(477c) Comparative Study of Hydrothermal and Nades-Assisted Deconstruction of Transgenic Crops for Enhanced Recovery of Lipids and Sugars

Modern technological progress, global climate concerns and the exhaustion of fossil-based feedstocks for energy and chemicals have driven the demand for viable alternatives to produce energy, chemical and materials. Thus, the development of efficient conversion technologies for second-generation biofuels has received greater interest from modern society to meet the upsurge in energy demand with bioeconomic developments. In view of this, newly developed energy crops, i.e., miscanthus, oilcane, and energy cane have been genetically engineered to simultaneously accumulate vegetative lipids and carbohydrates in their plant tissues [1, 2], thus can be considered as an alternative feedstock to cater for the enhanced biofuel yield by providing lipids along with cellulosic sugars for largescale biodiesel and bioethanol production [3-5]. However, the polymeric carbohydrate sugars are trapped in a recalcitrant lignin-carbohydrate matrix, which limits the efficient recovery of these components from transgenic crops for their downstream processing [6]. Therefore, the employment of an efficient pretreatment step is highly recommended to overcome the natural recalcitrant to facilitate the carbohydrate fractionation and their transformation into value-added chemicals, energy, and materials [7]. However, the conventional pretreatment methods involve the use of organic solvents, corrosive acids, and alkalis, which can be harmful to the environment and undermine the advocacy of a sustainable and circular economy. Besides, high energy, chemical input, production cost, inhibitor formation, low saccharification and fermentation yield are major key barriers to the development of efficient commercial biorefinery [7]. Thus, there is an immense need to develop and highly efficient fractionation of lipids and carbohydrates sugars for further processing into fuels and chemicals.

In view of this, hydrothermal and natural deep eutectic solvents (NADES) pretreatment potential were assessed for the deconstruction of genetically engineered bioenergy crops for their feasibility for high sugar and lipid recovery. Hydrothermal pretreatment is one of the mildest methods, which uses hot water at a relatively low temperature (up to 230 °C) and low pressure [8]. Hydrothermal pretreatment selectivity hydrolyses the hemicellulose fraction to xylose, arabinose and glucose and simultaneously generates a certain amount of degraded products such as furfural, HMF, formic acid etc., which can limit the enzymatic saccharification of lignocellulosic biomass [9]. On contrary, NADES is a combination of hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA), with exceptional solvent characteristics, an alternative to conventional organic solvents and benefits with easy preparation, low toxicity, high biodegradability, and high fractionation efficiency. NADES can act as adjuvants for weakening the lignin-carbohydrate recalcitrance matrix at the desired temperature of 100 to 160 °C and pretreatment circumstances while enhancing lignin solubilization and could attribute to enhanced digestibility of pretreated biomass towards cellulases.

Thus, several choline chloride-based NADES were prepared using bio-derived precursors, i.e., lactic acid by varying the molar ratio of HBD and HBA (1:1, 1:2) at 60 to 80 °C and were employed for the pretreatment of transgenic oilcane bagasse, and miscanthus for the fractionation of lipids and carbohydrates. A comparative study between hydrothermal pretreatment and NADES-assessed pretreatment was conducted in terms of compositional analysis, toxins generation, chemical input, severity effect, lignin removal and overall sugar and lipid recovery from pretreated oilcane, and miscanthus biomass. The initial study showed that the suitable eutectic combination of NADES, i.e., choline chloride and lactic acid in a 1:2 molar ratio, prepared at 60-80 °C, could effectively solubilize >75% lignin, while enabling high biomass digestibility (>85%) during enzymatic saccharification, and enhance lipid recovery (>60%). In a separate experiment, hydrothermal pretreatment optimization was investigated with varying pretreatment temperatures (170-210 °C), with a residence time of 10-20 min and was compared with NADES pretreatment in terms of toxins release, glucan/ xylan recovery, lignin solubilization, crystallinity reduction, enzymatic accessibility, lipid recovery etc. Hydrothermal pretreatment of oilcane bagasse followed by enzymatic saccharification resulted in a 2-fold increase in total lipids with improved enzymatic digestibility of >75%. These findings lead to an economical an environmentally friendly method to process genetically engineered crops for selective fractionation of lipids and sugars, and would aid in developing a sustainable biorefinery platform for the co-production of biodiesel and bioethanol.

Keywords: Natural deep eutectic solvents; hydrothermal pretreatment, transgenic crop, lipids, sugar, extraction

References:

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