Influence of the arabinoxylan composition on the susceptibility of mono‐ and dimeric ferulic acid release by Humicola insolens feruloyl esterases

Bioconversion of waste residues (by‐products) from cereal processing industries requires the cooperation of enzymes able to degrade xylanosic and cellulosic material. An enzyme preparation from Humicola insolens , Ultraflo, contains feruloyl esterases and glycoside hydrolases capable of solubilising brewers' spent grain and wheat bran, but total solubilisation was not achieved either through steric hindrance or through the lack of certain key activities. H. insolens feruloyl esterases released more diferulates from chemically extracted feruloylated arabinoxylan from both cereal sources than from the complex cell wall material, but less monomeric ferulic acid. The 8‐ O ‐4′‐form of diferulic acid was released only from spent grain‐derived material, whereas the chemically‐insoluble residue from wheat bran was more extensively degraded than the corresponding spent grain sample. Arabinoxylans with low amounts of arabinose substitutions were preferentially solubilised. These results show that some phenolic acids in cereals are less susceptible to enzyme and alkali cleavage than others. The results also show that the local environment and molecular arrangement of ferulic and diferulic acids on arabinoxylan chains differ between barley and wheat, thus influencing enzyme hydrolysis.