Abstract
Biochemical conversion of lignocellulosic biomass to liquid fuels requires pretreatment and enzymatic hydrolysis of the biomass to produce fermentable sugars. Degradation products produced during thermochemical pretreatment, however, inhibit the microbes with regard to both ethanol yield and cell growth. In this work, we used synthetic hydrolysates (SynH) to study the inhibition of yeast fermentation by water-soluble components (WSC) isolated from lignin streams obtained after extractive ammonia pretreatment (EA). We found that SynH with 20g/L WSC mimics real hydrolysate in cell growth, sugar consumption and ethanol production. However, a long lag phase was observed in the first 48 h of fermentation of SynH, which is not observed during fermentation with the crude extraction mixture. Ethyl acetate extraction was conducted to separate phenolic compounds from other water-soluble components. These phenolic compounds play a key inhibitory role during ethanol fermentation. The most abundant compounds were identified by Liquid Chromatography followed by Mass Spectrometry (LC-MS) and Gas Chromatography followed by Mass Spectrometry (GC-MS), including coumaroyl amide, feruloyl amide and coumaroyl glycerol. Chemical genomics profiling was employed to fingerprint the gene deletion response of yeast to different groups of inhibitors in WSC and AFEX-Pretreated Corn Stover Hydrolysate (ACSH). The sensitive/resistant genes cluster patterns for different fermentation media revealed their similarities and differences with regard to degradation compounds.
Highlights
In the fossil fuel-based economy, crude oil is the primary feedstock source for producing transportation fuels and industrial chemicals
The water-soluble components (WSC) were subjected to ethyl acetate extraction to enrich phenolic compounds, and this fraction was used in microbial fermentation and composition analysis
Lignocellulose-derived degradation products produced during thermochemical pretreatments are known to inhibit microbes during fermentation, and have been a major constraint in producing cost-effective lignocellulosic biofuels
Summary
In the fossil fuel-based economy, crude oil is the primary feedstock source for producing transportation fuels and industrial chemicals. Dependence on crude oil causes energy security concerns and greenhouse gas emissions drive climate change. These forces have triggered worldwide research towards the development of alternative, sustainable sources of energy [1]. A renewable alternative to fossil fuel-derived liquid fuels, such as gasoline and diesel, is lignocellulosic biofuels. These are expected to play a major role in satisfying our energy needs [2,3]. Pretreatment processes are commonly performed under high temperature, high pressure, caustic, or acidic conditions, which generate degradation compounds that inhibit microorganisms [6]. A previous comparison of AFEX and dilute acid treated corn stover showed that dilute acid pretreatment produces 316% more acidic compounds, 142% more aromatics, and 3555% more furans than AFEX, but no nitrogenous compounds [8]
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