Structural features, antioxidant and immunological activity of a new polysaccharide (SP1) from sisal residue.

A new water-soluble polysaccharide (SP1) with molecular weight of 9192Da was isolated from the residue after extracting fiber from sisal leaf and its structure was investigated. Monosaccharide composition analysis showed that SP1 was composed of Rha, GalA, Gal, Ara and Glc in a molar ratio of 1.82:1.69:1.00:0.23:0.15. The structure analysis indicated that the SP1 was comprised of a backbone of alternating 1,2-linked-α-l-Rhap and 1,4-linked-α-d-GalpA units, and the neutral polysaccharide side chains composed of Galp, Ara and Glcp residues were attached to the O-4 position of 1,2-linked-α-l-Rhap residues. SP1 could stimulate ConA-induced T lymphocyte proliferation and had noticeable DPPH radical-scavenging ability.