Abstract
Two milled wood lignins (MWLs) were isolated from tobacco leaves (laminae) and midrib material according to the Björkman procedure. Prior to MWL isolation, the material was extracted with cyclohexane/ethanol and hot water to remove extractives which could interfere with this isolation. MWLs were obtained with a yield of 0.03% (leaves) and 0.06% (midribs) based on dry pre-extracted material. FT-IR spectroscopy was used for quality control and classification of the isolates. Both preparations fulfilled the spectroscopic lignin criteria of a GS lignin with low syringyl content, although the isolates were not pure. Besides carbohydrate impurities, the lamina material, especially, was contaminated with nitrogen and fatty acid-containing substances. Proteins and cutin are discussed as probable contaminants. Both MWLs were characterized with quantitative pyrolysis—gas chromatography using a resistant heating instrument. Curie-point pyrolysis—gas chromatography/mass spectrometry and pyrolysis—mass spectrometry were used for additional characterization of yboth MWL samples. The results show that the tobacco MWL contains up to 22% carbohydrate-type impurities. Small amounts of alkaloids, proteins and lipids were also detected as contamination. Results of previous studies on mineral acid residues could be corroborated: tobacco lignin contains approximately 10% 4-hydroxyphenylpropane, 78–82% guaiacylpropane and 10–13% syringylpropane moieties.
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