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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #195634
Title: STRUCTURAL IDENTIFICATION OF DEHYDROTRIFERULIC AND DEHYDROTETRAFERULIC ACIDS ISOLATED FROM INSOLUBLE MAIZE FIBER

Author
item BUNZEL, MIRKO - UNIV. HAMBURG, GERMANY
item Ralph, John
item BRUNING, PHILIPP - UNIV. HAMBURG, GERMANY
item STEINHART, HANS - UNIV. HAMBURG, GERMANY

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2006
Publication Date: 8/15/2006
Citation: Bunzel, M., Ralph, J., Bruning, P., Steinhart, H. 2006. Structural identification of dehydrotriferulic and dehydrotetraferulic acids isolated from insoluble maize fiber. Journal of Agricultural and Food Chemistry. 54(17):6409-6418.

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) to create ferulate dimers. Such findings have opened up avenues of research into improving the utilization of large classes of plant fiber and other food commodities. A short time ago we reported the first structural evidence for three ferulates coupling together making a ferulate trimer. Now it is getting even more complicated (and perhaps ridiculous!) with the discovery that polysaccharides can be linked by four ferulates in a tetramer. It is tempting to infer that polysaccharide chains may be very heavily cross-linked, but in fact there is the possibility that the ferulate tetramers still only cross-links two polysaccharide chains. The significance is that cross-linking is even more prevalent than we previously thought, and that ferulates are capable of creating the cross-links in a variety of ways. 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: Two new dehydrotriferulic acids and two dehydrotetraferulic acids were isolated from saponified maize bran insoluble fiber using size exclusion chromatography on BioBeads S-X3 followed by Sephadex LH-20 chromatography and semi-preparative Phenyl-Hexyl-RP-HPLC. Based on UV-spectroscopy, mass spectroscopy, and one- and two-dimensional NMR experiments, the structures were identified as 8-5(non-cyclic)/5-5-dehydrotriferulic acid, 8-8(tetrahydrofuran)/5-5-dehydrotriferulic acid and 4-O-8/5-5/8-O-4-dehydrotetraferulic acid. The second tetramer was tentatively identified as 4-O-8/5-5/8-5(non-cyclic)-dehydrotetraferulic acid. Compounds containing an 8-5(non-cyclic)-coupled dimeric unit probably do not exist in-planta but are formed from their phenylcoumaran precursors containing an 8-5(cyclic)-coupled dimeric unit during saponification. The presented dehydrotrimers are the first dehydrotriferulates that do not contain an 8-O-4-coupled dimeric unit. The ferulate dehydrotetramers that are reported for the first time are presumed, like the dimers and trimers, to cross-link polysaccharides in the plant. Since both tetramers contain a 5-5/8-O-4-dehydrotriferulate moiety, the predominant dehydrotrimer in maize bran, it is not possible to deduce whether tetramers are formed by coupling of a fourth unit to a preformed dehydrotriferulate or by 5-5-coupling of preformed 8-O-4- and 8-5-dehydrodiferulates. Nevertheless, such compounds document expanded roles for ferulates in cross-linking polysaccharides in plant cell walls.