The efficient use of softwood in biorefineries requires harsh pretreatment conditions to overcome biomass recalcitrance. Following harsh pretreatments, the hemicellulose is solubilized. Here, we studied the material characteristics of Norway spruce following steam pretreatment at six different severities, relating chemical and structural information to the enzymatic hydrolyzability. Steam pretreatment conditions were defined by two different temperatures (180 °C and 210 °C), with and without the addition of various acids (CH3COOH, H3PO4, H2SO4, SO2). Structural knowledge of the streams is a cornerstone for developing an efficient saccharification process.This study combines advanced structural characterizations to gain fundamental understanding of the influence of severity of pretreatment on spruce. Structural knowledge is a cornerstone in developing an effective saccharification process by modulating pretreatment conditions and enzymes employed.Overall structural properties were assessed by scanning electron microscopy. The effect of stream pretreatment severity on lignin and lignin-carbohydrate bonds was investigated by two-dimensional heteronuclear single quantum correlation nuclear magnetic resonance. Finally, cellulose ultrastructure was studied by applying small/wide-angle X-ray scattering. The structural characteristics of the six pretreated softwood substrates were related to the enzymatic hydrolyzability.With increasing pretreatment severity, surface defibrillation, and lignin depolymeryzation were observed. Further, lignin-carbohydrate complexes signals were detected. Cellulose analysis revealed the rearrangement of microfibrils leading to the formation of larger microfibril aggregates. This microfibril rearrangement likely contributed to the observed increase in enzymatic hydrolysis yields as better enzyme accessibility resulted.
Background To realize the full potential of softwood-based forest biorefineries, the bottlenecks of enzymatic saccharification of softwood need to be better understood. Here, we investigated the potential of lytic polysaccharide monooxygenases (LPMO9s) in softwood saccharification. Norway spruce was steam-pretreated at three different severities, leading to varying hemicellulose retention, lignin condensation, and cellulose ultrastructure. Hydrolyzability of the three substrates was assessed after pretreatment and after an additional knife-milling step, comparing the efficiency of cellulolytic Celluclast + Novozym 188 and LPMO-containing Cellic CTec2 cocktails. The role of Thermoascus aurantiacus TaLPMO9 in saccharification was assessed through time-course analysis of sugar release and accumulation of oxidized sugars, as well as wide-angle X-ray scattering analysis of cellulose ultrastructural changes. Results Glucose yield was 6% (w/w) with the mildest pretreatment (steam pretreatment at 210 °C without catalyst) and 66% (w/w) with the harshest (steam pretreatment at 210 °C with 3%(w/w) SO2) when using Celluclast + Novozym 188. Surprisingly, the yield was lower with all substrates when Cellic CTec2 was used. Therefore, the conditions for optimal LPMO activity were tested and it was found that enough O2 was present over the headspace and that the reducing power of the lignin of all three substrates was sufficient for the LPMOs in Cellic CTec2 to be active. Supplementation of Celluclast + Novozym 188 with TaLPMO9 increased the conversion of glucan by 1.6-fold and xylan by 1.5-fold, which was evident primarily in the later stages of saccharification (24–72 h). Improved glucan conversion could be explained by drastically reduced cellulose crystallinity of spruce substrates upon TaLPMO9 supplementation. Conclusion Our study demonstrated that LPMO addition to hydrolytic enzymes improves the release of glucose and xylose from steam-pretreated softwood substrates. Furthermore, softwood lignin provides enough reducing power for LPMOs, irrespective of pretreatment severity. These results provided new insights into the potential role of LPMOs in saccharification of industrially relevant softwood substrates.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.