Critical redox processes during enzymatic saccharification of plant biomass: Lytic polysaccharide monooxygenases at play

The recent discovery of redox-active enzymes termed lytic polysaccharide monooxygenases (LPMOs) has led to a significant improvement in the efficiency of enzymatic hydrolysis and thus in the process of the production of biofuels. During saccharification of lignocellulose reactive oxygen species (•OH-; •O2-; H2O2) can be generated as an outcome of redox processes via enzymatic and non-enzymatic routes. These reactive oxygen species are toxic for the enzymes. In this project, redox processes of lignocellulosic biomass during enzymatic saccharification were investigated. A rapid decrease of pH was observed during lignocellulose incubation with and without enzymes which is an indication of redox reactions happening in the complex lignocellulosic material. We do not think that acetate release from hemicellulose alone could explain a decrease in pH values. Carbon dioxide release was observed in lignocellulose during incubation with and without enzymes. There was less carbon dioxide released in the enzyme mixtures where LPMO was present after two days of saccharification. Addition of catalase, which terminates chains of radical chemistry by the dismutation of H2O2 into water and O2, resulted in the improvement of enzymatic saccharification and reduction of acidifying reactions taking place