ISOLATION AND CHARACTERIZATION OF CELL-WALL POLYMERS FROM THE HEAVILYLIGNIFIED TISSUES OF OLIVE (OLEA-EUROPAEA) SEED HULL

Cell wall material (CWM) was prepared from olive seed hull, which is h eavily lignified and very tough. The material was cryomilled and delig nified with chlorite/acetic acid for 9 h to give the holocellulose. Po lymers were solubilised from the holocellulose by sequential extractio n with cyclohexane-bans-1,2-diamine-NNN'N'-tetra-acetate (CDTA, Na sal t), DMSO, 0.5, 1 and 4 M KOH and 4 M KOH + berate to leave the alpha-c ellulose residue. The suspension of alpha-cellulose on neutralisation released a small amount of pectic material virtually free of xylan to give alpha'-cellulose. The polymers from the various extracts were fra ctionated by graded precipitation with ethanol prior to anion-exchange chromatography, and selected fractions were subjected to methylation analysis. During delignification, glucuronoxylans with relatively low degrees of polymerisation (DP) and xylan-pectic polysaccharide complex es linked to degraded lignin were solubilised. A proportion of the xyl an-pectic polysaccharide complexes were solubilised by 0.5 M KOH. The major hemicellulosic polysaccharides of the olive seed hulls are glucu ronoxylans, which occur as highly branched short chains, with DP of 30 -60; or slightly branched chains with DP of 90-110. Partial acid hydro lysis of the major acidic xylan, gel-filtration chromatography and met hylation analysis allowed us to propose a tentative structure for the major glucuronoxylan in which one residue of GlcpA occurs in each 14 c ontinuously linked Xylp residues in a regular structure.