Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2007
Publication Date: 4/25/2007
Citation: Funk, C., Braune, A., Grabber, J.H., Steinhart, H., Bunzel, M. 2007. Moderate Ferulate and Diferulate Levels Do Not Impede Maize Cell Wall Degradation by Human Intestinal Microbiota. Journal of Agriculture and Food Chemistry. 55:2418-2423. Interpretive Summary: Dietary fiber from cereal crops like corn and wheat is primarily composed of polysaccharides (polymers of sugar molecules) that are in part held together (cross-linked) by small molecules known as “ferulates”. Digestion of polysaccharides by bacteria in the colon produces gases and small molecules known as “short-chain fatty acids”. Some short-chain fatty acids (particularly butyric acid) play a role in preventing intestinal disorders. When absorbed into the bloodstream, these short-chain fatty acids have other health promoting effects, such as suppressing cholesterol synthesis and enhancing immune responses to disease. Using conditions mimicking the colon, we investigated the specific role of ferulates and their cross-linking structures as constraints to fiber digestion. These studies showed that low to moderate levels of ferulates and their cross-linking structures do not impede fiber degradation by bacteria in the colon. Therefore, low to moderate levels of ferulates in dietary fiber should not hinder the production of health promoting short-chain fatty acids by bacteria in the colon.
Technical Abstract: The degradation of plant fiber by human gut microbiota could be restricted by xylan substitution and cross-linking by ferulate and diferulates, for example by hindering the association of enzymes like xylanases with their substrates. To test the influence of feruloylation on cell wall degradability by human intestinal microbiota, nonlignified primary cell walls from maize cell suspensions, containing varying degrees of ferulate substitution and diferulate cross-linking, were incubated in nylon bags in vitro with human fecal microbiota. Degradation rates were determined gravimetrically and the cell walls were analyzed for carbohydrates, ferulate monomers, dehydrodiferulates, dehydrotriferulates, and other minor phenolic constituents. Shifting cell wall concentrations of total ferulates from 1.5 to 15.8 mg/g and diferulates from 0.8 to 2.6 mg/g did not alter the release of carbohydrates or the overall degradation of cell walls. After 24 h of fermentation, the degradation of xylans and pectins exceeded 90% while cellulose remained undegraded. The results indicate that low to moderate levels of ferulates and diferulates do not interfere with hydrolysis of nonlignified cell walls by human gut microbiota.