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New studies on gum ghatti (Anogeissus latifolia) part II. Structure characterization of an arabinogalactan from the gum by 1D, 2D NMR spectroscopy and methylation analysis

Kang, J., Cui, S.W., Phillips, G.O., Chen, J., Guo, Q., Wang, Q. (2011). New studies on gum ghatti (Anogeissus latifolia) part II. Structure characterization of an arabinogalactan from the gum by 1D, 2D NMR spectroscopy and methylation analysis, 25(8), 1991-1998. http://dx.doi.org/10.1016/j.foodhyd.2010.11.021

Abstract

The structure of a water soluble arabinogalactan isolated from gum ghatti (Gatifolia SD) was elucidated by methylation analysis and 2D NMR spectroscopy. The arabinogalactan fraction (F80) was obtained by a sequential ethanol precipitation of gum ghatti (Gatifolia SD). Methylation and GC-MS analysis indicated that F80 was a highly branched polysaccharide; the terminal sugar residues were about 40.8% of the total sugars. The majority of the terminal units were α-l-Araf, with small amounts of T-GlcpA, T-Arap, T-Rhap and T-Galp. About 14.2% of the total sugar residues were →6)-β-d-Galp-(1→ branched at 3rd and 4th positions. The linear portion of the arabinogalactan was composed of →4)-GlcpA(1→, →6)-Galp(1→ and →2)-l-Araf-(1→ linkages. Based on the results from methylation analysis, 1D (1H, 13C) and 2D (COSY, TOCSY, HMQC and HMBC) NMR spectroscopy, the structure of F80 was proposed as follows:R is one of the following groups: →3)-β-d-Gal. p-(1→, →5)-β-d-Ara. f-(1→, →2,3-Man. p1→, T-α-l-Ara. f 1→, T-Glc. pA1→ and T-l-Ara. p 1→. Galactose has the -β-D configuration, while the arabinose and rhamnose are in the α-l form. © 2010.

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