Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2004
Publication Date: 2/1/2005
Citation: Funk, C., Ralph, J., Steinhart, H., Bunzel, M. 2004. Isolation and structural characterization of 8-0-4/8-0-4- and 8-0-4/8-8-coupled dehydrotriferulic acids from maize bran. Phytochemistry. 66:363-371. 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'. It is tempting to infer that polysaccharide chains may be very heavily cross-linked, but in fact we think that it is attached twice to one polysaccharide chain and once to another, so that the entity still only cross-links two chains. In proving that this was not some singular event, and is a common mechanism for plants to tie their fibers together, we have now discovered two more ferulate trimers, with quite different but reasonably predictable structures. 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 were isolated from saponified maize bran insoluble fiber using Sephadex LH-20 chromatography followed by semi-preparative RP-HPLC. Based on UV-spectroscopy, mass spectroscopy and one- and two-dimensional NMR experiments, the structures were identified as 8'O'4,8'O'4-dehydrotriferulic acid and 8'8(cyclic),8'O'4-dehydrotriferulic acid. Which of the possible phenols in the initially formed 8'8-dehydrodiferulate was etherified by 4'O'8-coupling with ferulate has been unambiguously elucidated. The ferulate dehydrotrimers which give rise to these dehydrotriferulic acids following saponification are presumed, like the dehydrodiferulates, to cross-link polysaccharides. Neither dehydrotriferulic acid described here involves a 5'5-dehydrodiferulic acid unit; only the 5'5-dehydrodimer may be formed intramolecularly. However, whether dehydrotriferulates are capable of cross-linking more than two polysaccharide chains remains open. Although the levels of the isolated ferulate dehydrotrimers are lower than those of the ferulate dehydrodimers, the isolation now of three different dehydrotriferulates indicates that trimers contribute to a strong network cross-linking plant cell wall polysaccharides.