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Chemical and Structural Features of Plants That Contribute to Biomass Recalcitrance

Abstract

Currently, the primary barrier to low cost biological conversion of cellulosic biomass to renewable fuels is a plant's recalcitrance to sugar release. The energy-intensive pretreatments and high enzyme loadings that are typically required to obtain high sugar yields result in elevated processing costs that must be reduced in order to make cellulosic fuels competitive with those derived from petroleum feedstocks. To lower processing costs, the natural recalcitrance of biomass must be overcome either through the identification and use of superior biomass candidates with reduced recalcitrance, the development of enzymes that are more effective, and/or the design and implementation of efficient pretreatment processes to reduce plants' recalcitrance prior to enzymatic conversion. Unfortunately, the current understanding of biomass recalcitrance is extremely limited, which makes such options difficult. Thus, this thesis will address the vital need for a better understanding of what plant structural and chemical features cause biomass recalcitrance and how they can be overcome with pretreatment.

Towards this end, three main objectives were pursued in this thesis. First, downscaled and high throughput tools were developed for screening large sets of biomass samples for composition as well as for sugar release from pretreatment and enzymatic saccharification. Next, the implementation of these tools facilitated the screening of multiple sets of biomass samples to identify superior feedstock candidates and general trends in sugar release behavior. Finally, from these trends, a more detailed analysis was undertaken for select species in order to investigate what plant structural and chemical features contribute most heavily to biomass recalcitrance and how pretreatment processes overcome these limitations to achieve high sugar yields in subsequent enzymatic saccharification.

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