Hydroxycinnamic acids and ferulic acid esterase in relation to biodegradation of complex plant cell walls

Ferulic acid (3-methoxy-4-hydroxycinnamic acid), present in complex plant cell walls, is covalently cross-linked to polysaccharides by ester bonds and to components of lignin mainly by ether bonds. Ferulic acid has also been shown to occur in dimer- and trimerized forms through oxidative coupling between esterified and/or etherified ferulic acid residues. These cross-links are among the factors most inhibitory to digestion of complex plant cell walls in ruminants. Recently obtained information on ferulic acid and ferulic acid esterases in relation to complex plant cell wall biodegradation is reviewed. A focus of the review is on structural characteristics of plant cell walls associated with ferulic acid, physicochemical properties of ferulic acid esterase and synergistic interaction between ferulic acid esterase and other accessary cell wall degrading enzymes on the release of ferulic acid and plant cell wall biodegradation.