Biorefining Strategies for Converting Waste Biomass into Fermentable Sugars

The annual solar energy captured by plant-based biomass is nearly ten times the current global human energy consumption. Terrestrial agricultural waste biomass (like corn stover, switchgrass, and forest residues), as well as carbohydrate-enriched organic food waste, therefore provides a significant carbon-rich resource that can be converted into transportation fuels, industrial chemicals, and advanced biomaterials. However, plant derived biomass is naturally resistant (or ‘recalcitrant’) to cost-effective enzyme catalyzed deconstruction into fermentable sugars that can be then upgraded into desired products.¹ The molecular origins of biomass recalcitrance are thought to arise from the native crystalline structure of polysaccharides like cellulose and the inhibitory role of lignin on the activity of carbohydrate-active enzymes (or ‘CAZymes’). Biorefinery processing strategies that can reduce biomass ‘recalcitrance’ would significantly enhance enzymatic activity and improve the economics of waste refining. Decrystallization of polysaccharides and lignin removal during thermochemical pretreatment of biomass is thus a necessary step to facilitate cost effective conversion of biomass to value-added products. Currently, most reported solvents for biorefinery pretreatment technologies that can completely decrystallize cellulose (and/or extract lignin) are expensive and/or difficult to recycle.² Here, I will discuss results from ongoing projects towards development of effective pretreatments for reducing biomass recalcitrance towards biorefining and also engineering enzymes³ for catalyzing polysaccharides hydrolysis to fermentable sugars like glucose.

1. Chundawat et al., 2011. Deconstruction of lignocellulosic biomass to fuels and chemicals. Annual Review of Chemical and Biomolecular Engineering, 2, 121–145
2. Chundawat et al., 2011. Restructuring the crystalline cellulose hydrogen bond network enhances its depolymerization rate. Journal of the American Chemical Society, 133(29), 11163–11174
3. Whitehead et al., 2017. Negatively supercharging cellulases render them lignin-resistant, ACS Sustainable Chemistry & Engineering, vol. 5, 2017, 6247–6252