Optimizing lignocellulosic feedstock for improved biofuel productivity and processing

Liquid fuels from lignocellulosic materials, such as wood, offer an attractive alternative to fossil fuel. Lignocellulosic biomass is composed of a complex mixture of cellulose, hemicellulose, and lignin. As structural polymers, the matrix of hemicellulose and lignin surround the cellulose component of the plant cell wall to protect it against enzymatic attack. The resistance of this complex to enzymatic attack is a major impediment to commercial bioconversion of lignocellulosic biomass. Furthermore, proportional variability within the mixture of the three major components varies, depending on the species of feedstock used, growing site, climate, age, and the part of the plant harvested. This fact presents process design and operating challenges for the fermentation of sugars derived from lignocellulosic feedstocks. The essentially uncontrolled variability of biomass properties also presents major difficulties in understanding the fundamental processes involved in limiting the digestion of cell walls to fermentable sugars. Energy crops must be optimized for 'low-input production' systems and efficiency of pretreatment and hydrolysis to derive sugars for further fermentation to produce ethanol. Recent advances in the molecular biology of wood formation and cell-wall biosynthesis have provided new tools to tailor the biomass composition. This review summarizes recent advances in the understanding of the molecular mechanisms regulating the biochemical and developmental processes of woody biomass production. Potential areas of future research in optimizing lignocellulosic feedstock for bioenergy production are identified. (c) 2007 Society of Chemical Industry and John Wiley & Sons, Ltd