Comparison of Different Methods for Lignin Determination as a Basis for Calibration of Near-Infrared Reflectance Spectroscopy and Implications of Lignoproteins
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Three commonly employed methods for lignin determination, i.e., the thioglycolic acid (TGA), the acetylbromide (AB), and the acid detergent fiber (ADF) method, were compared using leaves and xylem tissue from five species (Nicotiana tabacum, Populus x canescens, Fagus sylvatica. Quercus robur, and Picea abies). In each case, cell walls were isolated before lignin determination. Each of the three methods estimated a different lignin concentration in a given tissue, except for spruce wood. The “lignin” concentration determined with the AB method was strongly dependent on whether or not the cell walls were subjected to alkaline hydrolysis to remove covalently bound aromatic nonligneous components before lignin determination. Lignin concentrations determined in hydrolyzed cell walls of different tissues and species by the AB method showed a good correlation with those obtained by the TGA method and, thus, were convertible. In contrast, gravimetrically estimated ADF lignins did not or only moderately correlate with lignins measured with methods based on the UV absorbance of the solubilized lignin degradation products. Leaves of a given species generally contained higher ADF-lignin concentrations than the corresponding stem tissue. Both ADF and TGA lignin data of beech were used to calibrate near-infrared reflectance spectra (NIRS) for lignin prediction. Both NIRS calibration procedures gave good statistical fits with correlation coefficients close to 1, indicating that TGA and ADF lignin concentrations of beech can be estimated by NIRS with high accuracy. However, the two calibrations were based on different empirical terms, showing that TGA and ADF lignins did not share the same physical basis for calibration. C/N analysis revealed the presence of 3.1 and 1.4% nitrogen in ADF lignins of beech leaves and wood, respectively. The major fraction of this nitrogen was recovered in amino acids, which corresponded to 14% and 3% protein in ADF lignins of leaves and wood, respectively. These results show that ADF lignins contain significant concentrations of lignin-bound proteins, which renders this method unsuitable to determine genuine lignin.
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- Akin, D. E., Rigsby, L. L., Gamble, G. R., Morrison III, W. H., Kimball, B. A., Pinter, P. J., Jr., Wall, G. W., Garcia, R. L., and Lamorte, R. L. 1995. Biodegradation of plant cell walls, wall carbohydrates, and wall aromatics in wheat grown in ambient or enriched CO2 concentrations. J. Sci. Food Agric. 67:399–406.CrossRefGoogle Scholar
- Allen, S. E. 1989. Chemical Analysis of Ecological Materials 2nd ed. Blackwell Scientific Publications, Oxford, England.Google Scholar
- AOAC. 1990. Official Methods of Analysis. Association of Official Analytical Chemists, Washington, D.C.Google Scholar
- Chang, J. Y., Knecht, R., and Braun, D. G. 1992. Amino acid analysis in the picomole range by precolumn derivatization and high-performance liquid chromatography, pp. 41–48, in C.H.W. Hirs, and S. N. Timasheff (eds.). Methods in Enzymology, Enzyme Structure Part 1, Vol. 91, Academic Press, New York.Google Scholar
- Easty, D. B., Berben, S. A., Dethomas, F. A., and Brimmer, P. J. 1990. Near-infrared spectroscopy for the analysis of wood pulp: quantifying hartwood-softwood mixtures and estimating lignin contents. Tappi 257–261.Google Scholar
- Fengel, D. and Wegener, G. 1989. Wood. Chemistry, Ultrastructure, Reactions. De Gruyter, Berlin.Google Scholar
- Foley, W. J., MCilwee, A., Lawler, I., Aragones, L., Woolnough, A. P., and Berding, N. 1998. Ecological applications of near infra red reflectance spectroscopy—a tool for rapid, cost-effective prediction of the composition of plant animal tissues and aspects of animal performance. Oecology 116:293–308.CrossRefGoogle Scholar
- Monties, B. 1989. Lignins. pp. 113–157, in P. M. Dey and J. B. Harborne (eds.). Methods in Plant Biochemistry. Academic Press, New York.Google Scholar
- SjÖstrÖm, E. 1993. Wood Chemistry. Fundamentals and Applications. Academic Press, San Diego, California, pp. 80–86.Google Scholar
- Van Soest, E. 1963. Use of detergents in the analysis of fibrous feeds. II. A rapid method for the determination of fibre and lignin. Assoc. Off. Anal. Chem. J. 46:829–835.Google Scholar
- WallbÄcks, L., Edlund, U., Norden, B., and Berglund, I. 1991. Multivariate characterization of pulp using solid-state 13C NMR, FTIR, and NIR. Tappi 201–206.Google Scholar