Submitted to: Pesquisa Agropecuaria Brasileira
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/20/2003
Publication Date: 4/1/2003
Citation: FUKUSHIMA, R.S., HATFIELD, R.D. NUCLEAR MAGNETIC RESONANCE SPECTRA OF TWO TYPES OF LIGNIN. Pesquisa Agropecuaria Brasileira. 2003a. v. 38. p. 505-511. Interpretive Summary: The level of lignin is believed to be a major reason for poor digestion of forage by ruminant animals. A limitation of using lignin as an indicator of digestibility is the lack of an easy and reliable method for measuring lignin across a wide range of forages at different maturities. The acetyl bromide methods 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 were extracted with acidic dioxane and acetyl bromide reagent to use as standards. Characterization of each extract indicated the acetyl bromide soluble lignin was highly contaminated with carbohydrate, most likely cellulose, while the acid dioxane lignin had only minor levels of carbohydrate contamination. The acid dioxane lignin is a suitable material to use as lignin standard because it contains only small amounts of non-lignin materials. This overcomes an obstacle that has limited the use of the acetyl bromide method for determining lignin levels in forages. The rapid nature and ease of use of the acetyl bromide may allow analysis of a wider range of materials (different locations, environments, species) from different countries to develop a consistent database that may be used to predict digestibly based on a single lignin measurement. This would save a tremendous amount of time and greatly aid genetic selection programs aimed at improving forages digestibility.
Technical Abstract: Lignin content can be useful to estimate fiber digestion of forage plants. Quantitative determination of lignin by the spectrophotometric method presumes an efficient standard. The objective of this work was to evaluate, by the nuclear magnetic resonance (NMR), two lignins, one extracted with acetyl bromide (AcBrL) and another with acidic dioxane solution (DL), as standards in spectrophotometric analysis. Proton resonance revealed high presence of carbohydrates in the AcBrL residues. Because liquid chromatograph had already shown low contamination with carbohydrates in the DL samples, only carbon resonance, which is lengthier, but richer in details than proton resonance, was run on these lignin samples. The carbon resonance revealed typical peaks common to most lignins. NMR findings were harmonious with wet chemistry which revealed that the cell wall carbohydrates attached to AcBrL would possibly be cellulose whereas in the DL, the small carbohydrate components would come from pentosans. DL can be considered a better standard to the spectrophotometric analysis than AcBrL.