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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #142603

Title: STRUCTURAL PHENOLIC COMPONENTS IN CEREAL DIETARY FIBER:SOLUBLE AND INSOLUBLE RYE DIETARY FIBER

Author
item BUNZEL, MIRKO - U. HAMBURG, GERMANY
item STEINHART, HANS - U. HAMBURG, GERMANY
item Ralph, John

Submitted to: Grain Flour and Bread
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Cereal grains provide dietary fiber, an important nutritional commodity used for human and animal foods. We have found that so-called "ferulates" in plant fibers cross-link polysaccharides (forming diferulates) providing structural strength but limiting the availability of the polysaccharides for digestion. However, the presence of cross-linked ferulates in cereals has only begun to be addressed. As such compounds have antioxidant and other favorable properties, we analyzed rye grain for ferulates and other phenolic components. The whole spectrum of diferulates that had previously been found in plants by our laboratories, were also found at significant levels in the insoluble fiber fractions. The levels in soluble dietary fiber were about 39-fold lower, suggesting their important role in rendering the fiber insoluble. We also established that lignins (phenolic polymers) are present in the grains; polysaccharides can be further immobilized by cross-linking to lignins via ferulates. A knowledge of the contributions of ferulates and diferulates will help to elucidate their roles in some of the healthful properties of fiber, such as regulation of blood sugar, lowering of cholesterol, prevention of bowel cancer, etc. Such studies are aimed at understanding the limitations to fiber digestibility, and providing a basis for improving plant utilization and agricultural sustainability.

Technical Abstract: The physiological characteristics of cereal grain dietary indigestible fiber have a close relationship with the chemical structure of their components. Phenolic acids, e.g. ferulic acid, represent only minor components of the fiber, but they can have a large influence on the physicochemical characteristics of the material due to their ability to cross-link fibers. Ferulate is by far the major acid in both the insoluble and in the soluble rye fiber materials. Sinapic and p-coumaric acids were found in much lower quantities. In the alkaline hydrolysate of the insoluble and soluble rye fiber, the entire spectrum of the dehydrodiferulic acids which are anticipated after radical coupling were found. Arabinoxylans of the insoluble fiber are more frequently substituted with ferulate, and 39 times more frequently connected by diferulic acid cross-linking. Rye fiber was established to contain lignin structures by using the DFRC method, which selectively cleaves alpha-and beta-ethers releasing diagnostic monomers. Since cross-coupling of polysaccharides to lignin can also be mediated by ferulate, the phenolic components have the potential to significantly alter the physicochemical characteristics of fiber, and consequently influence their physiological properties.