Physico-chemical oxidative cleavage strategy facilitates the degradation of recalcitrant crystalline cellulose by cellulases hydrolysis

Efficient enzymatic conversion of recalcitrant crystalline cellulose is critical for enabling cost-effective industrial conversion of cellulosic biomass to biofuels and chemicals. Fully understanding enzyme digestion mechanism is paving a new way to design efficient process for biomass conversion. Accordingly, a continuing drive is inspiring to discover new routes to promote crystalline cellulose disruption. Herein, a physico-chemical oxidative cleavage strategy of irradiation oxidation/post-reduction (IOPR) was employed to treat crystalline cellulose I to cleave glycosidic bonds association with some new oxidized and reduced chain ends, thus boosting downstream degradation by cellulases from Trichoderma reesei. The hydrolysis performance of treated crystalline cellulose was conducted with either T. reesei Cel7A (TrCel7A) alone, or a cellulase enzyme mixture (90% Celluclast 1.5 L, 10% β-glucosidase). 81.6 and/or 97% of conversion efficiency have been reached for 24-h and 48-h cellulase hydrolysis, respectively. The high efficient conversion of crystalline cellulose after IOPR is mainly attributed to generating some new chain ends, which are identified by MAIDI-TOF–MS and HPLC. Furthermore, the nanoscale architectures of crystalline cellulose before and after IOPR are systematically investigated by XRD, EPR, ATR- FTIR, GPC, and XPS techniques. Together with TEM images, the results reveal a fascinating digestion mechanism of “peel-off” and “cavity-formation” paradigms toward degrading crystalline cellulose by cellulase mixtures after IOPR treatment. This encouraging results show that the proposed IOPR approach will become a potential competitive alternative to current biomass pretreatment. It opens a new avenue toward the implementation of pretreatment and the design of enzyme cocktails in lignocellulosic biorefinery.