Distinct cellulose nanofibrils generated for improved Pickering emulsions and lignocellulose-degradation enzyme secretion coupled with high bioethanol production in natural rice mutants

Abstract

Since lignocellulose represents an enormous and sustainable biomass resource convertible for biofuels and bioproducts, green-like and cost-effective technology is being increasingly considered to generate value-added bioproducts along with biofuel production. Herein, we took advantage of the natural rice mutant (Osfc16) that possesses recalcitrance-reduced lignocellulose, and performed a direct enzymatic hydrolysis of rice straw to achieve significantly increased bioethanol yields (by 19% at p < 0.01) compared with those from the wild type. Additionally, we generated optimal cellulose nanofibrils (CNFs) from the remaining enzymatic residues under far fewer cycles of high-pressure homogenization. Notably, due to their characteristic surfaces, the CNFs at low dosage not only act as effective inducers for the secretion of cellulase complexes by T. reesei, with protein yields significantly increased by 99% and enzyme (endoglucanases and xylanases) activities by 27% and 51%, respectively, using full rice straw as the carbon source, but also play a more efficient role as stabilizers for improving almost all major parameters of Pickering emulsions, including the emulsion index, droplet size, interfacial tension, zeta potential, water holding capacity and storage condition, compared to other chemical inducers and stabilizers (CNFs, proteins, and starch) that have been applied in previous studies. Hence, this study proposes a mechanistic model to elucidate why the desirable rice mutant enables the generation of distinct CNFs that are favorable for Pickering emulsion stabilization and mixed-cellulase induction coupled with relatively low-cost bioethanol production, providing multiple non-chemical processes as a novel green-like technology for complete biomass utilization towards the production of low-cost bioethanol and high-value bioproducts.