Current Understanding of the Correlation of Lignin Structure with Biomass Recalcitrance

Abstract

Lignin, a complex aromatic polymer in terrestrial plants, contributes significantly to biomass recalcitrance to microbial and/or enzymatic deconstruction. To reduce biomass recalcitrance, substantial endeavors have been exerted on pretreatment and lignin engineering in the past few decades. Lignin removal and/or alteration of lignin structure have been shown to result in reduced biomass recalcitrance with improved cell wall digestibility. While high lignin content is usually a barrier to a cost-efficient application of bioresources to biofuels, the direct correlation of lignin structure and its concomitant properties with biomass remains unclear due to the complexity of cell wall and lignin structure. Advancement in application of biorefinery to production of biofuels, chemicals, and bio-derived materials necessitates a fundamental understanding of the relationship of lignin structure and biomass recalcitrance. In this mini-review, we focus on recent investigations on the influence of lignin chemical properties on bioprocessability—pretreatment and enzymatic hydrolysis of biomass. Specifically, lignin-enzyme interactions and the effects of lignin compositional units, hydroxycinnamates, and lignin functional groups on biomass recalcitrance have been highlighted, which will be useful not only in addressing biomass recalcitrance but also in deploying renewable lignocelluloses efficiently.

Decoupling the direct and indirect effects of climate on plant litter decomposition: Accounting for stress‐induced modifications in plant chemistry

“…The resultant lignin polymer formed from acylated monolignols is more hydrophobic than normal lignin and hence is thought to be an adaptation for drought tolerance (Del Rio et al., , ). Because the biodegradation of lignin is primarily dependent on microbial exo‐enzymes (Wong, ), the increased hydrophobicity could increase the recalcitrance of lignin as it repels microbial enzymes and prevents the accessibility to cellulose (Li et al., ).…”

Direct analysis by time‐of‐flight secondary ion mass spectrometry reveals action of bacterial laccase‐mediator systems on both hardwood and softwood samples

“…Syringyl‐type (S) lignin, comprised of coniferyl and sinapyl alcohols, is dominant in deciduous hardwoods (angiosperms), guaiacyl‐type (G) lignin comprised mainly of coniferyl alcohols is dominant in coniferous softwoods (gymnosperms), whereas p ‐coumaryl‐type (H) lignin appears most commonly in grasses. Lignin decomposition is key to the carbon cycling on earth and is also central to the broader use of renewable biomass (lignocellulose) as feedstock for production of biofuels, as well as higher value bio‐based chemicals and materials (Ragauskas et al , Li et al ).…”

2D HSQC Chemical Shifts of Impurities from Biomass Pretreatment

“…Though desirable in order to reduce dependence on fossil fuels, the production of ethanol from renewable resources such as lignocellulosic biomass is hindered by the natural recalcitrance of the plant cell wall . In order to overcome cell wall recalcitrance and achieve high saccharification efficiency, lignocellulosic biomass is usually subjected to a variety of thermochemical pretreatments . Pretreatment methods such as dilute acid, alkali, and organosolv have been well explored for decades .…”