Dependence of Enzymatic Saccharification on Residual Lignin Structure in Sugarcane

Abstract

Effects of residual-lignin structure—expressed as the syringaldehyde to vanillin （S/V）ratio—on the enzymatic saccharification rate was studied as a key step of bio-ethanol production. Alkaline sulfite-anthraquinone （AS-AQ） and soda-AQ cooking methods were applied to delignification of sugarcane bagasse （SB）and oil palm trunk （OPT）, and the resulting pulp samples were subjected to enzymatic saccharification. The S/V ratios of residual lignin in the pulp were determined by the nitrobenzene oxidation method. This study showed that the AS-AQ method is more suitable for delignification of SB than the soda-AQ method is. SB pulp released more glucose than OPT pulp did under the same conditions of cooking and saccharification. A decrease in the kappa number （residual lignin content） significantly increased the saccharification rate. In a comparison of AS-AQ　pulp samples at the same kappa number （20）, the SB pulp with a lower S/V ratio （0.68） yielded a higher saccharification rate （0.0327）, whereas the OPT pulp（S/V ratio：2.56）yielded a lower saccharification rate （0.0252）. In a comparison of SB and OPT, we found that syringyl-rich lignin kept in pulp results in a lower saccharification rate of the pulp samples prepared by the AS-AQ cooking method.