Tirath Raj

Fractionated Miscanthus biorefinery generates designer hydrolysates for microbial lipid production and non-condensed lignin, enabling integrated biomass valorization.

Designer enzymatic hydrolysates deliver targeted, optimized fermentable sugars while reducing the formation of inhibitory by-products. Herein, five distinct enzymatic hydrolysates (EH) were generated from Miscanthus biomass using an alkaline-ethanol fractionation and hydrothermal-mechanical refining (HMR) pretreatment approaches. Noticeably, alkali-ethanol fractionated hemicellulose viz., HMA and HMB hydrolysis resulted in xylose-rich enzymatic hydrolysates with 104.8 ± 5.6 g/L and 173.4 ± 4.6 g/L xylose, respectively. All five hydrolysates encompassing varied carbon to nitrogen ratio were evaluated for lipid production using an engineered oleaginous yeast, R. toruloides 880-ADS. Microbial fermentation of xylose-rich hydrolysates, viz. HMR-EH2, HMA-EH, and HMB-EH resulted in lipid yields ranging from 0.05 to 0.12 g/g sugar. Compositional and 2D NMR analysis revealed that HMA-EH residues are highly lignin-enriched, while preserving the non-condensed structure conducive to valorization. Overall, findings highlighted a novel, selective trade-offs approach for maximizing lipid titers from designer hydrolysates, corroborating complete resource recovery for establishing integrated biorefineries.

Lignin recovery from lignocellulosic material is a prominent solution to environmental concerns and problems and establishes more sustainable and competitive lignocellulosic biorefineries. Lignin has the potential to produce various commodity chemicals, biofuels, plastics, dyes, adhesives, concrete binders, foaming agents, lubricants, and nanomaterials, and is a commitment step for a safer and sustainable circular bioeconomy development. However, lignin valorization is hindered by a series of factors, i.e., heterogeneous nature, intrinsic recalcitrance, and the presence of strong intermolecular bonding and functionalities. Most of the lignin residue generated during cellulosic or pulp industries is combusted for electricity production in an uneconomic manner. Therefore, we have critically assessed and discussed the main constraints of novel strategies concerning lignin isolation and valorization, which is widely used in the landscape of lignocellulose biomass-based biorefining to reduce the dependency on fossil reserves and indirectly impacts the circular economy and lifestyle of people. Finally, this review highlights the integrated approach linked to enzyme-to-microbe, microbe-to-microbe interactions, or modified lignin fraction via employing metabolic engineering, discusses the commercial aspects of lignin in the market, and describes the future perspectives as well. Additionally, various advanced catalytic approaches under oxidative/reductive environments and hydrodeoxygenation are well explored, illustrating their influence on the selectivity of lignin depolymerization. The article will consolidate existing knowledge but also incorporate some novel perspectives for future advancement concerning lignin valorization in a sustainable way, which is a prerequisite objective for various biorefinery developments.

Miscanthus x giganteus (Mxg) is a promising perennial crop for producing natural colorants, renewable fuels, and bioproducts. However, natural recalcitrance and high pretreatment cost are major barriers to their complete conversion. In this study, a green processing method has been investigated for efficient recovery of natural pigments (anthocyanins), fermentable sugars, and pure lignin from Mxg genotypes using choline chloride‐based natural deep eutectic solvents (NADES) systems. Interestingly, choline chloride: lactic acid (ChCl: LA) NADES‐processed biomass resulted in 67.8 ± 2.1 μg g⁻¹ of anthocyanins from dry biomass. A maximum of 87.4%–94.1% glucose yield was achieved after enzymatic saccharification. The effective extraction of lignin with high purity with higher β‐aryl ether (βO4) bonds from advanced crops is crucial for lignin valorization. Notably, highly pure lignin (≈93.4% ± 1.4%) is achieved after low‐temperature NADES pretreatment while retaining lignin's native structure. ³¹P nuclear magnetic resonance demonstrated that total phenolics for ChCl: LA‐lignin resulted in 1.20 mmol g⁻¹ hydroxyls. The relative monolignol composition of syringyl (S), guaiacyl (G), and p‐hydroxyphenyl (H) is 19.0, 65.7, and 14.3%, respectively, as evidenced by heteronuclear single quantum coherence analysis. This study provides a novel approach for obtaining high‐purity lignin for catalytic depolymerization for oligomers and bifunctional monoaromatics production and leverages current cellulosic biorefinery technologies.