New Insight into Enzymatic Hydrolysis of the Rice Straw and Poplar: an In-depth Statistical Analysis on the Multiscale Recalcitrance

Certain substrate-related parameters that determine sugar release from pretreated lignocellulosic biomass are important for the biorefinery process optimization. Unfortunately, phylogenetical differences in plants often complicate physicochemical variances and mask mechanisms of biomass recalcitrance. Herein, an in-depth statistical approach that combines correlation analysis, principal component analysis, multiple linear regression, and multiscale validation procedures was employed to comprehensively analyze 14 compositional and structural parameters of cell wall collected after acid and base pretreatment. Individual and sequential analysis provided quantitative proof of lignin-relevant parameters as particular constraints for sugar release in two typical plants, the rice straw ( Oryza sativa ) and poplar ( Populus girinensis ). More striking contributions of lignin removal to xylose release were found in both biomasses, while the combination of crystallinity index (CrI) and CrI/glucan highlighted the specific hindrance of crystallinity of cellulose to glucose release. The compositional changes of lignin additionally affected glucose release in rice straw, while functional groups of lignin played a less pronounced role in poplar. The direct impacts of xylan removal and concomitant changes in biomass porosities insignificantly improved the sugar release. These results suggest that innate differences in diverse plants and the targeted sugar species should be considered when designing proper pretreatment for efficient enzymatic hydrolysis.