Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 7, 1997
Publication Date: N/A
Interpretive Summary: Fiber makes up 15 to 80% of the dry weight of plants. Fiber is composed primarily of two types of polymers, polysaccharides and lignin. Polysaccharides can be degraded to simple sugars by enzymes. These sugars are an important source of energy for humans and for livestock. These sugars may also be converted into ethanol for use in automobile fuels or other purposes. Polysaccharides in fiber are poorly degraded into simple sugars because of their association with lignin. Lignin is made up of three different kinds of building blocks--p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. We ran experiments to determine if the type of building block used to make lignin affects the degradability of polysaccharides into simple sugars. To do this, we isolated fiber from plant cells that were composed of just polysaccharides. We then formed an artificial lignin within this fiber using the three types of lignin building blocks. We found that the type of building block used to make lignin had no effect on the degradation of polysaccharides by enzymes. Therefore, we recommend that biotechnology should not be used to change the type of lignin formed in plants used for food or for fuel production. Studies of this kind provide basic information needed for understanding and correcting factors which limit fiber digestion by livestock. Improved fiber degradability would reduce feed costs and manure disposal problems for livestock operations.
Technical Abstract: Studies with normal, mutant, and transgenic plants have not clearly established whether the proportion of p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units in lignin affects the degradability of cell walls by hydrolytic enzymes. Dehydrogenation polymer-cell wall complexes containing varying ratios of H, G, and S lignins were formed by peroxidase/H2O2-mediated polymerization of p-coumaryl, coniferyl and sinapyl alcohols into nonlignified walls isolated from cell suspensions of maize (Zea mays L). Lignification substantially reduced the degradability of cell walls by fungal hydrolases, but degradability was not affected by lignin composition. Based on these results, we propose that improvements in wall degradability, previously attributed to changes in lignin composition, were in fact due to other modifications in wall chemistry or antiquality factors.