H2O2 in Liquid Fractions of Hydrothermally Pretreated Biomasses: Implications of Lytic Polysaccharide Monooxygenases

Lytic polysaccharide monooxygenases (LPMOs) are important players in enzyme-aided valorization of lignocellulose. However, the recently discovered dependency of LPMO catalysis on H2O2 along with H2O2-caused inactivation of the enzyme calls for an in-depth understanding of the levels and the dynamics of H2O2 in various streams of the processing of lignocellulosic biomass. Using an LPMO-based sensitive detection, we assessed the dynamics of H2O2 in the liquid fractions (LFs) of hydrothermally pretreated wheat straw (agricultural residue), birch (hardwood), and pine (softwood). Upon contact with air, H2O2 was formed in the LFs of all biomasses. The initially high rate of H2O2 formation decayed with the half-life around 1–2 h to a low but stable plateau value. The rates of H2O2 formation were much higher than the rates of its accumulation, suggesting that H2O2 is an intermediate in aerobic oxidation of the compounds in LFs. Although the general traits were similar, LFs of different biomasses had different rates of H2O2 formation and accumulation. LFs of different biomasses also differed by their effect on the enzymatic degradation of cellulose. Compositional analyses revealed a number of different compounds that were formed and disappeared upon aerobic oxidation of LFs