Multienzymatic conversion of monosaccharides from birch biomass after pretreatment

Abstract

This study presents proof-of-concept validation of a multi enzymatic biocatalytic system, capable of producing monosaccharides from a birch biomass pretreated liquor with simultaneous cofactor regeneration. To improve the stability of the proposed biocatalyst, co-immobilization of NAD + -dependent xylose dehydrogenases, glucose dehydrogenase, and NADH-dependent 3-hydroxybutyrate dehydrogenase was performed on mesoporous silica SBA-15. The results of the physicochemical analysis confirmed the effectiveness of enzymes deposition on the support material and changes in the surface area and porous structure of silica before and after the process. Process conditions in which the three-enzymes system allowed to achieve the highest efficiency of the conducted reactions were optimized at 20 °C, pH 7, 90 min of process duration, 400 mM of levulinic acid addition and ratio of NAD + :NADH 1:5. Results from this study demonstrate excellent xylonic acid, gluconic acid and 4-hydroxyvaleric acid production at conversion rate of 98.7%, 95.6% and 99.2%, respectively. In addition, the high stability and reusability of the developed biocatalytic system was confirmed based on tests in ten successive catalytic cycles and the storage time of 10 days at 4 °C. At the end of the tests, co-immobilized enzymes were capable of catalyzing the process with >70% efficiency. The presented data confirmed the effectiveness of co-immobilization, improvement of enzyme properties including their high reusability, as well as indicated the application potential of the proposed multienzymatic system in the conversion of components of pretreated biomass solutions. • Three types of dehydrogenases have been successfully co-immobilized using silica SBA-15. • Monosaccharides from the birch biomass pretreated liquor were effectively converted. • Addition of levulinic acid ensured the creation of a cofactor regeneration system. • The production of three organic acids was carried out with over 95% of efficiency. • Co-immobilized enzymes retained 70% of acids productivity after 10 catalytic cycles.