Probing cellulase stability in low cost mineral acid ionic liquids

Abstract

Ionic liquid (IL) pretreatment has gained significant attention for biomass deconstruction. However, residual IL left in biomass can cause enzyme deactivation, leading to problems with further processing of biomass to sugars. Cellulases are enzymes commonly used in the saccharification process and the activity of this enzyme is severely affected by ILs. This thesis focuses on understanding how ILs affect the activity of cellulases in the enzymatic saccharification process. Sigmacell cellulose was used in the enzymatic saccharification process instead of biomass plant. Seven different ILs were added in the enzymatic saccharification mixtures and the activity of a mixture of commercially available cellulases was measured using high-performance liquid chromatography (HPLC) to measure glucose release. Sulphate based ILs were more harmful for cellulase action than [EMIM][OAc], [BMIM]Cl and phosphate based ILs. [HBIM][HSO4] inactivated commercial cellulases (Celluclast®) and cellobiase (Novozyme188) in 4 h in the enzymatic saccharification process. In this thesis, it was observed that the main factor that affects the activity of cellulase is pH. To overcome this, acidophilic cellulases were suggested to improve the activity of the enzymes in ILs. Endoglucanase from Cryptococcus sp.S-2 and β-glucosidase from Thermofilum pendens were studied and tested with ILs. The result of this study has shown endoglucanase from Cryptococcus sp. as a promising enzyme in IL biomass deconstruction. There was a slight improvement in the activity of β-glucosidase from T.pendens with cellobiose in 1% [TEA][HSO4] but when both of these enzymes were combined and acting against carboxymethylcellulose (CMC) with 10% (v/v) of [TEA][HSO4], the enzymes were still active. Based from these findings, pretreatment process using low cost IL is favourable as it is cost effective and more efficient.