Structure identification of feruloylated oligosaccharides from sugar-beet pulp by NMR spectroscopy

1D NMR (1H and 13C) and 2D NMR spectroscopy have been used to determine the structure of feruloylated oligosaccharides obtained by enzymic degradation or mild acid hydrolysis of sugar-beet pulp. Feruloylated oligosaccharides derived from pectic neutral side-chains containing arabinose or galactose residues were identified. In the feruloylated arabinose oligosaccharides, feruloyl groups were linked to O-2 of L-Ara f residues. The structure of the feruloylated arabinose disaccharide was identified as O-[2-O-(transferuloyl)-alpha-L-Ara f]-(1-->5)-L-Ara f and that of the feruloylated arabinose trisaccharide as O-alpha-L-Ara f-(1-->3)-O-[2-O-(trans-feruloyl)-alpha-L-Ara f]-(1-->5)-L- Ara f. The structure of the feruloylated galactose disaccharide was identified as O-[6-O-(trans-feruloyl) -beta-D-Gal p]-(1-->4)-D-Gal p. From our results, we suggest that the feruloyl groups present in sugar-beet pulp are linked to the arabinofuranosyl residues of the main core of alpha-(1-->5)-linked arabinan chains and to the galactopyranosyl residues of the main core of beta-(1-->4)-linked type I galactan chains.