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 0-2 of l,-Araf residues. The structure of the feruloylated arabinose disaccharide was identified as 0-[2-0-(trans-feruloyl)-α-l-Ara f]-(1 → 5)-l-Araf and that of the feruloylated arabinose trisaccharide as O-α-l-Araf-(1 → 3)-O-[2-0-(trans-feruloyl)-α-l-Araf]-(1 → 5)-l-Araf. The structure of the feruloylated galactose disaccharide was identified as 0-[6-0-(trans-feruloyl)-β-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 α-(1 → 5)-linked arabinan chains and to the galactopyranosyl residues of the main core of β-(1 → 4)-linked type I galactan chains.