Structural evaluation and bioethanol production by simultaneous saccharification and fermentation with biodegraded triploid poplar

Background: Pretreatment is a key step to decrease the recalcitrance of lignocelluloses and then increase the digestibility of cellulose in second-generation bioethanol production. In this study, wood chips from triploid poplar were biopretreated with white rot fungus Trametes velutina D10149. The effects of incubation duration on delignification efficiency and structural modification of cellulose were comparably studied, as well as the digestibility of cellulose by simultaneous saccharification and fermentation (SSF). Results: Although microbial pretreatments did not significantly introduce lignin degradation, the data from SSF exhibited higher cellulose conversion (21-75% for biopretreated samples for 4-16 weeks) as compared to the untreated poplar (18%). In spite of the essential maintain of crystallinity, the modification of lignin structure during fungal treatment undoubtedly played a key role in improving cellulose bioconversion rates. Finally, the ethanol concentration of 5.16 g/L was detected in the fermentation broth from the cellulosic sample biodegraded for 16 weeks after 24 h SSF, achieving 34.8% cellulose utilization in poplar. Conclusion: The potential fungal pretreatment with Trametes velutina D10149 was firstly explored in this study. It is found that the biopretreatment process had a significant effect on the digestibility of substrate probably due to the removal and unit variation of lignin, since the crystallinities of substrates were rarely changed. Additional investigation is still required especially to improve the selectivity for lignin degradation and optimize the digestibility of cellulose.