Structural Characterization of Lignins from Willow Bark and Wood

Research output: Contribution to journalArticleScientificpeer-review


Research units

  • University of Wisconsin-Madison


Understanding the chemical structure of lignin in willow bark is an indispensable step to design how to separate its fiber bundles. The whole cell wall and enzyme lignin preparations sequentially isolated from ball-milled bark, inner bark, and wood were comparatively investigated by nuclear magnetic resonance (NMR) spectroscopy and three classical degradative methods, i.e., alkaline nitrobenzene oxidation, derivatization followed by reductive cleavage, and analytical thioacidolysis. All results demonstrated that the guaiacyl (G) units were predominant in the willow bark lignin over syringyl (S) and minor p-hydroxyphenyl (H) units. Moreover, the monomer yields and S/G ratio rose progressively from bark to inner bark and wood, indicating that lignin may be more condensed in bark than in other tissues. Additionally, major interunit linkage substructures (β-aryl ethers, phenylcoumarans, and resinols) together with cinnamyl alcohol end groups were relatively quantitated by two-dimensional NMR spectroscopy. Bark and inner bark were rich in pectins and proteins, which were present in large quantities and also in the enzyme lignin preparations.


Original languageEnglish
Pages (from-to)7294-7300
Number of pages7
JournalJournal of Agricultural and Food Chemistry
Issue number28
Publication statusPublished - 18 Jul 2018
MoE publication typeA1 Journal article-refereed

    Research areas

  • bark, lignin, nuclear magnetic resonance spectroscopy, structural characterization, willow

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