Enzymatic in situ saccharification of lignocellulose in a compatible ionic liquid-cellulase system

• [Emim][DP] was effective to disrupt the shields formed by lignin inside rice straw.
• The cellulase from Trichoderma aureoviride showed high stability in [Emim][DP].
• The coupling of IL-activation and subsequent enzymatic hydrolysis process.
• An efficient IL-cellulase media for in situ enzymatic saccharification of biomass.

Although ionic liquids (ILs) have emerged as a promising type of solvent for lignocellulose pretreatment, the enzymatic saccharification of regenerated lignocellulose must occur in a separate step due to the toxicity of ILs to cellulase. It is critical to develop a compatible IL-cellulase system in which the IL effectively activates the lignocellulosic biomass, while the enzyme remains highly stable. In this context, an exploration of ILs with high lignin-extraction capacity, for the first time showed 1-ethyl-3-methyl-imidazolium dimethylphosphate ([Emim][DP]) to be effective in disrupting the lignin-based shield within rice straw, thus enhancing the biodegradability of this plant material. The cellulase obtained from Trichoderma aureoviride showed high stability in this IL. After incubation in [Emim][DP] for 24 h, more than 40% of the lignin was successfully leached from the rice straw. The spectroscopic and morphological analyses showed that the synergistic effect of delignification and the partial dissolution of cellulose during the activation process significantly changed the crystalline molecular structure of rice straw. When the activated straw slurry was enzymatically hydrolyzed in IL diluted to 15% (w/v), a high yield of reducing sugars, 61%, was obtained. Thus, an efficient system coupled the activation and subsequent enzymatic hydrolysis of a native biomass in a one-pot procedure was successfully developed.

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