STRUCTURE IDENTIFICATION OF FERULOYLATED OLIGOSACCHARIDES FROM SUGAR-BEET PULP BY NMR-SPECTROSCOPY

1D NMR (H-1 and C-13) 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-Araf residues. The structure of the feruloylated arabinose disaccharide was identified as O-[2-O-(trans-feruloyl)-alpha-L-Araf]-(1-->5)-L-Araf and that of the feruloylated arabinose trisaccharide as O-alpha-L-Araf-(1-->3)-O-[2-O-(trans-feruloyl)-alpha-L-Araf]-(1-->5)-L-Araf. The structure of the feruloylated galactose disaccharide was identified as O-[6-O-(trans-feruloyl)-beta-D-Galp]-(1-->4)-D-Galp. 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.