Development of a Novel Simultaneous Saccharification and Isomerization (SSI) Approach to Enhance Fructose Production for Catalytic Conversion to Drop-in Fuels

Development of a Novel Simultaneous Saccharification and Isomerization (SSI) Approach to Enhance Fructose Production for Catalytic Conversion to Drop-In Fuels

Christian Alcaraz^{1, 2}, Rajeev Kumar², and Charles E. Wyman^{1, 2}

¹Department of Chemical and Environmental Engineering, Bourns College of Engineering, University of California, Riverside, Riverside, CA

²Center for Environmental Research and Technology (CE-CERT), Bourns College of Engineering, University of California, Riverside, Riverside, CA

Secondary fuel precursors, e.g., furfural, HMF, and levulinic acid, made from sugars in cellulosic biomass can be thermo-catalytically converted into “drop-in” fuels, i.e., hydrocarbons that are compatible with the existing fuel infrastructure. Biological saccharification of glucan using C. thermocellum in a consolidated bioprocessing (CBP) approach promises to release glucose from glucan in biomass with high yields without the need for a separate enzyme productions step, thereby potentially reducing the cost compared to traditional cellulase enzymes.  However, CBP is currently pictured to ferment the glucose released to ethanol or other products while catalytic processes can realize higher yields product yields from fructose than from glucose.  Thus, the objective of this research is to develop a novel approach called simultaneous saccharification and isomerization (SSI) to convert the glucose released by CBP into fructose from glucan in a single step by coupling C. thermocellum CBP supplemented with β-glucosidase to reduce glucan consumption by C. thermocellum with simultaneous conversion of that glucose to fructose by glucose isomerase.  Advantages of producing fructose directly from cellulose by employing wild type C.thermocellum through SSI include 1) elimination of separate enzyme production, 2) negligible or no requirement for adding expensive fungal cellulases, 3) no need for genetic engineering, and 4) elimination of a separate isomerization step.  As a first step in developing this novel concept, 50 g/L and higher concentrations of Avicel glucan was saccharified by C. thermocellum supplemented with exogenous β-glucosidase and a commercial glucose isomerase at 60°C to 70°C and pH of 6.0 to pH 7.5.