Structure of arabinogalactan oligosaccharides derived from arabinogalactan-protein of Coffea arabica instant coffee powder

Arabinogalactan-protein, previously isolated from instant coffee powder of Coffea arabica, has been subjected to partial mild acidic and enzymatic hydrolyses. Separation of obtained mixtures by size exclusion and HPLC chromatographies afforded series of oligosaccharides, structure of which were studied by NMR spectroscopy. Mild acidic hydrolysis afforded oligosaccharides without any alpha Araf substituent while after enzymatic hydrolysis alpha Araf was found in di-, tri-, and tetrasaccharides. In all cases alpha Araf was a terminal substituent linked separately to 03, 06, and to both, 03 and 06, of beta Gal residues. Identification of di-, tri-, and tetrasaccharides containing alpha-Araf enabled to distinguish in the H-1 NMR spectra alpha Araf signals linked to 06 and 03 of neighboring beta Gal unit. Composition of polymeric residues after enzymatic and mild acidic hydrolyses was also analyzed. (C) 2011 Elsevier Ltd. All rights reserved.