Laccase-mediator pretreatment delignifies woody and nonwoody plant feedstocks and improves enzymatic saccharification

Abstract

This study shows the ability of laccases to remove lignin when applied on the (milled) whole lignocellulosic biomass in combination with 1-hydroxybenzotriazole or methyl syringate, in a multi-step sequence where the enzymatic stages alternate with alkaline extractions. Eucalypt (Eucalyptus globulus) and Elephant grass (Pennisetum purpureum) were selected as representative for rapid growth woody and nonwoody plant feedstocks, respectively. Paralleling lignin removal from E. globulus and P. purpureum (~50% and ~30% of the initial content, respectively) a positive effect on sugar yield was also observed. The modification of lignin was analyzed by 2D NMR of the whole samples at the gel state. Different removal of p-hydroxyphenyl, guaiacyl and syringyl lignin units, and a moderate removal of p-coumaric acid (present in P. purpureum) was observed without a substantial change in polysaccharide signals. However, the most noticeable change was the strong increase of Cα-oxidized syringyl units after the enzymatic sequence.