|Bunzel, Mirko - U. HAMBURG|
|Kim, Hoon - UW-MADISON|
|Lu, Fachuang - UW-MADISON|
|Ralph, Sally - US FOREST PRODUCTS|
|Steinhart, Hans - U. HAMBURG|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 19, 2002
Publication Date: N/A
Interpretive Summary: Cereals provide dietary fiber, an important nutritional commodity used for human/animal foods. They provide unique health benefits and some possesses a potent antioxidant activity. We have found that so-called ferulates cross-link polysaccharides in fiber providing structural strength but limiting the availability of the polysaccharides for digestion. In this work, we have found that wild rice, in particular, has an analogous cross-linking mechanism using sinapates. The actual mechanism by which the cross-linking occurs is shown to be the same as for ferulates. These same new cross-linking structures have now been found at lower levels in the more traditional cereal grains, but would have been difficult to identify without the wild rice used in this study; as often happens, studying less mainstream samples can reveal new insights into the more common commodities. Since cereals are an important source of dietary fiber, a knowledge of the contributions of ferulic and sinapic acids as cross-linking agents and antioxidants will help nutritionists to elucidate their roles in some of the healthful properties of fiber, such as regulation of blood sugar levels, lowering of cholesterol, and prevention of bowel cancer. Such studies are also aimed at understanding how these cross-linking agents limit fiber digestibility, providing a basis for improving plant utilization and agricultural sustainability.
Technical Abstract: Two 8 8-coupled sinapic acid dehydrodimers have been identified as saponification products from different insoluble and soluble cereal grain dietary fibers. The two 8-8-isomers were authenticated by comparison of their GLC retention times and mass spectra with authentic dehydrodimers synthesized from methyl or ethyl sinapate using two different single-electron metal oxidant systems. The highest amounts (481 µg g-1) were found in wild rice insoluble dietary fiber. Model reactions showed that it is unlikely that the dehydrodisinapates detected are artifacts formed from free sinapic acid during the saponification procedure. The dehydrodisinapates presumably derive from radical coupling of sinapate-polymer esters in the cell wall in an analogous way to the dehydrodiferulates that are found cross-linking polysaccharides in cereal grains (and grass cell walls in general).