DEGRADATION OF FERULOYLATED OLIGOSACCHARIDES FROM SUGAR-BEET PULP ANDWHEAT BRAN BY FERULIC ACID ESTERASES FROM ASPERGILLUS-NIGER

The activity of two forms of ferulic acid esterase (FAE) from Aspergil lus niger on a synthetic feruloylated substrate (methyl ferulate) and on 11 different feruloylated oligosaccharides from sugar-beet pulp and wheat bran was determined. The enzymes exhibited different specificit ies for the various feruloylated substrates and were more active on ce rtain substrates of cell-wall origin than on methyl ferulate. Both enz ymes preferred the arabinose residue to which ferulic acid is attached in the furanose form. FAE-I had no clear preference for the type of l inkage involved between the ferulic acid units and the oligosaccharide chain. In contrast, FAE-III had a clear requirement for ferulic acid to be attached to O-5 of the Araf ring while no catalysis was observed when ferulic acid was attached to O-2. Both enzymes showed maximum ac tivity on feruloylated trisaccharides. An increase in the length of th e oligosaccharide chain did not preclude catalysis, but feruloylated o ligosaccharides of a dp > 3 were hydrolysed at a reduced rate. Our res ults support the hypothesis that different kinds of ferulic acid ester ases exist with different specificities for the oligosaccharide chain of the feruloylated substrates.