(405a) In-Situ Lignin Functionalization during Pretreatment/Fractionation: For Robust Enzymatic Saccharification of Plant Biomass through pH Mediation

It has also been recognized that nonproductive binding of cellulase to substrate lignin decreases the amount cellulase available to hydrolyze cellulose, and results in substantially low saccharification efficiency and therefore sugar yield. Applications of proteins or surfactants to prevent substrate lignin from contacting cellulase showed effective, but not practical.

Studies on post-pretreatment lignin modification have shown decreasing lignin affinity to cellulase but not with limited effectiveness. In this presentation, I will discuss enhancing electrostatic repulsive interactions between lignin and cellulase to substantially decrease nonproductive cellulase binding to substrate lignin, thereby significantly improve lignocellulosic biomass saccharification. I will present in-situ lignin functionalization with increasing charged groups through chemical pretreatment/fractionation, specifically, by lignin esterification through either lignin sulfonation using sulfite pretreatment (SPORL) or lignin carboxylation using maleic acid hydrotropic fraction (MAHF). The charge of esterified lignin can be substantially increased under elevated pH. Most cellulases have a bulk isoelectric point (pI) around 5.0, indicating these cellulases become negatively charged when hydrolysis pH is greater than pI, i.e., pH > 5.0. Therefore, conducting enzymatic hydrolysis between 5.5 – 6.5 can substantially enhance the electrostatic repulsive interactions between lignin and cellulase to decrease nonproductive cellulase binding. Our results showed that up to 100% increase in enzymatic hydrolysis glucose yield can be achieved simply by conducting hydrolysis at around pH = 6.0 for sulfonated or carboxylated lignocellulosic substrates. This explains why SPORL and MAHF are highly robust for enzymatic sugar production. Due to the presence of native negative charge groups in lignocellulosic biomass, using elevated pH of ~ 6.0 can also improve enzymatic saccharification of substrates without esterification, pretreated by common dilute acid or alkali pretreatments, by about 15%. Using elevated pH can be easily implemented in practice with minimal cost and also compatible with most yeast fermentation, therefore the strategy of using pretreatment capable of in-situ lignin esterification together with pH mediation is commercially viable to substantially decrease enzyme and therefore sugar production cost.