Submitted to: Biomacromolecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 9, 2008
Publication Date: August 25, 2008
Citation: Grabber, J.H., Hatfield, R.D., Ralph, J., Lu, F. 2008. Coniferyl Ferulate Incorporation into Lignin Enhances the Alkaline Delignification and Enzymatic Degradation of Cell Walls. Biomacromolecules. 9:2510-2516. Interpretive Summary: Plant cell walls are by far the world’s most abundant source of polysaccharides. Used in papermaking and potentially for ethanol fuel production, these polysaccharides are difficult to utilize unless they are liberated by harsh and costly chemical treatments from another cell-wall polymer called lignin. Lignin is also a major barrier limiting the digestion of many feeds by livestock. In this study, we artificially lignified cell walls from corn (Zea mays L.) with varying levels of coniferyl ferulate, a potential building block of lignin that is readily broken down by mild chemical treatments. Adding coniferyl ferulate with other lignin precursors slightly reduced the amount of lignin formed in cell walls. Quite unexpectedly, we found that coniferyl ferulate reduced the activity of peroxidase (the enzyme responsible for lignin formation) and it interfered with the coupling of lignin to ferulates. (Ferulates are small molecules which help to interconnect polymers in cell walls of grasses.) As expected, coniferyl ferulate increased the extraction of cell wall lignin by up to 2-fold into mild alkaline solutions. Thus, this novel precursor provides the option of producing fiber under conventional cooking conditions with substantially less lignin contamination or of delignifying cell walls at lower temperatures to increase fiber yields. Coniferyl ferulate incorporation also increased sugar yields during enzymatic hydrolysis, both with and without alkaline pretreatment. Our results provide compelling evidence that bioengineering of plants to incorporate coniferyl ferulate into lignin should substantially reduce costs and enhance the pulping of plants for paper and the digestion of cell wall sugars by livestock and by enzymes used for ethanol fermentation.
Technical Abstract: Incorporating ester interunit linkages into lignin could facilitate fiber delignification and utilization. In model studies with maize cell walls, we examined how partial substitution of coniferyl alcohol (a normal monolignol) with coniferyl ferulate (an ester conjugate from lignan biosynthesis) alters the formation and alkaline extractability of lignin and the enzymatic hydrolysis of structural polysaccharides. Coniferyl ferulate moderately reduced lignification and cell-wall ferulate copolymerization with monolignols. Incorporation of coniferyl ferulate increased lignin extractability by up to 2-fold in aqueous NaOH, providing an avenue for producing fiber with less non-cellulosic and lignin contamination or of delignifying at lower temperatures. Cell walls lignified with coniferyl ferulate were more readily hydrolyzed with fibrolytic enzymes, both with and without alkaline pretreatment. Based on our results, bioengineering of plants to incorporate coniferyl ferulate into lignin should enhance lignocellulosic biomass saccharification and particularly pulping for paper production.