Tuesday, May 3, 2011
Lignin is a major obstacle to enzymatic saccharification of lignocellulose. This study discusses the changes and impacts of lignin during bioconversion of lignocellulose to ethanol. Pretreatment is a cannot-skip step for the bioconversion of lignocellulosic materials to fuels and chemicals. Chemical reactions, structural changes, and physicochemical properties of lignin during the pretreatment are summarized in this study. Lignin retards the enzymatic saccharification of lignocellulose by acting as a physical barrier, restricting the access of cellulases to cellulose, and an irreversible adsorbent of cellulases, resulting in non-productive binding of the enzymes. Irreversible adsorption of enzymes on lignin also limits the enzyme recycle and reuse. It is apparent that lignin content and distribution have substantial impact on enzymatic hydrolysis of cellulose. However, the inhibitory effect of lignin is not only depending on its content but also its structural features, such as hydrophilicity and functional groups. Novel approaches for removing the recalcitrance are briefly discussed.