Biomass recalcitrance. Part II: Fundamentals of different pre-treatments to increase the enzymatic digestibility of lignocellulose

A number of pre‐treatment methods have been developed during the last few decades to overcome biomass recalcitrance. Although the mechanisms of these pre‐treatments are different, the final objective is the same – increasing cellulose accessibility to cellulase enzymes. Generally, pre‐treatment is the process to disrupt the compact structure of lignocellulosic biomass and expose cellulose fibers, which can be achieved by mechanical comminution, chemical modifications of biomass compositions, biological degradation, or a combination of these methods. After pre‐treatment, the accessible surface area is increased resulting in the enhancement of cellulose digestibility. In this paper, we review the recent progress of the fundamental researches of various biomass pre‐treatment processes, especially on how these pre‐treatments alter chemical composition and physically change cell wall structure. Understanding these changes would be helpful to further optimize existing pre‐treatments, and would aid in developing novel pre‐treatment methods.© 2012 Society of Chemical Industry and John Wiley & Sons, Ltd