Biomass Characterization: Recent Progress in Understanding Biomass Recalcitrance

The ever-increasing global demand for energy and materials has a pronounced effect on worldwide economic stability, diplomacy, and technical advancement. In response, a recent key research area in biotechnology has centered on the biological conversion of lignocellulosic biomass to simple sugars. Lignocellulosic biomass, converted to fermentable sugars via enzymatic hydrolysis of cell wall polysaccharides, can be utilized to generate a variety of downstream fuels and chemicals. Ethanol, in particular, has a high potential as transportation fuel to supplement or even replace gasoline derived from petroleum feedstocks. Biological or enzymatic hydrolysis offers the potential for low-cost, highyield, and selective production of targeted chemicals and value-added coproducts at milder operating conditions than thermochemical processes such as gasification or pyrolysis. Due to the complex nature of biomass, degrading enzymes, and their interactions, there is a substantial knowledge gap with respect to the mechanism of enzymatic hydrolysis and the relationship between biomass structure and enzymatic performance. This knowledge gap has greatly contributed to the fact that biological conversion of lignocellulosic biomass has not met the target performance and cost requirements for large-scale production and market entrance. This review highlights recent advances in analytical methods to characterize the chemical and molecular features related to the ability of biomass to resist biological deconstruction, defined as biomass recalcitrance. We also briefly discuss the application of some of these methods in a variety of studies that draw attention to relationships between biomass structure, the effectiveness of enzymatic hydrolysis and biomass recalcitrance.