Lignin degradation and modification by laccase/mediator systems: Insights at the molecular level

Research output: Thesisinternal PhD, WU

Abstract

Lignin degradation and valorization is one of the major challenges in biorefinery. A potential green tool for lignin degradation or modification is the use of laccase/mediator systems (LMS). Treatment of lignin with LMS results in lignin radicals, which may react further via multiple pathways, resulting in lignin degradation, modification or polymerization. The overall outcome of LMS treatments of lignin is, currently, hard to predict, as the reactions of lignin induced by LMS treatments are insufficiently understood. In this thesis, we investigated the reactivity of lignin upon laccase and LMS treatments by using various lignin model compounds as well as lignocellulose and lignin isolates as substrates. We demonstrated that the balance between degradation, Cα-oxidation and polymerization of lignin is dependent on multiple factors, such as the choice of mediator and the initial structure of the lignin substrate. In addition, we revealed that buffer properties play a key role in the balance between Cα-oxidation and degradation of lignin structures by a laccase/hydroxybenzotriazole (HBT) system, and that altering buffer properties allows to enhance bond cleavage of a lignin structure by >1 order of magnitude. Laccase/HBT treatment of wheat straw and corn stover was shown to result in up to 51% delignification of the biomass. Based on the insights obtained from the model compound studies, and by using a combination of HSQC NMR spectroscopy and py-GC-MS, we showed, for the first time, that the laccase/HBT system degrades lignin via cleavage of Cβ-O, O-4’ and Cα-Cβ bonds. Overall, by studying the reactivity of various lignin substructures, this thesis provided in-depth insights into the reactivity of lignin upon laccase and LMS treatments.

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Vincken, Jean-Paul, Promotor
  • Kabel, Mirjam, Co-promotor
Award date4 Sep 2020
Place of PublicationWageningen
Publisher
Print ISBNs9789463953856
DOIs
Publication statusPublished - 2020

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