Structural and compositional changes induced by hydrothermal and organosolv pretreatments impacts enzymatic hydrolysis of a tropical forage grass grown under future climate conditions

Abstract

Panicum maximum represents an alternative as a dedicated energy crop for biorefinery. However, both pretreatment step and climate conditions impact its chemical composition and possibly its hydrolytic performance. Therefore, this study looks into integrating the future effect of the climate conditions and the pretreatment methods on the hydrolytic performance of P. maximum. Through a Trop-T-FACE system, P. maximum grown under three hypothetical future climate conditions: elevated temperature ((eT), which is 2 °C more than the ambient canopy temperature), elevated atmospheric CO2 concentration ((eC) up to 600 μmol mol-1) and the combined effects (eT + eC). Subsequently, the groups were subjected to the liquid hot water (LHW) and organosolv (ORG) pretreatments, which enhanced biomass digestibility by mostly hemicellulose and lignin removal, respectively. Furthermore, optimized hydrolysis and fluorescent protein-tagged carbohydrate-binding modules binding suggested that P. maximum pretreated by LHW has greater saccharification yields and higher cellulose surface accessibility/exposure. This shows that hemicellulose directly impacts P. maximum recalcitrance, and its removal was the optimum pretreatment strategy. Concerning the studied expected future climate conditions, LHW samples did not show significant differences in hydrolysis yields at low solids loading (2%). However, at 10 % solids, eC had higher conversion yields (likely due to minimum end-product inhibition). Similarly, for organosolv pretreated samples, eC (at 2 and 10 % solid loading) exhibited greater cellulose-glucan conversion yields among the climate conditions groups and the highest cellulose accessibility. Thus, this work contributes to understand better the influence of both studied pretreatment methods and future climate conditions on the conversion efficiency of a critical energy crop and might assist in selecting the best pretreatment method to mitigate the climate effects and achieve greater hydrolysis yields.