Ferulic acid and diferulic acids as components of sugar-beet pectins and maize bran heteroxylans

Enzymatic hydrolysis of sugar-beet pulp, and subsequent isolation of feruloylated oligosaccharides, has shown that ferulic acid groups are ester-linked mainly on O-2 of arabinose residues and on O-6 of galactose residues in the pectin side-chains. After saponification of sugar-beet pulp enzymatic digests, dehydrodiferulic acids (0.14%, w/w) have also been identified and characterised as 8-5′, 5-5′, 8-8′ and 8-O-4′ isomers, suggesting that covalent cross-linking of pectic polysaccharides through diferulic bridges occurs in sugar-beet pulp. Feruloylated oligosaccharides from the side-chains of heteroxylans have been isolated from maize bran by acid hydrolysis. Ferulic acid is esterified on O-5 of arabinofuranose residues. 8-8′, 8-5′, 8-O-4′ and 5-5′ coupled dimers, which represent 2.5% (w/w) of the bran, have also been detected. It has been calculated that, in the cell wall, each heteroxylan macromolecule bore ∽75 esterified ferulic acid groups and could be cross-linked through ∽30 diferulic bridges. This result suggests a high degree of cross-linking of heteroxylans chains through ferulic acid in maize bran cell walls.