Submitted to: Pesquisa Agropecuaria Brasileira
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/2/2003
Publication Date: 3/1/2003
Citation: FUKUSHIMA, R.S., HATFIELD, R.D. PHENOLIC COMPOSITION OF DIOXANE LIGNINS AS DETERMINED BY NITROBENZENE OXIDATIVE REACTION. MEETING ABSTRACT. 2003b. v. 38. p. 373-378. Interpretive Summary: The level of lignin is frequently cited as the major reason for poor digestion of forage by ruminant animals. A limitation of using lignin as an indicator of digestibility is the lack of a reliable method for measuring lignin across a wide range of forages at different maturities. The acetyl bromide method is a rapid and easy to use method to measure lignin in a wide range of plants. However, because it is based on light absorbance of the solubilized lignin (spectrophotometery) there must be accurate standards available to develop calibration procedures. Lignins extracted with acidic dioxane are relatively free of contaminating components and can be used for calibration standards. Analysis of these lignin extracts indicates they contain essentially the same phenolic composition as the original in the total cell wall. This eliminates the concern of acid dioxane lignin not being a true reflection of cell wall lignin and should provide an accurate standard. This is important to other research scientists who may be interested in utilizing the acetyl bromide lignin method. It also allows the potential of standardizing the method for accurate comparison accross forage species, maturities, and growing environments particularly samples collected and analyzed by different researchers.
Technical Abstract: The correct quantification of lignin concentration in forages through the spectrophotometric method presumes the existence of a reference standard. This standard must have a phenolic composition similar to the cell wall lignin. The objective of this work was to verify if the lignins extracted with acidic dioxane solution to be used as reference standard would present the same variation in the phenolic composition as it occurs in the cell wall lignin. Bromegrass, corn and red clover cell wall samples were submitted to the method for extraction of lignins with an acidic dioxane solution. The phenolic composition of the extracted lignins was analyzed by alkaline nitrobenzene oxidation followed by HPLC separation. Extracted lignins confirmed that they have phenolic composition variation the same way as do intact lignins present in the cell wall and that grass lignins showed substantial presence of cinnamic acids. Concerning to phenolic composition lignins extracted by acidic dioxane may potentially be used as reference standards in the spectro photo metric analysis.