Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2000
Publication Date: N/A
Interpretive Summary: Interpretive Summary Fiber makes up 15 to 80% of the dry weight of plants. Fiber is composed primarily of structural polysaccharides, proteins, and an inert substance known as lignin. In some plants, these components are knit together (cross-linked) by small molecules known as ferulate. Many plants use ferulate cross-linking to halt tissue growth and to ward off various pests. These cross-links also reduce digestibility and alter the physical properties of foods for humans and feeds for livestock. Attachment of ferulate to lignin makes it extremely difficult to measure the abundance and characterize the types of these cross-links in plants. We isolated nonlignified fiber from corn cells and measured the concentration of ferulate and of various dimers it forms. An artificial lignin was then formed in the fiber, permitting us to measure and characterize the types of cross-linked structures formed between lignin and ferulate. Our findings will help researchers working in the fields of plant physiology, human nutrition, feed utilization, and food science to better understand and characterize ferulate cross-linking in plants.
Technical Abstract: Abstract Cross-linking of xylans and lignin by ferulates were investigated with primary maize walls acylated with 2% ferulate and with ferulate ethyl esters. Peroxidase-mediated coupling of wall ferulate and ethyl ferulate yielded mostly 8-coupled products, including three new dehydrodimers. Significant quantities of 5-5-coupled diferulate formed only within walls suggesting that matrix effects influence dimer formation. Over 60% of wall ferulate dimerized at the onset of lignification suggesting that xylan feruloylation is highly regulated to permit extensive dimer formation. During lignification, ferulate and 5-5-coupled diferulate copolymerized more rapidly and formed fewer ether-linked structures with coniferyl alcohol than 8-5-, 8-O-4-, and 8-8-coupled diferulates. Incorporation of most ferulates and diferulates into lignin exceeded 90%. As a result, xylans become extensively cross-linked by ferulate dimerization and incorporation to lignin but only a small and variable proportion of these cross-links are measured by solvolysis of lignified walls.