Structural studies of a new fraction obtained by gradient ethanol precipitation from Acacia seyal gum

AY60 was a fraction precipitated from Acacia seyal gum by 60% ethanol, and its detailed structure was elucidated by methylation analysis and 1D/2D NMR spectroscopy. AY60 (Mw~92.4 kDa) was found to be a highly branched polysaccharide , and the terminal residues accounted for about 29.76% of total residues, which were t-Ara f (26.59%), t-Rha p (2.25%) and t-Gal p (0.92%) respectively. The branching residues included →3,6-Gal p 1→ (15.81%), →3,4-Gal p 1→ (13.59%) and →3,4,6-Gal p 1→ (11.25%). NMR spectroscopy ( 1 H NMR, 13 C NMR, 1 H– 1 H COSY, TOCSY, HSQC and HMBC) confirmed that the backbone of AY60 was composed of 1,3-linked galactopyransyl residues substituted at O -4 and O -6 positions. The side chains were mainly composed of →4)-β-Gal p A-(1→ (14.43%) and →3)-α-Ara f -(1→ (2.25%), and terminated by arabinofuranosyl (Ara f ) and occasionally by rhamnopyranosyl (Rha p ) or glacuronopyranosyl (Gla p ) residues.