Transgenic bioenergy crops as sustainable substrates for recovery of cellulosic sugars and lipids using natural deep eutectic solvents (NADESs)

Continuous exploitation of fossil resources and increasing energy consumption have urged the scientific community to look for a new alternative feedstock for producing bio-based materials, fuels, and chemicals. In view of this, a newly developed transgenic crop, i.e., oilcane, has been genetically engineered to accumulate vegetative lipids and carbohydrates in plant tissues; thus, it can be considered as an alternative feedstock to cater to the enhanced biofuel yield by providing lipids along with cellulosic sugars for large-scale biodiesel and bioethanol production. However, these components are entrapped in a highly recalcitrant lignin--carbohydrate matrix, which limits the efficient recovery of these components for their downstream processing.

Thus, NADESs, a combination of hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA), have demonstrated exceptional solvent characteristics as an alternative to conventional organic solvents and have benefited from easy preparation, low toxicity, high biodegradability, and high fractionation efficiency. NADESs can act as adjuvants for weakening the lignin--carbohydrate recalcitrance matrix at the desired temperature of 100–160 °C. Thus, herein, we have synthesized several choline-chloride-based NADES using bio-derived precursors, i.e., lactic acid, oxalic acid, glycerol, ethylene glycol, and acetic acid by varying the molar ratio of HBD and HBA (1:1, 1:2) at 60–80 °C and they were employed for the pretreatment of oilcane bagasse for the fractionation of lipids and carbohydrates. Compositional analysis showed that oilcane bagasse is enriched with 3.3% of total lipids and 51% of carbohydrates. The initial study showed that the suitable eutectic combination of NADES, i.e., choline chloride and lactic acid in a 1:1 molar ratio at 60–80 °C, could effectively solubilize >80% lignin while enabling high biomass digestibility (>85%) and enhance lipid recovery (>80%). These research findings could further promote the design and fabrication of a low-cost, environmentally friendly, biodegradable, NADES-assisted pretreatment for enhanced lipid and sugar recovery from transgenic oilcane for renewable production in a circular biorefinery.