The Role of Cellulose Accessibility On Enzymatic Saccharification of Lignocelluloses

So much research has been dedicated to understand the effects of various factors on enzymatic hydrolysis of lignocelluloses. It has been understood that removal of hemicelluloses is very important to improve lignocellulosic substrate digestibility. It has also been identified that improving enzyme accessibility to cellulose is more important than delignification to enzymatic saccharification. This study is attempted to develop a comprehensive understanding of various factors on enzymatic hydrolysis of lignocelluloses by taking a progressive approach. In the first phase, a set of lignocellulosic substrates were produced by drying to different degrees from the same never dried sample. Therefore, these dried substrates have exactly the same chemical composition and structure. However, drying induced fiber hornification produces irreversible change of cell wall structure when rewetting, i.e., fibrils are tightly packed together through hydrogen bonding to produce permanent fiber pore shrinkage and loss of pores in cell wall. As a result, the enzyme accessibilities of these samples were significantly reduced comparing with the never- dried sample and varied with the degree of drying. This set of samples is an excellent candidate to verify the effect of enzyme accessibility on enzymatic hydrolysis. In the second phase, two sets of samples, one produced from fractionation of the same sample, and another from disk milling of the same chemically pretreated biomass to different degrees, were used to determine the effect of substrate size/specific surface or degree of size reduction on enzymatic hydrolysis. Finally, different pretreatment methods were used to explain the effect of chemical composition on enzymatic hydrolysis. Both enzymatic hydrolyses and measurements of cellulase accessiblity to cellulose (CAC) were carried out to quantify the contributions of various factors to enzymatic hydrolysis of lignocelluloses.