ARS | Publication request: ISOLATION AND STRUCTURAL IDENTIFICATION OF COMPLEX FERULOYLATED HETEROXYLAN SIDE-CHAINS FROM MAIZE BRAN

Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 21, 2006
Publication Date: June 20, 2006
Citation: Allerdings, E., Ralph, J., Steinhart, H., Bunzel, M. 2006. Isolation and structural identification of complex feruloylated heteroxylan side-chains from maize bran. Phytochemistry. 67(12):1276-1286.

Interpretive Summary: A plant's fiber component provides a great deal of structural strength as well as considerable nutrition to ruminant animals. Grain fiber also has significant human health benefits. The fiber is reinforced in the plant by cross-linking of the polysaccharide polymers, on a micro-scale rather akin to the cross-bracing we use when building wooden structures. Some time ago we discovered new mechanisms by which wall cross-linking could be achieved by chemical coupling of two so-called ferulate molecules (that were each tied to one polysaccharide chain). Such findings have opened up avenues of research into improving the utilization of large classes of plant fiber and other food commodities. What is often not clear, however, is what components of the plant cell wall polysaccharides they are attached to. Determining this requires isolation and structural characterization of particularly complex compounds cleaved from the plant cell wall. Here we isolated and identified ferulic acid attached to 4-sugar-unit fragments from the wall and also, for the first time, one similarly complex structure involving another acid, p-coumaric acid. The complex carbohydrate side-chains are a likely factor contributing to limited enzymatic degradation of fiber. Future efforts are aimed at minimizing this cross-linking in forage plants to improve ruminant digestibility, and to ascertain the human and animal health benefits of the ferulates in cereal grains.

Technical Abstract: Three new complex heteroxylan side-chains acylated with ferulate and one arabinosyl ester of p-coumaric acid have been isolated from maize bran insoluble fibre after acidic hydrolysis and fractionation by gel permeation chromatography and semi-preparative RP-HPLC. The complete structural elucidation of all isolated compounds was achieved by 1D/2D NMR spectroscopy and HPLC-MS in combination with methylation analysis. The absolute configuration of the carbohydrate constituents was determined by chiral GC after acidic hydrolysis and trifluoroacetylation. The identified feruloylated tetrasaccharides alpha-D-xylopyranosyl-(1>3)-alpha-L-galactopyranosyl-(1>2)-beta-D-xylopyranosyl-(1>2)-5-O-trans-feruloyl-L-arabinofuranose (FAXGX) and alpha-D-galactopyranosyl-(1>3)-alpha-L-galactopyranosyl-(1>2)-beta-D-xylopyranosyl-(1>2)-5-O-trans-feruloyl-L-arabinofuranose (FAXGG) are the most complex heteroxylan side-chains from maize bran that have been isolated to date. The isolated trisaccharide alpha-L-galactopyranosyl-(1>2)-beta-D-xylopyranosyl-(1>2)-5-O-trans-feruloyl-L-arabinofuranose (FAXG) contributes to the complexity of heteroxylan side-chains from maize bran and 5-O-trans-p-coumaroyl-L-arabinofuranose represents the first p-coumaroylated heteroxylan side-chain isolated from cereal grains. Complex feruloylated heteroxylan side-chains are possibly, like ferulate cross-linking of the heteroxylans and binding of heteroxylans to lignin, a factor contributing to limited enzymatic degradation of fibre.