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 determ ine 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 ar abinose or galactose residues were identified. In the feruloylated ara binose oligosaccharides, feruloyl groups were linked to O-2 of L-Araf residues. The structure of the feruloylated arabinose disaccharide was identified as [2-O-(trans-feruloyl)-alpha-L-Araf]-(1-->5)-L-Araf and that of the feruloylated arabinose trisaccharide as 2-O-(trans-feruloy l)-alpha-L-Araf]-(1-->5)-L-Araf. The structure of the feruloylated gal actose disaccharide was identified as [6-O-(trans-feruloyl)-beta-D-Gal p]-(1-->4)-D-Galp. From our results, we suggest that the feruloyl grou ps present in sugar-beet pulp are linked to the arabinofuranosyl resid ues of the main core of alpha-(1-->5)-linked arabinan chains and to th e galactopyranosyl residues of the main core of beta-(1-->4)-linked ty pe I galactan chains.