analysis, the molecular weight of the xyloglucan moiety was also reduced. This confirmed that the xylan and xyloglucan moieties were strongly attached. The occurrence and structure of the xylan-xyloglucan complexes in the olive pulp cell walls is discussed.