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