Ferulate cross-links limit the enzymatic degradation of synthetically lignified primary walls of maize

Ferulate cross-linking of arabinoxylans to lignin may restrict the enzymatic degradation of structural polysaccharides, limiting the utilization of graminaceous crops and crop residues as feedstuffs and as feedstocks for fuel and chemical production. Maize walls from nonlignified cell suspensions with ca. 5.1 or 17.6 mg g(-1) of ferulates were synthetically lignified with coniferyl alcohol and H2O2 to form dehydrogenation polymer-cell wall complexes with ca. 4.8 or 15.8 mg g(-1) of ferulates incorporated into lignin. Ferulate concentrations in cell walls were reduced from normal levels by growing cell suspensions with 2-aminoindan-2-phosphonic acid or by methylating wall ferulates with diazomethane prior to complex formation. A 70% reduction in ferulate-lignin cross-linking increased carbohydrate solubilization by 24-46% after 6 h and by 0-25% after 72 h of hydrolysis with two fungal enzyme mixtures. Reduced cross-linking enhanced the hydrolysis of xylans and, to a lesser degree, cellulose from walls. The results presented indicate that reduced feruloylation of arabinoxylans will significantly improve the hydrolysis of lignified grass walls.