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Book Sections Year : 2022

Lignin Fungal Depolymerization: From Substrate Characterization to Oligomers Valorization

Abstract

Renewable resources obtained via sustainable methodologies provide an alternative to reduce the dependency on fossil resources. Lignin is the second most abundant class of macromolecules on earth. This complex biopolymer is the major source of phenolic compounds since its precursors are three types of phenylpropane units (or monolignols), i.e., conferyl alcohol (G), sinapyl alcohol (S), and p-coumaryl alcohol (H). Large amounts of lignin are recovered from the pulping industry using various processes such as Kraft, sulfite, soda anthraquinone, etc., due to its undesirability and high solubility during the cooking process. More recently, lignin is also being recovered during the pretreatment steps (Hydrolysis, Ionic Liquid, Organosolv processes) in biorefinery processes. Based on the extraction procedure and type of biomass used, the molecular structure of lignin will vary and has to be characterized for valorization. Due to the complexity of the structure of lignin, a combination of complementary techniques is used to characterize lignin. Various analytical techniques such as spectroscopy, chemical degradation, thermal degradation, chromatography, and the methods used to visualize the physical structural changes in lignin that help to determine the qualitative and quantitative properties bring different information. Of the techniques elaborated, magnetic resonance and Gel Permeation Chromatography (GPC) are found to be proficient in the elucidation of these complex biopolymers. Aromatic compounds are the basic building blocks in lignin and therefore, their potential in various applications is quite high. However, lignin’s recalcitrance makes it difficult to break it down for further applications and requires high temperatures and high pressure for the same. Therefore, fungal depolymerization is a more economical alternative to break down lignin without damaging the cellulose and hemicellulose. Lignin decaying fungi excrete a powerful enzyme cocktail that generates highly reactive mediators which in turn react with the polymer and trigger extracellular depolymerization. The resulting low molecular weight soluble molecules such as vanillin, syringaldehyde, syringic acid, etc. are valuable for further applications and thus the optimization of fungal lignin depolymerization and recovery of oligomers before their uptake by fungal cells are ongoing domains of research. Indeed, some of the generated oligomers can be used in the generation of other valuable products such as chemicals and materials through green chemistry. Lignin-derived phenols are also used in bioremediation strategies. Besides, the use of fungal lignin depolymerization has great valorization potential to produce renewable energies such as biomethane, biohydrogen, and bioethanol without generating products that may be inhibitory in the downstream process. Therefore, with the increasing lignin-centric biorefineries, there is strong interest for fungal lignin depolymerization in both valorization and application approaches.
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Dates and versions

hal-03704906 , version 1 (26-06-2022)

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Shruthi Meenakshisundaram, Estelle Léonard, Claire Ceballos, Antoine Fayeulle. Lignin Fungal Depolymerization: From Substrate Characterization to Oligomers Valorization. Fungal Biopolymers and Biocomposites, Springer Nature Singapore, pp.329-391, 2022, ⟨10.1007/978-981-19-1000-5_16⟩. ⟨hal-03704906⟩
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