Title : Green pretreatment strategies for enhanced microbial lipid fermentation and synergistic high-quality lignin recovery for next-generation integrated biorefineries
Abstract:
The development of sustainable biorefineries requires green, economically viable strategies that simultaneously maximize carbohydrate valorization and lignin utilization. Here, we report a natural deep eutectic solvent (NADES)-based pretreatment platform for integrated production of microbial lipids and high-quality lignin from Miscanthus × giganteus, a high-yield perennial bioenergy crop. Two aqueous NADES systems—choline chloride:lactic acid (ChCl:LA) and choline chloride:glycerol (ChCl:Gly)—were evaluated against hydrothermal processing. Pretreatment at 140 °C (2 h) significantly enhanced biomass fractionation, with ChCl:LA removing ~76% lignin and enriching glucan content to ~60%. Enzymatic hydrolysis of pretreated biomass achieved glucose conversions up to 83.5%, generating hydrolysates suitable for direct microbial fermentation without detoxification. Using a two-stage cultivation strategy, the oleaginous yeast Rhodotorula toruloides efficiently converted NADES-derived hydrolysates into microbial lipids, achieving lipid titers of 19.36 g/L and lipid contents of 34–45% (w/w). Notably, NADES hydrolysates supported ~51% higher biomass production compared to refined sugar controls, demonstrating reduced reliance on purified substrates. Beyond carbohydrate valorization, ChCl:LA enabled a lignin-first recovery approach, producing high-purity lignin (>89%) with enriched phenolic hydroxyl functionality (0.91 mmol/g). Structural characterization via 2D-HSQC and ³¹P NMR confirmed favorable syringyl-rich composition and enhanced depolymerization potential, supporting downstream production of renewable aromatics and sustainable aviation fuel (SAF) precursors.
This integrated NADES platform aligns with the principles of green chemistry by employing biodegradable solvents, enabling solvent recyclability, minimizing inhibitor formation, and promoting full biomass valorization. The strategy advances closed-loop biorefinery concepts for simultaneous production of renewable diesel-range lipids and value-added lignin intermediates from lignocellulosic feedstocks.
Keywords: Bioenergy crops, biofuels, fermentation, lignin, green solvents, eutectic solvents
