Structural investigations on the mucilaginous polysaccharides isolated from bark of the avocado tree (Persea americana mill)

Two arabinoxylans, a water-extractable (molecular weight ∼600,000) composed of l-arabinose and d-xylose in the molar ratio of 3:1, and an alkali-extractable (molecular weight ∼1,300,000) composed of d-xylose (95%) and l-arabinose (5%), have been isolated from the bark of Persea americana Mill. For structural elucidation, the purified polysaccharides were subjected to methylation analysis, partial hydrolysis, periodate oxidation, and Smith degradation. The results suggested that the water-extractable arabinoxylan has a highly branched structure consisting of a (1→4)-linked, β-d-xylan backbone in which each of the d-xylopyranosyl residues is substituted at O-2 and O-3 with l-arabinofuranosyl-(1→3)-l-arabinofuranosyl and l-arabinofuranosyl groups, respectively, whereas the alkali-extractable arabinoxylan is essentially a linear, (1→4)-linked β-d-xylan, with limited branches at O-2 or O-3 consisting of l-arabinofuranosyl groups.