Impact of lignin polymer backbone esters on ionic liquid pretreatment of poplar

Abstract

BackgroundBiomass pretreatment remains an essential step in lignocellulosic biofuel production, largely to facilitate the efficient removal of lignin and increase enzyme accessibility to the polysaccharides. In recent years, there have been significant efforts in planta to reduce lignin content or modify its composition to overcome the inherent recalcitrance that it imposes on lignocellulosic biomass during processing. Here, transgenic poplar lines in which monolignol ferulate conjugates were synthesized during cell wall development to introduce, during lignification, readily cleavable ester linkages into the lignin polymer backbone (i.e., “zip lignin”), along with wild-type (WT) controls, were pretreated with different ionic liquids (ILs).ResultsThe strategic introduction of ester bonds into the lignin backbone resulted in increased pretreatment efficiency and released more carbohydrates with lower energy input. After pretreatment with any of three different ILs, and after limited saccharification, the transgenic poplars, especially those with relatively higher amounts of incorporated monolignol ferulate conjugates, yielded up to 23% higher sugar levels compared to WT plants.ConclusionOur findings clearly demonstrate that the introduction of ester linkages into the lignin polymer backbone decreases biomass recalcitrance in poplar has the potential to reduce the energy and/or amount of IL required for effective pretreatment, and could enable the development of an economically viable and sustainable biorefinery process.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0784-2) contains supplementary material, which is available to authorized users.

Integration of renewable deep eutectic solvents with engineered biomass to achieve a closed-loop biorefinery

“…(FMT) gene in poplar resulted in the production of monolignol ferulate ester conjugates that are incorporated into lignin ("Zip lignin") (12). Structurally altered lignin with ester linkages in transgenics was found to be less recalcitrant, which led to improved cell wall digestibility and liberated more monosaccharides from biomass compared with the wild type (WT) (12,13). Such strategic modification of lignin structure can certainly enhance its overall processability by lowering the energy and chemicals required for biomass conversion (13).…”

“…Structurally altered lignin with ester linkages in transgenics was found to be less recalcitrant, which led to improved cell wall digestibility and liberated more monosaccharides from biomass compared with the wild type (WT) (12,13). Such strategic modification of lignin structure can certainly enhance its overall processability by lowering the energy and chemicals required for biomass conversion (13). Herein, a previously characterized CAD-deficient transgenic Arabidopsis line was used as a feedstock.…”

Response of Pseudomonas putida to Complex, Aromatic‐Rich Fractions from Biomass

“…In one approach, aL MW fraction was obtainedb yt he BCD reactiono ft he solid fraction after saccharification, whereas ar elatively HMW fraction was produced by another approach in which the acid-precipitation of the IL-solubilized lignin was performed. HSQC NMR spectra of the AP lignin were consistentw ith the condensation of lignin,w hich may arise during IL pretreatment or subsequenta cid precipitation, [45] whereas BCD provided depolymerized lignin streams without condensation. The BCD process included in this work and a previouss tudy [13] showed an 11-14 wt %y ield of eight quantified aromatic monomer,w hereas other depolymerization processes such as catalytic hydrogenolysis and hydrothermall iquefaction showed a6 -19 wt %y ield of 11-71 quantified monomers.…”

The response ofPseudomonas putidato a complex lignolysate

“…In one approach, a low molecular weight fraction was obtained by BCD reaction of the solid fraction after saccharification, while a relatively high molecular weight fraction was produced by another approach using acid precipitation of the IL-solubilized lignin. HSQC NMR of the AP lignin was consistent with condensation of lignin, which may arise during IL pretreatment or subsequent acid precipitation (33), whereas BCD provided depolymerized lignin streams without condensation.…”