The major factors determining enzymatic hydrolyzability of pretreated wheat straw were analyzed and their relative importance quantified. The effects of NaOH-delignification, autohydrolysis and their combination at different severities were analyzed by determining the pore size distribution (DSC-thermoporometry), cellulose surface area and the accessible phenolic hydroxyls on lignin surface (adsorption of Congo Red and Azure B; ATR-FTIR) and crystallinity (WAXD). The correlation of these factors with initial and overall enzymatic hydrolyzability was studied and further put in order through principal component analysis. The major positive factors affecting hydrolyzability were cellulose surface area and accessibility of the pore system, while lignin content was the major negative factor accompanied by cellulose crystallinity.Autohydrolysis effectively increased the cellulose surface area by hemicellulose dissolution, but the high lignin content associated with small pores led to a lower hydrolyzability compared to delignified straw. Besides the removal of lignin, delignification led to a more accessible pore structure, which was supported by the remaining hemicellulose. Additionally, delignification increased the hydrophilicity of the remaining lingin, which also increased hydrolyzability. All pretreatments decreased cellulose crystallinity, which particularly increased the initial hydrolysis, but also improved the final carbohydrate conversion. The established weighed order of the factors behind enzymatic carbohydrate conversion is an important milestone in the path towards more efficient lignocellulosic sugar utilization in biorefineries. Accessible / inaccessible porosity (solid lines) Final carbohyrate conversion Accessible porosity (dashed lines) J

Background Enzyme-aided valorization of lignocellulose represents a green and sustainable alternative to the traditional chemical industry. The recently discovered lytic polysaccharide monooxygenases (LPMOs) are important components of the state-of-the art enzyme cocktails for cellulose conversion. Yet, these monocopper enzymes are poorly characterized in terms of their kinetics, as exemplified by the growing evidence for that H2O2 may be a more efficient co-substrate for LPMOs than O2. LPMOs need external electron donors and one key question of relevance for bioprocess development is whether the required reducing power may be provided by the lignocellulosic substrate. Results Here, we show that the liquid fraction (LF) resulting from hydrothermal pretreatment of wheat straw supports LPMO activity on both chitin and cellulose. The initial, transient activity burst of the LPMO reaction was caused by the H2O2 present in the LF before addition of LPMO, while the steady-state rate of LPMO reaction was limited by the LPMO-independent production of H2O2 in the LF. H2O2 is an intermediate of LF oxidation as evidenced by a slow H2O2 accumulation in LF, despite high H2O2 production rates. This H2O2 scavenging ability of LF is important since high concentrations of H2O2 may lead to irreversible inactivation of LPMOs. Conclusions Our results support the growing understanding that fine-tuned control over the rates of H2O2 production and consumption in different, enzymatic and non-enzymatic reactions is essential for harnessing the full catalytic potential of LPMOs in lignocellulose valorization.

Pseudo-lignin accumulation in wheat straw autohydrolysis was revealed by relative double detection high-performance size-exclusion chromatography and confirmed by CuO oxidation.

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