Efficient Saccharification of Softwoods By an Integrated Thermochemical and Biological Process

Softwoods have great potentials as renewable feedstocks for biorefineries because of their high cellulose content. However, softwoods are more recalcitrant compared to herbaceous plants and hardwoods. Hence, the use of softwoods in biorefineries has been viewed as limited. To overcome their recalcitrance, we applied a cellulose solvent-based fractionation process on southern yellow pine and douglas fir at a mild condition: 50 ºC and 1 atm for 90 min. Pretreated softwood samples were hydrolyzed fast by cellulase enzyme (15 FPUs) and > 85% glucose yield was achieved by 24 h. Cellulose accessibility to cellulase of pretreated samples was characterized by the fusion protein and was found to increase by 39 folds, suggesting that enhanced surface accessibility via cellulose solvent-based fractionation was responsible for the high glucose yield. After fractionation, the degree of crystallinity of pretreated samples decreased and fibrous structure appeared to be disrupted as observed by solid-state 13C Cross-Polarization Magic Angle Spinning (CP/MAS) nuclear magnetic resonance (NMR) and scanning electron microscopy. No changes in lignin functionalities after fractionation were observed by 2D Heteronuclear Single-Quantum Correlation (HSQC) NMR, giving rise to the potential use of lignin as a co-product in biorefineries.