Effect of Maize Biomass Composition on the Optimization of Dilute-Acid Pretreatments and Enzymatic Saccharification

At the core of cellulosic ethanol research are innovations leading to reductions in the chemical and energetic stringency of thermochemical pretreatments and enzymatic saccharification. In this study, key compositional features of maize cell walls influencing the enzymatic conversion of biomass into fermentable sugars were identified. Stem samples from eight contrasting genotypes were subjected to a series of thermal dilute-acid pretreatments of increasing severity and evaluated for glucose release after enzymatic saccharification. The biochemically diverse set of genotypes displayed significant differences in glucose yields at all processing conditions evaluated. The results revealed that mechanisms controlling biomass conversion efficiency vary in relation to pretreatment severity. At highly severe pretreatments, cellulose conversion efficiency was primarily influenced by the inherent efficacy of the thermochemical process, and maximum glucose yields were obtained from cellulosic feedstocks harboring the highest cellulose contents per dry gram of biomass. When mild dilute-acid pretreatments were applied, however, maximum bioconversion efficiency and glucose yields were observed for genotypes combining high stem cellulose contents, reduced cell wall lignin and highly substituted hemicelluloses. For the best-performing genotype, glucose yields under sub-optimal processing regimes were only 10 % lower than the genotype-set mean at the most stringent processing conditions evaluated, while furfural production was reduced by approximately 95 %. Our results ultimately established that cellulosic feedstocks with tailored cell wall compositions can help reduce the chemical and energetic intensity of pretreatments used in the industry and improve the commercial and environmental performance of biomass-to-ethanol conversion technologies.