Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/6/1998
Publication Date: N/A
Citation: Interpretive Summary: Fiber makes up 15 to 80% of the dry weight of plants. Fiber is composed primarily of structural polysaccharides that are potentially an important source of energy for humans and for livestock. Structural polysaccharides may also be converted into ethanol for use in automobile fuels or other purposes. To be a source of food or fuel energy, structural polysaccharides smust be broken down by digestive enzymes into simple sugars, but this process is limited by an indigestible component in fiber called lignin. Lignin is attached (i.e., cross-linked) to structural polysaccharides by a molecule called ferulic acid; and it has been speculated, but never proven, that reduced ferulic acid cross-linking of fiber would improve structural polysaccharide digestion. To test this hypothesis, we isolated fiber from plant cells that had normal or low levels of ferulic acid but no lignin. Artificial lignins were then formed within the fiber matrix. We found that ferulic acid cross-links controlled the rate, and to a lesser degree, the extent of structural polysaccharide degradation by digestive enzymes. Based on these results we recommend that biotechnology should be used to develop plants that have low amounts of ferulic acid cross-links. Reducing ferulate cross-links in fiber should lower the cost and environmental impact of converting fibrous crops into food and fuel.
Technical Abstract: Ferulate cross-linking of arabinoxylans to lignin may restrict the enzymatic degradation of grass fiber, limiting the fermentation of structural polysaccharides into metabolizable energy for livestock or into ethanol and other products for industrial uses. 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 to 46% after 6 h and by 0 to 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. Our results indicate that reduced feruloylation of arabinoxylans will significantly improve the hydrolysis of lignified grass walls.