Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 7, 2004
Publication Date: February 11, 2005
Citation: Grabber, J.H. and R.D. Hatfield. 2005. Methyl Esterification Divergently Affects the Degradability of Pectic Uronosyls in Nonlignified and Lignified Maize Walls. Journal of Agriculture and Food Chemistry. 53: 1546-1549 Interpretive Summary: Forage legumes, forage grasses, and cereal crop residues are often the major feedstuff in livestock diets and they are a potential feedstock for producing biofuels, bioplastics, and other products. Typically one-half or more of the dry weight of forage crops is fiber. Fiber is a complex matrix of pectins and other carbohydrate polymers knit (i.e. cross-linked) together by protein and phenolic substances that include lignin. Pectins are an important component of many foods because of their ability to form jells but they are also an important source of digestible energy for livestock. We studied how the removal of methyl groups from pectins affects the enzymatic digestion of pectin in fiber isolated from cells of corn (Zea mays L.). Removal of methyl groups slightly enhanced pectin digestion in fiber that did not contain lignin. In contrast, removal of methyl groups prior to artificial lignification of fiber greatly reduced the digestibility of pectin. Further work suggested that removal of methyl groups allowed greater cross-linking of pectin to lignin. In ongoing work, we are investigating ways of reducing the cross-linking of lignin to pectin and other fiber carbohydrates so that lignin will be less of a barrier to fiber digestion. Ultimately these studies will lower the cost and environmental impact of converting forages and cereal crop residues into food, fuel, and industrial products.
Technical Abstract: Nonlignified walls from Zea mays (L.) cell suspensions were incubated with and without pectin methylesterase (PME) and a portion were artificially lignified to assess how methyl esters influence the release of pectic uronosyls and total sugars from cell walls by fungal enzymes. Treatment with PME reduced uronosyl concentrations from 97 to 92 mg/g, reduced uronosyl methylation from 57 to 21%, and increased Klason lignin concentrations in artificially lignified walls from 99 to 116 mg/g. Although PME treatment slightly enhanced uronosyl release from nonlignified walls, it reduced uronosyl release from artificially lignified walls by 55% after 4 h and by 7% after 72 h of enzymatic hydrolysis. Pectin hydrolysis in PME treated walls was probably impaired by enhanced benzyl ester cross-linking of uronosyls to lignin via quinone methide intermediates. Variations in uronosyl methylation had little effect on the overall release of total sugars from cell walls.